Compare a plain comparator with a Schmitt trigger in terms of noise immunity and switching behavior.

Compare a plain comparator with a Schmitt trigger in terms of noise immunity and switching behavior.

• A. Comparator without hysteresis is immune to noise around the threshold.
• B. Schmitt trigger provides hysteresis, yielding cleaner transitions.
• C. Schmitt trigger switches more slowly and is less immune to noise.
• D. Both have identical noise immunity and switching behavior.

Answer: (B)

The key idea here is how adding hysteresis changes a device’s response to noise and its switching behavior. A plain comparator has no hysteresis, so it uses a single threshold. Any noise near that threshold can push the input above or below it, causing rapid, unwanted toggling—chatter—because the output flips as soon as the input crosses that one point. A Schmitt trigger, by contrast, uses positive feedback to create two thresholds: one for switching high and a different one for switching low. This means the input must move significantly in one direction to change state and must travel past a different, typically lower or higher, value to switch back. That gives it strong noise immunity and results in cleaner, more decisive transitions. So the statement that the Schmitt trigger provides hysteresis, yielding cleaner transitions, best captures the behavior. The other ideas—that a plain comparator is immune to noise around the threshold, or that the Schmitt trigger switches more slowly or behaves identically to a plain comparator—don’t fit the actual behavior.

The key idea here is how adding hysteresis changes a device’s response to noise and its switching behavior. A plain comparator has no hysteresis, so it uses a single threshold. Any noise near that threshold can push the input above or below it, causing rapid, unwanted toggling—chatter—because the output flips as soon as the input crosses that one point. A Schmitt trigger, by contrast, uses positive feedback to create two thresholds: one for switching high and a different one for switching low. This means the input must move significantly in one direction to change state and must travel past a different, typically lower or higher, value to switch back. That gives it strong noise immunity and results in cleaner, more decisive transitions. So the statement that the Schmitt trigger provides hysteresis, yielding cleaner transitions, best captures the behavior. The other ideas—that a plain comparator is immune to noise around the threshold, or that the Schmitt trigger switches more slowly or behaves identically to a plain comparator—don’t fit the actual behavior.