Wireless power pad with local power activation for portable devices

Technical Note PR-TN 2007/00748 8.11.2007

Issued: 11/2007

Wireless power pad with local power activation for portable devices

E. Waffenschmidt, V. Zheglov

Philips Research Europe

Unclassified © Koninklijke Philips Electronics N.V. 2007

PR-TN 2007/00748 Unclassified

ii © Koninklijke Philips Electronics N.V. 2007

Authors’ address

E. Waffenschmidt V. Zheglov

[email protected]@philips.com

© KONINKLIJKE PHILIPS ELECTRONICS NV 2007All rights reserved. Reproduction or dissemination in whole or in part is prohibited without the prior written consent of the copyright holder .

Unclassified PR-TN 2007/00748

© Koninklijke Philips Electronics N.V. 2007 iii

Title: Wireless Power Pad with local power activation for portable devices

Author(s): E. Waffenschmidt, V. Zheglov

Reviewer(s):

Technical Note: PR-TN 2007/00748

Additional Numbers:

Subcategory:

Project: Wireless Power for Lighting (CRB 2006-435)

Customer:

Keywords: Power Pad, RFID, NFC, PN511, Controlling Board, wireless power, inductive coupled energy transmission system

Abstract: Wireless power transfer by magnetic induction offers a simple to use way to recharge mobile devices like e.g. mobile phone, music players or medical sensors. As shown by a previous report and an existing Power Pad demonstrator, wireless inductive power transfer is possible with a good power efficiency and low magnetic radiation only on a surface and with local activation underneath the mobile device. However, compared to the existing Power Pad, an improved detection method for the local activation is needed. This report investigates the use of RF-ID tags for the position detection. It addresses the problem to multiplex the RF-ID signal to a number of neighboured power cells to locate the device and the simultaneous transfer of power and information. To investigate the solution, a demonstrator is designed and built. This first circuit can activate 4 neighboured and overlapping cells. The circuit consists of a NFC/RF-ID PN511controller by NXP, an analogue multiplexer to direct the RF-ID signal to the cells and FETs as switches to switch the power signal to each cell. The system operates at 500 kHz for the power transmission and at 13.56 MHz for the RF ID data transmission. The circuit is controlled by an external computer using a dedicated software developed with LabView.

Conclusions: The results show that RF/ID is suitable for the position detection and local activation of an inductive power pad. The designed circuit can detect the position of a mobile device and switch on the power of the related cell. The operation with simultaneous power and data transmission needs a dedicated filtering effort. Less filtering is necessary, if data and power transmission are done sequentially. Based on the results of this work, an extended version to support up to 52 cells for a complete pad is in preparation.


v © Koninklijke Philips Electronics N.V. 2007

Table of contents

1 Introduction ..........................................................................................................................................7 1.1 Motivation .....................................................................................................................................7 1.2 Wireless power..............................................................................................................................7 1.3 Study of the available technology .................................................................................................9 1.4 Existing prototype .......................................................................................................................11 1.5 Concept .......................................................................................................................................13

2 RFID ....................................................................................................................................................15 2.1 Technology, history and use .......................................................................................................15 2.2 Mifare..........................................................................................................................................16

2.2.1 Tags .................................................................................................................................17 2.2.2 Standards .........................................................................................................................18

3 The Controlling Board .......................................................................................................................21 3.1 Components.................................................................................................................................22

3.1.1 PN511..............................................................................................................................22 3.1.2 ADG714 ..........................................................................................................................25 3.1.3 Remaining components ...................................................................................................26

3.2 Antenna design............................................................................................................................27 3.3 Filter design.................................................................................................................................32

3.3.1 Receiving filter of the PN511..........................................................................................32 3.3.2 Receiving filter of the Receiver PCB..............................................................................36

3.4 Functionality of the board ...........................................................................................................40

4 Software...............................................................................................................................................42 4.1 Configuration of the PN511 ........................................................................................................42 4.2 Implementation of the “Request” command using LabVIEW....................................................43 4.3 Configuration of the Controlling Board using LabVIEW...........................................................47

5 Results and Analysis ...........................................................................................................................53 5.1 Analog Switch measurements .....................................................................................................53 5.2 Voltage measurements ................................................................................................................55 5.3 Performance tests ........................................................................................................................60

6 Summary and future outlook ............................................................................................................65

7 References............................................................................................................................................66

8 List of figures ......................................................................................................................................67


© Koninklijke Philips Electronics N.V. 2007 vi

9 List of tables ........................................................................................................................................71

10 Appendix..............................................................................................................................................72 10.1 Miller Code .................................................................................................................................72 10.2 Manchester Code.........................................................................................................................72 10.3 Load modulation .........................................................................................................................73 10.4 Backscatter-Principle ..................................................................................................................74 10.5 SPI – Serial Peripheral Interface .................................................................................................74 TAMA demo board ..............................................................................................................................76 10.6 DAQCard ....................................................................................................................................82 10.7 Controlling Board schematic.......................................................................................................83


7 © Koninklijke Philips Electronics N.V. 2007

1 Introduction

This report is accomplished as diploma thesis by the co-author Vadim Zheglov to receive a diploma degree at the University of Applied Sciences Wurzburg – Schweinfurt. It was performed and supervised at the Philips Research Laboratories in the “Solid State Light-ing” department from May 2007 to September 2007.

1.1 Motivation

A century ago, Nicola Tesla tried to transmit power without using wires. The success was low but the idea has remained interesting up until our days. The recent researches in this area show that wireless power is not any longer utopian. Numerous companies worldwide work on possible configurations able to transmit power without using wires. A simple placing of a portable device on the surface of such configu-ration enables the power transport. The Massachusetts Institute of Technology (MIT) even claims to have a configuration able to power devices located in a standard-sized room. The high power efficiency of this solution is questionable but efficiency of some known products is high enough to compete with wired power supply solutions. But while wireless energy-transmission products gain in performance no configuration is known to be able to combine wireless energy transmission together with wireless data transmission. For example to charge a MP3 player it can simply be placed on a charging device but to be able to access the stored music it still need to be physically connected to the computer. Wireless charging of mobile handheld devices such as mobile phones, PDAs or MP3 players including data exchange between the charger and the mobile device could im-prove user comfort. In addition, it could lead to a standardized interface suitable for a multiplicity of devices, like USB.

1.2 Wireless power

Three ways of wireless energy transmission systems might be considered as possible candidates. These three are presented as follows. Capacitive coupled transmission systems may be used to transmit few mW at a dis-tance of a few cm. The idea behind it is the usage of at least two parallel conductive plates. Figure 1-1 shows a capacitive coupled transmission system, which consists of two transmitting and two receiving electrodes.


© Koninklijke Philips Electronics N.V. 2007 8

Figure 1-1: Energy transmission system based on Capacitive Coupling The distance between the electrodes is usually very low. The frequency ranges of these devices are limited in the lower MHz-range. Electromagnetic coupled transmission systems are more often used for purposes of communication. Nonetheless, some applications using this system might gain more interest in the near future. Transmission of power-levels up to 1W within a few cm seems reasonable and possible. However, with increasing distance the power-levels drop down to mW or even µW. Such systems consist of an antenna. The size of which depends on the energy value to be transmitted and the receiver. An Inductive coupled energy transmission system consists of at least one transmitter coil ( 1L ) and one receiver coil ( 2L ). See figure 1-2.

Figure 1-2: Inductively coupled power transmission system A part of the magnetic flux B generated by 1L penetrates 2L and inducts a voltage. By closing the circuit with a load, a current flow is enabled; therefore, energy is transferred. The latter transmission system seems to be the most useful one. This solution can pro-vide power efficiencies of more than 80% at close distances. This may even compete with wired power supply.



Considering the possibility of powering up portable devices, a coil within such devices can barely have a diameter bigger than 4 cm. Researches have shown that the effi-ciency of an inductive power transmission system highly depends on the distance and the size relation of the coils. An increase of the distance between the coils to a value of the coil diameter drops the efficiency to an unfeasible value. It also reduces, if one of the coils has a different size than the other. Applications with large space transmission (“Power Space”), using coils with sizes small enough to fit in a portable device, have efficiencies much less than 10%. Providing wire-less power in complete rooms, e.g. an office, seems to be not feasible for general pur-poses. However, if power transmitter and receiver are close together (facing each other on sur-face) and of similar size a high efficiency of 80% and more is possible. Furthermore shielding is possible and the magnetic field is concentrated in the small space between transmitter and receiver. Therefore power levels around 1000W/m2 are possible. Those solutions can be realized as a magnetic power surface, e.g. as a pad.

1.3 Study of the available technology

Several products, related to the charging pad described in this thesis, have been intro-duced by a number of companies worldwide. In this chapter three of these products are shown together with their properties and abilities. Splashpower Limited located in Cambridge, UK has developed a system, called Splash-PadTM. It uses an inductive field horizontal to the surface. To provide the receiver with maximum power, in any horizontal direction, the field is rotating by using two coils, which are orthogonally arranged and driven. The device is able to transmit 15W at an efficiency of 60%. Figure 1-3 shows a SplashPadTM as presented on [1].

Figure 1-3: SplashPadTM by Splashpower [1] Edison Electric Corp. introduced a wireless inductive power pad called PowerDeskTM [2]. No technical data related to PowerDeskTM could be found at [2]. However, the product is described as universal charging platform to power up mobile devices. Furthermore, PowerDeskTM can charge as many devices as fit on it as long as these devices are



PowerDeskTM-compatible. International standards and safety regulations are met [2]. Figure 1-4 shows the PowerDeskTM from [2].

Figure 1-4: PowerDeskTM by Edison Electric Corp. [2] University of Tokyo developed a plastic sheet, which transmits electricity using the elec-tromagnetic induction method [3]. At any position on the sheet a device can be detected (- no further information about realization available) and selectively powered. The square-shaped sheet with 21cm side length, 1mm thickness and 50g weight is able to transmit 29.3W with efficiency up to 62.3%. Figure 1-5 shows the powering sheet [3].

Figure 1-5: Power sheet introduced by University of Tokyo [3] The descriptions provided by the manufacturers for the introduced products don’t men-tion any data transfer between the charging configuration and the charging device. The charging pad developed at Philips Research in Aachen, should be provided with an ac-cessory supporting data exchange and position detection. However, to achieve the high efficiency and low magnetic stray field, only the area un-derneath the receiver device must be activated. If an arbitrary placement is desired, a position detection of the device is required.



1.4 Existing prototype

The purpose of this chapter is a short description of the existing prototype of the Power Pad. With respect to time and room, the complete functionality of the charging pad will not be explained in this thesis. For more information on the current researches related to the wireless power transmission please contact [4]. The Power Pad is a tablet or pad about the size of an A4 page, which allows for wireless charging of mobile electronic devices. The general idea is “Just smash on the pad to get it charged”. See figure 1-6.

Figure 1-6: Photograph of the current Charging Pad version with a MP3 player being charged The pad consists of a number of primary coils arranged in an array. The coils generate a vertical magnetic field that can be received by simple coreless coils. The primary array is made from a printed circuit board PCB (see figure 1-7). A similar arrangement is de-scribed by [16] The pad consists of three layers of round concentric coil pairs (52 alto-gether). The outside coil of such a coil pair is the actual charging coil for powering pur-poses. The inside coils are designed for communication purposes.



Power Coils

Sensor Coils

Connection Pads

Figure 1-7: Photograph of the antenna array PCB (top bottom) Every single coil can be connected using the connection pads on the sides of the Transmitter PCB. For demonstration purposes, a Receiver PCB consisting of a receiver circuit together with a planar winding coil and a power LED has been designed. When the receiver is placed on the pad, energy is transferred, and the LED emits light. See figure 1-8.



Figure 1-8: Photograph of two receive circuits on the pad The current version of the Power Pad is able to transmit up to 1W energy. Each coil can be turned on separately using ferrite detectors and trigger switches. The operation fre-quency of the pad is 500 kHz. A half bridge generator and auxiliary circuits in an external box are used as a driver.

1.5 Concept

In this thesis, an alternative solution for the existing separated coil activation has to be instantiated. The smaller coils of the coil pairs on the Transmitter PCB are used to transmit data between the controller and a chargeable device placed on the charging pad. According to these data, the controller activates the charging coils located next to the device. In addition to the exchange of data necessary to identify and locate the de-vice, an exchange of data blocks with varying size will be included (not part of this the-sis). A LabVIEW program controls the accurate run of the task. Figure 1-9 shows the block diagram for the implementation to be realized.



Figure 1-9: Block diagram of the construction The communication between the controller and the portable device is realized using RFID (see chapter 2). As explained above, the best efficiency of using inductive wireless power systems is achieved if the distance between the coils of the transmitting system is kept as small as possible. Additionally, the distance between the frequency of the signal used for communication purposes and the frequency of the signal used for charging purposes is kept as wide as possible. The used ISO/IEC 14443 standards define com-munication with a distance of maximal 10 cm between the communication partners and an operating frequency of 13,56 MHz (see chapter 2.2.2). The used NFC controller is the central feature of the implemented circuit. Besides the ability to support the completely used communication protocol to exchange data with the portable device, it is also able to support a widely used series interface in order to ex-change data with a host controller – in this case a PC. With respect to accuracy by locating a device that was placed on the pad, the number of simultaneously connected antennas to the controller is kept low (down to 1 antenna at a time). Therefore, a controlled sequential connection was realized allowing the communi-cation to use a fixed amount of antennas at the same time. This is possible using an analog switch (in figure above - switch). The switch for these purposes was chosen con-sidering the useful properties such as low connection resistor, high bandwidth connec-tion and short switch times. In addition, the analog switch is controllable using a series interface and is daisy-chain connectable, so that an optional number of coils on the charging pad can be supported. For the purposes of this project, a DAQCard-6024E digital board is used to connect (in case a chargeable device was detected) the charging coils of the Transmitter PCB to the power supply. It is also used to control the sequential switching of the analog switch (see chapter 3.1.2).



2 RFID

The first part of this chapter deals with the functionality and usage of RFID. A short de-velopment of the history is provided. More information also can be found in [7]. The sec-ond part aims at describing the MifareTM smart card technology. Further information can be found at [6].

2.1 Technology, history and use

RFID stands for Radio Frequency Identification and is an identification method. The first used RFID devices date back to the World War II, when the allies used it for plane identi-fication. However, the first commercial successful transportation application, electronic toll collection, was invented in 1990s. Several countries, worldwide, used the technology as a payment method for the use of the roads. Ever since, RFID is used for hundreds, if not thousands, of applications such as preventing theft of automobiles, collecting tolls, managing traffic or gaining entrance to buildings. Some scientists refer to it as “an inte-gral part of our life” [5]. The RFID-Journal even claims that “the applications of RFID are limited only by people's imagination” [7]. Figure 2-1 shows an RFID tag insert in a human hand, as it is used for purposes of identification [8].

Figure 2-1: RFID tag implant

According to the RFID market analysis firm IDTechEx, the push for digital inventory tracking and personal ID systems will expand the current annual market for RFID from $5 billion to as much as $25 billion by 2016 [9]. The general technology behind RFID can be explained by the system sketched in Figure 2-2. An RFID system consists of a reader with an antenna and a microchip with an an-tenna, called a RFID tag. The reader sends the data using the antenna in form of elec-tromagnetic waves. The tag is able to receive the data and response to them.



Reader Tag

Antenna Antenna

Radio wave

Figure 2-2: RFID system The frequencies used for the RFID systems depend on the application the system is used in. The most common are low-frequency (125 kHz), high-frequency (13.56 MHz) and ultra-high-frequency (860-960 MHz). Some applications require Microwaves (2.45 GHz). Inductive coupling and RF near field are used for LF and HF. Therefore the dis-tance between reader and tag is 0…1 m. The near field in UHF and Microwaves is too small to be used for any purposes, thus the electromagnetic far field is used. Distances of about 500 meters are possible [7]. Three different types of tags are used nowadays; passive, active and semi-passive. Passive tags do not have a power supply and use the power of the RF field, generated by the transmitter. The reply to the „Request“ from the transmitter is done via load modu-lation (see chapter 10.3). Active tags have an onboard power source. The energy is used to power up the integrated circuit and to broadcast the data, thus transmitting at higher power level is possible. The semi-passive tags are similar to the active ones in the point that their microchip is powered up by an onboard power source. Though, the transmitting of data is done by the usage of the field generated by the reader. The most common coding methods used, are Miller and Manchester Codes (see in chapters 10.1 and 10.2). The Backscatter-Principle (descriptions see in chapter 10.4) is widely used in applications operating in the far-field region.

2.2 Mifare

MifareTM is a contact-less smart card technology based on RFID and produced by NXP-Semiconductors. This standard is widely used for electronic ticketing in public transport, road tolling and access control. Worldwide more than 5 million MifareTM reader and more than 500 million contact-less and dual interface ICs are used. Like 80% of the contact-less smart cards worldwide, MifareTM is fully compliant to ISO/IEC 14443 (RFID) type A [6].



2.2.1 Tags

Today NXP-Semiconductors offers seven different MifareTM chips: Ultralight, Standard 1k, Standard 4k, Mini, DESFire, PORX and SmartMX. For the purposes of this thesis and the final application into the receiver circuit, the Standard 1k chip (MF1 IC S50) has been chosen. Together with an antenna the MF1 IC S50 forms a passive receiver tag. The data trans-mission can be operated at a distance up to 100mm with the frequency of 13.56MHz and a transfer speed of 106kbit/s. Figure 2-3 shows the block diagram of a MifareTM 1K chip.

antenna

Digital Control Unit

EEPROMRF -Interface Anticollision

Authentication

Control & ALU

EEPROM-Interface

Crypto

Figure 2-3: MF1 IC S50 Block diagram [10] As shown, a MF1 IC S50 chip consist of three parts, which are a 1Kbyte EEPROM, a RF-Interface and a Digital Control Unit. The power supply along with the data is trans-ferred via the antenna. The RF-Interface contains a modulator/demodulator for the incoming/outgoing signals together with a rectifier. A clock generator and a voltage regulator are a part of it as well. The tasks and purposes of Anti-collision and Authentication are described in paragraph 2.2.2. The Crypto unit provides the data security layer using, from Philips invented, CRYPTO1 stream cipher of the MifareTM Classic family. The task of the Control & Arith-metic Logic Unit is to control the values that are stored in a special redundant format so they can be incremented and decremented. The EEPROM is organized in 16 sectors with 4 blocks each. Every block contains 16 bytes. The programmable access conditions together with two secret keys of every sec-tor are stored in the last block called “trailer”. See figure 2-4.



Byte Number within a Block

DescriptionSector Block

3

2

1

0

3

2

1

0

3

2

1

0

3

2

1

0

.

.

.

.

.

.

.

.

.

.

.

.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Key A Access Bits Key B



Key A Access Bits Key B Section Trailer 0

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

Data

0

Section Trailer 15

Section Trailer 14

Section Trailer 1

315

314

31

00

Manufacturer Block

Figure 2-4: Memory organization of a MifareTM chip [10] The secret keys A and B return logical „0“ when read. The access conditions are stored in bytes 6…9. These bytes also specify the data blocks to read/write or value blocks. The read/write blocks can be read and/or data can be written to them. The value blocks have a fixed data format, which permits error detection, correction and backup manage-ment. A value is stored 3 times. Additionally to the read/write commands the value blocks also supplement increment, decrement, restore and transfer commands. The manufacturer block contains the IC manufacturer data. For security purposes this block is write-protected.

2.2.2 Standards

As mentioned above the communication layer of the MF1 IC S50 complies with parts 2 (RF signal & power interface) and 3 (Initialization & anti-collision) of the ISO/IEC 14443A standard. Figure 2-5 shows the physical layer of the communication described in ISO/IEC 14443A standard at a transfer speed of 106 kbit/s.

Figure 2-5: ISO/IEC 14443A standard communication diagram



The security is provided by a three pass authentication according to ISO/IEC DIS 9798-2 standard. Figure 2-6 shows the memory access procedure of the MF1 IC S50.

Read Block Halt

Write Block

Decre-ment

Incre-ment

Re-store

Transfer

3 Pass Authentication sector specific

Select Card

Anti-collision Loop Get Serial Number

Request Standard Request All

POR

Identification and Selection Procedure

Authentication Procedure

Memory Operations

Figure 2-6: Memory access [10] Before any memory operation can be carried out, the tag has to be selected and authen-ticated. The possible memory operations for an addressed block depend on the key used and the access conditions stored in the associated sector trailer. The used commands are established by the Reader and managed by the Digital Control Unit of the MF1 IC S50. After Power On Reset (POR) of a tag, it can answer to a “„Re-quest“” command REQA (0x26) with an ATQA (Answer to „Request“) sent by the reader to all tags in the antenna field. The ATQA (2 bytes) includes information about the UID (Unique Identifier) size, some propriety coded information (to be ignored) and informa-tion concerning whether the “bit frame anti-collision” is supported or not. In the “anti-collision” loop, the UID (4 bytes) of a tag is read. If there are several tags in the operat-ing range of the reader, they can be distinguished by their unique serial numbers, and one can be selected (Select Tag) for further transactions. The unselected tags are set to “HALT” mode and will not respond to any other command besides a new “„Request“” command. With the “select tag” command, the reader selects one individual tag for au-thentication and memory related operations. The tag returns the Answer To Select (ATS) code (=08h), which determines the type of the selected tag. After selection of a tag, the reader specifies the memory location of the following memory access and uses the cor-responding key for the three pass authentication procedure.



The possible memory operations for an addressed block depend on the key used and the access conditions stored in the associated sector trailer. The sequence of the three pass authentication can be described as follows:

• The reader specifies the sector to be accessed and chooses key A or B. • The tag reads the secret key and the access conditions from the sector trailer.

Then the tag sends a random number as the challenge to the reader (pass one). • The reader calculates the response using the secret key and additional input. The

response, together with a random challenge from the reader, is then transmitted to the tag (pass two).

• The tag verifies the response of the reader by comparing it with its own challenge, and then it calculates the response to the challenge and transmits it (pass three).

• The reader verifies the response of the tag by comparing it to its own challenge. After a successful authentication, all memory operations are encrypted. The access conditions for every data block and sector trailer are defined by 3 bits, which are stored non-inverted and inverted in the sector trailer of the specified block. The ac-cess bits control the rights of memory access using the secret keys A and B. The access conditions may be altered, provided that one knows the relevant key, and the current access conditions allow the operation. With each memory access, the internal logic veri-fies the format of the access conditions. If it detects a violation, the whole sector is irre-versibly blocked.



3 The Controlling Board

The Controlling Board is the controlling device for the charging pad. It is based on the TAMA board (see chapter 10.6 for the schematic and assembly list of the TAMA board and chapter 10.8 for schematic of the Controlling Board) and extended by several com-ponents described in following sections (see chapter 10.8 for Controlling Board sche-matic). TAMA is a co-development project between Philips and Sony. The product is based on the 80C51 micro controller and integrating the contact-less interface supporting MifareTM, FeliCaTM and NFC communication schemes and several interfaces or communications to HOST processor. The board is a complete reader based on the PN511 NFC IC. The Board can be divided in 3 parts (see figure 3-1). The numbers shown in the picture are mentioned trough this paragraph following the specific component in parentheses without further explanations.

Interface PCB Antenna PCB

NFC Reader PCB

2

3

5

4

7

8 9

12

11

1416 10

6

15

13

1

Figure 3-1: Photo of the Controlling Board

• The “NFC reader PCB” part is the NFC reader module. This module is the basic PCB including the PN511 NFC IC (14) and all required components for a NFC reader plus the filter circuitry (13).

• The “Antenna PCB” includes the relevant matching components (See chapter 3.5), the analog switch ADG714 (12), the interface for connection of the antenna PCB (7), the interface for DAQCard-6024E (10 – also see chapter 10.7 for DAQCard-6024E descriptions) and the power supply for the charging antennas (9). See figure 3-12 for the complete configuration.

• The “interface PCB” enables the direct connection to a RS232 interface using a DB9 (17) connector and a power supply using a plug (1).



The implemented version controls the sequential activation of four coils on the antenna PCB (using the implemented principle that a communication using all coils can be per-formed).

3.1 Components

The following chapters explain the functions of the used components of all three parts apart along with the functions of the whole board. Specifications of how to dimension some parts of the board together with descriptions of additionally used devices are given as well. 3.1.1 PN511

The PN511 (number 12 in figure 4-1) is a highly integrated transmission module for con-tact-less communication. This transmission module utilizes a modulation and demodula-tion concept completely integrated for different kinds of passive contact-less communica-tion methods and protocols at 15,56MHz. It supports three different operating modes:

• Reader/writer for FeliCaTM and ISO14443A cards • Card interface mode for FeliCaTM and ISO14443A/MifareTM • NFC IP-1 mode

Within this project, only the Reader/writer mode for FeliCaTM and ISO14443A cards are used. Therefore the descriptions of the functional specifications are limited to this mode. For more information on the remaining modes refer to [12]. The Figure 3-2 shows the pinning diagram of the PN511.

Figure 3-2: Pinning diagram PN511 To drive the antenna, the PN511 provides the energy carrier of 13,56MHz through TX1 and TX2. The Card response is received by the antenna and forwarded to the Rx-pin. Inside the PN511, the receiver senses and intensifies the signal and processes it. The driver stage has a separated power supply provided by the pins TVDD and TVSS.



The analog part power supply (pins AVDD and AVSS) provides the oscillator, the analog demodulator and the decoder circuitry with energy. The waveform character at SIGOUT is a digital 13,56MHz Miller-coded signal with levels between PVSS and PVDD. The on-chip oscillator buffer operates with a 27.12MHz crystal connected to OSCIN and OSCOUT. If the device shall operate with an external clock, it may be applied to pin OSCIN. A Hard Power Down is enabled with LOW level on pin RSTPD . This turns off all internal current sinks as well as the oscillator. All digital input buffers are separated from the input pads and clamped within (except pin RSTPD itself). If RSTPD is released, the PN511 implements the power up sequence. The PN511 supports the 8 bit parallel, SPI, serial UART and I2C host interface. Several control pins are used for the host interface. The configuration of the enabled interface is done according to an explicit connection of the pins. The PN511 identifies the host con-troller interface by the means of the logic levels on the control pins after the Reset Phase. Table 3-1 provides a summary for the pin description of the PN511.



Name Type Function

Antenna interface

TX1, TX2 Output Buffered Antenna Drivers VMID Analog Reference Voltage

Rx Input Analog Antenna Input Signal LoadMod Output Load modulation output signal

TVDD Power Transmitter Supply Voltage TVSS Power Transmitter Supply Ground

Analog part

AVDD Power Analog Positive Supply Voltage AVSS Power Analog Supply Ground

Digital supply

DVDD Power Digital Positive Supply Voltage DVSS Power Digital Supply Ground

Pad supply

PVDD Power Pad Positive Supply Voltage PVSS Power Pad Supply Ground

AUX part

AUX1 Output Auxiliary and test signal AUX2 Output Auxiliary and test signal

Oscillator pat

OSCIN Input Oscillator Buffer Input OSCOUT Output Oscillator Buffer Output

Communication interface

SIGIN Input with Schmitt Trigger Communication interface input SIGOUT Output Communication interface output

Reset pin

RSTPD Input Reset and Power down input

Host interfaces

D0…D7 I/O with Schmitt Trigger A0…A3 I/O with Schmitt Trigger NWR I/O with Schmitt Trigger NRD I/O with Schmitt Trigger NCS I/O with Schmitt Trigger ALE I/O with Schmitt Trigger IRQ I/O with Schmitt Trigger

Functionality depends on the used host interface

Table 3-1: Pin description of PN511

For purposes of this project the UART (Universal Asynchronous Receiver Transmitter) interface, which is compatible to a RS232 interface, has been used. The connection scheme for the RS232 pins connected to the PN511 pins looks as follows.



Rx ⇒ ALE TX ⇒ D7 IRQ ⇒ D5

To read or write data using the UART interface 1 byte needs to be sent to define the mode and the address. The MSB (Most Significant Bit) of the first byte sets the used mode. To read data from the PN511, the MSB is set to logic 1. To write data, the MSB is set to logic 0. The bits 3 to 0 define the address. The data bytes can be sent directly after the address byte if sending data to the PN511. For example to read out the register 0x0A, the byte 0Ah needs to be sent to the interface. To write to the same register, the byte 8Ah needs to be sent. After the mode and the address bytes are received, the PN511 sends a response, which is the address of the called register if the writing mode was chosen. With the register chosen to read from, the PN511 answers with the content of the register.

3.1.2 ADG714

To allow a sequential communication with every coil on the charging pad, a serially con-trolled SPST (single pole, single throw) analog switch ADG714 (12) is used. The pur-pose of the ADG714 is to establish a connection between the PN511 pins TX1, TX2 and a designated antenna to be able to transmit the “„Request“” command. Figure 3-3 shows a functional block diagram of the ADG714.

Figure 3-3: ADG714 block diagram [11]



The ADG714 is SPI (Serial Peripheral Interface Bus - see chapter 10.5) compatible. It is controlled using the digital inputs (e.g. SCLK, DIN, SYNC and RESET ). The on-resistance is closely matched between switches ( ONR = 2,5Ω) and very flat over the full signal range. Each switch conducts equally well in both directions. These proper-ties are very important since the analog switch is placed between the PN511, and the antennas and all of the transmitted data will pass through it as shown in figure 3-5. Data is written to the 8-bit shift register via the DIN pin under the control of the SCLK and SYNC signals. When SYNC goes low, the input shift register is enabled. Data from DIN is clocked into the shift register on the falling edge of SCLK. Each bit of the 8 bit word represented by the DIN signal corresponds with one of the eight switches. Every bit is measured by 2 tact of the SCLK signal. Therefore to write 8 bits to the DIN input of the ADG714m, 16 tact at the SCLK input are needed. Figure 3-4 shows the timing diagram for the analog switch.

Figure 3-4: Wire Serial Interface Timing Diagram [11] The energy supply of the ADG714 requires a symmetric voltage feed, which requires a negative voltage. Thus, a volt converter ICL7660CBAZ (5) has been used to convert the on board available voltage of 2,8V.

3.1.3 Remaining components

The power supply is connected with a 2,5mm dc plug (1). In the interface section, the voltage supply is regulated down to 3,3V main-supply-voltage using the LM1117MP-3.3 (3) voltage regulator. This voltage is used to supply the ADM3202 (16) line driver, which serves the RS232 interface. Also the 3,3V voltage can be used to supply the PN511 (e.g. AVDD, DVDD, PVDD and TVDD) since the recommended operating conditions for these voltages can be between 1,6V and 3,6V [12]. For these and other purposes, the voltages of 1,8V and 2,8V regulated by LP2985AIM5-1.8 and LP2985AIM-2.8 (4) voltage regulators are available on the NFC reader PCB. An external 27,12 MHz quartz (15)



supplies the PN511 with stable clock frequency, which is used as time basis for the coder and the decoder of the synchronous system. The circuits for all in this paragraph mentioned ICs that can be found in the accordant datasheets at [14]. To control the current flow through the charging coils, the BSS670S2L MOSFETs (8) are chosen. With a maximum drain-source on-state resistance )(ONDSR under 1Ω and a drain-source breakdown voltage DSSBRV )( = 55V along with the possible continuous drain current

DI = 0,54A, the MOSFETs are able to handle the power supplying the charging coils. Under the number 6, shown components are the parts of the EMC filter, which is ex-plained as a part of the antenna in the following chapter.

3.2 Antenna design

While the parts “Interface PCB” and “NFC Reader PCB” do not need to be changed and can be used as references for parts of its own circuit, the Antenna part can vary from application to application. This chapter intends to describe the dimensioning of the RF parts for existing antennas in order to achieve the best performance for a communication according to the different communication scheme of the PN511 IC. The figure 3-5 shows the RF part and the related power supply (TVDD and TVSS). The procedure is similar to the one described in [13]. However, examples shown are measurements related to the board used in this work.

QR

0C

0L

1C

2C

QR

2C0C

1C

0L

RXR 1R 2RFL

1FC

2FC

RXC

EMC Filter Matching Circuit Antenna

Receiver Circuit

Figure 3-5: Block diagram of the complete RF part To get a proper working of the complete device all of these blocks need to be adjusted properly.



The EMC filter diminishes 13.56 MHz harmonics and performs an impedance transfor-mation. The main functions of this impedance transformation are to reduce the amplitude rise time after a modulation phase and to increase the receiving bandwidth. The match-ing circuit acts as an impedance transformation block. The antenna coil itself generates the magnetic field. The receiving part provides the received signal to the PN511 internal receiving stage. The main point of matching is to alter the antenna impedance to the required resis-tance matchR . The transmitter matching resistance matchR describes the equivalent resis-tance at the operating frequency present between the transmitter output pins TX1 and TX2 of the PN511. Figure 3-6 shows the impedance transformation.

Figure 3-6: Impedance transformation of the matching part [12] Different equivalent resistive loads guide to different transmitter supply currents. The maximum RF power can be obtained when transforming to a matchR of approximately 30Ω. A higher matching resistance means less power expenditure with only slightly less available RF power compared to the maximum available RF power. A good compromise between available RF power and TX power consumption can be found for a matching resistance matchR between 40Ω and 60Ω. [13] To be able to adjust the EMC filter and the matching circuit to an antenna in the previous described order, the components of the series equivalent circuit (see figure 3-7) of the antenna need to have certain values.

Figure 3-7: Series equivalent circuit



Typical values of the components are: aL = 0.3…3µH aC = 3…30pF aR = 0.3…8 Ω

Using the values of the serial circuit the quality factor aQ of the antenna can be calcu-lated.

a

aa R

LQ

⋅=

ω Equation (3.1)

If the calculated value of aQ is higher than the aim value of 35, an external damping resistor QR has to be inserted on each antenna side to diminish the Q-factor to a value of 35 (±10%) [13]. The value of QR can be calculated using the following equation: Error! Objects cannot be created from editing field codes. Equation (3.2) The acquired values can be used to calculate the values of the parallel equivalent circuit (see figure 3-8). This is needed to simplify the resonance circuit and make the calcula-tion easier.

Figure 3-8: Parallel equivalent circuit The following can be assumed:

apa LL ≅

apa CC ≅

Qa

apa RR

LR

⋅+⋅

≅2

)( 2ω Equation (3.3)

To design the EMC filter general design rules can be applied.

0L = 390nH - 1µH [13] The EMC filter resonance frequency 0rf has to be near the upper sideband frequency determined by the highest data rate (848 kHz sub carrier) in the system to attain a broadband characteristic.

0rf = 14.1 MHz…14.5 MHz [13] Using these values the EMC filter capacitance 0C can be calculated.



02

00 )2(

1Lf

Cr⋅⋅

=π

Equation (3.4)

The selected values are L0 = 560 nH and C0 = 220 pF. The matching circuit components can be calculated using the real trR and the imaginary part trX of the transformation impedance trZ . As shown in figure 3-9, the circuit in figure 3-6 needs to be split between EMC filter and matching circuit to obtain the transforma-tion impedance.

Figure 3-9: Definition of transformation impedance trZ [13]

Using the splitting the following applies:

trtrtr jXRZ += Equation (3.5.1)

trtrtr jXRZ −=* Equation (3.5.2)

( )2

02

002

21 ⎟

⎠⎞

⎜⎝⎛ ⋅⋅+⋅⋅−

=C

RCL

RR

match

matchtr

ωω Equation (3.5.3)

( )

( )2

02

002

0

2

002

0

21

41

2

⎟⎠⎞

⎜⎝⎛ ⋅⋅+⋅⋅−

⋅−⋅⋅−⋅⋅⋅=

CR

CL

CR

CLLX

match

match

tr

ωω


With the following formula the series and parallel matching capacitances can be calcu-lated:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛+

⋅⋅

≈

24

11

trpatr XRRC

ω

Equation (3.6.1)

papatrpa

CRRL

C ⋅−⋅

⋅

−⋅

≈ 2

4

1

2

12

2




Due to simplification of the formulas and lenience of the measured equivalent antenna circuit value, a final tuning of the matching circuit is necessary to reach the required matching resistance at the transmitter output pins. Figure 3-10 shows the magnitude and the figure 3-11 shows the phase of the matchR of a matched TAMA board and two anten-nas on the antenna PCB. The green areas mark the area between 13.5 MHz and 13,6 MHz.

Figure 3-10: Magnitude of the matchR

Around the working frequency of 13,56 MHz the figures range between 40 and 60 Ohms. The properties of the self-matched antennas are similar to those of the antenna on the TAMA board. (TAMA: ≈ 57Ω; L51: ≈ 45 Ω; L52 ≈ 58 Ω)



Figure 3-11: Phase of the matchR

The values of the graphs, within the green area, range between -20° and 20°. Even though the phases are not exactly 0°, they are small enough so that the antennas could generate RF fields strong enough for communication purposes. (TAMA: ≈ 17°; L51: ≈ -11°; L52 ≈ -5°) The dimensioning of the receiver circuit, including the filter for received signals, is ex-plained in the following chapter.

3.3 Filter design

Two filters are necessary to run the application clearly. The first is integrated into the receiving circuit of the PN511 on the Controlling Board (figure 3.5). The second filter was implemented as an additional part of the Receiver PCB (chapter 1.3). This chapter aims at explaining the purposes of both filters together with their functionalities and dimen-sions.

3.3.1 Receiving filter of the PN511

The magnetic flux generated by a charging coil (see figure 1-2) penetrates not only the coil of the receiving device, but also the sensor coil placed inside the charging coil. Thus additional to the signal of the RF field with a frequency of 13,56 MHz, a signal from the charging field with a frequency of 500 kHz appears on the Rx pin of the PN511. Since



the integrated high pass-filter of the PN511 is not able to completely keep these two signals apart, additional filter has been developed. Figure 3-12 shows the filter circuit.

Figure 3-12: Filter on the Controlling Board Rx is the Receiver Input pin of the PN511, and midV is the Internal Reference Voltage pin. The components directly connected to these pins ( RXR and RXC ) are predefined by the constructor and are integrated as a part of the filter.

nFCRX 100= : midV decoupling capacitance [13]. Ω= kRRX 1 : Predefined part of the voltage divider [13].

According to [11] the pin Rx also has an input capacitance inRXC _ and an input resistor

inRXR _ of 10pF and 350Ω respectively. To simplify the circuit and to make the calculation easier the input part (red circle) is simplified to the one shown in figure 3-13 (see red circuit). In order to do that the parallel resistors inR and RXR are combined to eqRXR − with 259,2Ω. Considering the value of the impedance of RXC at the frequency of 13,56 MHz (≈ 0,18Ω) it can be neglected. There-fore capacitance eqRXC − equals the value of the capacitance inRXC − .



Figure 3-13: Transformed circuit of the filter on the Controlling Board The capacitor 2FC together with the inductor FL (yellow circuit) builds a 2nd order high-pass filter. Thus, the amplitude (voltage ratio) of the transfer function applies to following equation:

22 )(

|)(|CFLF

LF

XX

XH

+=ω Equation (3.7)

Where LFX is the impedance of the inductor, FL and 2CFX are the impedance of the capacitor 2FC . These can be calculated using:

LX LF ω= Equation (3.7.1)

22

1

FCF C

Xω

−= Equation (3.7.2)

With the value of |H(ω)| going as high as possible, to achieve a advantageous voltage ration, FL and 2FC have to have a resonance with a resonance frequency of 13,56 MHz. Using the equation for resonance frequency:

221

FFres CL

fπ

= Equation (3.8)

2FF CL is calculated to 1,38e-16s. For |H(ω)| > 1 the loaded quality factor of the circuit has to be > 1. The value of the quality factor is affected by the ratio between eqRXR − and

characteristic Impedance CZ , defined as LFX , 2CFX or 2F

F

CL respectively. In cases

eqRXR − = LFX or eqRXR − = 2CFX the quality factor equals 1. Thus the value of eqRXR − has to



be comparatively bigger than the values of the mentioned impedances at the resonance frequency. Using the rule of thumb:

LFeqRX XR ⋅⋅⋅⋅≈− )102( following values are calculated:

eqRXF RHL −≈Ω≅=31851μ and

pFCF 1502 = As well as the high-pass filter, the FL is also building a LC series circuit with the series capacitor 1FC (green circuit). It is used to short-circuit frequencies around 500 kHz. Us-ing the equation for the impedance of a series LC circuit:

1|)(| CFLFLC XXZ +=ω Equation (3.9) and the assumption that 0|)(| =ωLCZ at 500 kHz, 1FC is calculated to a value of 100nF. The purpose of 1R and 2R is to build a voltage divider (blue circuit) with the voltage ratio of 1/10. It is necessary to decrease the high amplitudes of the inducted signal from the charging coil by factor 10, because otherwise the input signal would overload the Rx input. In this case, the following equation applies:

21

1

RRR

VV

in

out

+= Equation (3.10)

Using the equation above, the values for the resistors are calculated to:

Ω= 471R Ω= 4702R

The Figure 3-14 shows the simulated graph of the voltage ratio between the voltage at the Rx pin ( RXV ) and the inducted voltage ( indV ).



10KHz 100KHz 1MHz 10MHz 100MHz1e-005

0.0001

0.001

0.01

0.1

1V(vrx)/V(vind)

Figure 3-14: Ratio of voltage at Rx and Vind The parts of the Signal with the frequency of 13,56 MHz are completely received at the Rx pin after being decreased by the voltage divider with the ration 1/10 (red circle). The received parts with the frequency of 500 kHz are suppressed by more than three orders of magnitude ≅ 70dB (blue circle).

3.3.2 Receiving filter of the Receiver PCB

Unlike the Transmitter PCB using the coil pairs to transmit the 500 kHz charging and the 13,56 MHz signals, the receiver circuit is built using only one coil. To achieve the best performance, the received signal has to be split into two signals. Figure 3-15 shows the equivalent circuit of the Receiver PCB with the filter and the MF1 IC S50 chip.



Figure 3-15: Filter on the Receiver PCB

The red circle represents the equivalent circuit of the coil. With the coil depending com-ponents:

Ω= kRcoil 3001 : Eddy current loses Ω= 41,42coilR : Power loss in the windings

HLcoil μ30= : Inductivity of the coil pFCcoil 5,2= : Parasitic capacity of the windings

These parameters are necessary to perform truthful simulations using the tool LT_Spice. The simulations are needed to develop a universal circuit to perform with any load rep-resenting the device to be charged. Therefore, the simulations are performed using vari-able loads (represented by loadR ) ranging from 20Ω (≈ used LED) and 1MΩ (open circuit mode in case the battery of a device is completely loaded). Additionally, the coupling factor between the receiver coil and the associated coil pairs on the Transmitter PCB depends on the location of the Receiver PCB. In the built version, the coupling factor varies from 0,1 (coils hardly “see” each other) and 0,5 (the coils are located relatively close to each other). Thus, the coupling factor values are included in the simulations as well. The blue circle represents the input properties of the used RFID chip [10]. Additionally

obeCPr is taken into account, since this is the capacitance of the probe used for later measurements performed on this circuit. The components have the following values:

Ω= kRRF 15 pFCRF 16= pFC obe 5Pr =

Using the predefined components together with the simulations and the equations ex-plained in the preceding section, the following values are obtained.



The LC series circuit represented by 3L and 3C (green circuit) is dimensioned consistent with the LC series circuit used in the Rx filter and represented by FL (1µH) and 1FC (100nF) in figure 3-12.

2C , 4C and 3L (purple circuit) built a LC parallel circuit with the resonance frequency at around 13,56 MHz. Using the equation (3.8) where 3L corresponds to FL and the total impedance of 2C and 4C corresponds to 2CFC , 2C is calculated to 120pF. Due to this comparable high value, the small probe capacity of 5pF has negligible influence on the measurement. The capacitor 5C builds a LC series circuit with coilL (yellow circuit) and a resonance frequency close to 500 kHz to compensate the weak coupling for the power path. Using equation (3.8), 5C is calculated to 3,9nF. For frequencies at around 13,56 MHz it can be considered as a short. To avoid the low-pass property of coilL together with 6C it builds a LC series circuit with a resonance frequency at around 13,56 MHz. Using the equation (3.8) and 30µH as the Value for coilL , 6C is calculated to 4,7pF. As described above the coupling factor is vari-able, depending on it the value of coilL varies as well. Thus, the resonance frequency of the series circuit is shifted depending on the location of the Receiver PCB. To avoid resonance fainting of the complete filter a damping resistor 6R is used. The task of this resistor is to damp down the resonance magnitude evoked by coilL and 6C . The inductance 4L and the capacitance 1C (orange circuit) are dimensioned in order to build a Band-Stop filter together with loadR to avoid the 13,56 MHz signal at the load. Since loadR can vary between a couple of Ohms and several mega Ohms, the amount of the used current varies as well. Considering that the complete current used by loadR has to pass 4L , the value of this needs to be kept relatively low to avoid losses. On the other hand to assure a satisfying filtering of the 13,56 MHz signal the value of 4L has to be relatively high. Best performance of the Band-Stop, using LT_Spice, is obtained using

pFC 331 = and HL μ7,44 = . Figure 3-16 shows the simulated voltage ratio RFIDV / COILV . The green graph in the figure shows the simulated ratio with k = 0,5 and loadR = 1MΩ, the blue graph respectively represent the simulation done with k = 0,1 and loadR = 20Ω.



Figure 3-16: Simulated voltage ratio of the signal filter on the Receiver PCB The red circle marks the area around the frequency of 500 kHz. In this area the ratio is suppressed by more than four orders of magnitude ≅ 90dB. The gray circle marks the area around 13,56 MHz where the voltage ratio ideally equals 1. Figure 3-17 shows the measured equivalent to the simulated voltage ratio pictured in figure 3-16.

Figure 3-17: Measured voltage ratio of the signal filter on the Receiver PCB The red and blue circles mark the 500 kHz and the 13,56 MHz respectively. The voltage ratio marked with the red circle is suppressed by three orders of magnitude ≅ 60dB. Compared to the simulated 90dB the value seems to be relatively low. The area around 13,56 MHz is suppressed by ≅ 10dB.



The reason for such difference between the simulated and the measured results are real properties, losses and parasitics of the used passive devices. The measured values of the filter seem to be not sufficient enough. The performed tests have shown that the filter performance with current configuration delivers unreliable results. An performance improvement has to be done.

3.4 Functionality of the board

This section aims at describing the complete functionality of the Controlling Board. Gen-erally, it is used as a communication interface between the host controller (PC) and the portable device. Furthermore, it serves as controlling hardware in order to provide the connection between the power source and the charging coils. As described in section 3.1.1, the PN511 provides a signal at a frequency of 13,56 MHz through the pins TX1 and TX2. This signal generates a RF field using an antenna con-nected to these two pins. The generated RF field enables the communication with de-vices located within its range. Data coming from the device are captured at the Rx pin and evaluated using intern logic. Since altogether four antennas have to be connected to the pins TX1 and TX2, an analog switch is used. Figure 3-18 shows the block diagram of the described implementation.

1

2

3

4

ADG714

S1

S2

S3

S4

S5

S6

S7

S8

D1

D2

D3

D4

D5

D6

D7

D8

TX1

TX2

PN511PC

RX

Figure 3-18: Antennas connection using ADG714



Using the analog switch, it is possible that every used antenna generates a separate RF field. Therefore, devices placed within an antenna’s field can be kept apart from the ones within the field of a different antenna. Thus the data provided by the four communication coils are used to enable energy flow for the separately controllable charging coils. The current flow through these coils is controlled by the MOSFETs described in section 3.1.3. The analog switch and the MOSFETs are controlled using the two-level-DC volt-age (0V/5V) provided by the digital outputs of the DAQmxCARD 6024E analog board (see chapter 10.7) via the DAQmxCard interface (number 10 in figure 3-1). Figure 3-19 shows the devices connected to the DAQmxCard interface.

SCLK

SYNC

DIN

RESET

ADG714

1CCV

2CCV

3CCV

4CCV

DA

Qm

xCAR

D60

24E

1

2

3

4

5

6

7

8

R

R

R

R

C2

C2

C2

C2

C1

C1

C1

C1

G D

S

S

S

S

D

D

D

G

G

G

Power Coils

Figure 3-19: Connections of the DAQmxCARD interface

The LEDs at the four digital inputs (12) of the ADG714 analog switch stabilize the sup-plied voltage and visualize the frequency of the signal connected to the according input pin. The series resistors R shown in the figure above are necessary for current limiting purposes. The pins 5 through 8 of the DAQmxCard interface are used to control the current flow through the MOSFETs. If the level of the voltage is provided by the analog board 5V, the circuit is closed, the current flow is enabled and the corresponding charging coil emits magnetic flux – the device within the magnetic field is being charged. With 0V connected to the “Gate” pin the MOSFET is blocked and the current flow disabled. CCV is the charg-ing coil supply voltage connected to the board via the charging power supply interface (9). The Capacitor C1 and C2 compensate the reactive power issued by the charging coil power supply.



4 Software

This chapter consists of the software part of the project. The following sections explain the configuration of the PN511 needed to communicate with MifareTM chips. The per-formed implementation into LabVIEW is also a part of this chapter.

4.1 Configuration of the PN511

The contact-less UART and the host controller are required to control the complete ISO1443/MifareTM protocol. For the purposes of this thesis, only the configuration of the PN511 and the „Request“ command are implemented into software. Therefore, only the register settings for these tasks will be explained. The table 4-1 shows the configuration settings. The cells which have yellow background are default values and do not have to be configured after a power-up or a soft reset.

Starts transmission of data0x870x000x0D BitFramingReg

0x26 is written to the buffer0x26XXh0x09 FIFODataReg

Controls logical behaviour of the antenna driver pins TX1 and TX20x830x80

0x14TxControlReg

Defines demodulator settings0x4D0x8D0x19

DemodReg

Request

Starts the wake up procedure0x000x200x01 CommandReg

Controls the setting of the antenna driver0x400x00

0x15TxAutoReg

Clears the internal FIFO buffer0x800x000x0A FIFOLevelReg

Activates the transceive command0x0C0x200x01 CommandReg

Configuration

The PN511 acts like an initiator0x100x000x0C

ControlReg

DescriptionISO/IEC14443ARegister Reset Value

Register Name and Address

Table 4-1: Register setup during communication The configuration procedure always needs to precede any other tasks involving the an-tenna driver in case of ISO14443A/MifareTM standards (other settings might be neces-sary if another operating mode is required). The PN511 is defined to be the initiator. In case of communication with a MifareTM card, this means that after starting the “Tranceive-Command” the in FIFO buffer stored data will be transmitted using the “self-generated” RF field. Afterwards, the PN511 changes into the “Receiver Mode” to receive



the responses from the cards located within the RF field. Then, the pins TX1 and TX2 are set to deliver the 13,56MHz energy carrier modulated by the transmission data, which results in the RF field being switched on. To send a „Request“ to all cards in the RF field, the “Tranceive-Command” needs to be activated. As mentioned before, this circular command repeats transmitting data from the FIFO buffer and receiving data from the RF field continuously (see chapter 2.2.2). Each transmission process has to be started by setting bit StartSend in the register Bit-FramingReg to 1. Additional to the bit TxLastBits in this, register needs to be set to 111 in order to define the number of bits of the last byte ( in this case the bits 100110 as a part of the REQA = 0x26) to be transmitted. As the closure of the „Request“ procedure, the FIFO buffer has to be checked for the ATQA (2 bytes). If the FIFO buffer contains these two bytes; a MifareTM tag has been detected.

4.2 Implementation of the “Request” command using LabVIEW

Using the development environment LabVIEW, the MifareTM „Request“ function of the PN511 is implemented. Figure 4-1 shows the screenshot of the “Front Panel” of the “RS232 MifareTM request regulation.vi”. This VI sets certain registers to send a „Request“ to a MifareTM card within the RF field and to receive an answer, using the RS232 inter-face. The purpose of this program is to check the different properties of the PN511. The adjusted settings for an optimum communication (range between the communication partners, used energy etc.) can afterward be used as references in later applications. This chapter explains the functionality of the written VI.



Figure 4-1: VI to execute the MifareTM „Request“ function The “VISA resource name” is a control, which specifies which resource is to be opened. It can be chosen between several series ports. The control “Output power during modulation” defines the value of the conductance of the output N-driver during times of modulation. The conductance value is binary weighted. Therefore using the bits 0-3 (16 values) of the register “GsNOnReg” (0x27) can be set in order to regulate the modulation index. Thus, the control “Output power during no modulation” defines the conductance of the N-driver during times of no modu-lation. For these purposes, the bits 4-7 of “GsNOnReg” need to be set. This may be used to regulate the output power. To achieve the farthest distance between the com-munications partners both controllers need to set to their highest values. The “RS232 MifareTM power regulation.VI” performs the setting of this register. “Gain” regulates the receiver signal voltage gain factor. It can be chosen between 8 values (from 18dB to 48dB in 5dB steps). The values are binary weighted and are set using the bits 4-6 in the register “RFCfgReg” (0x26). During usage of this VI, the value 5 (38dB) had given the best performance conditions. Everything above this value caused interferences. The controls “Sensitivity” and “Detector amplifier” have no use for the MifareTM „Request“ function. Using them, the sensitivity of the RF field detector of the PN511 is adjustable as well as an additional amplifier can be activated. These tasks are only necessary for NFCIP-1 (NFC communication) protocol purposes. The settings of this register take place using the “RS232 sensitivity-gain regulation.VI” The PN511 has an internal high pass filter in the receiver chain. It can be activated using the “High Pass Filter” control. If set, the bits 0-1 in the register “ManualRCVReg” (0x1D)



are set to 3h, which selects the corner frequency to 848kHz. The “RS232 high pass filter.VI” is written for these purposes. The purpose of the “CollLevel” control is to define the minimum signal strength at the decoder input that has to be reached by the weaker half-bit of the Manchester-coded signal to generate a bit-collision relatively to the amplitude of the stronger half-bit (See chapter 10.2). This means that the highest possible value would give the best perform-ance. The experience had shown that the value 5 gives the best performance. “CollLev” is set using the bits 0-2 of the “RxThresholdReg” register (0x18). The same register (bits 4-7) is used to set the “MinLev” control. It defines the minimum signal strength at the detector input that shall be accepted. If the signal is below this level, it is not evaluated. This control should be kept as low as possible to get the best performance for the pur-poses of this thesis. However, the performance of the detector seems to be at the best when the control is set to 3 or 4. The register “RxThresholdReg” is set by the “RS232 MinLev-CollLev.VI”. If a card is detected within the RF field, the indicator “Card detected” is activated, and “Card response” would show the received ATQA in this case. The “STOP” control fin-ishes the program after being pushed. The “Reset PN511.VI” activates the “SoftReset” Command by writing 0Fh to the “Com-mandReg” register. In consequence of this, all registers are set to the reset values. The occurrence of an error is indicated by the “Simple Error Handler.VI”. If an error oc-currs, this VI returns a description of the error in an optional dialog box. The algorithm of this VI is represented by the following flowchart.



Figure 4-2: Flowchart of “RS232 MifareTM request regulation.VI”



4.3 Configuration of the Controlling Board using LabVIEW

The purpose of this chapter is to describe the functionality of the “Digital Pattern.VI”, which had been written to run the Controlling Board. Figure 4-3 shows the “front panel” of the VI. The purpose of this software is to control the analog switch ADG714 so that a sequential connection to the antennas is possible. Every time a different antenna is connected to the PN511, a “„Request“” is sent. If a MifareTM tag is within the RF field of this antenna, which answers the “Request”, one or more (depending on the size of the antenna used by the tag) of the four LEDs (e.g Coil1, Coil2, Coil3, Coil4) is turned on and the proper DAQCard-6024E (see 10.7) channels, connected to the MOSFETs, are activated.

Figure 4-3: Front Panel – Digital Pattern.VI The “VISA resource name”, as explained in 4.2, is a control, which specifies which re-source is to be opened. The so called “Timed Loop” is used in this VI. It is generally a “While Loop,” meaning only that each iteration of the loop is executed using a specified period of time. The con-trol “Period High” defines this specified period in ms. The “Timed Loop” is necessary to write precise timing data to the DAQCard-6024E. One period of the SCLK wire, shown in figure 4-4, are two iterations of the “Timed Loop” sending a logical “0” and a logical “1” to the channel 0 of the DAQCard-6024E. Since all 8 digital outputs of the DAQCard-6024E are necessary to run the Controlling Board (e.g. four digital inputs of the ADG714 and for the charging coils used MOSFETs), it would have been too extensive to address every single channel of the DAQCard. Therefore, the control “port” is used to address all eight ports at one time. This is done by sending a number between 0 (0V on all channels) and 255 (all channels active) to the specified “port”. For example, the ports 0 and 7 are activated by sending 129. The control “Pattern” is an array of numbers. These numbers are used to be written to the port. With every iteration of the “Timed Loop,” one of the 82 numbers, stored in the



array, is sent to the port. Every number represents one tact or half a bit of the SCLK signal connected to the ADG714. Figure 4-4 shows the timing diagram of the bits 7 and 6 (switches 7 and 6) represented by the numbers stored in the “Pattern” array.

SCLK

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

SYNC

DIN Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

RESET

Tact

131130

133 133 129 129 129 129 129 129 131 131132 132 128 128 128 128 128 128 130 130

Pattern

MIFARE

REQUEST

Figure 4-4: Timing diagram generated by the Digital Pattern.VI

Between the transmission of the 21st and the 22nd tact (out of the 22 tact used to send any of the 8 bits) to the DAQCard-6024E, the “Request” command is performed. The algorithm of the “Digital Pattern.VI” is schematically represented by the following flowchart.



Figure 4-5: Flowchart of „Digital Pattern.VI“



The gained findings from the previous section (e.g. “power output during modulation/no modulation”, “Gain”, “CollLev” and “MinLev”) are used for an optimal communication of the PN511 with the MifareTM tags in this program. The procedure for setting the registers using these findings is performed in the “RS232 „Request“ adjustment.VI”. The purpose of the “DAQmx Create Channel (DO-Digital Output.VI)” is to create a task (e.g. virtual channel). The instances of this VI correspond to the I/O type of the channel (e.g. “Port”), which is a digital output in this case. The “DAQmx Start Task.VI” transitions the task to the running state. LabVIEW requires the usage of this VI for the present ap-plication. To write the data to the channel the “DAQmx Write (Digital U32 1Chan 1Samp).VI” is used. Additional to an execution with every iteration of the “Timed Loop”, it is also exe-cuted at the end of the program to write a 0 to the channel, which deactivates all active ports. This is followed by the “DAQmx Clear Task.VI”, which stops and clears the per-formed task. Any resources reserved by the executed task are released. As shown in chapter 3.3 the filter developed for the receiver part of the application doesn’t deliver reliable results. Therefore, to be able to use a MifareTM tag attached to a Receiver PCB without a filter, a software solution has been found. Every time before a “RS232 MifareTM request.VI” is executed, the charging coil “belonging” to the communi-cation coil, to send the “Request”, is deactivated. Thus, using the formula ((“Tact Num-ber”/20)+2)2 the “Port Number” responsible for the charging coil is calculated. The value is abstracted from the actual “Pattern” number. Using the “DAQmx Write (Digital U32 1Chan 1Samp).VI” this number is written to the channel, disabling the port. The charging coil is deactivated and the communication coil can perform the “Request” command without being interfered. The “CARD 6024E charging-coil activation.VI” is called after each execution of the “RS232 MifareTM request.VI”. It returns the values of the ports (e.g. 8, 16, 32, and 64) of the virtual channel according to the location of the detected MifareTM tag (see 3.4 for explanation about the usage of these ports). The location is done using the actual tact number (e.g. 20, 40, 60, and 80). The port values are stored in “Gate Port” and added to the “Pattern” before each iteration of the loop is performed. The default value for the first 20 iterations of the application is 0. Additionally, the returned values are also used to activate the “Active Coils”-LEDs. Figure 4-6 shows the flowchart of the “CARD 6024E charging-coil-activation.VI”.



Figure 4-6: Flowchart of “CARD 6024E charging-coil activation.VI”



After being started the VI reads in “Tact Number” (e.g. 20, 40, 60, and 80), “Gate Port” (sum of the active ports serving the charging coils) and “Card Detected” (location of a RFID tag within the currently activated RF field). Using “Tact Number” the number of the port for the currently used antenna (“Port Number”) is calculated. When the port with the according number is already active and a RFID tag has been detected no further changes are done to the “Gate Port”. The same procedure is done when the port is not active and no tag has been located. In case of a detected tag with a non-active port the number of this port is added to “Gate Port” and it is subtracted with no card within the field but an active port. After finishing the calculations “Gate Port” is converted into a Boolean array for “Active Coil’s” sake. “Gate Port” together with this array is returned in order to fulfill the cycle of the “Digital Pattern.VI”.



5 Results and Analysis

This chapter consists of measurements and simulations, which are done to analyze current achievements.

5.1 Analog Switch measurements

According to [9] the “ON” Switch Source/Drain Capacitances Error! Objects cannot be created from editing field codes./Error! Objects cannot be created from editing field codes.(ON) are 22pF and the “OFF” Switch Source/Drain Capacitances Error! Objects cannot be created from editing field codes./Error! Objects cannot be created from editing field codes.(OFF) are 11pF. Figure 5-1 shows the equivalent circuit of these capacitances and how they are connected to Tx1. The same equivalent circuit can be applied to Tx2.

Figure 5-1: Equivalent circuit of the ADG714 including the parallel capacitances According to the picture above following applies:

CP = CS(ON) + CD(ON) + 3CS(OFF) Equation (5.1) At any time during the performance of the ADG714 every one of the Tx-outputs of the PN511 is “facing” one opened and three closed channels of the analog switch (see fig-ure above). Therefore, the complete capacitance Cp, measured with reference to ground, should be around 77pF. To get the exact values, measurements on the switch are performed. Figure 5-2 shows the values of the parallel capacitance Cp measured at the connection point of the Tx1 pin and the four odd numbered inputs of the ADG714. The same condi-tions are used to measure the parallel capacitance at the connection point of the Tx2 pin



and the four even numbered inputs of the ADG714. The results are shown in the figure 5-3. The red marked areas show the values around 13,56 MHz.

Figure 5-2: Parallel capacitance at Tx1 with reference to the ground The measured value of the parasitic parallel capacitance Cp at the Tx1 pin is around 70pF at 13,56 MHz.

Figure 5-3: Parallel capacitance at Tx2 with reference to the ground A value of around 80pF is measured at 13,56 MHz, at the connection point of Tx2 with the four even numbered inputs of the ADG714. Additionally a capacitance measurement between these two points (capacitance Cv) is also performed. The measurement is done with one closed and three opened channels at each Tx-output. The value measured for the frequency of around 2pF. The measured values, shown in the two figures above are included into the calculations done in order to adjust Error! Objects cannot be created from editing field codes. of the used an-tennas. The measured value of Cv is neglected.



5.2 Voltage measurements

This section shows the results of the voltage measurements performed, between the PN511 and the antenna, on the controlling and the TAMA boards respectively. Figure 5-4 shows the circuit with numbers 1, 2 and 3 marking the positions, where the measurements, with reference to ground, are taken. The upper part of the figure repre-sents the equivalent circuit on the TAMA board as a reference. Correspondingly, the lower part of the figure represents the equivalent circuit of the Controlling Board.

Figure 5-4: Equivalent circuits, of the sections between PN511 and the antennas, of the TAMA (for reference) and

the Controlling Boards with marked position for voltage measurements These measurements are done in order to evaluate the influence of the analog switch ADG714. The figure 5-5a shows the voltage measured at the Tx1 output of the PN511 (number 1 in the figure above) on the TAMA board. The figure 5-5b shows the voltage at the same location (with one channel of the ADG714 closed) measured on the Controlling Board. Additional voltages at the matching circuit - number 2 in the figure above (TAMA: figure 5-6a and Controlling Board: figure 5-6b) and at the antenna - number 3 in the figure above (TAMA: figure 5-7a and Controlling Board: figure 5-7b) are measured. The number provided underneath every figure can be used to compare the shown graphs. On the first configuration of the Controlling Board the analog switch was placed between the EMC filter and the matching circuit. In this case only one EMC filter was necessary. But the strength of the signal pictured above is beyond the maximum allowed voltage



connected to the analog switch (±2,4V). This causes crosstalk between the channels. Moving the analog switch closer to the PN 511 and providing every antenna with an own EMC filter raised the performance of the ADG714 and reduced the crosstalk signifi-cantly. The provided graphs seem to show similar properties. Even thought the measured volt-ages, which belong to the TAMA board, seem to be a little higher. This can be explained with the bigger size of the antenna used on the board. Therefore the analog switch turns out not to influence the signal flow between the PN511 and the antennas.



Figure 5-5a: Voltage at the Tx1 pin (1) of the PN511 on the TAMA board with reference to the ground

Error! Objects cannot be created from editing field

codes.

Figure 5-5b: Voltage at the Tx1 pin (1) of the PN511 on the Controlling Board with reference to the ground



Figure 5-6a: Voltage at the matching circuit (2) on the TAMA board with reference to the ground

Figure 5-6b: Voltage at the matching circuit (2) on the Controlling Board with reference to the ground



Figure 5-7a: Voltage at the antenna (3) on the TAMA board with reference to the ground

Figure 5-7b: Voltage at the antenna (3) on the Controlling Board with reference to the ground



5.3 Performance tests

This section describes the performance of the complete device including the location of the Receiver PCB. Figure 5-8 shows a photograph of the Controlling Board connected to all devices neces-sary for the performance.

Figure 5-8: Photograph of the complete Controlling Board structure The complete structure consists of following parts: Power supply for the charging coils Connector Block of the DAQmxCard Transmitter PCB (used coils are marked with green sticker) Controlling Board To demonstrate the achieved results a Receiver PCB with an integrated filter (figure 5.9) is used. Placed on the Transmitter PCB the LED started to emit light (figure 5.10).

Figure 5-9: Photograph of the Receiver PCB with the filter and RFID chip



The Receiver PCB consists of following parts: 1. Printed receiver coils for 2. Power LED 3. RFID circuit including the MF1 IC S50 chip and the filter circuit 4. Receiver circuit together with a ferrite sheet.

Figure 5-10 shows the photograph of the Receiver PCB with the explained filter and a MF1 IC S50 chip. To evaluate the performance of the filter an additional Receiver PCB is used. A self –made tag is stacked to the bottom of it (figure 5-11). Since the tag uses its own antenna to receive and sent data, no filter is necessary.

Figure 5-10: Photograph of the Controlling Board with the Antenna PCB and two Receiver PCBs The performance of the Receiver PCB with the integrated filter is unreliable. As shown in chapter 3.3 the measured properties of the built filter differ enormously from the simu-lated ones. Relying upon the performance of the filter observed during the done tests the circuit seems to be in need of improvement. On the other hand the Receiver PCB with the tag stacked to its bottom seemed to per-form really well; as long as the energy transfer is disabled during the data transfer (see 4.3). Thus, the following tests are performed using the self-made MifareTM tag as the communication partner of the PN511. The timeslots, during which the energy transport is interrupted for communication pur-poses, are noticeable and disturbing. The LED turns off for a split second every time the “Request” is performed. But compared to the period of time when the LED emits light, this slot is negligible. Although this solution seemed to deliver a good performance, a Receiver PCB with an improved filter is preferable.



Figure 5-11: Photograph of a Receiver PCB with a MifareTM tag stacked to the bottom of it The rubber sticks in the photograph above are used to evaluate the maximum possible height (distance between the tag and the Transmitter PCB) at witch a communication between reader and receiver is still possible. At a distance above 6mm no communica-tion could be accomplished. See figure 5-12 for the experimental setup.

Figure 5-12: Photograph of the experimental setup in order to determine the maximal distance between the Trans-mitter PCB and the Receiver PCB at which a communication still can be performed

Additionally to the height measurements location measurements are performed. These are done to determine all of the locations (within the area of the four used antennas) where the used tag is able to communicate with the PN511. The location measurements are done on the surface of the Transmitter PCB (figures 5-13a) as well as 3mm (figures 5-13b) and 6mm (figures 5-132c) above it. In order to have a better observation of the



exact location of the tag, a transparent plastic lid is used. The tag is fixed to the bottom of the lid, so that there is no barrier between the coils and the tag.

Figure 5-13: Photograph of the performed observation for the communication of the used tag and the reader with

respect to the location of the tag. a) surface; b) 3mm above; c) 6mm above; The results of this experiment are shown in figures 5-14 (a, b and c). The dark coils in the figure represent the four coils connected to the Controlling Board. The colored areas show the locations where the tag could be located (using the “Active Coils” of the “Digital Pattern.VI”). Different colors are chosen to clarify these locations for each coil. Figure 5-14a pictures the results from the location experiment performed on the surface of the Receiver PCB. The figure 5-14b represents the experiment done with the tag being 3mm above the coils. Figure 5-14c shows the results of the experiment done at a height of 6mm. While on the surface, the tag could be located within the complete area covered by the four coils. Placed exactly between two coils the tag is located by both of these coils. 3mm above the coils the location areas got limited. Placed between two coils the tag couldn’t be located at all. But moving the tag, just one mm toward one of these anten-nas, caused one of the “Active Coils” to turn on. With 6mm between the tag and the Receiver PCB there are just a few places for the tag to be clearly located. Placed exactly above the center of a coil the tag could be located. Is the tag moved just a few mm into any direction, no location could be performed. To provide a comfortable and accurate function of the charging pad the maximal location height should be increased from 6mm to at least 10mm with a location performance shown in figure 5-14a. The possible ways to achieve this would be to increase the size of the receiver coil, improve the performance of the receiver filter and/or amplify the generated RF field.



Figure 5-14a: Locations on the Transmitter PCB where the used RFID tag can be located at a distance of 0mm

Figure 5-14b: Locations on the Transmitter PCB where the used RFID tag can be located at a distance of 3mm

Figure 5-14c: Locations on the Transmitter PCB where the used RFID tag can be located at a distance of 6mm



6 Summary and future outlook

An inductive wireless Power Pad using RFID technology for communication is con-structed and realized. The pad includes a RFID reader in order to detect and to commu-nicate with RFID tags added to receiver circuits. Depending on the data received from such a tag the energy transfer is started or terminated at the location the receiver is placed. Using an on ISO14443 based transmission module a Controlling Board is built. The Controlling Board includes the NFC controller module for communication purposes and an analog switch for signal routing purposes. A Transmitter PCB connected to the Con-trolling Board is used to transmit data and energy. For these purposes two kinds of coils are used on the Transmitter PCB: sensor coils to transmit data and power coils to transmit energy. The sensor coils on the Transmitter PCB are sequentially multiplexed to the NFC module to generate a RF field, which is used to communicate with chargeable devices. Depending on the data received by such a sensor coil, the according power coil is enabled or disabled. The current version controls four of the sensor and four of the power coils on the Trans-mitter PCB. In the current version, during data transmission the energy transmission of the according power coil is disabled because the signal used to transmit energy interferes with the data signal. The complete system is controlled by a program written in LabVIEW. Further developments should be performed to increase the number of served coils. Fur-thermore, an on-board microcontroller would make the device independent of a com-puter. An improved filter could allow a simultaneous power and data transmission.



7 References

[1] http://www.splashpower.com/ [2] http://www.aiye.com.cn/prod_pd_intro_01.html [3] http://www.ntech.t.u-tokyo.ac.jp/index.en.htm [4] Dr. E. Waffenschmidt, Senior Scientist at Philips Research in Aachen,

[email protected], Philips GmbH Forschungslaboratorien, Weißhausstr.2, 52066 Aachen, Germany

[5] Landt, Jerry (2001). Shrouds of Time: The history of RFID (PDF). AIM, Inc.. Re-

trieved on 2006-05-31 [6] http://www.nxp.com/#/pip/cb=[type=product,path=/53420/53422]|pip=

[pfp=53422][0] [7] Management-Leitfahden-RFID-2006-12-VDEB-AIM.pdf

(www.aim-d.de/getasset.php?asid=304) [8] http://www.adsx.com/ [9] http://www.idtechex.com/products/en/articles/00000638.asp [10] Product data sheet, “MF1 IC S50-Functional specification”, NXP-Semiconductors,

15 January 2007 [11] Datasheet analog switch ADG714 from ANALOG DEVICES [12] Product data sheet, “PN511 Transmission Module”, NXP-Semiconductors, 25

January 2007 [13] Application Note, “NFC Transmission Module Antenna and RF Design Guide”,

Philips, 12 April 2005 [14] http://www.datasheetcatalog.net/de/datasheets_pdf/ [15] National Instruments, “DAQ 6023E/6024E6025E User Manual”, National Instru-

ments, 2000 [16] R.Hui, W.Ho. A new generation of universal contactless battery charging platform

for portable consumer electronic equipment. PESC 2004



8 List of figures

Figure 1-1: Energy transmission system based on Capacitive Coupling .............................8

Figure 1-2: Inductively coupled power transmission system ................................................8

Figure 1-3: SplashPadTM by Splashpower [1].......................................................................9

Figure 1-4: PowerDeskTM by Edison Electric Corp. [2].......................................................10

Figure 1-5: Power sheet introduced by University of Tokyo [3] ..........................................10

Figure 1-6: Photograph of the current Charging Pad version with a MP3 player being charged .............................................................................................................11

Figure 1-7: Photograph of the antenna array PCB (top bottom).........................................12

Figure 1-8: Photograph of two receive circuits on the pad .................................................13

Figure 1-9: Block diagram of the construction....................................................................14

Figure 2-1: RFID tag implant..............................................................................................15

Figure 2-2: RFID system....................................................................................................16

Figure 2-3: MF1 IC S50 Block diagram [10] .......................................................................17

Figure 2-4: Memory organization of a MifareTM chip [10] ...................................................18

Figure 2-5: ISO/IEC 14443A standard communication diagram ........................................18

Figure 2-6: Memory access [10].........................................................................................19

Figure 3-1: Photo of the Controlling Board.........................................................................21

Figure 3-2: Pinning diagram PN511...................................................................................22

Figure 3-3: ADG714 block diagram [11].............................................................................25

Figure 3-4: Wire Serial Interface Timing Diagram [11] .......................................................26

Figure 3-5: Block diagram of the complete RF part............................................................27

Figure 3-6: Impedance transformation of the matching part [12]........................................28

Figure 3-7: Series equivalent circuit ...................................................................................28

Figure 3-8: Parallel equivalent circuit .................................................................................29

Figure 3-9: Definition of transformation impedance trZ [13] ..............................................30

Figure 3-10: Magnitude of the matchR ..................................................................................31

Figure 3-11: Phase of the matchR .........................................................................................32

Figure 3-12: Filter on the Controlling Board .......................................................................33

Figure 3-13: Transformed circuit of the filter on the Controlling Board...............................34

Figure 3-14: Ratio of voltage at Rx and Vind .....................................................................36

Figure 3-15: Filter on the Receiver PCB ............................................................................37



Figure 3-16: Simulated voltage ratio of the signal filter on the Receiver PCB....................39

Figure 3-17: Measured voltage ratio of the signal filter on the Receiver PCB....................39

Figure 3-18: Antennas connection using ADG714 .............................................................40

Figure 3-19: Connections of the DAQmxCARD interface...................................................41

Figure 4-1: VI to execute the MifareTM „Request“ function .................................................44

Figure 4-2: Flowchart of “RS232 MifareTM request regulation.VI”.......................................46

Figure 4-3: Front Panel – Digital Pattern.VI .......................................................................47

Figure 4-4: Timing diagram generated by the Digital Pattern.VI ........................................48

Figure 4-5: Flowchart of „Digital Pattern.VI“ .......................................................................49

Figure 4-6: Flowchart of “CARD 6024E charging-coil activation.VI”...................................51

Figure 5-1: Equivalent circuit of the ADG714 including the parallel capacitances..............53

Figure 5-2: Parallel capacitance at Tx1 with reference to the ground ................................54

Figure 5-3: Parallel capacitance at Tx2 with reference to the ground ................................54

Figure 5-4: Equivalent circuits, of the sections between PN511 and the antennas, of the TAMA (for reference) and the Controlling Boards with marked position for voltage measurements......................................................................................55

Figure 5-5a: Voltage at the Tx1 pin (1) of the PN511 on the TAMA board with reference to the ground.........................................................................................................57

Figure 5-5b: Voltage at the Tx1 pin (1) of the PN511 on the Controlling Board with reference to the ground.....................................................................................57

Figure 5-6a: Voltage at the matching circuit (2) on the TAMA board with reference to the ground...............................................................................................................58

Figure 5-6b: Voltage at the matching circuit (2) on the Controlling Board with reference to the ground.........................................................................................................58

Figure 5-7a: Voltage at the antenna (3) on the TAMA board with reference to the ground59

Figure 5-7b: Voltage at the antenna (3) on the Controlling Board with reference to the ground...............................................................................................................59

Figure 5-8: Photograph of the complete Controlling Board structure .................................60

Figure 5-9: Photograph of the Receiver PCB with the filter and RFID chip ........................60

Figure 5-10: Photograph of the Controlling Board with the Antenna PCB and two Receiver PCBs.................................................................................................................61

Figure 5-11: Photograph of a Receiver PCB with a MifareTM tag stacked to the bottom of it62

Figure 5-12: Photograph of the experimental setup in order to determine the maximal distance between the Transmitter PCB and the Receiver PCB at which a communication still can be performed...............................................................62



Figure 5-13: Photograph of the performed observation for the communication of the used tag and the reader with respect to the location of the tag. a) surface; b) 3mm above; c) 6mm above;.......................................................................................63

Figure 5-14a: Locations on the Transmitter PCB where the used RFID tag can be located at a distance of 0mm.........................................................................................64

Figure 5-14b: Locations on the Transmitter PCB where the used RFID tag can be located at a distance of 3mm.........................................................................................64

Figure 5-14c: Locations on the Transmitter PCB where the used RFID tag can be located at a distance of 6mm.........................................................................................64

Figure 10-1: Miller Code.....................................................................................................72

Figure 10-2: Manchester Code ..........................................................................................73

Figure 10-3: Possible connections for the SPI using four or three wires............................74

Figure 10-4: SPI “Daisy-chain”...........................................................................................75

Figure 10-5: Photograph of the TAMA demo board ...........................................................76

Figure 10-6: Schematic of the TAMA board .......................................................................77

Figure 10-7: Assembly list of the TAMA board...................................................................81

Figure 10-8: DAQCard 6024E with BNC-2110 Connector Block [15].................................82

Figure 10-9: Controlling Board schematic ..........................................................................83



9 List of tables

Table 3-1: Pin description of PN511 ..................................................................................24

Table 4-1: Register setup during communication...............................................................42

Table 10-1: 6024 E Series specifications [8] ......................................................................82



10 Appendix

10.1 Miller Code

The Miller Code or Delay Encoding is a way to encode binary data to form a two-level signal. A “0” causes no change of signal level unless it is followed by another “0” in which case a transition to the other level takes place at the end of the first bit period. A “1” causes a transition from one level to the other in the middle of the bit period. The Figure 9-1 shows a screenshot of an oscilloscope containing four different Bytes trans-mitted by the TAMA board in Active Communication mode. The sent Bytes are:

0000 0000 1111 1111 1010 1010 0101 0101

0 0 0 0 0 0 0 0

1 1 1 1 1 1 1 1

1 1 1 10 0 0 0

0 0 0 01 1 1 1

Figure 10-1: Miller Code

The Delay Encoding is used primarily for encoding radio signals because the frequency spectrum of the encoded signal contains less low-frequency energy than a conventional non-return-to-zero (NRZ) signal and less high-frequency energy than a biphase signal.

10.2 Manchester Code

Manchester Code is an encoding method in which data and clock signals are combined to form a single self-synchronizing data stream. Each encoded bit contains a transition at the midpoint of a bit period. The direction of the transition determines whether the bit is a “0” or a “1”. The first half is the true bit value and the second half is the complement of the true bit value. Two conventions exist to define logical behavior of the Manchester code.



Definition by G.E. Thomas – for a “0” bit the signal levels are Low-High and for a “1” bit the signal levels are High-Low. Definition by IEEE 802.3 – for a “0” bit the signal levels are High-Low and for a “1” bit the signal levels are Low-High. To inform the reader device which way the logic “1” is defined, a preamble is sent. Since two signals are necessary to present a bit, the bit rate is half of the baud rate. Figure 9-2 shows a screenshot of an oscilloscope demonstrating a „Request“ response of a MifareTM 4k standard card.

Figure 10-2: Manchester Code

10.3 Load modulation

Load modulation is a type of data transfer widely used for passive tags in RF identifica-tion to transmit data from the tag to the reader. The self-resonant frequency of the tag/transponder corresponds with the transmission frequency of the reader. Therefore if a resonant tag is placed within the RF field of the reader’s antenna, it draws energy from the magnetic field. This can be measured as voltage drop at the resistance of the reader antenna. The switching on and off of a load resistance at the transponder’s antenna effects voltage changes at the reader’s antenna and accordingly has an effect of amplitude modulation. Consequently using the switch-ing, the data are transferred from tag to reader. To reclaim the data in the reader, the voltage measured at the reader’s antenna is rectified.



10.4 Backscatter-Principle

Backscatter is the principle of reflection of waves, particles or signals back to the direc-tion they came from. In the identification process between reader and tag, backscatter is used to return the signal from the reader by the tag. Electromagnetic waves can be reflected by objects with dimensions greater than half the wavelength of the wave. The strength of the reflected wave depends on the object’s reflection cross-section. As a result, objects that are in resonance with the wave front have a large reflection cross-section. This, for example, is the case for antennas at the appropriate frequency. Reader’s antenna emits a wave with power P1. Because of free space attenuation, only a part of this power reaches the transponder’s antenna. A portion of the received power is converted into HF voltage, rectified, and is used in turn on voltage for the tag. The remaining part is reflected by the antenna and returned as power P2. To modulate the amplitude of power P2 a load resistor, connected parallel to the antenna, is switched on and off in time with the data stream to be transmitted. The reflection characteristics (= reflection cross section) of the antenna are influenced by the altering properties of the antenna. This kind of modulated reflection is called modulated backscatter.

10.5 SPI – Serial Peripheral Interface

The Serial Peripheral Interface is a simple hardware and firmware communication proto-col. The data is synchronously transmitted and received guided by a serial clock signal (SCLK or SCK), which is generated by the master. It is used for communication between microcontroller and peripheral chips or intercommunication between two or more micro-controller. Several SPI devices (slaves) can be connected to one master. Every slave is selected by the master using the CS (alternative naming: SS – Select Slave or SYNC ) signal. The SPI is sometimes called a “four wire” serial bus, but some devices require only three wires. See figure 10.3 for a possible single master – single slave connection using four or three wires.

Figure 10-3: Possible connections for the SPI using four or three wires



The used signal names are: MOSI/SIMO (or DIN) – Master Output, Slave Input. Signal is generated by the master and received by the slave. MISO/SOMI – Master Input, Slave Output. Signal is generated by the Slave and re-ceived by the master. SCLK and SYNC are also generated by the master. The data transfer is organized by shift registers. The master transfers data from its regis-ter to the slave, which stores the received data in its own register. If full duplex is used, data can be transferred in both directions simultaneously. Some chips (like the ADG714) have the ability (if connected in series) to transmit the data through themselves to the following device. This way of data transfer is called “Daisy-chain”. See figure 10-4.

Figure 10-4: SPI “Daisy-chain” Every slave passes on the exact data it received from the predecessor during a clock cycle to the subsequent device in the following clock cycle. In this case, only one single SYNC line from the master is necessary to control the complete arrangement.



TAMA demo board

Figure 10-5: Photograph of the TAMA demo board



Figure 10-6: Schematic of the TAMA board



Figure 10-7: Assembly list of the TAMA board



10.6 DAQCard

The 6024 E Series board is high-performance multifunction analog and timing I/O board for PCMCIA (Personal Computer Memory Card International Association) bus com-puters. Supported functions include analog input, analog output, digital I/O and timing I/O. It features 16 channels of analog input, two channels of analog output, a 68-pin connector and eight lines of digital I/O [15]. The Figure 10-8 shows the used card to-gether with the Shield Connector Block.

analog I/O

digital I/O

PCMCIA Bus connection port

Figure 10-8: DAQCard 6024E with BNC-2110 Connector Block [15]

Table 10-1 shows the specifications for the digital logic levels of the 6024 E Series.

Table 10-1: 6024 E Series specifications [8]



10.7 Controlling Board schematic

Figure 10-9: Controlling Board schematic

Wireless power pad with local power activation for portable devices

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