Adaptive linearisation using pre-distortion

One method of linearisation for class C RF power amplifiers is to pre-distort the drive signal. It is necessary to adjust the pre-distort waveform so that it can track changes in amplifier characteristics. An adaptive predistortion technique which uses a digital signal-processing microprocessor and memory look-up tables is described. The method differs from a previously described adaptive predistortion technique by using much smaller table sizes, with the result that conversion speeds are much higher. The disadvantage is that the processing overhead is higher, which puts a limit on the maximum data rate of the system. Low data rate services such as are found in mobile satellite applications (<17 kb/s) can be handled by this digital signal-processing approach. System requirements are examined, some alternative linearization techniques are described, and a more detailed analysis of adaptive predistortion is given. Finally a prototype system which uses digital signal-processing (DSP) techniques is described