Increasing frequency of ring oscillators by using negative capacitors

Abstract

A new method is proposed for increasing the oscillation frequency of resistive load ring oscillators. Frequency increment is achieved by decreasing of the output equivalent capacitor. That is, a negative capacitor circuit is used to decrease the output equivalent capacitor. Oscillation frequency will be increased, even if capacitors in output nodes are only due to internal capacitors of transistors. The advantages of this new structure are examined by simulating a three-stage ring oscillator in TSMC 0.18 µm technology. Simulation results show a nine times increase in oscillation frequency of the proposed structure. The results of using this structure are even better than the situation in which the ideal negative capacitor is used.