OP177

Rev. E | Page 10 of 16

PRECISION HIGH GAIN DIFFERENTIAL AMPLIFIER

OP177 make it possible to obtain performance not previously

available in single stage, very high gain amplifier applications.

See Figure 27.

For best CMR,

R2

R1

must equal

R4

R3

In this example, with a 10 mV differential signal, the maximum

errors are listed in Table 6.

0.1µF

+15V

1kΩ

1kΩ

1MΩ

0.1µF

–15V

1MΩ

2

3

7

6

4

OP177

–

+

Figure 27. Precision High Gain Differential Amplifier

Table 6. High Gain Differential Amp Performance

Type

Amount

Common-Mode Voltage

0.1%/V

Gain Linearity, Worst Case

0.02%

0.0003%/°C

0.008%/°C

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.

–

+

OP177

0.1µF

+15V

0.1µF

–15V

2

3

7

6

4

INPUT

100Ω

10pF

OUTPUT

Figure 28. Isolating Capacitive Loads

BILATERAL CURRENT SOURCE

The current sources shown in Figure 29 supply both positive

and negative currents into a grounded load.

Note that

1

3

2

4

5

1

2

4

5

R

R

R

R

R

R

R

R

Z

O

−

+

⎟

⎠

⎞

⎜

⎝

⎛

+

=

1

3

2

4

5

R

R

must

R

R

R

=

+

PRECISION ABSOLUTE VALUE AMPLIFIER

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).