The design of a ring oscillator with digital calibration

In order to compensate for the effects of supply voltage, process and temperature on the oscillator frequency, we design a ring oscillator with digital calibration. By comparing the frequency deviation between the ring oscillator and the external reference clock source, adjusting the state of the control word, and then changing the number of resistors in the analog circuit to adjust the output frequency of the ring oscillator, so as to compensate the output frequency deviation. Firstly, we analyze the analog circuit and digital circuit, and then get the result of simulation, finally carry out the layout design. Simulation results show that by digital calibration, the output frequency can be adjusted up or down by 30%, so that the deviation can be compensated to a great extent.