REV. D

OP97

–9–

The digitally programmable gain amplifier shown in Figure 10

has 12-bit gain resolution with 10-bit gain linearity over the

range of –1 to –1024. The low bias current of the OP97 main-

tains this linearity, while C1 limits the noise voltage bandwidth

allowing accurate measurement down to microvolt levels.

DIGITAL IN

GAIN (Av)

4095

–1.00024

2048

–2

1024

–4

512

–8

256

–16

128

–32

64

–64

32

–128

16

–256

8

–512

4

–1024

2

–2048

1

–4096

0

OPEN LOOP

Many high-speed amplifiers suffer from less-than-perfect low-

frequency performance. A combination amplifier consisting of a

high precision, slow device like the OP97 and a faster device

such as the OP44 results in uniformly accurate performance

from dc to the high frequency limit of the OP44, which has a

gain-bandwidth product of 23 MHz. The circuit shown in Figure 11

accomplishes this, with the OP44 providing high frequency

amplification and the OP97 operating on low frequency signals

and providing offset correction. Offset voltage and drift of the

circuit are controlled by the OP97.

OP97

2

3

6

0.1 F

+15V

C1

220pF

17

16

PM7541

1

2

3

18

2.5mV TO

10V

RANGE DEPENDING

ON GAIN SETTING

–15V

0.1 F

+15V

0.1 F

Figure 10. Precision Programmable Gain Amplifier

OP44

2

3

6

OP97

2

3

6

R2

20k

5

10k

1 F

R1

2k

0.1 F

10k

5pF

R2

R1

Figure 11. Combination High-Speed, Precision Amplifier

Figure 12. Combination Amplifier Transient Response

.