Precision Rectifier

Introduction The precision rectifier is also known as a super diode. It is a configuration obtained with an operational amplifier in order to have a circuit behaving like an ideal diode and rectifier. It can be useful for high-precision signal processing.

Precision Rectifier

Basic Circuit The basic circuit implementing such a feature is shown on the right, where RL can be any load.

Basic circuit of precision rectifier

Cont., When the input voltage is negative, there is a negative voltage on the diode, too, so it works like an open circuit, there is no current in the load and the output voltage is zero.

Cont., When the input is positive, it is amplified by the operational amplifier and it turns the diode on. There is current in the load and, because of the feedback, the output voltage is equal to the input.

Circuit Diagram

Cont., In fact the threshold of the super diode is not actually zero, as it should be for an ideal one, but it equals the threshold of the normal diode divided by the gain of the operational amplifier, that is almost zero.

Saturation When the input becomes negative, the output of the operational amplifier can easily become greater than the voltage supplied to the op-amp, thus causing saturation.

Cont., If the input becomes positive again, the op-amp has to get out of the saturation to amplify again. This change takes some time, and this greatly reduces the frequency response of the circuit.

Improved Precision Rectifier circuit

Precision Half wave Rectifier

Precision Full wave Rectifier

Peak detector With little modifications basic precision rectifier can be used also for detecting peak levels of signal. In the following circuit a capacitor keeps the peak voltage level of signal and switch can be used for resetting detected level.

Peak detector

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