A buffer for converting sinusoidal waves to square waves with reduced phase noise is described herein. The buffer shunts current from the outputs of a differential amplifier during sinusoidal state transition periods at the differential amplifier inputs to increase the finite slope of square wave transition periods of the output square wave. More particularly, a sinusoidal wave having alternating peaks and valleys connected by sinusoidal state transition periods is applied to differential inputs of a differential amplifier to generate a square wave at the differential outputs, where the output square wave comprises alternating high and low states connected by square wave state transition periods having a finite slope. The output square wave is shaped to increase the finite slope of the square wave transition periods by providing additional paths between the differential outputs and ground that shunt current from the differential amplifier during the sinusoidal state transition periods.