| Summary: | Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2006. === Nonlinear transistor modeling is becoming increasingly popular due to the demand for high
linearity and high efficiency microwave amplifiers. The available models often fail to accurately
predict the higher order harmonics and intermodulation distortion, which are essential
when designing high-linearity amplifier circuits.
This thesis describes the design of hardware and software used for the development of nonlinear
CAD models. A multiline TRL calibration kit is designed and manufactured so that the
characterisation of a LDMOSFET, with a RF output power capability of 10W, can be performed
using an adaptive-bias S-parameter measurement algorithm. Verification standards are also
manufactured and used to determine the measurement accuracy after calibration. A series of
GUIs are developed to ease the model extraction process. The extraction of the small-signal
model parameters is performed between 0.4 and 3 GHz, and the extraction of the parameter
values for the Fager large-signal model is then performed. An improved model is defined that
implements two nonlinear charge sources in stead of the three nonlinear capacitors used in the
Fager model. The nonlinear charge equations are formulated using the voltage-derivatives of
the calculated nonlinear charge at each port of the device. By accurately modeling the voltagederivatives
of the charge, where the voltages are functions of time, the prediction of the current
produced by each of the charge sources is improved.
The nonlinear models are verified against the MET model, and all three models are compared
to measured data. It is shown that the models are able to accurately predict the single-tone and
two-tone output harmonics for class-AB operation, and in many cases the predictions outperform
that of the MET model. The single-tone output power is also verified for class-C operation.
Although this prediction is not extremely accurate, it is found that the correct trend for
the output harmonic power can be predicted.
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