LMC660_06 Datasheet, PDF (10/14 Pages) National Semiconductor (TI) – CMOS Quad Operational Amplifier

Application Hints (Continued)
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_b−, the leakage of the capacitor and socket
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)
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(Input pins are lifted out of PC board and soldered directly to components.
All other pins connected to PC board.)
FIGURE 7. Air Wiring
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
where C_x is the stray capacitance at the + input.
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FIGURE 8. Simple Input Bias Current Test Circuit
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