lmc660aimep National Semiconductor Corporation, lmc660aimep Datasheet - Page 10

• Manufacturer Part Number: lmc660aimep
• Description: Cmos Quad Operational Amplifier
• Manufacturer: National Semiconductor Corporation

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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 LMC660AIMEP,
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
(b) Non-Inverting Amplifier
(d) Howland Current Pump
(a) Inverting Amplifier
(c) Follower
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