Voltage-Controlled Ring Oscillator With FOM Improvement by Inductive Loading

A hybrid voltage-controlled oscillator (VCO) architecture based on a ring oscillator with inductive loading is proposed. It exhibits a better phase noise/power figure-of-merit (FOM) than a standard ring VCO while retaining some of its desirable properties. It can be used as a “drop-in” replacement in a ring-VCO-based phase-locked loop to obtain a predictable improvement in FOM. Accurate and concise expressions are provided for predicting the frequency and the FOM improvement. A prototype exhibited 8 dB of FOM improvement with respect to a standard ring VCO, while the error on the theoretical prediction was less than 1 dB when compared to measured data.