Zero Crossing Detector

Op-Amp as Zero Crossing Detector

• The basic non-inverting comparator can be used as a zero crossing detector
• This circuit tells wether the input siganl is greater than or less than zero and indicates the zero crossing points of the input
• A typical circuit for such a detector


• It is a non-inverting comparator circuit with Vref=0V.
• During the positive half cycle, the input voltage is positive i.e above the reference voltage. Hence voltage is +Vsat
• During negative half cycle, the input Vin is negative, i.e below the references voltage. The output voltage is than -Vsat.
• Thus the output voltage switches between +Vsat and -Vsat whenever the input signal crosses the zero level. Thus the output indicates the zero crossing of the input by changing the state of the output
• waveforms

• we realize that zero crossing detector can be used as a sine to square wave converter