Comparators - GATE ECE Engineering (ECE) Digital Circuits Free MCQ Test

A comparator is some time called as voltage level detector because, for a desired value of reference voltage, the voltage level of the input can be detected.

The bandwidth of the op-amp comparator must be wider so that the output of comparator can switch rapidly between saturation levels. Also, the op-amp responds instantly to any change in condition at the input.

In zero crossing detectors, the output waveform is always a square wave for the applied sinusoidal input signal.

The drawback of zero crossing detectors can be in cured with the use of regenerative or positive feedback that causes the output to change faster and eliminate any false output transition due to noise signals at the input.

Phase angle between different voltages can be measured using phase detector circuit. The corresponding voltage to be measured is converted into spikes and the time interval between the pulse spikes is measured, which is proportional to the phase difference.

The diodes protect the op-amp from damage due to excessive input voltage. Because of these diodes the difference input voltage of the op-amp is clamped to 0.7v or -0.7 v, hence these diodes are clamp diodes.

High voltage gain causes comparator output voltage to switch between saturation levels. High CMRR rejects noise at input terminal and input offset (voltage & current) help to keep changes in temperature variation very slight.

To keep the output voltage swing within specific limit, op-amps are used with external wired components such as zeners or diodes. In the resulting circuit, the outputs are limited to predetermined values.

Due to low frequency signal, the output voltage may not switch quickly from one saturation voltage to other. The presence of noise can fluctuate the output between two saturation voltages.

The input can be fed to the op-amp when the green LED glows, which is considered to be safe input that is when the input voltage is between 3v and 6v.