Design Of Robust And Adjustable Ring Oscillator Based On Feedback

Ring oscillator is increasingly widespread used in the fields of radio frequency identification technology, wireless sensor networks, short distance transmission,measurement and so on. In this thesis, ring oscillator was used to realize the function of time digital conversion in laser ranging read-out circuit (ROIC) based on its advantages of easy on-chip integration and multi-phase clock output. However, the output frequency of traditional ring oscillator is greatly impacted by process, temperature and supply voltage, which is seriously restricting the accuracy of time-digital converter (TDC). Thus it can’t meet the application requirements of ROIC.This thesis focused on solving the problem of frequency’s serious drift with the fluctuations of process, temperature and supply voltage. Based on analyzing the work principle of ring oscillator, clarified the reason why ring oscillator was sensitive to process, temperature and supply voltage. By using the frequency voltage conversion circuit, based on the principle of feedback control,the output frequency of ring oscillator was converted to a voltage, which is compared with reference voltage. Then the output of the error amplifier was used for stabilizing the output frequency of ring oscillator, thus the problem of stabilizing the output frequency was changed into the issue of designing stable reference voltage and current. The closed-loop control structure was similar to phase-locked loop, but it adopted reference circuit on-chip or off-chip, not external crystal oscillator. The control of high-frequency signal was converted to the control of DC voltage volume, which dramatically reduces the influence of high-frequency noise. At last,based on Cadence spectre tools to complete the circuit layout design and simulation verification. Participating MPW tape, complete chip test analysis.The test results show that, the output of on-chip reference voltage at room temperature(27℃) is 1.59 V. The temperature coefficient of reference is 44.75ppm/℃ in a temperature range of-40-100℃, and the PSRR is 30dB@100kHz. The output frequency of oscillator is 154.8MHz, and its temperature coefficient is 215ppm/℃. The output of ring oscillator is modulated by external DC voltage source. Oscillation frequency is respectively 132MHz @Vref=2V,145MHz @Vref=1.8V,154MHz @Vref=1.6V at three reference points. Their temperature coefficient are less than 160ppm/℃ in a temperature range of-40-100℃. The test results of the chips had a good consistency, which indicates that the oscillator chips are less affected by process drift to meet the requirements of ROIC. Need to further improve the problem that startup time is longer.