Advanced Doherty Transmitter Architectures for Wireless Communication Systems
Date
2021-02-02
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Abstract
Power amplifier (PA) is a critical and energy-consuming building block in wireless communication transmitters. Base stations need to be efficient to minimize the electricity consumption. The wasted energy in wireless transmitters is converted to heat, which degrades the reliability of the system. Over the years, many efficiency enhanced PA architectures have been developed. Due to its good performance and simple structure, the Doherty PA (DPA) has been widely used in base station applications. However, conventional DPA focuses on the design of the amplifier module itself and the needed quarter wavelength transmission line limits the bandwidth of the DPA. In this thesis, first, the high efficiency Doherty transmitter based on the array antenna is proposed and its dynamic load modulation scheme is investigated. The design equations are derived based on the impedance matrix of the generalized load modulation network. The antenna array is then proposed and optimized to achieve the required impedance matrix. The measured results show good performances, which successfully verify the proposed theory and design equations. Second, the dual-branch dynamic reverse load modulation (RMDB) PA is analyzed. Different from the conventional DPA, the carrier PA is a current biased transistor and the peaking amplifier is a voltage biased transistor in the RMDB PA. The working principle of the dynamic load modulation is thoroughly analyzed. To verify the design theory, a Monolithic Microwave Integrated Circuit (MMIC) PA is designed and fabricated using the United Monolithic Semiconductors GH25 process. It is also the first reported MMIC that covers both 4th generation and 5th generation wireless communication frequency bands. Third, to further increase the efficiency of the RMDB PA, the harmonic control technique is implemented in a second MMIC PA design. The constraints of implementing harmonic control in RMDB MMIC PA are thoroughly discussed. By introducing extra offset lines in the carrier and peaking amplifier branches, the second harmonic control was successfully realized. Finally, optimal fundamental load modulation design space for Class-X harmonically tuned power amplifiers (PAs) was studied. Optimal fundamental load trajectories with different sets of second and third harmonic impedances are calculated and verified with harmonic load-pull measurement.
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Keywords
Power amplifier, Doherty, Wireless communication, RMDB PA, MMIC, Current-biased, Array antenna
Citation
Zhao, Y. (2021). Advanced Doherty Transmitter Architectures for Wireless Communication Systems (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.