CMOS ring oscillators with enhanced frequency operation

This paper presents a new technique to improve frequency performance of CMOS ring oscillator. It is based on the adding of a CR differentiators-based MOS transistor to boost switching speed of the oscillator delay cell. The method can be used for simple and differential oscillator and offers a simple way to implement frequency tuning without introduction of any additional phase noise. Using 0.35 μm CMOS technology, simulation results show that applying the technique to the simple ring oscillator allows a frequency oscillation improvement of 78 %. Also, simulations show that frequency improvement can reach 250 % if the technique is associated to a positive feedback.