Triple-Mode Reciprocal Doherty Power Amplifier With Multi-Band Operation and Extended High Efficiency Range

This article presents the methodology for designing triple-mode Doherty power amplifier (DPA) with multi-band operation and extended high efficiency range. It is illustrated that three different Doherty operation modes can be realized by simply re-setting the gate bias voltages while the DPA circuits keep unchanged. By employing a novel reciprocal gate bias DPA architecture, five operation bands have been achieved by the proposed DPA with larger than 9 dB high efficiency power range. The active load modulation process and theoretical performance of proposed DPA are analyzed in detail for each mode. For verification, a commercial GaN transistors-based DPA is designed and implemented with 1.76-1.96 GHz band in Mode I, 1.13-1.20/2.48-2.58 GHz bands in Mode II and 0.7-0.76/2.34-2.40 GHz bands in Mode III. The fabricated DPA achieves 7.0-10.5 dB saturation gain, 44.18-46.86 dBm peak output power and 41.9%-61.5% back-off efficiency. When stimulated by a 10 MHz long term evolution (LTE) modulation signal with 8.6 dB peaking-to-average ratio (PAPR), the adjacent channel power ratio (ACPR) of the fabricated DPA is better than -45 dBc after digital pre-distortion at 0.73, 1.18 and 1.85 GHz.