Precision rectifier (superdiode)
A diode alone cannot rectify a 0.3 V signal: it needs 0.6 V just to conduct. Put it inside an op-amp’s feedback loop and the op-amp drives its output as far as needed to make the cathode follow the input exactly. The diode drop disappears.
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How it works
Input peak 283 mV. The output follows positive half-cycles exactly: peak 283 mV, and stays at 0 V on negative half-cycles.
A bare diode would give nothing at all.
Try it on the bench
- Raise the frequency to 10 kHz: the op-amp cannot slew out of negative saturation fast enough and the output gets late.
Parts on the bench
- 2 × Bench power supply
- AC source
- Op-amp
- Signal diode
- Resistor
In the course
Electronics Engineering, module “Op-amps and feedback”.