Design Of High Linearity Integrated RF Front-end For The Receivers Of UHF RFID Reader

RFID(Radio Frequency Identification) has the advantages such as high data capacity, contactless reading and high security. It has been widely used in entrance guard and automatic fare collection. As UHF RFID is the far-fields coupling system of RFID, it has more advantages such as high data rate, longer reading range, suitable for adverse circumstances and recognizable for moving objects. The popularization of UHF RFID makes researches on the low cost, high performance chip of UHF RFID readers becoming more and more.A kind of RF front-end circuit for the receiver of UHF RFID resder is designed, which supports the RFID international protocol of EPC C1Gen2. The main achievements are shown as follows:(1) According to the requirements of EPC C1G2protocol, readers transmit high-power carrier without modulation to tags. Tags will reflex part of the carrier signal to the input of the reader’s receiver. This carrier-leakage makes the performance of front-end be worse. After all, improving the linearity of the front-end to overcome the carrier-leakage’s interference is the key characteristic of this article.(2) The classical font-end is composed of Low Noise Amplifier(LNA) and active or passive down-conversion mixer. And sometimes, it is composed of active or passive down-conversion mixer without LNA. However, most of them have the disadvantage that can’t pursue the performance both of noise and linearity. As aresult, a kind of integrated RF front-end for zero-IF receiver is proposed based on0.18μm BiCMOS process. It consists of three parts. Firstly, transconductance stage transforms voltage signal to current signal. The high linearity can be achieved by choosing suitable driving voltage. Secondly, the I/Q switching stage is realized by passive structure without bringing noise. Thirdly, the transimpedance stage transforms the current signal to voltage signal and achieves the proper gain of this integrated RF front-end.(3) The area of this integrated RF front-end is670μm×580μm. The post simulation shows the IPldB is6.05dBm, IIP3is15.5dBm, and NF is18.88dB without carrier-leakage at3.3V power supply. To know the influence of carrier-leakage under this linearity, NF simulated on the conditions of-30dBm and-10dBm are respectively 19dB and28.04dB, which indicates that high linearity reduces the influence of carrier-leakage.