Systematic Crest Factor Reduction and Efficiency Enhancement of Dual-Band Power Amplifier Based Transmitters

A systematic design methodology including novel crest factor reduction (CFR) and power amplifier (PA) efficiency enhancement techniques for concurrent dual-band transmitters is proposed to improve performance under concurrent modulated stimulus, in terms of both efficiency and output power. Conventional energy efficient PAs are typically implemented separately in analog circuit or digital signal domains. However, the proposed method combines a digital domain 2-D power distribution reshaping (2-D-PDR) method to adaptively reshape the signals' distribution to fit the target PA's characterization and an analog domain inter-modulation tuning design to enhance the PA's output capability. Based on the proposed method, an example of concurrent dual-band Doherty PA (DPA) working at 1.9-2.6 GHz LTE bands was designed using two 10-Watt GaN HEMTs. A 2-D-PDR procedure was developed for the designed DPA. The fabricated DPA was measured in concurrent mode under the stimulus of a pair of 10 MHz LTE signals. According to the measured results, the proposed DPA achieved a drain efficiency of 46.6% at an output power of 6.2 W while maintaining a good adjacent channel power ratio and error vector magnitude. To the best of the authors' acknowledge, this is the state-of-the-art performance for concurrent dual-band PAs. Additionally, measurements are performed on three varied type of PAs using the proposed 2-D-PDR. According to the measured results, about 0.3~0.8 dB power improvement and 1.5%~3% efficiency improvement can be achieved using the proposed 2-D-PDR compared with the conventional 2-D-CFR, proving the feasibility of the proposed technique.