A CMOS VCO ring oscillator suitable for wide supply range applications

In this paper, a wide supply voltage range CMOS VCO ring oscillator is proposed. The core of the VCO consists of a simple three-stage CMOS inverter-based ring oscillator while the frequency tuning is achieved by modulating the gate of a pMOS transistor. The proposed design utilizes an op amp connected as a voltage controlled current source that provides a reference bias current for the ring oscillator, in order to keep the internal voltage supply node as stable as possible and independent from the voltage supply variations. The proposed CMOS ring oscillator has been designed in 110nm technology node for a voltage supply range from 1V up to 3.6V at a frequency of 80MHz. Simulation results over pvt corners have verified that a relatively constant VCO gain can be achieved over the full supply voltage span.