Concurrent low cost multi-carrier compensation of amplitude and phase distortions in RF power amplifiers

Distortion effects of wideband power amplifiers vary significantly with carrier frequency and need to be tested and characterized across a specified (wide) frequency range during production. In this paper, a low cost test approach is presented that allows AM-AM and AM-PM distortion effects of RF power amplifiers to be evaluated at multiple frequencies with a single multi-tone test. The response of the power amplifier is observed using a low cost envelope detector on the tester load board. The observed response is then used to determine the parameters of digital predistortion functions that allow accurate compensation of distortion effects at the relevant frequencies of interest. The predistortion functions are optimized using a two-step procedure that exhibits rapid convergence to the optimal function parameter values.