The Study Of RF Power Amplifier Modeling And Linearization Based On Memory Effects

Radio frequency power amplifier is the key component of the transmitter inmodem wireless communication system, and its performance highly affects thecommunication quality and efficiency. At present, most power amplifier models andlinearization methods are limited to narrowband application. When memory effects ofthe amplifier become obvious due to widen of signal bandwidth, compensation effectsof the traditional linearization technique can not be satisfying. In order to improve thelinearity of wideband amplifiers, research on modeling and linearization of poweramplifiers considering memory effects has become a new trend in recent years.Nonlinearity and memory effects of power amplifiers in widebandcommunication system are deeply analyzed including the phenomenon and sources ofmemory effects. There types of nonlinear amplifier models: memoryless model,quasi-memoryless model and memory model are presented. First, input-outputrelations of the quasi-memoryless model are developed respectively in polar,quadrature and polynomial function versions. Then the emphasis is laid on theconstruction principle of the memory polynomial model including memorypolynomial with unity time delay taps and memory polynomial with non-uniformtime delay taps. Modeling strategy and complexity of these two memory models arecompared and a new algorithm of realizing non-uniform time delay taps:sinusoidal-like function computation is put forward bases on MRF9742 powertransistor.Traditional predistortion technique is improved using memory polynomialmodeling method. Non-uniform time delay memory polynomial predistortiontechnique and the realization of memory predistorter are represented in details. On thebasis of above analyses, a practical MRF9742 linearization power amplifier system isdesigned. First, nonlinear characteristics and memory effects of MRF9742 model aresimulated and analyzed using ADS software. Then linearization effects of traditionalpredistortion and non-uniform time delay predistortion are compared and the simulation results prove that non-uniform time delay predistortion techniquedepending on sinusoidal-like function computation can suppress the intermodulationdistortion products of the power amplifier system and improve its linearity greatly.