3-10 DUT Test Connections Series 2600 System SourceMeters Reference Manual
2600S-901-01 Rev. A / May 2006 Return to Section 3 topics
Guarding and shielding
Source-measure performance and safety are optimized with the effective use of guarding
and shielding (noise and safety shields).
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.
Guarding (shown in Figure 3-9) should be used for the following source-measure
condition:
• Test circuit impedance is >1GΩ
Figure 3-9
High-impedance guarding
Noise shield
A noise shield (see Figure 3-10) is used to prevent unwanted signals from being
induced into the test circuit. Low level signals may benefit from effective shielding.
NOTE See “Guard” in Section 8 for details on the
principles of guarding.
CHANNEL A
LO GLO HI G G G HI
SS
KEITHLEY Series 2600
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
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