A wide-band digitally controlled ring oscillator

This paper presents an analysis and design of a digitally controlled ring oscillator with a new band-extension technique to achieve wide-band operation. The proposed technique is based on inclusion of an LC tank to boost the frequency range. Two frequency sub-ranges are covered with the tank on and off respectively, and they jointly constitute a very wide frequency tuning range. Implemented as a building block of a digital frequency synthesizer, the ring oscillator has a measured tuning range of 2.65-6.3 GHz, with power consumption less than 16 mW from a 1.2-V supply. The worst-case measured phase noise at 1-MHz offset is -85 dBc/Hz.