Guarding And Shielding - Keithley 2651A Reference Manual

High power system sourcemeter instrument

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Model 2651A High Power System SourceMeter® Instrument Reference Manual

The figure below illustrates the connection scheme of two Model 2651A instruments connected in

parallel. Two Model 2651A can output up to 100 A at 36 V (see

48)). The current delivered to the DUT is the sum of currents output by SMU channels (I

the two Model 2651A instrument's expands the power envelope. For further information, visit the

Keithley Instruments website

2651A instruments' channels.

Single SMU maximum pulse current: 50 A

Paralleled SMU channels maximum pulse current (as shown): 100 A

Guarding and shielding

Source-measure performance and safety are optimized with the effective use of guarding and

shielding (noise and safety shields).

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 Model 2651A.

Guarding (shown below) should be used when test circuit impedance is >1 GΩ.

2651A-901-01 Rev. A / March 2011

(http://www.keithley.com) for application notes on combining two Model

Figure 18: Connecting channels in parallel for higher current

(on page 4-17) for details on the principles of guarding.

Combining SMU outputs

Section 2: General operation

). Combining