OP497_15 Datasheet, PDF (11/16 Pages) Analog Devices – Precision Picoampere Input Current Quad Operational Amplifier

GUARDING AND SHIELDING
To maintain the extremely high input impedances of the OP497,
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 PCB can have 100 pA of leakage
currents between adjacent traces; therefore, use guard rings
around the inputs. Guard traces are operated at a voltage close
to that on the inputs, as shown in Figure 34, so that leakage
currents become minimal. In noninverting applications, connect
the guard ring to the common-mode voltage at the inverting
input. In inverting applications, both inputs remain at ground;
therefore, the guard trace should be grounded. Place guard
traces on both sides of the circuit board.
UNITY-GAIN FOLLOWER
NONINVERTING AMPLIFIER
–
1/4
OP497
+
–
1/4
OP497
+
INVERTING AMPLIFIER
–
1/4
OP497
+
PDIP
BOTTOM VIEW
8
1
A
B
Figure 34. Guard Ring Layout and Connections
OP497
OPEN-LOOP GAIN LINEARITY
The OP497 has both an extremely high gain of 2000 V/mV
typical and constant gain linearity. This enhances the precision
of the OP497 and provides for very high accuracy in high
closed-loop gain applications. Figure 35 illustrates the typical
open-loop gain linearity of the OP497.
R_L = 10kΩ
V_S = ±15V
V_CM = 0V
T_A = 125°C
T_A = 25°C
–15
–10
–5
0
5
10
15
OUTPUT VOLTAGE (V)
Figure 35. Open-Loop Gain Linearity
Rev. E | Page 11 of 16