Dual-source 4-port Network Analyzers True-Mode Stimulus Application (TMSA)

Testing balanced devices using true-mode drive 

• Apply true-differential or true-common-mode stimulus in both forward and reverse direction, in frequency sweep or CW
• Accurately characterize the performance of balanced devices while operating under real-world conditions
• Differential sources are fully match-corrected calibrated to maintain a precise differential or common-mode drive at the reference plane of the DUT
• All balanced parameters are fully error-corrected to account for DUT/VNA mismatch in both forward and reverse direction
• Both the source amplitude and phase calibration, and the 4-port error correction are obtained using the same 4-port calibration established during the singled-ended measurements
• Differential sources can generate a pair of CW signals with arbitrary amplitude and phase control
• Configurations include balanced-input and balanced-output as well as one port single-ended and one port balanced
• Easily access measurement results with true-mode drive as well as single-ended drive

True-mode stimulus 

By using a dual-source 4-port network analyzer, we are able to accurately control both internal sources simultaneously and therefore, to correct for the phase and amplitude differences at every frequency point for each true-mode measurement, at the reference plane of the device-under-test (DUT). This way, we can set the phase difference to zero for common-mode stimulus, or to 180 degrees for differential-mode stimulus, while maintaining the same amplitude. In addition, we provide a mode where the user can set the phase difference of a continuous-wave (CW) to any arbitrary value between 0 and 180, as well as setting the amplitude difference to an arbitrary value. This allows for imbalanced stimulus to perform stress tests on the DUT as needed. 

Fully match-corrected calibrated differential sources 

The match-corrected source calibration is the calibration of the waves so that the actual waveform at the reference plane of the DUT is modified to maintain a precise differential- or common-mode drive, taking into account the mis-match of the DUT and the test system. This modification does not require any extra work from the user, but it does require the network analyzer to make two measurements at each frequency point. All the necessary steps are managed and executed by the True-Mode Stimulus Application (TMSA). At each frequency point, the application will: 

1. Measure the match of the DUT with an approximately differential signal
2. Compute the required change to amplitude and phase to produce an exact differential signal at the DUT, modify the source amplitude and phase to produce this signal, and measure the DUT response to this signal
3. Reset the sources to a common-mode signal (zero phase difference), and measure the DUT response
4. Repeat steps 1 through 3 for each frequency point. At the end of the forward sweep, the sources are changed from the forward drive to the reverse drive, and repeat steps 1 through 3 again
5. At the end of both forward and reverse sweeps, the full 4-port error correction is computed, and any traces that are in the display of the PNA are updated with the True-Mode results
6. At this point, the PNA sweep is put into Hold. Since all the scattered waves have been measured, any additional traces may be added to the existing or new windows, and the True-Mode parameter result will be shown
7. These traces may be placed in memory; if the PNA trigger is changed from Hold to Single or Continuous, a single-ended sweep will occur. This way, the True-Mode results can be compared to the single-ended results

Fully error-corrected measurements 

After the fully-calibrated true-mode drive signal is applied, all the scattered waves (S-parameters) from the DUT are measured, and the effects of the re-reflections from the network analyzer are removed through a modified full 4-port error-correction. A modification is required because, unlike the single ended measurement, only two of the ports are terminated during a measurement, the other two ports are being driven by the true-mode signal. Once again, all necessary steps are managed and executed by TMSA with no added work required from the user. Because error correction is possible by applying standard 4- or 3-port calibration techniques and then modifying the error-term matrix, the error-correction process is simply to perform a full 4- or 3-port single-ended calibration (depending on the topology being measured), using either an Electronic Calibration (ECal) module or mechanical calibration kit, before launching the true-mode stimulus application. An ECal module, either 2- or 4-port, would provide the fastest and most convenient approach. 

Measurement process overview 

Whether you are measuring a 4-port device, with balanced-input and balanced- output (BAL-BAL), or a 3-port device, with one port single-ended and one port balanced (SE-BAL), a dual-source 4-port network analyzer is required for true-mode stimulus. To obtain true-mode stimulus parameters, the user only needs to add one more step to the measurement process and that is to activate TMSA. In general, the following steps do apply: 

1. Setup device topology (BAL-BAL or SE-BAL), see Figure 2 for details
2. Setup measurement parameters such as: frequency range, number of points, IF BW, power level, etc
3. Setup display (if desired, 16 parameters for BAL-BAL, 9 parameters for SE-BAL). Mixed-mode S-parameters will be displayed as “Sdd12,” for example. See Figure 2
4. Perform calibration using Calibration Wizard — easiest and quickest with an ECal module (4-port calibration for BAL-BAL, 3-port calibration for SE-BAL)
5. Connect the DUT and perform measurements. At this point, mixed-mode S-parameters are available from single-ended stimulus
6. To obtain true-mode S-parameters, press the front panel hardkey [Macro], press the software [TMSA], and then click “Launch TMSA.” (Make sure the active trace is one of the traces in the channel that is intended for true-mode stimulus.) Although the display will not be updated, a status bar will appear during measurements. See Figure 3 for details. Depending on the number of points and the IF BW, measurements can take a while due to the number of corrections being applied at each measurement point.