Christopher C. Riddle

A novel adaptive predistortion technique for power amplifiers

One of the main concerns in wireless communication systems is high-power amplifier (HPA) efficiency as this has a direct impact on size, power consumption, and cost. At the same time, HPA linearity is critical for linear modulation schemes. Nonlinear devices introduce intermodulation products to a bandlimited waveform resulting in violation of emission specifications. This paper explores an adaptive predistortion algorithm that compensates for the nonlinear distortion of an HPA by predistorting the input waveform. Predistortion is applied in the form of digital gain and phase changes that are functions of instantaneous input waveform amplitudes. Measured out-of-band emission levels are used as a metric for the convergence of the algorithm. Upon convergence, the combined nonlinearities of predistortion and the HPA cancel, effectively producing a linear device. The use of waveform predistortion improves the overall efficiency by allowing amplifier operation closer to the saturation point.