lmc660aimx National Semiconductor Corporation, lmc660aimx Datasheet - Page 9

• Manufacturer Part Number: lmc660aimx
• Description: Cmos Quad Operational Amplifier
• Manufacturer: National Semiconductor Corporation

Application Hints
cause only 0.05 pA of leakage current, or perhaps a minor
(2:1) degradation of the amplifier’s performance. See Figure
6a,Figure 6b, Figure 6c for typical connections of guard rings
for standard 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 6d.
FIGURE 5. Example, using the LMC660,
of Guard Ring in P.C. Board Layout
(Continued)
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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
insulator. Air is an excellent insulator. In this case you may
have to forego some of the advantages of PC board con-
struction, but the advantages are sometimes well worth the
effort of using point-to-point up-in-the-air wiring. See Figure
7.
FIGURE 6. Guard Ring Connections
(d) Howland Current Pump
(b) Non-Inverting Amplifier
(a) Inverting Amplifier
(c) Follower
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