A microprocessor includes an on-chip low phase noise CMOS LC capacitance oscillator. The LC oscillator is relatively insensitive to power supply fluctuations. In addition, the LC oscillator is operable over a range of frequencies sufficient to support both normal full power operation, and reduced power operation of the microprocessor. The LC oscillator minimizes clock jitter problems and so permits extension of the microprocessor operating frequency to even higher levels than heretofore were possible. An output signal from a phase-frequency detector is a frequency control signal on a frequency control input line of a level converter and filter circuit of the LC oscillator. The output signal from level converter and filter circuit is a filtered frequency control signal on a control voltage input line to a continuously modifiable gigahertz frequency voltage controlled oscillator (VCO) circuit. Continuously modifiable gigahertz frequency VCO circuit generates an output signal with a frequency that is dependent on the voltage on control voltage input line. The output signal from the continuously modifiable gigahertz frequency VCO is a differential current signal to a level shifter output circuit. The level shifter output circuit converts the current signal to a single-ended voltage that is supplied to an output driver. The output driver provides the output signal to a clock distribution network.