In this dissertation an analytical large signal electro-thermal LDMOSFET model---Agere Electro-Thermal (AET) model---is presented. Composed by three parts: a die level device model, an equivalent circuit for the package portion and a thermal network, AET model was implemented in Agilent EESOF's RF circuit design software---Advanced Design System (ADS). Device model extraction procedures are established systematically. The methodology developed could be applied to other high power device models development as well. An unproved automated isothermal device characterization system and parameter extraction programs were also developed. The LDMOSFET's distributed and dynamic thermal responses are computed by a modified image method. Thermal memory effects are studied with the aid of the newly developed distributed and dynamic thermal models.; The package model in such discrete devices plays an important role in RF power amplifier performances and the procedures are also developed to extract package model elements from geometry estimation, and S-parameter measurements. Several power amplifiers were designed, built and tested to verify the model's accuracy. Load-pull design technique was implemented in simulation level, and the contours of output power and efficiency obtained in simulation agree with those obtained in loadpull measurement. The model exhibits a good accuracy for the prediction of IdB compression power, gain, power added efficiency and the third and fifth order intermodulation. Pros and cons between analytical model and table based model are compared by using AET and a formally developed BSpline table model---OSUFET.; A distributed electro-thermal model was developed to investigate the impact of a non-uniformly distributed temperature profile on the model accuracy. A 3D image method was used to compute the device's thermal resistance matrix, in which the device's physical structure is approximated as multiple planar layers with different thermal properties, and the active areas are approximated as multiple rectangular surface heat sources in parallel. To achieve high computation efficiency, the complexity of the distributed electro-thermal model was further reduced by using its symmetry. Temperature distribution is reproduced in this model and it is found to have the same performance as that of the non-distributed device using an averaged temperature.; The image method was further extended to compute the 3D transient temperature step responses, from which the thermal time constants can be extracted. It is found that the multiple thermal time constants must be included in the model to accurately predict the transient temperature responses. The transient thermal model is found to have a strong impact on the thermal memory effects in RF power amplifiers. With the aid of several electro-thermal models with different thermal transient accuracy, thermal memory effects and electrical memory effects can be identified separately. Thermal memory effects are found to be stronger in amplifiers where predistortion technique is present, and is most significant for envelop frequency below 1 MHz.
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