Comparator behavior with sinusoidal input: when a comparator (with a fixed reference near 0 V and adequate hysteresis for clean switching) is driven by a sine-wave input, what is the expected general waveform shape at the output?

Introduction / Context:
A comparator is a high-gain device used to convert analog variations into clean logic-level transitions. Understanding the qualitative input-output relationship helps with signal conditioning, zero-crossing detection, and waveform shaping. This question asks what happens when the input is a continuous sine wave and the comparator switches according to its threshold(s).

Given Data / Assumptions:

• Comparator with a single threshold near 0 V; optional small hysteresis (Schmitt action) to avoid chatter.
• Input is a sine wave that crosses the threshold twice per cycle.
• Comparator saturates between its output rails.

Concept / Approach:
As the sine wave swings positive and negative, it crosses the threshold. The comparator output saturates high when the input exceeds the threshold and saturates low when the input falls below it. The result is a two-level waveform with fast transitions—i.e., a rectangular (square-like) wave at the same fundamental frequency as the input, with duty cycle determined by the threshold relative to the sine amplitude and any hysteresis window.

Step-by-Step Solution:

Verification / Alternative check:
Scope traces in zero-crossing detector circuits show a clean rectangular wave at the comparator output for a sinusoidal input, often with slight propagation delay and finite slew limiting the edge speed but not the rectangular nature.

Why Other Options Are Wrong:

• Ramp or sawtooth: require integrators/relaxation generators, not a simple comparator.
• Sine wave: would be the input, not the saturated output.
• Triangle: requires a constant-current charge/discharge circuit, not just a thresholding comparator.

Common Pitfalls:
Expecting a perfect square; in practice, finite slew and saturation levels introduce edge rounding and rail limits. Without hysteresis, noise can cause chatter near the threshold.

Final Answer:
Rectangular wave