Wideband digital feedback predistortion employing segmented memory compensation for linearization of Doherty amplifier

A novel wideband digital feedback predistortion (WDFBPD) technique employing segmented memory compensation method is proposed for linearization of Doherty amplifier. Its memory effect modeling and linearization capabilities are demonstrated. Starting with an investigation of an abnormal memory effect of the Doherty amplifier, an appropriate dynamic system in the WDFBPD is deduced. The model has two segmented memory compensation elements for carrier PA correction at a low power and peaking PA correction at a high power. The validation of the proposed model in predicting a dynamic nonlinear behavior is carried out by comparing the output spectra, dynamic AM/AM and AM/PM characteristics, and the normalized mean square error. The superiority of the linearization performance is verified using the Doherty amplifier with 90 W Si LDMOSFETs. For a 2.14 GHz forward-link WCDMA 4FA signal, the adjacent channel leakage ratio at 5 MHz offset frequency is -51.5 dBc, which is an improvement of 5 dB compared to the conventional WDFBPD, at an average output power of 44 dBm.