A New Solution to Analysis of CMOS Ring Oscillators

New equations are proposed for frequency and amplitude of a ring oscillator. The method is general enough to be used for all types of delay stages. Using exact largesignal circuit analysis, closed form equations for estimating the frequency and amplitude of a high frequency ring oscillator are derived as an example. The method takes into account the effect of various parasitic capacitors to have better accuracy. Based on the loop gain of the ring, the transistors may only be in saturation or experience cutoff and triode regions. The analysis considers all of the above mentioned scenarios respectively and gives distinct equations. The validity of the resulted equations is verified through simulations using TSMC 0.18 µm CMOS process. Simulation results show the better accuracy of the proposed method compared with others.