REV. A

OP227

–13–

A1

A2

30pF

1N914

1k

2N4393

2k

A1, A2: OP27

1k

Figure 5. High Speed Precision Rectifier

High Speed Precision Rectifier

The low offsets and excellent load driving capability of the OP27

are key advantages in this precision rectifier circuit. The summing

impedances can be as low as 1 k

W which helps to reduce the

effects of stray capacitance.

For positive inputs, D2 conducts and D1 is biased OFF. Ampli-

fiers A1 and A2 act as a follower with output-to-output feedback

and the R1 resistors are not critical. For negative inputs, D1

conducts and D2 is biased OFF. A1 acts as a follower and A2

serves as a precision inverter. In this mode, matching of the two

R1 resistors is critical to gain accuracy.

Typical component values are 30 pF for C1 and 2 k

W for R3.

The drop across D1 must be less than the drop across the FET

diode D2. A 1N914 for D1 and a 2N4393 for the JFET were

used successfully.

The circuit provides full-wave rectification for inputs of up to

±10 V and up to 20 kHz in frequency. To assure frequency stability,

be sure to decouple the power supply inputs and minimize any

capactive loading. An OP227, which is two OP27 amplifiers in a

single package, can be used to improve packaging density.