Broadband Continuous-Mode Doherty Power Amplifiers With Noninfinity Peaking Impedance

In this paper, a broadband continuous-mode Doherty power amplifier (CM-DPA) is realized taking advantage of the noninfinity output impedances of peaking stage. Specifically, the carrier PA of the designed DPA operates in a continuous class-J mode when the peaking PA is in the OFF-state, where the output impedance of the peaking PA has some influences on the carrier PA. When the peaking transistor is in the OFF-state, the load impedance variation of the carrier transistor versus noninfinity peaking impedance is presented in this contribution. The proposed method surmounts the back-off drain efficiency deterioration of DPAs at two side working bands through elaborately processing the noninfinity peaking impedance. This paper also presents a method to derive the required OFF-state output impedance of the peaking stage by the carrier PA in a symmetrical broadband DPA. A broadband CM-DPA working over 1.6-2.7 GHz (bandwidth of 51%) is designed and fabricated for interpreting our theories. The simulated load trajectory of the carrier transistor is in line with the design space of continuous class-J mode. Under continuous wave excitation, experimental results show the drain efficiencies of 46.5%-63.5% at 6-dB output back-off power levels and 56%-75.3% at peaking power levels. The maximum output power of this DPA is 43.8-45.2 dBm with a gain of 9.4-11.5 dB across the whole working band. Furthermore, a 20-MHz LTE modulated signal with a peak-to-average power ratio of 7.4 dB is also applied to the fabricated CM-DPA at 2.2 GHz. At an average output power of 37.5 dBm, measurement results show the adjacent channel power ratios of -30.2 and -50.1 dBc before and after digital predistortion, respectively.