Technical data

5- 4 Agilent 41000 Administration Guide, Edition 3
Measurement Techniques
Kelvin Connections
Kelvin Connections
This section describes the Kelvin connections effective for the high current measurement
or the low resistance measurement. The Kelvin connection is available for the source
monitor unit (SMU) installed in the Agilent 4156C and E5270B.
• “About Kelvin Connections”
• “To Make Kelvin Connections”
• “To Control Switching Matrix”
• “To Connect Ground Unit”
About Kelvin Connections
When you measure a low resistance, high current flows through the DUT. This high current
increases the measurement error caused by the residual resistance of cables. To cancel the
effect of this resistance, you can use Kelvin connections (4-wire) which mean that the force
and sense lines are extended separately to the DUT. The next figure shows the equivalent
circuits for Kelvin and non-Kelvin connections.
• For the non-Kelvin connection, the voltmeter measures the voltage drop of resistances
R
F1
, R
dut
, and R
F2
.
• For the Kelvin connection, the voltmeter measures the voltage drop of resistance R
dut
only. The impedance of the voltmeter is very high, so the voltage drop of resistances
R
S1
and R
S2
can be ignored.
The Kelvin connection is effective even when forcing voltage. The voltage drop due to the
residual resistance of the force line wiring is fed back to the voltage source via a
comparator in the sense line. The input impedance of comparator is high, and current flow
into the sense line is very low. So output error is not significant if the sense line wiring has
a residual resistance of 10 Ω or less. Therefore, the specified voltage appears at the sense
point (point where sense line contacts force line).
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