Design Of The Filter In Analog Base Band Of UHF RFID Reader

RFID(Radio Frequency Identification) is a technology which using a way of radio frequency contactless communication between tag and reader. Due to advantages such as long working distance, being able to identify moving target, non-contact, being suitable for harsh environments and so on , RFID technology has been widely used in a number of important areas. Because of advantages of single-chip integration programmes like small chip area, the system easy to move and so on, this article has been conducted in-depth research in analog baseband filters applied for single-chip UHF RFID reader.The following work have been made in this paper:1. UHF RFID protocols are analysed, and the bandwidth of analog baseband filters used on UHF RFID single-chip reader is identified.2. Analysis of the types of filters and parameters, and determine Chebyshev low-pass as the structure of the design filter.3. According to the analysis realization method for high-order filters, make sure using classic cascade realization method for designing high-order filter in this paper.4. Due to study on Tow-Thomas structure, understand its and Q values is on the same level compared to passive devices and other double-integral filter,but it has greater gain. So the Tow-Thomas structure is selected for the filter.5. Analysis and identify the design method of the key circuit module in the filter, including operational amplifier, common mode feedback circuit bandgap reference circuits, DC offset elimination circuit(DCOC) as well as variable bandwidth.6. The layout and simulation have been made for the sixth-order filter with DCOC and the fourth-order channel-select filter. According to the result, we know that the bandwidth of six-order filter is 125kHz and it can inhibits well static DC offset as well as slowly changing DC offset. The fourth-order filter has variable bandwidth, which is 100kHz, 400kHz, 600kHz, 800kHz, 1MHz and 1.3MHz. The gain of the operational amplifier they share is 62 dB, and a unity gain bandwidth of 60MHz is designed. And common mode feedback circuit is able to output stable level and bandgap reference voltage source can provide an excellent source. UMC 0.18 ? m CMOS technology is used in the design for chip, and the sixth-order filter has a better suppression performance for external harmonic than fourth-order filter while increasing appropriate area.7. According the testing result of the bandwidth tunable channel-select filter, the next direction of efforts was identified.