UHF RFID “Micro Reader” Reference Design – …...The Micro Reader is designed to support the...

Application Note AS399x Micro Reader Reference Design

www.austriamicrosystems.com/RFID Rev 1.0 1 - 16

Application Note

AS399x UHF RFID Reader ICs

UHF RFID “Micro Reader” Reference Design – Hardware

Description

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Top View – RF Part

Bottom View – RF Part


Table of Contents:

1 Introduction .................................................................................................. 3 1.1 Key Features Micro Reader (Stand-alone operation)................................................. 3 2 Hardware Description .................................................................................. 4 2.1 Controller - Port Definitions ...................................................................................... 6 2.1.1 Detailed Description................................................................................................... 6 2.2 AS399X Pinout: ......................................................................................................... 8 2.3 MCU - C8051F340 Pin out ........................................................................................ 8 2.4 Controller - Debugging Connector............................................................................. 9 2.5 Supply Concept .......................................................................................................... 9 2.6 Controller - Reset Circuit ........................................................................................... 9 2.7 RF - Oscillator Circuit............................................................................................. 10 2.8 RF - VCO Concept................................................................................................... 10 3 Schematics. ................................................................................................11 3.1 RF Board .................................................................................................................. 11 3.2 Controller Board....................................................................................................... 11 4 Layouts .......................................................................................................12 4.1 RF Board .................................................................................................................. 12 4.2 Controller Board....................................................................................................... 13 5 Bill of Material .............................................................................................14 5.1 RF Board .................................................................................................................. 14 5.2 Controller Board....................................................................................................... 15 6 Disclaimer ...................................................................................................16

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1 Introduction

The Micro Reader Reference Design is a small form factor UHF RFID reader system with an extremely low BOM cost on external components and therefore suitable for embedded application in fast moving consumer goods applications. The Micro Reader is designed to support the ISO 18000-6b and the EPC Generation 2 standards. The reference design consists of two PCBs, a controller board and a RF board which contains the AS399x device. This modular approach was chosen in order to comply with the need to have the RF part separately since typically the host controller of the target application will control the RFID module. A graphical user interface (GUI) for PC is available giving access to all internal registers of the AS399x RFID device and allows diagnostic features like reflected power measurements or continuous modulation of the Tx signal. The Micro Reader communicates with the host computer and draws its power via a conventional USB interface. The Micro Reader is designed to operate on a 5V supply not exceeding the current capability of the USB interface. The communication between the controller board and the RF board is done via a standard SPI interface. The Micro Reader outputs 23 dBm on the antenna port but can be adjusted to lower values using the internal step attenuator of the AS399x device. The Micro Reader may be set to all world-wide allowed UHF RFID frequencies.

1.1 Key Features Micro Reader (Stand-alone operation)

• Small Form Factor • Low BOM Cost on external components • Reading and writing UHF RFID tags (ISO 6b and Gen2)

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• Communication with host computer using the USB interface • USB HID device (automatically installed on host side) • Low cost 8- bit MCU (Silabs) • Controller software written in C enables fast porting to other controller types • Host software written in C++ and QT 4.6 • 23 dBm output power • Less than 250mA current consumption. • Operational world wide • USB powered device • SPI interface between controller and Micro Reader • U.FL antenna connector



2 Hardware Description

The reference design consists of two PCBs which are stacked on top of each other while the top board is the RF part. The controller board on bottom contains the 8-bit MCU and the USB connector for power supply and communication with the host controller.

Stacking of controller board and reader board The dimensions of the two boards are equal: 26,85mm x 20,83mm. Stacking height is 10,2mm.

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Interface Connector positions



The RF board is a 4 layer PCB. The top layer is used for routing the loop filter and the 50 ohm RF tracks which are designed as coplanar waveguides.

Impedance calculation of 50 ohm tracks (AppCAD – Agilent Techn.)

The second layer is a ground layer with a distance of 0.27mm from the top layer. The third layer is mainly used for the power tracks and has a distance of 0.9mm from the second layer. The bottom layer is used for general routing and has a distance of 0.27mm from the third layer.

Layer Stack (Altium)

Components on the RF board are placed on the top and on the bottom layer.

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The controller board is a dual layer board since it has no special requirements on the impedance of the tracks. The thickness of the PCB core is 1.6mm and components are placed only on the top layer. The communication between the controller board and the RF board is done via a standard SPI interface. SPI Pin AS399x Pin MOSI IO7 MISO IO6 SS IO4 CLK CLK IO0 is tied to ground and IO1 is connected to 3.3V.



The Micro Reader outputs the differential RF signal on its high linear Zero-dBm ports (pin 32, 33). A 2:1 Balun from Johanson Technology (T1) converts the differential signal to a single ended one. A power amplifier RF2172 (U2) from RFMD amplifies the transmit signal up to 23 dBm output power. The PA is supplied by the AS399x device using one of its internal programmable LDOs. After the PA the transmit signal is routed to a directional device which is a combination of a coupler and a low pass filter. The antenna connector is a U.FL connector from Hirose. The received signal is routed via a coupling capacitor to the single ended receiver input.

2.1 Controller - Port Definitions

2.1.1 Detailed Description

Pin Signal Description P0.0 MOSI Master out Slave in P0.1 MISO Slave in Master out P0.2 CLK SPI CLK P0.3 IRQ External Interrupt Input P0.4 - Not used P0.5 - Not used P0.6 - Not used P0.7 - Not used

Table 1: Port 0

Pin Signal Description P1.0 - Not used P1.1 - Not used P1.2 IO2 IO Data, Address and Ctrl Bit P1.3 IO3 IO Data, Address and Ctrl Bit P1.4 SS Slave Select P1.5 IO5 IO Data, Address and Ctrl Bit P1.6 - Not used P1.7 - Not used

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Table 2: Port 1

Pin Signal Description P2.0 - Not used P2.1 - Not used P2.2 LED LED Output P2.3 - Not used P2.4 - Not used P2.5 - Not used P2.6 - Not used P2.7 - Not used

Table 3: Port



Pin Signal Description P3.0 PA_PD PA Power down pin P3.1 - Not used P3.2 - Not used P3.3 - Not used P3.4 - Not used P3.5 - Not used P3.6 - Not used P3.7 - Not used

Table 4: Port 3

Pin Signal Description P4.0 - Not used P4.1 - Not used P4.2 - Not used P4.3 - Not used P4.4 - Not used P4.5 - Not used P4.6 - Not used P4.7 RESET Output for resetting the MCU

Table 5: Port 4

Pin Signal Description 7 GND GND Pin 8 D+ USB Data + Signal 9 D- USB Data - Signal 10 VDD VDD Pin 11 REGIN Not used 12 VBUS USB Power In 13 RST Reset Pin 14 C2D Debugging Interface

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Table 6: Other uC Pins



2.2 AS399X Pinout:

Pinout of AS399x

Picture 1: AS399x Pinout

2.3 MCU - C8051F340 Pin out

The pinout from Silabs microcontroller C8051F340 is shown below.

Picture 2: C8051F340 Pin out [Silabs 2006]

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2.4 Controller - Debugging Connector 2.4 Controller - Debugging Connector

A special interface is highlighted which is used to directly connect the Silabs USB Debug Adapter. This interface is used to program the boot loader. A special interface is highlighted which is used to directly connect the Silabs USB Debug Adapter. This interface is used to program the boot loader.

Silabs Debug Interface

Picture 3: Schematic - Debug Interface

2.5 Supply Concept

During power down mode the majority of the AS399x reader chip is switched off but the device still generates a 3.3V supply voltage (VDD_D = pin 38) which supplies the microcontroller unit (MCU). This mode is configured by the resistor R7 (10kΩ) at OAD2 (pin 30) to GND. After start up the microcontroller has to pull the AS399X enable pin (EN = pin 39) to high in order to start the operation of the AS399X finalizing the power up sequence.

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2.6 Controller - Reset Circuit

To enable a reset trough the software, resistor R2 is connected between port pin P4.7 and the reset pin (/RST = pin 13). If the microcontroller needs to be reset, the software writes a logic zero to P4.7.



2.7 RF - Oscillator Circuit

The Micro Reader uses a 20 MHz quartz crystal with two 12pF load capacitors (C3, C4). The crystal should have an accuracy of 10ppm (ETSI requirement).

2.8 RF - VCO Concept.

To generate the high frequency carrier signal for the communication with the tag (840 MHz – 960 MHz) the internal VCO is used and thus only a few passive external components are needed. For this particular reference design following settings was used:

• 915 MHz • 1.2 mA charge pump current • 50 kHz reference frequency • Internal VCO

VCO Reference Frequency

[kHz]

Charge Pump Current [mA]

C25 [pF]

R3 [kΩ]

C24 [nF]

R2 [kΩ] C21 [pF]

20 MHz / V 50 1.2 220 27 3.3 56 110 (100)

Table 7: Loop Filter Reference Settings

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Picture 4: Loop Filter Circuit

Loop Filter



5 Bill of Material

5.1 RF Board

Footprint (SMD = metric) Value Designator Description, Size Tolerance Quantity

Capacitance 2.2uF C1, C5, C13, C15, C17, C19, C26, C29, C33, C35, C43, C45, C47

Ceramic Cap, 1005 +/- 20% 13

Capacitance 10nF C2, C7, C12, C14, C16, C18, C27, C28, C32, C34, C37, C39, C40, C41, C42, C46

Ceramic Cap, 1005 +/- 10% 16

Capacitance 12pF C3, C4, C6, C11 Ceramic Cap, 1005 +/- 5% 4

Capacitance 47pF C9, C10 Ceramic Cap, 1005 +/- 10% 2

Capacitance 22nF C20, C23, C30, C31, C48, C49

Ceramic Cap, 1005 +/- 5% 6

Capacitance 100pF C21 Ceramic Cap, 1005 +/- 1% 1

Capacitance 4pF C22, C36 Ceramic Cap, 1005 +/- 0.25% 2

Capacitance 3.3nF C24 Ceramic Cap, 1005 +/- 10% 1

Capacitance 220pF C25, C50 Ceramic Cap, 1005 +/- 5% 2

Capacitance 10u/10V C38 Ceramic Cap, 1608 +/- 20% 1

Capacitance 100nF C44 Ceramic Cap, 1005 +/- 10% 1

Resistor 10k R1 Resistor 1005 +/- 0.5% 1

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Resistor 51R R4, R5 +/- 0.5% 1


Inductor 39nH L1, L2 Inductor +/- 5% 2

Inductor 3.9nH L3, L4 Inductor '+/- 0.3nH 2

Inductor 2.7nH L5 Inductor '+/- 0.3nH 1

Connector U.FL socket J1 U.FL-R-SMT(10) 1

Connector Header 2 P5, P6 DNP (Do not place) 2

Connector Header 1X5 P2, P7, P8 Header 1X5, 1.27mm 3

AS399x AS399x - UHF Gen2 RFID Reader IC

U1 64-pin QFN (9mm x 9mm)

1

Balun BALUN 900MHZ - T1 Johanson Tech. - 0900BL18B100E

1



Footprint (SMD = metric) Value Designator Description, Size Tolerance Quantity

LP/Coupler Directional Couplers with Low Pass Filter

T2 Johanson Tech.- LPF0910CF15B0100

1

PA RF2172* U2 RFMD – RF2172 1

CRYSTAL Crystal Oscillator Y1 TXC CORPORATION-'7M-20.000MEEQ-T

1

* MRC Components GmbH & Co. KG


Footprint Comment Designator Description Tolerance Quantity

Capacitor 10uF C1 Ceramic Cap, X7R, 10%, 50V, 1005 +/- 20% 1

Capacitor 100nF C2, C3, C5 Ceramic Cap, X7R, 10%, 50V, 1005 +/- 10% 3

Capacitor 1uF C4 Ceramic Cap, X7R, 10%, 50V, 1005 1

Resistor 1K R1, R2, R3 Resistor +/- 5% 3

LED LED2 D1 GREEN, LED (5 mA) 1

MCU TQFP48_L U1 TQFP48_L 1

Connector Receptacle 5 P2, P3, P4 Receptacle 5, 1,27mm 3

Connector USB_B_MINI_AB U2 USB_B_MINI_AB rcpt 1

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6 Disclaimer

Devices sold by austriamicrosystems AG are covered by the warranty and patent identification provisions appearing in its Term of Sale. austriamicrosystems AG makes no warranty, express, statutory, implied, or by description regarding the information set forth herein or regarding the freedom of the described devices from patent infringement. austriamicrosystems AG reserves the right to change specifications and prices at any time and without notice. Therefore, prior to designing this product into a system, it is necessary to check with austriamicrosystems AG for current information. This product is intended for use in normal commercial applications. Applications requiring extended temperature range, unusual environmental requirements, or high reliability applications, such as military, medical life-support or life-sustaining equipment are specifically not recommended without additional processing by austriamicrosystems AG for each application. The information furnished here by austriamicrosystems AG is believed to be correct and accurate. However, austriamicrosystems AG shall not be liable to recipient or any third party for any damages, including but not limited to personal injury, property damage, loss of profits, loss of use, interruption of business or indirect, special, incidental or consequential damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical data herein. No obligation or liability to recipient or any third party shall arise or flow out of austriamicrosystems AG rendering of technical or other services. Copyright © 2010, austriamicrosystems AG, Tobelbaderstrasse 30, 8141 Unterpremstaetten, Austria. For further information please contact: austriamicrosystems AG Business Unit CNC Tobelbaderstrasse 30 A-8141 Unterpremstaetten AUSTRIA Tel: +43-(0)3136-500-5473 FAX: +43-(0)3136-500-4141 [email protected] For Sales Offices, Distributors and Representatives, please visit: http://www.austriamicrosystems.com/contact Subject to change without notice

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UHF RFID “Micro Reader” Reference Design – …...The Micro Reader is designed to support the...

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