op227e Analog Devices, Inc., op227e Datasheet - Page 13

• Manufacturer Part Number: op227e
• Description: Dual, Low Noise, Low Offset Instrumentation Operational Amplifier
• Manufacturer: Analog Devices, Inc.

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 kW 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.
REV. A
V
1
A1
Figure 5. High Speed Precision Rectifier
30pF
C
1
A1, A2: OP27
– 1 3 –
Typical component values are 30 pF for C1 and 2 kW 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.
D
1N914
1
2N4393
1k
R
1
*
2k
R
3
D
2
*
MATCHED
A2
1k
R
2
*
V
O
OP227