Zero-crossing Detector

The circuit configuration shown on Picture 1 is called zero-crossing detector. The inverted input of the operational amplifier is connected to the ground and the input signal Vi is leaded to the non-inverting input. The output of the OA flows through the capacitor C and diode D leading to the output of the circuit.

Picture 1: Zero-crossing Detector


The input and output signals wave forms are shown on the Picture 2. The input signal is sinusoidal with amplitude of 10 mV at frequency of 500 Hz. The input signal Vi is represented with the green line plot. The output signal Vo1 (right after the OA) is represented with the blue line plot, the Vo2 (right after capacitor C) is represented with the red line plot and the Vo3 (right after the diode D) which is actually the output signal of the circuit is represented with the green (see foam) line plot. As we can see from the picture, the output signal of this circuit has only positive peaks which appears when the input signals is in positive half-period.

Picture 2: Input and Output wave forms of the Zero-crossing Detector