Using True Differential Mode    Related Topics

In True Differential Mode, the analyzer can generate balanced waves at arbitrary reference planes in the test setup and determine balanced results. The true differential mode also provides two additional sweep types.

Measuring balanced wave quantities and ratios

Measuring mixed mode S-parameters

Performing an amplitude or phase imbalance sweep

Measurements on frequency-converting DUTs


Measuring balanced wave quantities and ratios...

The following example shows how to activate the true differential mode in order to perform balanced measurements on a 2-port DUT with balanced input and balanced output using a 4-port network analyzer. You can use a predefined port configuration with fixed port assignments.

To prepare the measurement,  

  1. Perform a full calibration of all four (single-ended) analyzer ports, preferably using a calibration unit for automatic (TOSM) calibration. You can also use the calibration wizard, e.g. if you want to use one of the 7-term calibration types (TNA, TRL, ...); see Calibrating a Measurement Channel.

  2. Preferably, perform a source power calibration at the input of your DUT.  

To obtain balanced ratios,  

  1. Click Trace – Measure – Ratios – More Ratios...

  2. In the Port Configuration panel of the More Ratios dialog opened, click Balanced Ports and Port Groups.

  3. In the Predefined Configs tab of the Balanced Ports and Port Groups dialog opened, select the port configuration that is suitable for your DUT.

   

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.
Exception:
On R&S ZVA-Z67 network analyzers, all ports have independent internal sources. You can use true differential mode with an arbitrary combination of two source ports.   

 

  1. Still in the Predefined Configs tab, enable True Differential Mode.

  2. Open the Def Balanced Port tab and assign the appropriate differential and common mode reference impedances to both logical ports.

  3. Click OK to close the Balanced Ports and Port Groups dialog.

  4. 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.

  5. Back in the More Ratios dialog, select the balanced ratio that you wish to measure.

  6. Click OK to close the More Ratios dialog and perform the measurement.

To obtain balanced wave quantities,

  1. Calibrate your test setup, define the balanced port configuration and set the reference impedances as described above.

  2. Click Trace – Measure – Wave Quantities – More Wave Quantities...

  3. Select the balanced wave quantity that you wish to measure.

  4. Click OK to close the More Wave Quantities dialog and perform the measurement.


Measuring balanced S-parameters...

The following example shows how to activate the true differential mode in order to obtain mixed-mode S-parameters. We use a 2-port DUT with balanced input and balanced output and a 4-port network analyzer as described above.

  1. Calibrate your test setup as outlined above (Measuring balanced wave quantities and ratios)

  2. Click Trace – Measure – More S-Params...

  3. In the Port Configuration panel of the More S-Parameters dialog opened, click Balanced Ports and Port Groups.

  4. In the Predefined Configs tab of the Balanced Ports and Port Groups dialog opened, select the port configuration that is suitable for your DUT.

   

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.

  1. Open the True Diff Mode tab and enable True Differential Mode.

  2. Open the Def Balanced Port tab and assign the appropriate differential and common mode reference impedances to both logical ports.

  3. Click OK to close the Balanced Ports and Port Groups dialog.

  4. 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.

  5. Back in the More S-Parameters dialog, select the mixed-mode S-parameter that you wish to measure.

  6. Click OK to close the More S-Parameters dialog and perform the measurement.

You can also access all the described settings from the Measurement Wizard.


Performing an amplitude or phase imbalance sweep...

Amplitude or phase imbalance sweeps are special sweep types in true differential mode. The analyzer generates a balanced signal at one of its logical ports, however, the amplitude of one signal component or the relative phase of the two components is varied according to a selected sweep range.

In the following examples we use a 2-port DUT with balanced input and balanced output and a 4-port network analyzer as described above.  

  1. Calibrate your test setup, define the appropriate port configuration and enable true differential mode as outlined above (Measuring balanced wave quantities and ratios).

To perform an amplitude imbalance sweep,

  1. Click Channel – Sweep – Sweep Type: Amplitude Imbalance.

  2. In the Amplitude Imbalance Sweep dialog opened, select the logical Port 1 (comprising the physical ports 1 and 3) as the swept port. The second logical port will continue providing an undisturbed balanced stimulus signal.

  3. Select the CW Frequency and the reference power (Source Power at 0 dB) for the sweep.

  4. Close the dialog, click Channel – Stimulus – Start to define the start power of port 3 relative to the Source Power at 0 dB.

  5. Click Channel – Stimulus – Stop to define the stop power of port 3 relative to the Source Power at 0 dB.  

  6. Click Trace – Measure – More S-Params... and select the measured mixed-mode S-parameter.

  7. Click OK to close the More S-Parameters dialog and perform the measurement.

To perform a phase imbalance sweep,

  1. Click Channel – Sweep – Sweep Type: Phase Imbalance.

  2. In the Phase Imbalance Sweep dialog opened, select the logical Port 1 (comprising the physical ports 1 and 3) as the swept port. The second logical port will continue providing an undisturbed balanced stimulus signal.

  3. Select the CW Frequency and the constant Source Power for the sweep.

  4. Close the dialog, click Channel – Stimulus – Start to define the start phase difference between the physical ports 3 and 1.

  5. Click Channel – Stimulus – Stop to define the stop  phase difference between the physical ports 3 and 1.  

  6. Click Trace – Measure – More S-Params... and select the measured mixed-mode S-parameter.

  7. Click OK to close the More S-Parameters dialog and perform the measurement.


Measuring frequency converting DUTs...

In a true differential measurement on frequency-converting DUTs, accurate powers are of particular importance. This means that a system error calibration and a subsequent power calibration is required (see True Differential Mode on Frequency-Converting DUTs).

The following example shows how to perform scalar mixer measurements on a differential mixer with balanced RF input and IF output ports and a single-ended LO input. With a four-port analyzer, a possible test setup involves the following connections:

Perform the measurement steps in the following order:

  1. Activate scalar mixer mode: Click Channel – Mode – Scalar Mixer – Define Scalar Mixer Meas. Select the external generator as LO source and define the RF frequency range.

  2. System error correction: Connect a calibration to the four (single-ended) analyzer ports and perform a full four-port (UOSM) calibration.

  3. Power calibration: Perform a source power calibration at ports 1 and 3 (one power calibration for each true differential port).

  4. Activate true differential mode: Open the Balanced Ports and Port Groups dialog as described above, combine ports 1 / 3 and ports 2/ 4 to balanced ports, and enable true differential mode.

  5. Measurement: Connect the DUT and measure the desired balanced or mixed mode S-parameters (Trace – Measure...).