2600AS-901-01 Rev. B / September 2008 Return to Section Topics 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 Figure 2-16) should be used for the following source-measure condition:
• Test circuit impedance is >1GΩ.
NOTE See Guarding and shielding 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 GLO HI G G G HI
SS
KEITHLEY Series 2600A
DUT
HILO
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.
>1GW
B LO A LO
Guard
CHANNEL B
HISense
HI
LO Sense
LO
Guard
CHANNEL A
HI
Sense
HILO
Sense
LO
DUT
>1GΩ
GND
Guard
LO HI
LO HI
Floating
GND
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