Comparator fundamentals — is a zero-level detector simply a comparator that switches when the input crosses 0 V?

Introduction / Context:
Comparators are used to decide whether an input is above or below a reference. A special case is the “zero-level detector,” widely used for zero-crossing detection in AC measurements and waveform shaping. Understanding the equivalence clarifies design choices, including when to add hysteresis for noise immunity.

Given Data / Assumptions:

• Ideal comparator or op-amp used as a comparator without linear feedback.
• Reference voltage set to 0 V (ground).
• Input may be a slowly varying or sinusoidal signal.

Concept / Approach:
A comparator outputs a high or low level depending on the sign of V_in − V_ref. With V_ref = 0 V, the device toggles when the input crosses zero. This meets the definition of a zero-level detector. In practice, a Schmitt trigger (comparator with positive feedback) is often preferred to add hysteresis and prevent chatter near 0 V when noise is present.

Step-by-Step Solution:

Verification / Alternative check:
Oscilloscope shows crisp transitions at zero crossings; with hysteresis, switching occurs at ±V_H/2, improving noise immunity.

Why Other Options Are Wrong:

Common Pitfalls:
Using a linear op-amp in open loop without considering input common-mode range; forgetting pull-up requirements with open-collector comparators; omitting hysteresis in noisy environments.

Final Answer:
Correct