OP497

Rev. E | Page 11 of 16

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.

1/4

OP497

UNITY-GAIN FOLLOWER

NONINVERTING AMPLIFIER

INVERTING AMPLIFIER

B

8

A

1

PDIP

BOTTOM VIEW

–

+

–

+

–

+

1/4

OP497

1/4

OP497

Figure 34. Guard Ring Layout and Connections

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.

OUTPUT VOLTAGE (V)

–15

–10

–5

0

5

10

15

Figure 35. Open-Loop Gain Linearity