&S ZVA / R&S ZVT True Differential Mode
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differ from the default settings. A subsequent source power calibration is recommended.
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Test Setup and Preparations
True Differential Mode
This application sheet describes the use of option R&S ZVA-K6, True Differential
Mode, on R&S ZVA or R&S ZVT vector network analyzers. In this mode, the analyzers
can generate true differential and common mode stimuli at arbitrary reference planes in
the test setup and determine mixed-mode S-parameters, wave quantities and ratios.
The true differential mode is suitable for testing nonlinear balanced devices under real
operating conditions.
Test Setup and Preparations
The true differential mode requires a port configuration with at least one balanced port.
In the following we use a four-port network analyzer to measure a 2-port DUT with
balanced input and balanced output.
Calibration and stimulus power
A consistent system error correction is essential for accurate balanced waves at the
reference planes and accurate measurement results. You should always perform a full
n-port calibration (TOSM, UOSM or one of the Txx calibration types) of all physical p
involved in the true differential measurement and change the port impedances, if they
Note that the power setting of a true differential source refers to the differential and
common modes directly.
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&S ZVA / R&S ZVT True Differential Mode
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Measuring Balanced S-Parameters
Measuring Balanced S-Parameters
The following example shows how to activate the true differential mode in order to
obtain mixed-mode S-parameters for the test setup shown above.
1. Perform a full calibration of all four analyzer ports, preferably using a calibration
nit for automatic (TOSM) calibration.
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2. Preferably, perform a source power calibration at the input of your DUT.
3. Click “Trace > Measure > More S-Params...”.
4. In the “Port Configuration” panel of the “More S-Parameters” dialog opened, click
“Balanced and Measured Ports”.
5. In the “Predefined Configs” tab of the “Balanced and Measured Ports” dialog
opened, select the port configuration that is suitable for your DUT.
Allowed port combinations
The true differential mode requires logical port combinations with independent power
sources. Do not use ports 1/2 or ports 3/4 to create a logical port.
6. Still in the “Predefined Configs” tab, enable “True Differential Mode”.
7. Open the “Def Balanced Port” tab and assign the appropriate differential and
common mode reference impedances to both logical ports.
8. Click “OK” to close the “Balanced and Measured Ports” dialog.
9. Connect one balanced port of your DUT to ports 1 and 3 of the network analyzer,
the other balanced port of your DUT to ports 2 and 4 of the network analyzer, in
accordance with the selected port combination and reference impedances.
10. Back in the “More S-Parameters” dialog, select the mixed-mode S-parameter that
you wish to measure.
11. Click OK to close the “More S-Parameters” dialog and observe the measurement
result in the diagram area.
Measurement Wizard
You can also access all the described settings from the „Measurement Wizard“.
You can also use the calibration wizard for step no. 1, e.g. if you want to use one of the
7-term calibration types (TNA, TRL, ...).
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&S ZVA / R&S ZVT True Differential Mode
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Discussion of Results
Discussion of Results
For linear DUTs, the S-matrices acquired in virtual and in true differential mode are
expected to be equal. The following figure shows a comparison for the transmission
coefficient S
(below, measured in virtual differential mode) is almost identical over the entire sweep
range.
. The red trace was measured in true differential mode. The blue trace
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Differences may appear for nonlinear devices at high stimulus power levels. For
example, the bias of semiconductor devices like transistors may depend on the kind of
stimulus signal. The following figure shows a power sweep performed in virtual
differential mode (green) and in true differential mode (magenta). In true differential
mode, the compression effects occur at much smaller stimulus powers.
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&S ZVA / R&S ZVT True Differential Mode
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Possible Extensions
Possible Extensions
In true differential mode, can also determine mixed-mode wave quantities and ratios of
wave quantities. Furthermore, the true differential mode also provides two additional
sweep types, the amplitude imbalance and phase imbalance sweeps:
In an amplitude imbalance sweep, the analyzer generates a balanced signal at one
H
of its logical ports, however, the amplitude of one signal component is varied
according to the selected power sweep range.
H In a phase imbalance sweep, the analyzer generates a balanced signal at one of
its logical ports, however, the relative phase of the two signal components is varied
according to the selected phase range.
Related Measurements and Products
In virtual differential mode, the R&S vector network analyzers generate unbalanced
stimulus signals and use a mathematical transformation to convert unbalanced wave
quantities into balanced S-parameters. Linear balanced devices can be tested with
sufficient accuracy in this mode. The virtual differential mode is available on all
R&S ZVB, R&S ZVA, and R&S ZVT vector network analyzers.
Equipment Required
Measurements in true differential mode can be carried out with the following
equipment:
H Vector network analyzer R&S ZVA or R&S ZVT
H Option R&S ZVA-K6, True Differential Mode
H A calibration unit R&S ZV-Z52/Z53 or R&S ZV-Z58 (for R&S ZVT network
analyzers) is recommended
Additional Information
For a comprehensive description of the true differential mode including remote control
refer to the R&S ZVA/ZVT online help system or to the printable operating manual,
which is available for download at http://www.rohde-schwarz.com/product/zva
The text book "Fundamentals of Vector Network Analysis" by Michael Hiebel is an
ideal complement for the information given in the user documentation. The book
combines theoretical background and practical measurements on an R&S ZVA
network analyzer. In case of interest please contact your local R&S office.
.
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