OP97 Datasheet, PDF (8/12 Pages) Analog Devices – Low-Power, High-Precision Operational Amplifier

OP97
10k⍀
2
6
OP97
V_IN
3
V_OUT
Figure 5. Unity-Gain Follower
Figure 6. Small-Signal Transient Response with Overcom-
pensation (C_LOAD = 1000 pF, A_VCL = 1, C_OC = 220 pF)
GUARDING AND SHIELDING
To maintain the extremely high input impedances of the OP97,
care must be taken in circuit board layout and manufacturing.
Board surfaces must be kept scrupulously clean and free of moisture.
Conformal coating is recommended to provide a humidity barrier.
Even a clean PC board can have 100 pA of leakage currents between
adjacent traces, so that guard rings should be used around the
inputs. Guard traces are operated at a voltage close to that on the
inputs, so that leakage currents become minimal. In nonin-
verting applications, the guard ring should be connected to the
common-mode voltage at the inverting input (Pin 2). In inverting
applications, both inputs remain at ground, so that the guard trace
should be grounded. Guard traces should be made on both sides
of the circuit board.
R_FB
30pF
I_O
2
PM7548
OP97 ⁶
3
I_O
V_OUT
DIGITAL
INPUTS
Figure 7. DAC Output Amplifier
R1
10k⍀
V1
R2
R3
10k⍀ 10k⍀
R4
10k⍀
R5
10k⍀
+15V
2
7
6
OP97
3
4
–15V
I_L
R_L
V_OUT
Figure 8. Current Monitor
High impedance circuitry is extremely susceptible to RF pickup,
line frequency hum, and radiated noise from switching power
supplies. Enclosing sensitive analog sections within grounded
shields is generally necessary to prevent excessive noise pickup.
Twisted-pair cable will aid in rejection of line frequency hum.
The OP97 is an excellent choice as an output amplifier for higher
resolution CMOS DACs. Its tightly trimmed offset voltage and
minimal bias current result in virtually no degradation of linear-
ity, even over wide temperature ranges.
Figure 8 shows a versatile monitor circuit that can typically
sense current at any point between the ± 15 V supplies. This
makes it ideal for sensing current in applications such as full
bridge drivers where bidirectional current is associated with large
common-mode voltage changes. The 114 dB CMRR of the OP97
makes the amplifier’s contribution to common-mode error
negligible, leaving only the error due to the resistor ratio
inequality. Ideally, R2/R4 = R3/R5. This is best trimmed via R4
UNITY-GAIN FOLLOWER
2
6
OP97
3
NONINVERTING AMPLIFIER
2
6
OP97
3
INVERTING AMPLIFIER
2
6
OP97
3
TO-99
BOTTOM VIEW
1
8
MINI-DIP
BOTTOM VIEW
8
1
Figure 9. Guard Ring Layout and Connections
–8–
REV. D