Specifications

4.3.3 Open/short/load compensation
There are numerous measurement conditions where complicated residual parameters cannot be
modeled as the simple equivalent circuit in Figure 4-4. Open/short/load compensation is an
advanced compensation technique that can be applied to complicated residual circuits. To carry out
the open/short/load compensation, three measurements are required before measuring the DUT,
with the test fixture terminals opened, shorted, and with a reference DUT (load) connected. These
measurement results (data) are used for compensation calculation when the DUT is undergoing
measurement. As shown in Figure 4-6, the open/short/load compensation models the test fixture
residuals as a four-terminal network circuit represented by the ABCD parameters. Each parameter
value is derived by calculation if three conditions are known and if the four-terminal circuit is a
linear circuit. The details of the calculation method for the open/short/load compensation are
described in Appendix C.
The open/short/load compensation should be used in the following situations:
(1) An additional passive circuit or component (e.g. external DC bias circuit, balun transformer,
attenuator and filter) is connected.
(2) A component scanner, multiplexer, or matrix switch is used.
(3) Non-standard length test cables are used or 4TP extension cables are connected in series with
Agilent test cables.
(4) An amplifier is used to enhance the test signal.
(5) A component handler is used.
(6) A custom-made test fixture is used.
In the cases listed above, open/short compensation will not work effectively and the measurement
result contains some error. It is not necessary to use the open/short/load compensation for simple
measurement, like measuring an axial leaded component using the Agilent 16047A test fixture. The
open/short compensation is adequate for such measurements.
Figure 4-6. Open/short/load compensation
Unknown four-terminal
circuit
Z
du t
=
(Z
s
–Z
xm
) (Z
sm
–Z
o
)
(Z
xm
–Z
o
) (Z
s
–Z
sm
)
Z
std
Z
dut
: Corrected DUT impedance
Z
xm
: Measured DUT impedance
Z
o
: Measured open impedance
Z
s
: Measured short impedance
Z
sm
: Measured impedance of the load device
Z
std
: True value of the load device
A B
C D
DUT
V
2
Measurement
instrument
I
1
I
2
V
1
Z
du t
Open/short/load compensation formula
4-6