(2:1) degradation of the amplifier’s performance. See

Fig-

ures 5, 6, 7 for typical connections of guard rings for stan-

dard op-amp configurations. If both inputs are active and at

high impedance, the guard can be tied to ground and still

provide some protection; see

Figure 8.

The designer should be aware that when it is inappropriate

to lay out a PC board for the sake of just a few circuits, there

is another technique which is even better than a guard ring

on a PC board: Don’t insert the amplifier’s input pin into the

board at all, but bend it up in the air and use only air as an in-

sulator. Air is an excellent insulator. In this case you may

have to forego some of the advantages of PC board con-

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FIGURE 4. Example of Guard Ring in P.C. Board Layout, Using the LPC660

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FIGURE 5. Inverting Amplifier

Guard Ring Connections

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FIGURE 6. Non-Inverting Amplifier

Guard Ring Connections

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FIGURE 7. Follower

Guard Ring Connections

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FIGURE 8. Howland Current Pump

Guard Ring Connections

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