Voltage controlled oscillators (VCOs) usually include a regulating cascode circuit and a current controlled oscillator (CCO). In an existing VCO using a low input-output (IO) supply voltage, some transistors in the regulating cascode circuit function out of a saturation mode at some process, voltage, and temperature (PVT) conditions or corners. In such a situation, the power supply rejection ratio (PSRR) of the VCO is decreased and affects performance of the phase lock loop (PLL) having the VCO.
Like reference symbols in the various drawings indicate like elements.