OP97 Datasheet, PDF (9/12 Pages) Analog Devices – Low-Power, High-Precision Operational Amplifier

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
4095
2048
1024
512
256
128
64
32
16
8
4
2
1
0
GAIN (Av)
–1.00024
–2
–4
–8
–16
–32
–64
–128
–256
–512
–1024
–2048
–4096
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
R2
20k⍀
R1
2k⍀
V_IN
1␮F
5pF
2
10k⍀
10k⍀
OP44
6
3
2
OP97
6
3
5
0.1␮F
A_V =
R2
R1
V_OUT
Figure 11. Combination High-Speed, Precision Amplifier
Figure 12. Combination Amplifier Transient Response
.
+15V
V_IN
؎2.5mV TO ؎10V
RANGE DEPENDING
ON GAIN SETTING
1
18
R_FB
I_{OUT 1}
16
V_REF 17
0.1␮F
2
3 ^{IOUT 2} PM7541
C1
220pF
+15V
2
OP97
0.1␮F
6
V_OUT
3
–15V
0.1␮F
Figure 10. Precision Programmable Gain Amplifier
REV. D
–9–