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NVNA, Time Domain Waveforms and X-Parameter Measurements

Introduction


Device characterization is required for power amplifier design, and the ideal form of the device data is a large signal model. With a model, the performance can be analyzed for varying drive and impedance conditions, so complex or multi-stage circuits can be designed. A method of formulating a large signal model is to use a measurement-based behavioral approach, as with the X-Parameter model. This is based on measurements of X-parameters, which are a superset of S-parameters for nonlinear components, and are measured using an NVNA (Non-linear Vector Network Analyzer).

Load Pull with X-Parameters


Load pull with NVNA measurements of X-parameters can be used directly by the X-Parameter model over a wide impedance range. The operator of the combined load pull NVNA system can select an impedance range of interest, possibly over the entire Smith chart. The X-Parameter model can then be used as a circuit element in a non-linear analysis with great confidence, since it is based on measurement at the actual operating conditions of the device. The load pull X-parameter measurement can include a complete sweep plan. Stimulus variables can include impedance, power drive, bias, and frequency, for example. This can extend the applicability of the X-Parameter model over a much wider range of validity - over the range of actual applications for many high-power and multi-stage PA designs.

The process has three steps:

1) The load pull system measures the X-parameters at each impedance setting, like a standard load pull, with X-parameters added to the measurement data set. When the measurements are complete at all the impedances, the measured X-parameters are saved into a single file.

2) An enhanced design kit available for use in the ADS non-linear simulator then reads the file saved by the load pull- NVNA system and creates a X-Parameter component associated with the file. This is a very quick step.

3) This component can then be dragged and dropped directly into a circuit schematic as a non-linear device, and analysis can start immediately.

Demonstrations


Click here to view a Demo of this ATSv5 PNA-X application as seen at IMS-2010 +


Non-50Ω Time-Domain and X-Parameters Modeling System



Comparison of simulated (blue) and independent measured (red) delivered power contours (left) and efficiency contours (right) from a typical packaged FET show extremely accurate agreement.

Application Notes and Data Sheets


5A-041 Load Pull + NVNA = Enhanced X-Parameters for PA Designs with High Mismatch and Technology-Independent Large-Signal Device Models.
5C-083 Setting Up Load Pull with X-Parameters Using the Agilent NVNA.

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