OP177
PRECISION HIGH GAIN DIFFERENTIAL AMPLIFIER
The high gain, gain linearity, CMRR, and low TCV
OS
of the
OP177 make it possible to obtain performance not previously
available in single stage, very high gain amplifier applications.
See Figure 27.
For best CMR,
ISOLATING LARGE CAPACITIVE LOADS
The circuit shown in Figure 28 reduces maximum slew rate but
allows driving capacitive loads of any size without instability.
Because the 100 Ω resistor is inside the feedback loop, its effect
on output impedance is reduced to insignificance by the high
open loop gain of the OP177.
R
F
10pF
+15V
0.1µF
INPUT
R
S
2
3
R1
R3
must equal
R2
R4
In this example, with a 10 mV differential signal, the maximum
errors are listed in Table 6.
R
2
1MΩ
+15V
0.1µF
R
1
1kΩ
R
3
1kΩ
R
4
1MΩ
7
–
+
7
6
100Ω
OUTPUT
OP177
4 0.1µF
C
LOAD
00289-028
2
3
–
OP177
+
4
0.1µF
6
–15V
Figure 28. Isolating Capacitive Loads
BILATERAL CURRENT SOURCE
00289-027
–15V
Figure 27. Precision High Gain Differential Amplifier
The current sources shown in Figure 29 supply both positive
and negative currents into a grounded load.
Note that
Table 6. High Gain Differential Amp Performance
Type
Common-Mode Voltage
Gain Linearity, Worst Case
TCV
OS
TCI
OS
Amount
0.1%/V
0.02%
0.0003%/°C
0.008%/°C
⎛
R
4
⎞
+
1
⎟
R
5
⎜
⎝
R
2
⎠
Z
O
=
R
5
+
R
4
R
3
−
R
2
R
1
and that for Z
O
to be infinite
R
5
+
R
4
R
2
must
=
R
3
R
1
PRECISION ABSOLUTE VALUE AMPLIFIER
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 (for details,
see Figure 30).
Rev. E | Page 10 of 16
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