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2600AS-901-01 Rev. B / September 2008
Return to
2-13
Series 2600A System SourceMeter® Instruments Reference Manual
Section 2: DUT Test Connections
Guarding
A driven guard is always enabled and provides a buffered voltage that is at the same level as the
input/output HI voltage. The purpose of guarding is to eliminate the effects of leakage current (and
capacitance) that can exist between input/output high and low. Without guarding, leakage and
capacitance in the external high-impedance test circuit could be high enough to adversely affect
the performance of the SourceMeter instrument.
Guarding (shown in
) should be used for the following source-measure condition:
•
Test circuit impedance is >1G
Ω.
NOTE See
for details on the principles of guarding.
Figure 2-17
Models 2602A and 2612A high-impedance guarding
Figure 2-18
Model 2636A high-impedance guarding (floating)
CHANNEL A
LO
G
LO
HI G G G HI
S
S
KEITHLEY Series 2600A
DUT
HI
LO
Metal Guard
Shield
Guard Shield
The guard shield can be the shield of a
coaxial cable, or it can be an insulated
foil that surrounds the conductor.
>1G
W
B LO
A LO
Guard
CHANNEL B
HI
Sense
HI
LO
Sense
LO
Guard
CHANNEL A
HI
Sense
HI
LO
Sense
LO
DUT
>1G
Ω
GND
Guard
LO
HI
LO
HI
Floating
GND