R&S
®
ZVA / R&S
®
ZVB / R&S
®
ZVT GUI Reference
Channel Menu
Operating Manual 1145.1084.12 – 30 391
or Mechanical Attenuator.
Virtual and true differential mode
The analyzer uses different stimulus signals and different mathematical methods to obtain results in
normal, virtual differential, or true differential mode. The following table gives an overview.
Measurement of wave quantities and S-parameters for unbalanced ports. Unbalanced stimulus signals.
Virtual differential
mode
Precondition: At least one balanced port is defined.
Measurement of unbalanced wave quantities using unbalanced stimulus signals. Unbalanced system error
correction. Conversion of unbalanced wave quantities into balanced and mixed-mode S-parameters with
possible renormalization of port impedances.
Precondition: At least one balanced port is defined.
Measurement of unbalanced wave quantities using balanced stimulus signals (differential and common mode).
System error correction and conversion of unbalanced into balanced wave quantities. Calculation of balanced
and mixed-mode S-parameters with possible renormalization of port impedances.
True Differential mode relies on Enhanced Wave Correction. A consistent system error correction is
essential for accurate balanced waves at the reference planes and accurate measurement results. You
must perform a full n-port calibration (TOSM, UOSM or one of the Txx calibration types) of all physical
ports involved in the true differential measurement and change the differential and common mode
reference impedances, if they differ from the default settings. A subsequent source power calibration is
recommended.
You can also use offset parameters or additional two-port transmission factors in order to move the
reference plane where the analyzer provides an accurate differential or common mode signal.
See also True Differential Mode on Frequency-Converting DUTs.
Option R&S ZVA-K6 provides an alternative Defined Coherence Mode where you can generate
several continuous signals with specific relative amplitude and phase. True differential mode and defined
coherence mode cannot be active at the same time because they require a different source port
configuration.
Source Power in True Differential Mode
A single-ended stimulus can be thought of as resulting from the superposition of a differential and a
common mode stimulus, where the signals add at one single-ended port and cancel at the other (see
equations in section Wave Quantities and Ratios in True Differential Mode below). Therefore the
differential content of a single-ended signal is 3 dB lower than the total signal power.
The stimulus power in true differential mode can be set in two different ways:
If Same Differential and Common Mode Voltages as in Single-Ended Mode is selected, the
analyzer ensures that the stimulus voltages in true differential or common mode are the same as
the respective stimulus components in virtual differential mode. The single ended voltages at the
involved physical test ports are divided by 2 and the output power levels with reference Z
0
by 4
(see table below).
If Apply to Differential (Z
d
= 2Z
0
) and Common Mode (Z
c
= Z
0
/2) Waves is selected, the channel
power P
ch
is interpreted as the power of the true differential or common mode stimulus signal,
referenced to the corresponding mode impedance Z
d
= 2Z
0
or Z
c
= Z
0
/2. The single ended
voltages at the involved physical test ports are divided by sqrt(2) and the output power levels with
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