The Design And Realization Of Clock Generator Suitable For Passive UHF RFID Tag Chip

Passive UHF Radio Frequency Identification (RFID) technology, characterized by long distance, high speed, low cost and convenient, has already been used for identification, logistics, storage management, ETC, and so on. It is expected to become the basic technology of information society. This thesis focuses on the core technology of the clock circuit which is propitious to Passive UHF RFID and presents two sorts of the circuit, the ring oscillator and the relaxation oscillator, which are deeply studied on the circuit structure and the operating principle. The corresponding simulation results are shown and the advantages and disadvantages of the two circuits are compared.The circuit design and working principles are given for the ring oscillator in this paper. The frequency expression shows that the stability of the output clock depends strictly on the operating voltage and current and the circuit structure itself don’t inhibit the clock jitter. The output frequency will fluctuate or deviate when the operating voltage or current fluctuates or biases. The fluctuations of the operating voltage and current must be decreased to minimum to meet the digital baseband requirements. The filter which uses large capacitance or resistance is needed to decrease fluctuations and reduce the output clock jitter of the ring oscillator.Different from the ring oscillator, the output frequency of the relaxation oscillator is independent with the operating voltage and current. There is no jitter when the operating voltage or current fluctuates, and no deviations when biases. Therefore, the design resolves the problem of the clock jitter and deviation. Six-bit current ratio calibration circuit is designed to overcome the frequency deviation because of the process and ensure the calibration accuracy. The resistance compensation circuitry is used to resolve the frequency drift problem and reduce the temperature coefficient.At the end of the article, three kings of oscillator are compared to highlight the advantages of the improved relaxation oscillator.The two kings of oscillator, designed in the paper, have been applied to the UHF RFID tag chip which have been taped out in TSMC0.18μm.