Investigation On Broadband Highly Efficient Power Amplifier And Wideband Modulated Signal Doherty For Linearization

The rapid explosions in mobile customers and services have proposed the new requirement of wireless communication systems, which especially highlight the wide bandwidth and high-speed data transmission, such as the 1Gbps peak data rate for LTE-Advanced specification in high mobility. To meet this Gbps peak data rate in traffic, spectrum-efficient modulation techniques as carrier aggregation (CA) was widely employed in systems. It utilizes the fragmented and unused spectral resources over a wide frequency bandwidth and aggregates the sub-carrier over a modulated signal bandwidth up to 100 MHz, which results the 10 dB peak-to-average power ratio (PAPR) for original signal. As the key component in transmitter, broadband and highly-efficient characters of power amplifier (PA) will be estimated given the wide bandwidth and high PAPR application. Aiming at the CA technology for LTE-Advanced system, this dissertation studies the methodology for designing broadband and highly-efficient single-ended PA. On basis of these investigations, the broadband and highly-efficient Doherty design were carried out, which are supported by the National Science and Technology Major Project of China and NSFC. The main researches of this dissertation are following:1) To design PA with synthesized method and explore the sub-amplifier design strategy for Doherty, conventional simplified real frequency technique (SRFT) was modified to realize an harmonic impedance control. By sweeping the stop-band frequency parameter fe, broadband highly-efficient PA is synthesized with reduced circuit size. Based on this modified SRFT, single-ended PA with compact size 50mm×60mm and 55% fractional bandwidth was implemented. Continuous wave measurements shown a drain efficiency of 55%～70%. With digital pre-distortion (DPD), output adjacent channel leakage ratio (ACLR) of PA lower than-47.0 dBc were obtained under 100 MHz modulated signal excitation. Simulation and measurement indicated excellent performance of this modified SRFT. The relative research results have been published in Microwave Journal.2) From the investigations on different highly-efficient PA mode, mode combination principle was proposed for PA design, which could combine the different modes to perform broadband or multi-band characteristic in single-ended and Doherty PAs. By low-pass matching method, the designed controllable mode PA combined the Class-F-1 and Class-J mode over 49% bandwidth, where two modes presented a tunable frequency separation. By this way, the efficiency peaks were allocated to two communication channels as 1.9～2.0 GHz and 2.3～2.6 GHz. Measured drain efficiency in two channels ranged from 75.6%～80.3% and 68.8%～76.6%. Then, the broadband 100MHz modulated signals and dual-band signals with 140/300 MHz frequency separation were applied to evaluate this PA. With DPD linearization, ACLR lower than -47.5,-48.6 and -46.1 dBc were achieved. The relative research results have been accepted by IEEE Transactions on Microwave Theory and Techniques, and one patent has been filed.3) Analyses about Doherty PA (DPA) with wideband modulated signal excitation were carried out, which investigated the impact of peaking PA on output power and efficiency of DPA. To mitigate the non-consistent turn-on and output current behavior in peaking PA, modified DPA was proposed utilizing the broadband input match in peaking way. Compared to the conventional structure, proposed DPA used an broadband input match from SRFT in peaking PA to improve the consistency of output power and efficiency. Measurements of the modified DPA gave the drain efficiency 46%～48% to the conventional 38%～47% in the same 100 MHz bandwidth, presenting only 2% deviation over 2.1-2.2 GHz. For the output power and drain efficiency, proposed DPA shown better performance from 49.2 dBm to 49.7 dBm and 58% to 63% as well. For LTE-Advanced 100 MHz modulated signal evaluation,2 dB improvement of ACLR were obtained with/without DPD, which verified our analyses about peaking PA’s impact on DPA. The relative research results have been published in Journal of Microwave and 2015 NCMMW. One patent has been filed.4) A broadband and highly-efficient DPA utilizing a proposed bi-objective optimization SRFT was proposed. From the bandwidth limitations in DPA structure, the impedance boundary in DPA operation and the frequency response of offset-line and λ/4 impedance inverter were analyzed. Applying the new bi-objective SRFT design method, DPA with 2.0～2.6 GHz frequency range was designed and implemented, which using the dual impedance transformation network to eliminate the offset-line and λ/4 impedance inverter in carrier way. By joining the harmonic-control into new SRFT, highly-efficient continuous Class-F-1 mode was performed. The fabricated broadband DPA achieved saturated drain efficiency of 61.4%～75% over the band and 45%～63.3% drain efficiency at 6 dB back-off power level, which presented a 26% fractional bandwidth. To the conventional design method, it presented the wide bandwidth, high efficiency and non-tunable post-design at back-off power level. With DPD linearization, output ACLRs lower than -50 dBc were obtained with 40 MHz modulated signals excitation. Part of research results have published in IEEE Microwave and Wireless Components Letters, and relative research results have been submitted to IEEE Transaction on Circuit and Systems II.