Question

If the input to an OP-AMP comparator is a sine wave, then the output is a

• A. Sine wave
• B. Triangular wave
• C. Square wave
• D. Trapezoidal wave

Hint:

An op-amp comparator produces a digital output (high or low saturation level) based on the comparison of two analog input voltages.
When a sinusoidal input is compared against a reference, the output switches states as the sinusoid crosses the reference, resulting in a square or rectangular wave.

Answer 1

The Correct Option is C

An op-amp comparator compares two input voltages. Let the sine wave be applied to one input (e.g., non-inverting) and a reference voltage (e.g., ground or some other DC level) be applied to the other input (e.g., inverting). The op-amp in comparator mode (open-loop or with positive feedback for hysteresis) has very high open-loop gain.
When the sine wave voltage at the non-inverting input is greater than the reference voltage at the inverting input, the output of the op-amp swings to its positive saturation voltage (e.g., \(+V_{sat}\)).
When the sine wave voltage at the non-inverting input is less than the reference voltage at the inverting input, the output swings to its negative saturation voltage (e.g., \(-V_{sat}\) or ground, depending on the supply). As the input sine wave crosses the reference voltage level, the output rapidly switches between these two saturation levels. This results in an output waveform that is a square wave (or a rectangular wave if the duty cycle is not 50%, which depends on the reference voltage and sine wave amplitude/offset). If the reference is zero and the sine wave is symmetrical about zero, the output will be a square wave with a 50% duty cycle. \[ \boxed{\text{Square wave}} \]