How does hysteresis improve a comparator's performance in noisy environments?

• A. It reduces input impedance.
• B. It speeds up the switching without noise considerations.
• C. It prevents any switching by keeping the output fixed.
• D. It creates two thresholds to prevent rapid switching due to noise.

Answer: (D)

Hysteresis adds a pair of switching points to a comparator, creating a high and a low threshold. As the input signal rises, the output only changes when the input crosses the upper threshold; as it falls, the output only changes again when the input crosses the lower threshold. This creates a deadband that prevents the output from chattering when noise or small fluctuations occur near the switching point. The result is a stable, clean transition in noisy conditions.

This approach doesn’t aim to speed up switching on its own, nor does it reduce input impedance, nor keep the output fixed forever. It deliberately introduces two thresholds so that only a sufficiently large change in the input—and in the appropriate direction—will flip the state, which is exactly what stops rapid, noise-driven switching.