Circuit Design And Implementation For Low-power Oscillator Of UHF RFID Tag

With the implementation of the national Internet of things(IOT) strategy, smart car, smart home and other new concepts have been proposed one after another. As a kind of developing trend, the IOT gave us great imagination space. The development of the IOT cannot leave the Radio Frequency Identification technology(Radio Frequency Identification, RFID) – a technique that make RF signal space coupling achieve non-contact information transmission. Passive UHF RFID tag is to use this technique to perform its characteristics, such as identification distance, high accuracy,and identifying multiple targets, which being popular with the market. It’s very important that analog frond-end connect with base band in Passive UHF RFID tag chips critical, So as the bridge between analog and base band the tag chip oscillator is particularly important.The design of Clock circuit for UHF RFID is mainly studied in this paper, which propose three kinds of Clock circuit including a three-stage ring oscillator 、 a relaxation oscillator and a improved relaxation oscillator. Firstly, except concrete analysis are made in every part of circuit, all of them are in strict formula derivation;Secondly further study of the three kinds of circuit structure and working principle are carried out;Lastly, relevant simulation results are provided to make sure of function and performance of the circuit.Especially, design schematics and deduction in principle of the ring oscillator are developed in the paper in detail. As shown in the frequency expression, the stability of the output is strictly dependent on the working voltage and current. The circuit consists of four parts:The three-stage ring oscillator is hardcore of the circuit, which produce a sine wave by amplifying noise, and keep it stable;A level shift is used to improve the output signal amplitude of ring oscillator;A two-frequency circuit is trying to keep frequency stable by controlling duty circle.In addition, a calibration circuit is added in reference circuit, which can calibrate frequency to amend the deviation caused by process.The design of relaxation oscillator is not only to achieve the function of the circuit but also improvement can make basing on the analysis. Although the structure of relaxation oscillator is simple, there are something we can learn both in function and performance, such as whether in temperature coefficient or in power, it is superiorto the ring oscillator.The improved relaxation oscillator make the performance of the circuit more perfectly by improving supply voltage、reference current and temperature rejection capability. What is more, a seven resistance self-calibration circuit is designed to make sure to meet demand of clock precision, and at the same time it fixes the clock deviation because of the process. A design of Clock circuit with advantages of stronger rejection capability in current、voltage、temperature,higher clock precision,smaller deviation not only meet demands of UHF RFID tag chip.