Design Of Self-tuning Programmable Analog Baseband Circuit In UHF RFID Receiver

Under the background that the technology of "Internet of things" has been gradually applied to various fields, as one of the core technologies, ultra high frequency radio frequency identification technology (UHF RFID) is developing towards the general trend. And the trend is a representative of rapid, low cost, high performance and high levels of integration. The purpose of research in this paper is to design a filter for analog baseband which is suitable for low cost, high integration degree UHF RFID reader receiver. Therefore, careful analysis, design and realization of circuit are implemented on the basis of studying related papers about UHF RFID reader and summarizing relevant knowledge of the filter. The results of the research are listed as follows:Firstly, according to UHF RFID EPC C1G2international agreement and China local UHF RFID regulations, This dissertation puts forward the way to realize receiving link baseband circuit which includes Dc offset Cancel Circuit (DCOC), integrated filter amplifier and all pass filter which is also used as buffer circuit.Secondly, Design single chip active high-pass loop filter Dc offset cancellation circuit to remove the dc offset mainly caused by self-jamming in UHF RFID Receiver. Dc offset removing time is programmabled from35μs to290μs according to the communication data rate. Setting6dB gain in the DCOC circuit to ease the noise of baseband link.Thirdly, the Integrated filter amplifieris synthesized by the structure of TOW-THOMAS as a8th-order Butterworth filter. It has250KHz and1.35MHz two cut-off frequency and achieves variable gain from4dB～64dB with10dB per step, it realizes good compromise among high linearity, high dynamic range and low noise in the UHF RFID reader. Considering the inaccurate cut off frequency caused by passive device parameters in Active-RC filter which changes with technology and temperature, an automatic frequency tuning circuit is designed in the filter to solve the problem. The cut-off frequency deviation is controlled within5%.Fourthly, in order to drive A/D converter and improve group delay characteristics, an all-pass filter(APF) with buffered output is also proposed. The insertion of APF is0.2dB.Finally, based on the analog baseband solution proposed in this paper, The analog baseband circuit in UHF RFID reader'receiving link is realized by cascading the modules. An adjacent channel rejection of40dB is achieved. The dc offset removing time can be less than100μs. The baseband bandpass achieves variable gain from10dB-70dB with10dB per step. The baseband ⅡP3(Input3rd order intercept point) is about10dBm at the10dB gain mode; When the total baseband gain is30dB, the passband'integral noise less than25dB. Meet the short distance communication requirements in portable UHF RFID reader.