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Design and analysis of a low power passive UHF RFIDtransponder IC

Li-Ying Chen • Lu-Hong Mao • Xiao-Zong Huang

Received: 17 August 2009 / Revised: 15 March 2010 / Accepted: 5 August 2010/ Published online: 15 August 2010

Ó Springer Science+Business Media, LLC 2010

Abstract This paper presents a low power passive UHF

RFID transponder IC, which is compatible with ISO/IEC18000-6B Standard, operating at the 915 MHz ISM band

with the total supply current consumption less than 10 lA.

The fully integrated passive transponder, whose reading

distance more than 3 m at 4 W (36 dBm) EIRP with an

antenna gain less than 1.5 dBi, is powered by the received

RF energy. There are no external components, except for

the antenna. The transponder IC includes matching net-

work, rectifier, regulator, power on reset circuit, local

oscillator, bandgap reference, AM demodulator, backscat-

ter, control logic and memory. The IC is fabricated using

Chartered 0.35 lm two-poly four-metal CMOS process

with Schottky diodes and EEPROM supported. The die

size is 1.5 mm 9 1.0 mm.

Keywords Low power Á UHF Á RFID Á Passive

transponder

1 Introduction

Radio frequency identification (RFID) is an automatic

wireless data collection technology with a long history since

the Second World War. Recently, RFID is becoming more

and more popular in many applications, such as supply

chain management, wireless sensing, access to control

buildings, tracking, personal identification and security, etc.

Some big corporations have employed the technology, for

example the Wal-Mart Stores Inc. The increasing applica-

tions have required for high volume, low cost, small size

and higher data rates. This paper describes a long range, low

power, passive UHF RFID transponder IC.

Nowadays, RFID technology operates in several differ-

ent frequency bands, such as low frequency (LF, 125 kHz),

high frequency (HF, 13.56 MHz), ultra high frequency

(UHF, 860–960 MHz) and microwave (2.4 GHz). IF and

HF RFID have been widely employed in many years. But

their reading range is typically limited to less than 1.2 m.

Also, the bandwidth in Europe and other regions is limited

by regulations to a few kilohertz [1]. The passive tran-

sponders that operate in the UHF and microwave frequency

bands allow longer reading distance, higher data rates, and

small antenna sizes. The UHF frequency band RFID tran-

sponders are becoming a hot spot. In North and South

America, the center frequency is 915 MHz, whereas Eur-

ope, Middle East, and Russian Federation mainly use

866 MHz. Asia and Australia use frequencies within the

band from 866 to 954 MHz. Korea made an allocation in

908 to 914 MHz [1, 2].

This paper presents a low power, fully integrated, pas-

sive UHF RFID transponder IC, which is compatible with

ISO/IEC 18000-6B Standard, operating at the 915 MHz

ISM band. The transponder IC is fabricated by Chartered

0.35 lm two-poly four-metal CMOS process with Schottky

L.-Y. Chen is supported by the National High Technology Research

and Development Program of China (No. 2008AA04A102).

L.-Y. Chen (&) Á L.-H. Mao Á X.-Z. Huang

School of Electronic and Information Engineering,

Tianjin University, Tianjin 300072, China

e-mail: [email protected]

L.-Y. Chen

Institute of Microelectronics, Nankai University,

Tianjin 300457, China

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Analog Integr Circ Sig Process (2011) 66:61–66

DOI 10.1007/s10470-010-9521-5

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diodes and EEPROM supported. The reading distance of

the transponder IC is more than 3 m with the total supply

current consumption less than 10 lA at 4 W (36 dBm)

EIRP base-station transmit power. The transponder archi-

tecture and the operation of the different building blocks

are described, respectively. The experimental results are

presented and a conclusion is provided.

2 Architecture

The block diagram of the proposed UHF RFID transponder

is shown in Fig. 1. The antenna is the only external com-

ponent. The individual building blocks of this diagram are

described in details in the following paragraphs. The tran-

sponder chip includes the RF analog front end (RF AFE)

circuit and the signal processing unit. The RF AFE consists

of matching network, rectifier, and regulator, power on reset

circuit, local oscillator, bandgap reference, AM demodula-

tor, and backscatter. The processing unit includes controllogic and memory. The matching network circuit is used to

achieve maximum power transfer between the reader,

antenna and transponder. The rectifier converts the incident

RF input signal from the reader to a DC supply voltage. The

regulator provides the stable voltage to all analog and dig-

ital circuits. The AM demodulator extracts out the digital

data bitstream from the received RF signal. The backscatter

circuit sends the data back to the reader by alternating the

input impedance of the transponder. The low power local

oscillator generates the clock signal to the control logic,

which is initialized at power-up by the power on reset

(POR) circuit. The bandgap reference circuit provides the

reference voltage and current to both analog and digital

circuits. The POR circuit generates the chip power on reset

signal. The control logic disposes of the protocols, such as

anticollision, encoding and decoding, cyclic redundancy

checks (CRC), commands, etc.

3 Building blocks

3.1 Rectifier and regulator

Figure 2 shows schematic of the rectifier, which converts

the incident RF signal to a DC supply voltage for the whole

transponder chip. The rectifier is basically a cascade of N-

stage diode-capacitor peak detector [3, 4], which is alsocalled Dickson charge pump in the context of memory ICs

[5]. All diodes and capacitors are identical. The Schottky

diodes with low series resistance and low junction capac-

itance are used, which can achieve a higher power con-

version efficiency of the received RF input energy to a DC

power supply. In AC analysis, all capacitors will appear as

short circuit and all the diodes are connected in parallel (or

antiparallel) to the RF input signal by the capacitors. In DC

analysis, all capacitors are open circuit, and all diodes are

connected in series to allow a DC current flowing. Thus,

the generated voltage is approximately equal to [3]

V DC ¼ N Á V RF;in À V dÀ Á

ð1Þ

where V RF,in is the amplitude of the RF input signal and V dis the forward voltage of each Schottky diode.

The regulator provides constant supply voltage to the RF

AFE circuit and the signal processing unit, as shown in

Fig. 3. The regulator prevents the transponder chip from

breaking down with the varied amplitude of RF input

signal at different locations. The resistors R1 and R2 form

a voltage divider. The error amplifier compares the voltage

V - with the reference voltage V? from the voltage refer-

ence circuit. The transistor M1 is used to sink the current

according to the output of the error amplifier. To achieve

the low power circuit, the startup circuit is used, and

completely turns off once the voltage reference circuit is

started and no dissipation during typical operation state.

3.2 AM demodulator and backscatter

The AM demodulator is used to extract the digital data

bitstream from the incident input carrier signal. Figure 4

shows a block diagram of the AM demodulator. A four-

stage Dickson charge pump is used as the envelope

detector to boost up the input signal. The following two

low-pass filters are used to average the boosted input signal

with large time circuit, which eliminates the carrier noise

and power ripple [6, 7]. The output voltages of two low-

pass filters are then compared with a gain amplifier to

generate the output data bitstream.

The ASK modulation is achieved by a backscattering

approach. The ASK modulator can be regarded as a simple

switch that modulates the input impedance of the tran-

sponder chip [8, 9]. As shown in Fig. 5, by switching on or

off the transistors M1 and M2, the Bi-state amplitudeFig. 1 Block diagram of the transponder chip

62 Analog Integr Circ Sig Process (2011) 66:61–66

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modulated backscatter is achieved. With the modulation

approach, high power conversion efficiency for dc supply

voltage and high modulated backscattering power for the

backward link are implemented simultaneously. The

schematic of the backscatter modulation circuit is shown in

Fig. 5.

Fig. 2 Schematic of the

rectifier

Fig. 3 Schematic of the

regulator

Fig. 4 Schematic of the AM

demodulator

Analog Integr Circ Sig Process (2011) 66:61–66 63

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3.3 Local oscillator

Figure 6 shows a block diagram of the on-chip local oscil-

lator that generates the clock signal for the digital circuits. It

is based on RC relaxation oscillator. The transistors M1 and

M4 are the current source and sink. When the output of the

local oscillator is low, M3 is on and M2 is off. The capacitor

C is charged with the constant current from M4. When theoutput is high, the capacitor is discharged with the constant

current from M1. The local oscillator is sensitive to the

variations of the temperature, supply voltage, and process

parameters. But the bit rate accuracy of the chosen protocol

ISO/IEC 18000-6B is less than ±15%, which is tolerant to

these variations. Therefore, the performance of the digital

circuits cannot be affected.

3.4 Control logic

The control logic is used to utilize the communication

protocols. As shown in Fig. 7, the control logic which is

clocked by the low-power local oscillator includes decoder

module, encoder module, clock synchronization module,

cyclic redundancy checks module, control unit, power

management unit, and shift registers, etc. The clock syn-

chronization algorithm is implemented in order to resolve

the frequency error and synchronization problem, because

the clock signal of the local oscillator slightly varies with

the temperature, supply voltage, and process parameters.

Because of all commands following by the preamble,

which is equivalent to nine bits of Manchester 0 in NRZformat [10], the clock signal of the local oscillator is

synchronized with the Rx signal by the preamble. The ISO

18000-6B standard defines the protocol for a UHF passive

backscatter RFID system, featuring the capabilities as

follows: identification and communication with multiple

tags in the field, selection of a subgroup of tags for iden-

tification or communication, reading from and writing to or

rewriting data many times to individual tags, user-con-

trolled permanently lockable memory, data integrity pro-

tection, interrogator-to-tag communications link with error

detection, tag-to-interrogator communications link with

error detection [5]. In the version of the prototype tagdescribed below, all of the mandatory commands and a

subset of the optional and custom commands defined by the

ISO standard have been implemented.

Fig. 5 Schematic of the backscatter circuit

Fig. 6 Block diagram of the local oscillator

Fig. 7 Block diagram of the

control logic


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4 Experimental results

The transponder chip is fabricated using Chartered0.35 lm two-poly four-metal CMOS process with Schottky

diodes and EEPROM supported. The die size is

1.5 mm 9 1.0 mm. A die photograph is shown in Fig. 8.

The only two bonding wires are required to connect the

antenna to the transponder. Figure 9 shows the measured

results of the transponder IC chip with Tektronix 3308B

real-time spectrum analyzer by the UHF RFID reader of

Model XCRMF-801 (Invengo IT Co., Ltd., Shenzhen),

which is compatible with ISO/IEC 18000-6B Standard.

The received power of the transponder versus the time is

shown in Fig. 9. As shown in Fig. 9(a), the minimum

received power of the transponder is less than -7 dBm.

And, the data rate is 80 kbit/s. Figure 9(b) shows the

waveform of the GROUP_SELECT_NE command from

the reader. With 4 W (36 dBm) EIRP at 915 MHz andthe antenna gain less than 1.5 dBi, the reading distance

of the transponder is more than 3 m. The performance of

the proposed transponder is summarized in Table 1.

Fig. 9 Measured waveforms

of the transponder chip

Table 1 Performance summary of the proposed transponder

Process 0.35 lm 2P4 M CMOS

Carrier frequency 860–960 MHz

Current consumption \10 lA

Tag impedance at 915 MHz 7.3-247j@915 MHzFree space reading distance [3 m

Rx data rate 80 kbit/s

Tx data rate 80 kbit/s

Modulation format ASK

Commands supported ISO/IEC 18000-6B

Die size 1.5 mm 9 1.0 mm

Fig. 8 Die photomicrograph of the transponder chip

Analog Integr Circ Sig Process (2011) 66:61–66 65

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5 Conclusion

This paper presents a low power, fully integrated, passive

UHF RFID transponder IC, which is compatible with ISO/

IEC 18000-6B Standard, operating at the 915 MHz ISM

band with the total supply current consumption less than

10 lA. Theoretical analyses and circuit simulations used

for the design optimization have been proposed. Thetransponder chip has been fabricated by Chartered 0.35 lm

two-poly four-metal CMOS process with Schottky diodes

and EEPROM supported. The free space reading distance

of the transponder IC is more than 3 m with 4 W (36 dBm)

EIRP base-station transmit power and the antenna gain less

than 1.5 dBi. The measurement result meets the specifi-

cation of the proposed system.

Acknowledgments The authors would like to thank Xuan Zheng

and Liyuan Ma for their help in the process of design and

measurements.

References

1. Finkenzeller, K. (2003). RFID handbook (2nd ed.). New York,

USA: Wiley.

2. EPC Regulatory status for using RFID in the UHF spectrum 20.

http://www.epcglobalcanada.org.

3. Karthaus, U., & Fischer, M. (2003). Fully integrated passive UHF

RFID transponder IC with 16.7 uW minimum RF input power.

IEEE Journal of Solid-State Circuits, 38(10), 1602–1608.

4. Vita, G. D., & Iannaccone, G. (2005). Design criteria for the RF

section of UHF and microwave passive RFID transponder. IEEE

Transaction on Microwave Theory and Techniques, 53(9),

2978–2990.

5. Tran, N., Lee, B., & Lee, J. W. (2007). Development of long-range UHF-band RFID Tag chip using Schottky diodes in

standard CMOS technology. IEEE Radio Frequency Integrated

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6. Yu, H., & Najafi, K. (2003). Low-power interface circuits for bio-

implantable microsystems. IEEE International Solid -state cir-

cuits conference digital technology papers, pp. 194–487.

7. Rongsawat, K., & Thanachayanont, A. (2006). Ultra low power

analog front-end for UHF RFID transponder. International Sym-

posium on Communications and Information, pp. 1195–1198.

8. Fuschini, F., Piersani, C., Paolazzi, F., & Falciasecca, G. (2008).

Analytical approach to the backscatter from UHF RFID tran-

sponder. IEEE Antennas and Wireless Propagation Letters, 7 ,

33–35.

9. Ashry, A., & Sharaf, K. (2007). Ultra low power UHF RFID tag

0.13 lm CMOS. International Conference on Microelectronics,pp. 283–286.

10. ISO/IEC 18000: Information technology automatic identification

and data capture techniques—Radio frequency identification for

item management air interface. http://www.iso.org.

Li-Ying Chen received his

Ph.D. degrees in microelectron-

ics from Tianjin University,

Tianjin, China, in 2008. He is a

lecturer in Nankai University

now. His current research inter-

ests are UHF RFID transponder

ICs, low-noise phase-locked

loops, and RF front-ends for

wireless communications

Lu-Hong Mao received his

Ph.D. degrees in microelectron-

ics from Tianjin University,

Tianjin, China, in 2000. He is a

professor in Tianjin University.

His current research interests

are UHF RFID transponder ICs,

optoelectronic integrated recei-

ver, and RF front-ends for

wireless communications.

Xiao-Zong Huang received his

B.S. degrees in microelectronics

from Tianjin University, Tian-

jin, China, in 2007. He is cur-rently working toward the M.S.

degree in microelectronics in

Tianjin University. His current

research interests are UHF

RFID transponder ICs.


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http://www.epcglobalcanada.org/

http://www.iso.org/

http://www.iso.org/

http://www.epcglobalcanada.org/

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