What primarily limits the performance of a peak detector circuit that uses an op-amp and a diode?

What primarily limits the performance of a peak detector circuit that uses an op-amp and a diode?

• A. The op-amp’s supply rails limit the maximum output amplitude.
• B. The signal frequency is too high for the op-amp’s input bandwidth.
• C. The diode’s reverse recovery time is negligible at all frequencies.
• D. Diode forward drop, leakage, and recovery issues with very fast or low-level signals.

Answer: (D)

In a peak detector, the held value is set by charging a storage element through a diode to the peak of the input signal. The main thing that limits how accurately and how fast this works is the diode itself. The forward voltage drop means the capacitor charges only to the peak minus roughly the diode drop, so you don’t capture the true peak value, especially when the signal is small. The leakage current through the diode (and any load leakage) causes the stored voltage to decay over time, so the detected peak drifts downward between peaks or while holding, which is a big accuracy issue for high-impedance reads or long hold times. The recovery behavior of the diode also matters: if the input changes rapidly or the signal is very fast or very small, the diode’s finite recovery time can introduce errors or delay in following the true peak. These diode non-idealities—forward drop, leakage, and recovery—are the dominant constraints on performance for a peak detector. The op-amp and its supply rails can affect limits in other ways, but they don’t override the diode’s non-ideal effects as the primary limiter in the typical peak-detection scenario.

In a peak detector, the held value is set by charging a storage element through a diode to the peak of the input signal. The main thing that limits how accurately and how fast this works is the diode itself. The forward voltage drop means the capacitor charges only to the peak minus roughly the diode drop, so you don’t capture the true peak value, especially when the signal is small. The leakage current through the diode (and any load leakage) causes the stored voltage to decay over time, so the detected peak drifts downward between peaks or while holding, which is a big accuracy issue for high-impedance reads or long hold times. The recovery behavior of the diode also matters: if the input changes rapidly or the signal is very fast or very small, the diode’s finite recovery time can introduce errors or delay in following the true peak. These diode non-idealities—forward drop, leakage, and recovery—are the dominant constraints on performance for a peak detector. The op-amp and its supply rails can affect limits in other ways, but they don’t override the diode’s non-ideal effects as the primary limiter in the typical peak-detection scenario.