Investigation of a high frequency CMOS unsaturated ring oscillator

摘要

Investigation of a high frequency unsaturated ring oscillator with cross coupled load is presented, and oscillation frequency compared with multi-path high frequency ring oscillators. Stability of oscillation is shown heuristically, via geometric argument on a phase plane, where the presence of negative impedance in the cross coupled pair of the delay cell is deemed important. Oscillation frequency formula is presented, and design insight given. In addition, a novel design methodology on lowering its phase noise is developed. Simulations on example circuit designs using 0.18 μm CMOS technology demonstrate the higher frequency obtained, oscillation stability, frequency formula and design insight, as well as phase noise methodology.