What Is a Zero Crossing Detector?

Zero crossing detectors are essential in transmitting digital signals over alternating current.

Transmitting digital signals over alternating current, or AC, proves impossible without zero crossing detectors -- electrical circuits that detect when the current reaches the zero crossing point of the wave.

The Facts

On a waveform graph, the zero crossing is the straight line that bisects the wave. In electronics, a zero crossing identifies where the wave function changes from positive to negative or vice versa. In a light dimmer, for example, a zero crossing detector enables power level adjustments of live current, as those points have no voltage. Interruption of the current anywhere else in the wave cycle creates a potentially harmful power spike.

Function

Zero crossing detectors are vital for the transmission of digital signals over AC circuits, as in modems and other digital devices. The absence of a zero crossing detector circuit explains why digitally controlled audio devices produce noise when a user turns up the volume too quickly. When the gain only increases at zero crossing points, there's no input and no signal noise.

Comparators

Zero crossing detectors typically work in conjunction with comparators -- electrical devices that compare signal strength (voltage or current) and switch output based on the stronger signal. While analog operational amplifier comparators are widely used, dedicated voltage comparator chips work best for digital devices.

References

• Elliott Sound Products: Zero Crossing Detectors and Comparators
• Maxim Integrated Products: Selecting the Right Comparator

Resources

• Read this Article in Spanish