Analog Electronics
An ordinary diode cannot rectify signals below 0.6–0.7 V — useless for small sensor signals. Put the diode inside an op-amp’s feedback loop, however, and the op-amp automatically compensates for the diode drop.
On the positive half, the op-amp’s output adds the diode drop on top and drives the load to the full input voltage; on the negative half the diode opens, the loop breaks, and the output stays at 0: an ideal (lossless) half-wave rectifier.
On this principle you can build precision full-wave rectifiers, peak detectors, and AC voltmeter front-ends (down to the mV range).
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