Agilent E5250A User’s Guide, Edition 9 4-23
Setting up Measurement Environment
Measurement Cable Length
Measurement Cable Length This section describes how to calculate the total guard capacitance when using a
Source Monitor Unit (SMU), such as in Agilent 4155/4156 Semiconductor
Parameter Analyzer, Agilent 4142B Modular DC Source/Monitor, Agilent E5270
Series of Parametric Measurement Solution, and so on.
When using an SMU, the length of measurement cables is limited by the guard
capacitance of the cables. Guard capacitance means the capacitance between the
signal line (FORCE or SENSE) and the GUARD line.
Table 4-6 lists the guard capacitance for each element of the E5250A measurement
environment.
When using the 4155/4156/4142B/E5270, the maximum limit of the guard
capacitance is approximately 900 pF. So, you add the following and total must be
less than 900 pF:
• Guard capacitance of cable from SMU to E5250A SMU INPUT.
• Guard capacitance of E5250A and installed plug-in cards.
• Guard capacitance of cable from plug-in card output to connector plate.
• Guard capacitance of cable from connector plate to DUT.
• Other capacitances, such as for probe card.
The following is an example to calculate the guard capacitance of a measurement
environment:
Installed Plug-in cards: Four E5252A cards (145 pF + 8 pF × 3)
Input Cable: 16494A-003 (75 pF)
Output Cable: 16494A-001 (125 pF)
Cable from Connector
Plate to DUT: 8121-1191, 2 m (130 pF × 2)
Probe Card: Guard Capacitance approximately 10 pF (example)
In this environment, the total guard capacitance (Cg-total) is as follows.
Cg-total = 145+(8×3)+75+125+(130×2)+10 pF = 639 pF < 900 pF
Even if you use other instruments, you can use the table for reference about the
measurement cable length and capacitance.