LINEARIZATION OF RF POWER AMPLIFIER USING PREDISTORTION TECHNIQUES

Abstract

Thin thesis is concerned with the study of linearizing RF power amplifiers using predistortion techniques. The study proposes two novel techniques employing samples o[ multiple channels (SMC) method and cross-correlation method for both single and multiple carries source. In SMC scheme, multi-carrier power amplifiers (MCPA) can be linearized by cancelling the third- and fifth-order intermodulation (IMD) products. Two, three and four sample channels, either analog or digital modulated carriers, are used to obtain characteristics of predistorters. The best performance of the scheme is observed when the peak power levels of sample channels and actual transmitting signals are the same. The performance of this scheme is evaluated by noise power ratio (NPR) approach and carrier to intermodulation ratio ( C /IM) simulation. In the cross-correlation scheme, the IMD products can be minimised at the output of a power amplifier without using filters. Because nonlinear distortions are orthogonal to signal components at the output of a nonlinear device, the scheme applies a noise cross-correlator to obtain the equivalent gain and nonlinear distortions at the output of a power amplifier. Therefore, both in-band and out-of-band IMD products may be exploited for linearization. Computer simulation results of two-tone test, time-domain waveform and symbol error rate (SER) are used to test the performance for the single channel case, while simulation results of NPR, C/IM and time-domain waveform are used for mulitcarrier cases. Both samples of multiple channels and cross-correlation schemes are shown to be effective for linearizing power amplifiers.