Zero crossing threshold detector
 | This article provides insufficient context for those unfamiliar with the subject. |
A zero crossing threshold detector is an electronic circuit that consists of an operational amplifier with an input voltage at its positive input (see circuit diagram). It can be defined as a device for detecting the point where the voltage crosses zero in either direction. Often used in conjunction with other circuit elements, it usually functions as a simple voltage switch.
When the input voltage is positive, the output voltage is a positive value, when the input voltage is negative, the output voltage is a negative value. The magnitude of the output voltage is a property of the operational amplifier and its power supply. When used with a ±15 V power supply and a 741C operational amplifier, Vsat+ is approximately 13.6 V and Vsat- is approximately -14.3 V.
This detector exploits the property that the instantaneous frequency of an FM wave is approximately given by where is the time difference between adjacent zero crossings of FM wave
