OP177
BILATERAL CURRENT SOURCE
PRECISION ABSOLUTE VALUE AMPLIFIER
The current sources shown in Figure 28 will supply both
positive and negative current into a grounded load.
R4
R5
+1
R2
Note that Z
O
=
R5+ R4 R3
–
R1
R2
and that for Z
O
to be infinite,
R5+ R4
R3
must
=
R2
R1
The high gain and low TCV
OS
assure accurate operation with
inputs from microvolts to volts. In this circuit, the signal always
appears as a common-mode signal to the op amps. The
OP177E CMRR of 140 dB assures errors of less than 1 ppm.
See Figure 29.
Figure 30. Precision Positive Peak Detector
PRECISION POSITIVE PEAK DETECTOR
In Figure 30, the C
H
must be of polystyrene, Teflon*, or
polyethylene to minimize dielectric absorption and leakage. The
droop rate is determined by the size of C
H
and the bias current
of the OP41.
PRECISION THRESHOLD DETECTOR/AMPLIFIER
In Figure 32, when V
IN
< V
TH
, amplifier output swings nega-
tive, reverse biasing diode D
1
. V
OUT
= V
TH
if R
L
=
∞.
When
V
IN
≥
V
TH
, the loop closes,
R
V
OUT
=V
TH
+
(
V
IN
–V
TH
)
1+
F
R
S
C
C
is selected to smooth the response of the loop.
*Teflon is a registered trademark of the Dupont Company.
Figure 31
.
Precision Threshold Detector/Amplifier
–10–
REV. B
AD [ ANALOG DEVICES ]
