Precision rectifier

[1] The op-amp-based precision rectifier should not be confused with the power MOSFET-based active rectification ideal diode.

It equals the actual threshold of the diode, divided by the gain of the opamp.

When the input becomes (even slightly) negative, the opamp runs open-loop, as there is no feedback signal through the diode.

For a typical opamp with high open-loop gain, the output saturates.

This change generates some ringing and takes some time, greatly reducing the frequency response of the circuit.

Its input–output relationship is the following: This circuit has the benefit that the op-amp never goes into saturation, but its output must change by two diode voltage drops (about 1.2 V) each time the input signal crosses zero.

Hence, the slew rate of the opamp and its frequency response (gain–bandwidth product) will limit high-frequency performance, especially for low signal levels, although an error of less than 1% at 100 kHz is possible.

Similar circuitry can be used to create a precision full-wave rectifier circuit.

With a little modification, the basic precision rectifier can be used for detecting signal level peaks.