What factors limit the speed of a peak detector using an op-amp, and how can you mitigate slow recovery?

What factors limit the speed of a peak detector using an op-amp, and how can you mitigate slow recovery?

• A. The diode speed, op-amp bandwidth, capacitor size; use fast diodes (Schottky), a faster op-amp, smaller hold capacitor or active peak detector design to improve recovery.
• B. The diode speed is the sole limiter to recovery.
• C. The hold capacitor value does not affect recovery.
• D. Recovery is independent of diode and op-amp specs.

Answer: (B)

Recovery speed in a peak detector is governed by how quickly the stored peak can be released and the circuit can start tracking a new peak. The diode in the feedback path acts as the gate that transfers the input peak to the hold capacitor. When the input falls, the diode must stop conducting. If the diode has slow reverse recovery, it continues to conduct for a short time, effectively tying the hold capacitor to the input and delaying the detector’s return to tracking. In many simplified or idealized designs, the op-amp’s bandwidth and the hold capacitor are assumed fast enough not to limit recovery, so the diode’s switching behavior becomes the dominant factor. That’s why using fast switching diodes, especially Schottky diodes with negligible reverse-recovery time and low forward drop, is the most effective way to mitigate slow recovery. They allow the diode to stop conducting almost instantly as the input changes, letting the hold capacitor voltage respond quickly and the detector to follow subsequent peaks promptly. In real designs, you’d also consider the op-amp’s speed and leakage through the hold capacitor, but the diode speed often remains the primary lever for improving recovery performance.

Recovery speed in a peak detector is governed by how quickly the stored peak can be released and the circuit can start tracking a new peak. The diode in the feedback path acts as the gate that transfers the input peak to the hold capacitor. When the input falls, the diode must stop conducting. If the diode has slow reverse recovery, it continues to conduct for a short time, effectively tying the hold capacitor to the input and delaying the detector’s return to tracking. In many simplified or idealized designs, the op-amp’s bandwidth and the hold capacitor are assumed fast enough not to limit recovery, so the diode’s switching behavior becomes the dominant factor.

That’s why using fast switching diodes, especially Schottky diodes with negligible reverse-recovery time and low forward drop, is the most effective way to mitigate slow recovery. They allow the diode to stop conducting almost instantly as the input changes, letting the hold capacitor voltage respond quickly and the detector to follow subsequent peaks promptly. In real designs, you’d also consider the op-amp’s speed and leakage through the hold capacitor, but the diode speed often remains the primary lever for improving recovery performance.