Techniques for Adaptive Input-Power Distribution in Doherty Power Amplifier and Load Modulation of Its Driver-Stage Power Amplifier

Techniques for adaptive input-power distribution in Doherty power amplifier (DPA) with the modified Wilkinson power divider and load modulation of its driver-stage PA are described. Combination of these techniques improves the linearity and efficiency of the two-stage PA with DPA as a final stage. Both the techniques leverage the nonlinearity of the input impedance of the auxiliary power amplifier in the DPA. The first technique is applied to a 3.5-GHz 32-W single-stage DPA using GaN high electron mobility transistor (HEMT) devices. Evaluation results showed that by using the technique, adjacent channel leakage ratio (ACLR) improvement of 9 dB was obtained under 8.5-dB peak to average power ratio (PAPR) 10-MHz long-term evolution (LTE) signal without digital predistortion (DPD), and the demonstrator achieved an average drain efficiency (DE) of 55% and ACLR of −50 dBc with DPD. Using the same DPA as a final stage, a two-stage PA was also designed and fabricated to verify the second technique. Due to the load modulation of the driver stage PA, efficiency improvement of 2.6% for the two-stage power added efficiency (PAE) is confirmed by simulation, and the demonstrator achieved a two-stage PAE of 45.4% under 8.5-dB PAPR 20-MHz LTE signal with ACLR of −50 dBc with DPD.