A Single-Chip CMOS Transceiver for UHF Mobile RFID Reader

A Single-Chip CMOS Transceiver for UHF

Mobile RFID Reader

Ickjin Kwon ,Member,IEEE ,Yunseong Eo ,Member,IEEE ,Heemun Bang,Kyudon Choi,Sangyoon Jeon,

Sungjae Jung,Donghyun Lee,and Heungbae Lee

Abstract—This paper describes a single-antenna low-power single-chip radio frequency identi?cation (RFID)reader for mobile phone applications.The reader integrates an RF trans-ceiver,data converters,a digital baseband modem,an MPU,memory,and host interfaces.The direct conversion RF receiver architecture with the highly linear RF front-end circuit and DC offset cancellation circuit is used to give good immunity to the large transmitter leakage.It is suitable for a mobile phone reader with single-antenna architecture and low-power reader solution.

The transmitter is implemented in the

direct

up-conversion architecture.The frequency synthesizer based on a fractional-N phase-locked-loop topology offering 900MHz quadrature LO signals is also integrated with the RF transceiver.The reader is fabricated in a

0.18m CMOS technology,and its die size is 4.5

mm 5.3mm including electrostatic discharge I/O pads.The reader consumes a total current of 89mA apart from the external power ampli?er with 1.8V supply voltage.It achieves an 8dBm P1dB,an 18.5dBm IIP3,and a maximum transmitter output power of 4dBm.

Index Terms—Mobile RFID reader,radio frequency identi?ca-tion (RFID),RFID reader,single-antenna UHF reader,single-chip CMOS reader.

I.I NTRODUCTION

R

ADIO frequency identi?cation (RFID)application is growing rapidly in many areas,such as supply chain managements,antifraud systems,and object tracking systems [1].The mobile RFID technology currently integrates the RFID technology with the mobile communication network and it enables one to access the information from the tag with the mobile phone.

A mobile RFID reader reads tags attached to the various ap-plications in all places through an RFID reader-embedded mo-bile phone.The tag data contains a unique service code and the mobile phone acquires the relevant information and con-tents corresponding to the service code using the mobile net-work.The mobile RFID technology will enable users to re-ceive real-time information on consumer products or data ser-vices through the mobile RFID reader chip embedded in their handsets.Customers can receive information on digital music content by touching the RFID tags at record shops.The mobile

Manuscript received April 19,2007;revised August 21,2007.

I.Kwon was with the Samsung Advanced Institute of Technology,Yongin 449-712,Korea.He is now with the Division of Electrical and Computer Engi-neering,College of Information Technology,Ajou University,Suwon 443-749,Korea (e-mail:ijkwon@ajou.ac.kr;ickjinkwon@https://www.360docs.net/doc/f42495179.html,).

H.Bang,K.Choi,S.Jeon,S.Jung,D.Lee,and H.Lee are with the Samsung Advanced Institute of Technology,Yongin 449-712,Korea.Y.Eo is with Kwangwoon University,Seoul 139-701,Korea.Digital Object Identi?er 10.1109/JSSC.2007.914302

RFID service will enable users to obtain traf?c information by recognizing RFID tags at bus stops.A user can send the plate number of a taxi he is riding in to his acquaintances,just by touching an RFID-enabled tag in the taxi.RFID applications can be used for travel and tourism information,and for veri?ca-tion of the authenticity of medical products.

The RFID systems operating at low frequencies (125kHz or 13.56MHz)are limited in their data rates and distances.Due to the great demand for higher data rates,longer reading distance,and small antenna size,much attention has been given to the UHF frequency band RFID system [2]–[4].It is suitable for the mobile phone reader which requires a small form factor.

To meet the demands of longer battery life and lower cost of mobile communication devices,the low-cost,low-power,single-chip reader draws great attention and thus the CMOS technology is believed to be the most promising candidate toward the system-on-a-chip (SoC),which integrates all the functions of a RF transceiver,data converters,a digital base-band modem,an MPU,memory,and host interfaces.

In this paper,a CMOS RF transceiver for a single-antenna UHF mobile RFID reader operating at 900MHz is designed and fabrication results in the

0.18m CMOS process are reported.Section II describes the reader speci?cation,and Section III de-scribes the reader architecture.The detailed circuit designs are discussed in Section IV.Section V reports chip implementation results and Section VI concludes this paper.

II.R EADER S PECIFICATION

Mobile RFID reader speci?cation is based on the UHF RFID standard including ISO/IEC 18000-6Type C and Type B stan-dard [2]–[4].ISO/IEC 18000-6type C standard is a partially modi?ed standard from the EPCglobal Class-1Generation 2[3].The ISO 18000-6standard speci?es the air interface at the 860–960MHz band.The comparison of the mobile UHF RFID and the ISO/IEC 18000-6type C standard is shown in Table I.The reader operation frequency is determined by the regulation of each region within the 860–960MHz band.For Korea,the UHF RFID band ranges from 908.5to 914MHz with 200kHz channel space [4].

The data modulation scheme for the reader to the tag com-munication are double-sideband ASK (DSB-ASK),single-side-band ASK (SSB-ASK),and phase-reversal ASK (PR-ASK).The maximum data rate is different from the channel bandwidth.The designed reader operates at a maximum tag-to-reader data rate of 240kb/s due to the bandwidth of the receiver chain of the reader.The tag-to-reader data rate can be extended to 640kb/s by modifying the receiver bandwidth of the reader.The target maximum read range speci?cation is 1m.It is a relatively

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TABLE I

S PECIFICATION OF THE ISO/IEC 18000-6T YPE C AND M OBILE UHF

RFID

Fig.1.Single-antenna RFID reader operation.

short range compared with other ?xed UHF RFID reader sys-tems since it is for mobile phone application.

In the return link of the RFID operation,the receiver of the reader listens to the response of the tag (transponder)while the transmitter sends a continuous wave (CW)to the tag for power transfer.One of the most critical components is how to reject a leakage signal from the transmitter to the receiver.Convention-ally,an RFID reader module contains two antennas with suf ?-cient spacing because the isolation from transmitter to receiver is much better in a two-antenna reader than in a single-antenna reader.However,it is not suitable for the mobile phone reader system,due to the physical dimension and the high cost [1].Fig.1shows the single-antenna RFID reader operation for the return link of the tag to the reader communication.In a single-antenna reader system,the backscattered desired signal returning from the tag is mixed with the transmitter carrier.The amount of the transmitter carrier leakage,which is typically more than 0dBm at the receiver input,is determined by the an-tenna re ?ection coef ?cient and the isolation of the directional coupler.The transmitter carrier leakage leads to the saturation of receiver block and degradation of the sensitivity.Hence,the P1dB characteristic needs to be high in the receiver front-end to avoid the receiver saturation caused by the large transmitter

carrier leakage.The focus of the design is on the linearity rather than the noise ?gure.

Typically,passive UHF RFID tags need to have an input

power

of

dBm

(100)[5].The minimum output power at the reader antenna should be greater than 20dBm with the consideration of the link loss in air of 31dB for 1m communication range,the tag antenna gain of 2dBi,and the embedded reader antenna gain of 0dBi.Typically,the output

power of the tag modulator is greater than 30dBm

(1

).With the link budget analysis,the minimum received power is calculated as 60dBm.Including the loss of the directional coupler,the minimum RF sensitivity of 70dBm is required in the UHF band mobile RFID application.

The receiver noise ?oor depends on the cascade noise ?gure as well as on the noise bandwidth.Then the sensitivity can be calculated as

follows:

The noise bandwidth of the receiver under consideration is about 120kHz for 40kb/s data rate.The required sensitivity is 70dBm.Assuming that there is a minimum signal-to-noise

ratio

of 11.6dB for 0.001%BER [4],the receiver noise ?oor should be less than 81.6dBm.For the required sensitivity,the maximum allowable noise ?gure is calculated from (1)as 39dB.

For the maximum output power of 27dBm,the maximum transmitter carrier leakage is calculated as 5dBm.The trans-mitter carrier leakage is determined by the antenna re ?ection co-ef ?cient and the isolation of the directional coupler.The trans-mitter leakage power re ?ected from the antenna with a re ?ec-tion of 15dB and coupling loss of 10dB is about 2dBm at the maximum output power.The CW leakage power due to the limited isolation performance of the directional coupler is about 2dBm for the 25dB isolation.To cope with large in-band blocker of transmitter leakage signal,the authors specify a re-quired P1dB of 5dBm.The input IP3(IIP3)needs to be greater than 15dBm considering IIP3is about 10dB higher than input P1dB.

The radio speci ?cation for mobile RFID reader requires 18dB rejection at the adjacent

channel 200kHz and 47dB rejection at the alternate

channel 400kHz ,respectively,in the condition of dense reader environment [4].In the condition of multiple reader environments,the 5dB rejection at the adjacent channel and 35dB rejection at the alternate channel are speci ?ed.The analog-to-digital converter (ADC)budget ?nally determines the required receiver selectivity.To limit any interferer to 0dB above the desired channel at the ADC,an adjacent

channel 200kHz rejection of 20dB and alternate

channel 400kHz rejection of 50dB are speci ?ed,including a margin.

In a wireless receiver based on the down-conversion scheme,an undesired signal located at adjacent channel will be down-converted to the desired channel due to the close-in phase noise of frequency synthesizer.This phenomenon is called the reciprocal mixing and depends on the phase noise performance of the frequency synthesizer,the adjacent channel spacing,and system noise bandwidth (the amount of the noise