lmc6022imx National Semiconductor Corporation, lmc6022imx Datasheet - Page 11

• Manufacturer Part Number: lmc6022imx
• Description: Low Power Cmos Dual Operational Amplifier
• Manufacturer: National Semiconductor Corporation

Application Hints
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
(Input pins are lifted out of PC board and soldered directly to components. All other pins connected to PC board.)
BIAS CURRENT TESTING
The test method of Figure 7 is appropriate for bench-testing
bias current with reasonable accuracy. To understand its
operation, first close switch S2 momentarily. When S2 is
opened, then
A suitable capacitor for C2 would be a 5 pF or 10 pF silver
mica, NPO ceramic, or air-dielectric. When determining the
magnitude of I
must be taken into account. Switch S2 should be left shorted
most of the time, or else the dielectric absorption of the
capacitor C2 could cause errors.
Similarly, if S1 is shorted momentarily (while leaving S2
shorted)
FIGURE 7. Simple Input Bias Current Test Circuit
−
, the leakage of the capacitor and socket
(Continued)
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FIGURE 6. Air Wiring
11
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
6.
where C
Typical Single-Supply Applications
Note: A 5V bias on the photodiode can cut its capacitance by a factor of 2
or 3, leading to improved response and lower noise. However, this bias on
the photodiode will cause photodiode leakage (also known as its dark
current).
(V+ = 5.0 V
Photodiode Current-to-Voltage Converter
x
is the stray capacitance at the + input.
DC
)
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