Bandwidth Extension of Doherty Power Amplifier Using Complex Combining Load With Noninfinity Peaking Impedance

In this paper, a high-efficiency Doherty power amplifier (DPA) using the complex combining load (CCL) with noninfinity peaking impedance for broadband operation is presented. By applying the CCL, the load impedance of the carrier amplifier at saturation power level can be compensated at different operation frequencies. Considering the influences of the output impedance of the peaking PA on the carrier PA, a detailed analysis of the optimal noninfinity peaking output impedance with the CCL is carried out on the whole operation frequency range. Theoretical analysis of the output power and drain efficiency (DE) reveals that the CCL can offer a new degree of freedom for extending the bandwidth of the DPA. Based on the proposed theory, a modified DPA working over the frequency band of 1.1-2.4 GHz (bandwidth of 74%) is designed and fabricated based on GaN HEMT devices. Experimental results exhibit 6-dB output back-off drain efficiencies of 43.8%-54.9% and saturated drain efficiencies of 55.4%-68% can be obtained. The saturated output power of the DPA is 43.3-45.4 dBm with a gain of 9.5-11.1 dB across the whole operation band. When driven with long-term evolution modulated signals with 6.5-dB peak-to-average power ratio, the DPA exhibits an adjacent channel leakage ratio better than -49 dBc while maintaining a DE of 44% after digital predistortion linearization.