Abstract: A frequency generator is disclosed in which the phase modulation of a sta carrier frequency is precisely and repeatedly controlled by a digital input. A digital-to-analog converter (DAC) receives a digital input from the output of a computer and provides an analog voltage output. An analog ramp signal generator is also provided such that the output of the analog ramp signal generator and the output of the digital-to-analog converter form the inputs to a voltage comparator network. The output of the voltage comparator network switches state each time the ramp signal generator output exceeds the digital-to-analog converter output. The output of the voltage comparator network is used to trigger a one-shot multivibrator which thereby produces a square wave that is advanced or retarded in phase in response to the value of the digital input to the digital-to-analog converter.