Zero crossing threshold detector

Circuit Diagram

A zero crossing detector is used for detecting the zero crossings of AC signals. A typical AC signal is the sine wave which goes up and down the zero level. Many electronic systems need to know 'when' the signal crossed the zero level. The answer to that problem is the zero crossing detector.

Implementation

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). Often used in conjunction with other circuit elements, it usually functions as a simple voltage switch.

Operation

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.

Applications

This detector exploits the property that the instantaneous frequency of an FM wave is approximately given by $f_i=\frac{\Delta t}{2}$ where Δt is the time difference between adjacent zero crossings of FM wave

See also

• Comparator
• Operational amplifier

References

• Elliott Sound Products Application Notes : Zero Crossing Detectors and Comparators