Keysight Technologies N6700C Serie Guide D'utilisation page 60

4. If the load capacitor (CL) is not located at the sense point, the distance from the sense point to the
load capacitor cannot exceed 15 cm and must be twisted-pair, coax, or pc traces.
5. If the test fixture consists of pc traces, the positive and negative traces should be directly facing on
adjacent layers.
To minimize inductance, the width (w) of the traces should be at least as great as the thickness of the
dielectric (h). It is better to make the traces much wider than this minimum requirement in order to
minimize the DC resistance.
Low Bandwidth Mode with Remote or Local Sensing
All previously stated wiring requirements still apply in Low bandwidth mode except for the following.
The 15 cm maximum limit between the sense point and the load capacitor (see #4) does not apply
when using Low bandwidth mode.
Guard Connections
The purpose of a cable guard is to eliminate the effects of leakage current that can exist in the current
path of the external test circuit. The cable guard can be used when the test fixture requires guarding
and the power system is sourcing or measuring DC currents under 1 μA. Without a guard, leakage
currents in the test circuit could affect the accuracy of the micro-amp measurements. Guarding is
generally not required when measuring currents 1 μA and greater.
As shown below, cable guards are available at the output connector of Keysight Models N678xA SMU.
The guard is typically used to drive the shields of cables and test fixtures. It provides a buffered
voltage that is at the same potential as the + output terminals of the module connector. The guard
current is limited to about 300 μA.
1. N678xA SMU connector
2. Guard shield (can be the
shield of a coaxial cable)
Keysight N6700C Series User's Guide
2 Installation
59