Reducing estimator biases due to equalization errors in adaptive digital predistortion systems for RF power amplifiers

This paper investigates degradations in a RF power amplifier, linearized using digital predistortion (DPD), due to biases in the DPD coefficient estimation. Of specific interest is the effect of equalization errors in the observation path on the distortion spectrum of the RF output signal. It is proposed that the frequencies allocated to the input signal be notched within the estimator to reduce the effects of equalizer errors. Results show that the use of an estimator notch improves the ACLR2 performance by 11 dB and 16 dB for DPD implemented using memory and gain polynomials, respectively. The notch also allows the order (rank) of the estimation to be reduced.