Agilent Technologies 34420A, User Manual

Page: 256 / 294

Loading Errors Due to Input Bias Current (Leakage Current)
The semiconductor devices used in the input circuits of the meter have
slight leakage currents, called bias currents. The effect of the input bias
current is an loading error at the meter’s input terminals.
The leakage current will approximately double for every 10°C
temperature rise, making the problem much more apparent at higher
temperatures. You can adjust the input bias current to remove these
errors. The bias current is automatically minimized during the zero
calibration procedure (see chapter 4 in the
34420A Service Guide ).
You should perform the zero calibration procedure if you are operating
the meter at a temperature more than 5
°
C from the calibration
temperature.
i
b
= meter bias current
R
S
= DUT source resistance
C
i
= meter input capacitance
Error
(
v
) ≈ i
b
x
R
S
Ideal
Meter
Chapter 7 Measurement Tutorial
Measurement Techniques and Sources of Error
256