1

A Passive UHF RFID Tag IC

CLASS REPRESENTATION: Represented by: Khalil Monfaredi

Advanced VLSI Course Seminar

2

Outline

Introduction to RFID (Radio Frequency Identification) Tag LSI (30%) Current Mode Rectifier (30%) Current Mode Demodulator (20%) FeRAM (10%) Summary (10%)

3

Block diagram of the UHF RFID tag LSI with 2Kb FeRAM.

[1]

4

RFID: Ubiquitous Sensing Networks

Thing-to-thing networking will begin Sensing tags will play an important role

The presentPerson-to-person networking

The futureThing-to-thing networking

Thermometer

Acceleration

Infrared

Danger

Health care Security

5

Requirements

Communication distance Long distance (10 m)

Incorporation of sensor device Transmit not only ID but also sensing data

Necessity of battery Battery life: as long as possible

Low cost

6

Comparison of Tags Active tag Semi-

passive tagPassive

tag

Communication distance

Good Fair Poor

Incorporation of sensor

Easy Possible Difficult

Necessity of Battery

Need Need No need

Cost High Fair Low

Limited battery life: Solves by wireless power transmission

7

Required conversion efficiency Base

station

Tag

Time=1s Time=3ms

Consume energy=0.3Ws

Supply energy =40Ws

Conversion efficiency > 0.75 %

CW CW

Standby Downlink UplinkRecharge

8

Issues concerning rectifier

Cannot be rectified below threshold voltage Vth.

Vth=0V: There is a possibility that off-leak will occur.

CMOS rectifier

DCcurrentThreshold voltage Vth

0Vth

Region that cannot be rectified

|Zin|=700Vin=0.2V

Zin

Vin

Vin=0.2VRFin=40W

[2]

9

Proposed rectifier

0Vth

Vbth

Apply a bias voltage Vbth Vth

- Generating voltage of Vbth in the same IC chip

Region that cannot be rectified

RFin Vbth

M2

M1(D)

(G)(S)

Vbth-Vth0

Vbth

DC+ = 0.3V @RFin=0.2V

RFin

0.2V

[2]

10

Stacked configuration

DC+

DC-

Stack 6 units

How will 12 Vbth voltage sources be realized?

Stack 6 units of rectifiers to obtain over 1.5V DC

>1.5V

0.3V

Output DC voltage

RFinVbth

Vbth

Vbth

Vbth

Vbth

Vbth

[2]

11

RFin

DC+

DC-

Vbth

PLS

Cb1

Cb3

INV1 INV2

Cb4

Cb2

Vbth distributor

Realization of proposed rectifier

6 units stacked

Vbth

distributor

High Low

Vbth generator

VDD

Vbth=Vth

[2]

12

RFin

DC+

DC-

Vbth

PLS

Cb3

INV1 INV2

Cb4

Vbth distributor

Realization of proposed rectifier

6 units stacked

Vbth

distributor

HighLow

Vbth

Vbth

Cb1

Cb2

[2]

13

DC+

IN

DC -

CP

CP2

Mn2

Vbth

Vbth

Mn1

CP3

Conventional NMOS Half-wave Rectifier

Vbth : External

[2]

Parasitic capacitance CP : LargeVth drop : External cancellation

14

Ferrocap.

Mp1

IN CP

DC+

DC -

(Internal Vth cancellation)

Cb

Cb

Mn1

Proposed CMOS Half-wave Rectifier

IVC

CINF PMOS

Parasitic capacitance CP : SmallVth drop : Internal cancellation

[1]

15

VDD

IV

C

VSS

IN+

IN -

D1

D2

Proposed CMOS Full-wave Rectifier Circuit

Ove

r-cu

rren

tp

rote

ctio

n

(AC GND)

Overcurrent

CP

IV

C

Good configuration for high efficiency

CINF

IV

C

IV

C

[1]

16

Why Current Mode Demodulator?

17

Far

Near

Incoming Power Prec

Operating region

Voltage Detection for Demodulator

Devicebreakdown (4V)

II ININ

Small

Large

Time

VINVIN

NearFar

Detectionresult

Modulationindex : (15%)

VIN,

TagIC

I IN

Prec Taginput

[1]

18

Current Detection for Demodulator

IIININ

Large

VIN

Incoming Power Prec Time

IINIIN

Modulationindex : (15%)

VIN,

TagIC

I IN

Prec

Devicebreakdown (4V)

NearFar

Far

Near

Large

Operating regionDetection

result

Taginput

[1]

19

+ VASK

Currentcomparator

ReferenceCurrent

Generator

Subtraction IASK

IPK

ISIG

IREF

Current-mode Demodulator Block Diagram

Modulatedcurrent

IREF

= IPK x nIPK

ISIG

= (IPK – IASK)IASK

Current Peak Hold

LPF

(baseband)

[1]

20

[3]

21

[3]

[3]

22

[3]

[3]

23

[3]

[3]

24

FeRAM

Stefano Bonetti, Johan Dahlbäck, Hanna Henricsson and Jutta Müntjes

2B1750 Smart Electonic Materials, KTH 26th of October 2005

Adopted from ISSCC 2006 and also

25

FeRAM - Theory

• Spontaneous polarization: above the Curie-temperature TC is the

structure cubic, below a dipole moment occurs (displacement)

• A different charge ΔQ can be observed whether the material is switching or non-switching:

Binary state 1Negative electric fieldNegative polarization

Binary state 0Positive electric fieldPositive polarization

Example: PZT(lead zirconate-titanate)

Q Acap P

[4]

26

WL WL

PL PLBL’BL

Sense AMP

WL

PL

BLSense AMP Vref

[4]

27

Offset cell[4]

28

[4]

29

FeRAM - Requirements

• Small size

• High speed

• High lifetime➔ Destructive reading (after every reading operation is a writing

operation required)

• Low coercive field➔ Low power memory devices

• Large hysteresis➔ High remanent polarization

30

EEPROM FeRAM

Cell

structure

Programming principle

Charge injection Polarization change

ReadSpeed 25µs

Power 12.5µW

Write

Speed 3ms 25µs

Voltage 16V 3V

Power 35.0µW 15.7µW

FeRAM Characteristics

BL

CG

AG

SG

High speedLow power

BL

PL

WL XBL

[1]

31

129tags/s

44tags/s

2.9 timeshigher

EEPROM

FeRAM

Advantages of the Tag with FeRAM

Condition : Read/Write operations

66%reduction

Operating time Throughput

Read3.6ms

Read3.6ms

Write19.4ms

Write4.2ms

[1]

32

Tag IC Performance Summary

Operating Frequency 860MHz - 960MHzModulation Index (Forward) 15% (Minimum)Communication Range Read: 0m - 4.3m(4W EIRP F40k / R40k) Write: 0m - 4.3mRead/Write Throughput(F40k / R160k)

129tags/s

Tag IC Power 80µWESD Protection (HBM) 3,000VAnti-collision Binary tree protocolTechnology 0.35-µm CMOS FeRAMDie Size 1.23mm x 1.50mm

33

Summary

Passive UHF Read/Write Tag IC with FeRAM

4.3m Read/Write communication distance

CMOS only rectifier which has 36.6% efficiency, 2.1 times higher than the conventional

Low-voltage current-mode demodulatorwhich has 27dB dynamic range for the incoming power

Fabricated in 0.35-µm CMOS/FeRAM technology

Tag throughput with FeRAM

2.9 times higher than tags with EEPROMfor both read and write operations

34

References:

[1] H. Nakamoto et al., “A Passive UHF RFID Tag LSI with 36.6% Efficiency CMOS-Only Rectifier and Current-Mode Demodulator in 0.35μm FeRAM Technology,” ISSCC Dig. Tech. Papers, session 17, 2006.

[2] T. Umeda et al., “A 950MHz Rectifier Circuit for Sensor Networks with 10m-Distance,” ISSCC Dig. Tech. Papers, pp. 256-257, Feb., 2005.

[3] A. Djemouai And M. Sawan., “New Cmos Current-mode Amplitude Shift Keying Demodulator (Askd) Dedicated For Implantable Electronic Devices,” IEEE (ISCAS), pp. 441-444, 2004.

[4] S. Bonetti et al., “FeRAM, MRAM, RRAM ,” [online resource] Oct., 2005.