Precision Rectifier Circuit

The post explains a simple precision rectifier circuit using just two opamps.

This precision rectifier operates from an asymmetrical supply, handles
input signals up to 3 Vpp and has a frequency range that extends from DC
to about 2 kHz. Its amplification is unity, and depends mainly on the
ratio R4/R3. Opamp A1 is connected as a voltage amplifier (Ao=l), Az as
an inverting amplifier (Ao:-l). Opamp Az, transistor T1 and diode D2
ensure that the output voltage, U2, is identical to the positive
excursions of the input voltage, U1. When U1 is positive, the out- put
of A1 is held low at about 0.25 V, so that T2 is disabled and can not
affect the rectified out- put signal. Components R2 and D1 protect the
pnp input stage in Az against negative voltages, which are effectively
limited to -0.6 V.

For negative excursions of the input signal, the function of A1, T2 and
Dz is similar to the previously mentioned components. The peak output
voltage . of the rectifier circuit is deter- ; mined mainly by the
maximum output swing of the opamps and the voltage drop across the
transistors plus D2: this amounts to about 3 V in all. When the circuit
is not driven, it l consumes about lmA, and is therefore eminently
suitable for building into portable, battery- operated equipment.