Abstract: A sawtooth voltage is applied to an integrated optic phase modulator by means of a high impedance variable current source in response to a charge rate control signal. The phase modulator's capacitance accumulates the charge which manifests a voltage comprising the sawtooth signal. The sawtooth signal is also provided to a comparator which in turn provides a discharge signal upon detecting the sawtooth voltage as being greater than a selected reference signal magnitude. The discharge signal is provided to a means for discharging the accumulated charge from the capacitance of the integrated optic phase modulator. A compensating resistor may be connected between the current source and the phase modulator to automatically correct for sawtooth overshoot.