Describe how a peak detector using an op-amp and a diode operates.

Describe how a peak detector using an op-amp and a diode operates.

• A. The op-amp drives the diode to charge a capacitor to the input peak; the capacitor holds the peak and discharges through a resistor.
• B. The diode network converts the signal to a DC level without any storage.
• C. The capacitor is charged to the average value of the input signal.
• D. The op-amp simply buffers the input without affecting the peak.

Answer: (A)

This question tests how a peak detector with an op-amp and a diode captures and holds the highest voltage of the input signal. The op-amp drives the diode so that, as the input rises, the diode conducts and charges the storage capacitor toward the input peak (the op-amp can compensate for the diode’s drop by pushing its output higher). Once the input falls below that stored peak, the diode becomes reverse-biased and the capacitor retains its voltage, slowly discharging only through the resistor. This arrangement stores the peak value rather than the average and keeps it available as a DC-like level for downstream circuitry. The op-amp’s role is essential: it provides low-impedance drive to charge the capacitor accurately and offsets the diode drop, ensuring the stored value reflects the true peak.

This question tests how a peak detector with an op-amp and a diode captures and holds the highest voltage of the input signal. The op-amp drives the diode so that, as the input rises, the diode conducts and charges the storage capacitor toward the input peak (the op-amp can compensate for the diode’s drop by pushing its output higher). Once the input falls below that stored peak, the diode becomes reverse-biased and the capacitor retains its voltage, slowly discharging only through the resistor. This arrangement stores the peak value rather than the average and keeps it available as a DC-like level for downstream circuitry. The op-amp’s role is essential: it provides low-impedance drive to charge the capacitor accurately and offsets the diode drop, ensuring the stored value reflects the true peak.