Model 8010 High Power Device Test Fixture User's Manual
Section 3: Working with devices and instruments
8010-900-01 Rev. C / March 2017
3-27
Stray capacitance, resistance, and inductance in the test setup cause measurement errors. These
errors will vary with setup and their impact varies with frequency. To remove these errors from the
measurement, perform connection compensation. See the
(on page 3-17)
topic and the Typical coaxial bias tee block diagram that shows the parasitic elements in a typical test
circuit and the simplified model used to derive the device impedance.
Small capacitance measurements are high impedance and are particularly affected by the stray
capacitance in the test setup. During open compensation, stray capacitance is measured so that it
may be removed from the calculation of the DUT capacitance. Perform open compensation by
removing the DUT from the test fixture.
Carefully, remove the DUT from the test fixture without altering the connection to the test fixture. For
example, the distance between the instrument terminals should remain the same. Run the open
compensation routine on the C-V instrument and it will measure impedance across the frequency to
capture the stray capacitance.
Larger capacitance measurements are low impedance and are particularly affected by the stray
series resistance and test setup inductance. Short compensation measures the stray resistance and
inductance as a function of test frequency. Perform short compensation by shorting the C-V
instrument terminals at the DUT. Carefully, short the device terminals without altering the connections
to the test instrument, including the distance between the test instrument leads. Run the short
compensation routine on the C-V instrument and it will measure impedance across the frequency to
capture the stray capacitance.
When performing C-V measurements with the CVU-3K-KIT or the CVU-200-KIT option, short and
open compensation help to cancel the impact of the capacitance, resistance, and inductance of the
bias tees from the device measurement.
Perform open and short compensation whenever the test setup changes. This includes cabling and
adapter changes, as well as changes to the bias tee configurations. For measurements of three-
terminal devices, such as MOSFETs, note that each capacitance measurement type (that is, Ciss,
Coss, Crss, Cgs, Cds) requires its own open and short connection compensations. ACS basic
software version 2.1 and later contains built-in compensation routines that permit you to save the
compensation data for each of these measurements. Therefore, you can perform the complete open
and short compensation routines for all measurements.
The Model 4210-CVU C-V instrument also includes cable length compensation for its supplied coaxial
cables that allows it to compensate for phase errors in the cables up to the point at which the 4-wire
measurement point ends. For Model 8010 and CVU-3K-KIT or the CVU-200-KIT connections, the 4-
wire measurement point ends at the bias tee.
The next figure is a simplified example of an AC impedance measurement system. Note that Zshort
represents the impedance measured when the device is shorted. It includes the stray resistance and
inductance of all the elements in the system, including cabling, adapters, and bias tees. Also, Zopen
represents the impedance measured when the device terminals are opened. It includes the stray
capacitance of all the elements in the test system.
