Symmetrical Doherty Power Amplifier With Extended Bandwidth and Back-Off Range Based on Nonlinear Current Profile

There are lots of works on the bandwidth extension of symmetrical Doherty power amplifier (S-DPA) with a back-off range of 6 dB. However, it is still a challenge to simultaneously extend the bandwidth and back-off range of a S-DPA. This paper proposes a design methodology for extending the back-off range of a broadband S-DPA. Nonlinear current profile is introduced into the carrier sub-amplifier of the S-DPA. In this way, unequal power will be delivered to the load by the carrier and peaking amplifiers, leading to an extended high efficiency power range. More importantly, compared with previous works, the inversion ratio of the impedance inverter after the carrier transistor will be reduced in the proposed S-DPA, increasing the operation bandwidth. The combiner parameters of the proposed S-DPA with extended back-off range are derived based on a pre-determined nonlinear current profile. It is illustrated that the combiner parameters of the S-DPA can be expressed as a function of the combining load. Then, the bandwidth of the proposed S-DPA is subsequently analyzed under different combining load conditions. As a validation, a 1.4-2.2 GHz S-DPA with extended back-off range is implemented in this paper. Under a continuous-wave (CW) signal excitation, the fabricated S-DPA achieves a maximum output power of 40.2-43 dBm, a saturation drain efficiency (DE) of 56%-74% and a 9.0 dB back-off DE of 45%-52.5% over 1.4-2.2 GHz. Moreover, the fabricated S-DPA is also measured by the excitation of a 20 MHz modulated signal with a peak-to-average power ratio (PAPR) of 8.0 dB. The measured adjacent channel leakage ratios (ACLRs) of the fabricated S-DPA changes from - 30.7 dBc to - 21.1 dBc at the lower band and from - 31.9 to - 21.1 dBc at the upper band over 1.4-2.2 GHz when the average output power is 33.0 dBm.