Described herein is apparatus and system for a digitally controlled oscillator (DCO). The apparatus comprises a voltage regulator to provide an adjustable power supply; and a DCO to generate an output clock signal, the DCO including one or more delay elements, each delay element operable to change its propagation delay via the adjustable power supply, wherein each delay element comprising an inverter with adjustable drive strength, wherein the inverter is powered by the adjustable power supply. The apparatus further comprises a digital controller to generate a first signal for instructing the voltage regulator to adjust a voltage level of the adjustable power supply.