Fast Calculation Scheme for Frequency Characteristic Compensator of Digital Predistortion Linearizer

This paper proposes a fast calculation scheme for the coefficient values of a frequency characteristic compensator in a digital predistortion linearizer (DPDL). The proposed scheme uses a quadratic function based on the relationship between the coefficient values of the frequency characteristic compensator and the intermodulation distortion (IMD) components. The coefficients of the quadratic function are calculated using the least square method employing three measurements of the IMD components at three different coefficient values. The proposed scheme can directly obtain the optimum coefficient values of the frequency characteristic compensator by minimizing the IMD based on the identified quadratic function. The performance of the calculation time and that of the IMD cancellation are evaluated based on experiments employing a 2-GHz, 1 W class power amplifier and OFDM signals. The results show that the proposed scheme achieves a 73% faster calculation time compared to the conventional scheme, which is based on a perturbation algorithm. The IMD cancellation performance of the proposed scheme is the same as that for the conventional scheme.