The phase of a voltage controlled oscillator (VCO) can be controlled and changed by a series of pulses applied through an isolating element such as a capacitor. A small amount of current injected into the reactive element distorts the waveform of the VCO during the period of injection. Depending on the power of the pulse of injected current, a corresponding phase shift in the output of the VCO will result during the period of injection. The pulses are applied at a frequency equivalent to the desired frequency. Assuming the waveform of the VCO to be sinusoidal or otherwise symmetrical, the injected current pulses result in one point on the waveform where the distortion will be symmetrical and stable. The injection of repeated pulses results in this stable point eventually occurring symmetrically about the peak of the VCO waveform thereby locking the phase of the VCO to correspond to the frequency of the injected pulses.