In a precision rectifier circuit, which statement best explains the role of the op-amp in achieving near-ideal rectification at small input voltages?

In a precision rectifier circuit, which statement best explains the role of the op-amp in achieving near-ideal rectification at small input voltages?

• A. The op-amp reduces the diode forward drop by increasing its bias current.
• B. The op-amp drives the diode in the feedback path so the diode drop is compensated.
• C. The diode conducts on both polarities, eliminating the diode drop entirely.
• D. The output is clamped to zero regardless of input.

Answer: (B)

The key idea is that the op-amp uses its feedback to cancel the diode’s forward drop, giving nearly ideal rectification for small input voltages. In a precision rectifier, the diode is placed in the feedback path so the op-amp can drive it with whatever voltage is needed to make the inverting input follow the reference (often ground). When the input is small but positive, the op-amp output rises just enough to forward-bias the diode, and once the diode conducts, the feedback loop closes. The op-amp then adjusts its output so that the voltage at the inverting input stays equal to the reference, effectively “hiding” the diode’s drop inside the op-amp’s output and delivering an output that mirrors the input with almost no offset. In the negative half-cycle, the diode is reverse-biased and the path to the output is blocked, so the output sits at zero, producing the rectified result. So this configuration works not by changing the diode’s properties with bias current, but by using the op-amp’s high gain in a closed loop to force the diode drop to be compensated within the feedback, yielding near-ideal rectification for small signals.

The key idea is that the op-amp uses its feedback to cancel the diode’s forward drop, giving nearly ideal rectification for small input voltages. In a precision rectifier, the diode is placed in the feedback path so the op-amp can drive it with whatever voltage is needed to make the inverting input follow the reference (often ground). When the input is small but positive, the op-amp output rises just enough to forward-bias the diode, and once the diode conducts, the feedback loop closes. The op-amp then adjusts its output so that the voltage at the inverting input stays equal to the reference, effectively “hiding” the diode’s drop inside the op-amp’s output and delivering an output that mirrors the input with almost no offset. In the negative half-cycle, the diode is reverse-biased and the path to the output is blocked, so the output sits at zero, producing the rectified result.

So this configuration works not by changing the diode’s properties with bias current, but by using the op-amp’s high gain in a closed loop to force the diode drop to be compensated within the feedback, yielding near-ideal rectification for small signals.