Integration of the Linear Parameter-Varying framework in the design of supply modulated high frequent power amplifiers
Modern power amplifier designs attempt to trade off the power efficiency and the nonlinear distortion of the amplifier. This leads to complex amplifier structures, such as supply modulated amplifies, where the drain supply of the transistor device is modulated in function of the envelope of the high-frequency input signal.
Current design strategies of supply modulated amplifier structures use relatively simple design strategies, usually based on one or two-tone tests. State-of-the-art analysis techniques, such as the use of multisines and Linear Parameter-Varying (LPV) models are hardly ever used in the design, at most as a verification step in the final design stages to check the nonlinear performance of the already finished system.
The targeted application of the power amplifier under design most likely introduces a modulated signal at the input port of the device. It goes without saying that the simple one or two-tone design techniques, which were chosen for their ease of use, can only result in rough estimates of the correct device behavior under the modulated conditions. Thus the design would have to be properly refined by optimization in further design stages where actual modulated signals are applied to the input ports of the device. The initial design step thus only serves to produce adequate starting values for the optimizer used in subsequent stages. Accuracy of the design parameters is thus relinquished in favor of simplicity. Usage of a multisine as modulated signal, and as a result the entire theoretical framework that has been constructed to support this signal, is a possible way to immediately take into account the correct nonlinear and dynamic behavior at the initial design stage of the power amplifier.
The aim of this PhD research is to integrate recently developed modeling techniques (developed for both time-invariant and time-varying systems) in the design of the supply modulated power amplifier. The nonlinear interaction between the amplifier and the modulated supply unit can either be seen as a nonlinear or as a time-varying effect. Hence, the general theory for parameter-varying systems might be an ideal candidate to setup a theoretical framework that enables the systematic design of these complex amplifiers in a more efficient way while still being interpretable by non-experts. This will require the adaptation of the LPV framework for this special case, as well as a practical realization of the proposed design strategy.
The current main research goals for this project are the following:
- Creation of an accurate simulation framework that allows to easily check the research hypotheses.
- Verification of the proposed design strategy on actual measurements instead of simulation results.
- Usage of the design method to create a supply modulated amplifier. Which will allow to check the advantages of the technique in comparison to the traditional design method