Linear and Nonlinear Compact Transistor Modeling

Maury and AMCAD complete the cycle from Pulsed-IV and S-Parameters, to Linear and Nonlinear Compact Transistor Models, and Harmonic Load Pull for model validation !

Introduction

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Amplifier designers have been making use of modern transistor models since their first appearance in the mid-1970s. Models have allowed engineers to create advanced designs with first-pass success, without the need for multiple prototypes and design iterations. But with so many different modeling techniques, how does one select which one to use?

Compact transistor models, based on measured IV and S-parameters, allow designers to shift focus from transistor designs to circuit designs. Extracted from quasi-isothermal pulsed IV and pulsed S-parameter data and validated with load-pull characterization, compact transistor models contain a reduced set of parameters. Unlike other model types, compact models take into account complex phenomena, such as electro-thermal and trapping effects. For simulations under nonlinear operating conditions, responses to complex modulated signals (such as EVM or ACPR) are accurately predicted as low-frequency and high-frequency memory effects are taken into account. Compact transistor models are ideal for die-level applications, as developing such a model from IV and S-parameters is straightforward and relatively quick.

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Typical Pulsed IV Curve Traces

Press Release

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• Maury Microwave And AMCAD Engineering Announce A Development And Distribution Partnership For Advanced Measurement and Modeling Software and Pulsed IV Systems +

NVNA, Time Domain Waveforms and X-Parameter Measurements

Introduction

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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

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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

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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

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• 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.

• Maury Application Notes Library Maury Software and System Application Notes.

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