Precision rectifier (op-amp rectifier): What is its primary purpose compared to a standard diode rectifier stage?

Introduction / Context:
Standard diode rectifiers exhibit a forward drop (about 0.2–0.7 V depending on diode type), which distorts or entirely blocks low-amplitude signals. Precision rectifiers use op-amps with diodes inside the feedback path to effectively cancel this drop and rectify tiny signals accurately.

Given Data / Assumptions:

• Input signals may be only millivolts to tens of millivolts.
• Goal is accurate half-wave or full-wave rectification without threshold error.
• Op-amp has sufficient slew rate and bandwidth for the signal.

Concept / Approach:
By placing the diode(s) in the feedback loop of an op-amp, the op-amp drives its output to overcome the diode drop, keeping the effective input transfer linear down to near 0 V. This enables rectification of signals too small for ordinary diode rectifiers.

Step-by-Step Solution:

Verification / Alternative check:
Compare outputs with a 50 mV sine: standard diode stage yields nothing; precision rectifier produces a faithful rectified waveform, confirming the purpose.

Why Other Options Are Wrong:
Very large swings: a simple diode bridge already handles large signals well.

“Rectify precision waveforms”: vague; the key advantage is handling small amplitudes.

Amplify and rectify: some variants add gain, but the core purpose is low-threshold rectification.

Common Pitfalls:
Ignoring op-amp slew rate and bandwidth limits, which can distort high-frequency rectification. Forgetting diode recovery effects at high speed.

Final Answer:
rectify waveforms with very small voltage swings