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

THE END

……. Thank You …….