A novel model on phase noise of ring oscillator based on last passage time

Ring oscillators´ phase noise, when their delay cells are modeled as buffers and the noise sources assumed to be thermal noise, has some distinctive characteristics. We investigate one of the distinct characteristics, the threshold crossing property. The resulting model is shown to arise from the last passage time behavior of thermal noise present in the circuits. Simulation results on ring oscillators operating in gigahertz range and having timing jitter in picoseconds range confirm the model.