volume | PIER Journals

Abstract

This paper presents the design of an asymmetrical Doherty power amplifier (DPA) with improved linearity and efficiency performance. Resonator-type drain bias networks, providing high impedances at the carrier frequency and low impedances with small variation at the envelope frequency, are introduced to reduce the DPA's memory effects when transmitting wideband signals. The general criteria for DPA design are summarized, and the approach to obtain optimum fundamental and harmonic impedances is proposed to achieve back-off efficiency enhancement. For experimental validation, the asymmetrical DPA is designed and implemented using two identical GaN HEMTs. Measured with continuous wave (CW), the proposed DPA delivers a saturation power greater than 49.3 dBm from 3400 to 3600 MHz, along with high drain efficiency of over 62% and 48% at peak and 8-dB back-off power, respectively. Driven with 100-MHz LTE-advanced signals, the adjacent channel leakage ratio (ACLR) asymmetry of the DPA at 20-MHz offset is lower than 1-dB. After digital predistortion (DPD) linearization, the proposed DPA achieves an ACLR of better than -48 dBc at an average output power about 41 dBm and the drain efficiency over 45% across the frequency band.

1. Kim, J., J. Cha, I. Kim, and B. Kim, "Optimum operation of asymmetrical-cells-based linear Doherty power amplifiers --- uneven power drive and power matching," IEEE Trans. Microw. Theory Tech., Vol. 53, No. 5, 1802-1809, 2005.
doi:10.1109/TMTT.2005.847073

2. Moon, J., J. Kim, and B. Kim, "A wideband envelope tracking Doherty amplifier for WiMAX systems," IEEE Microw. Wireless Compon. Lett., Vol. 18, No. 1, 49-51, 2008.
doi:10.1109/LMWC.2007.912019

3. Sahan, N. and S. Demir, "Analysis, design optimization and performance comparision of bias adapted and asymmetrical Doherty power amplifiers," Progress In Electromagnetics Research B, Vol. 54, 337-356, 2013.
doi:10.2528/PIERB13071502

4. Xia, J., X. Zhu, L. Zhang, J. Zhai, and Y. Sun, "High-efficiency GaN Doherty power amplifier for 100-MHz LTE-advanced application based on modified load modulation network," IEEE Trans. Microw. Theory Tech., Vol. 61, No. 8, 2911-2921, 2013.
doi:10.1109/TMTT.2013.2269052

5. Colantonio, P., F. Giannini, R. Giofre, and L. Piazzon, "Theory and experimental results of a Class F AB-C Doherty power amplifier," IEEE Trans. Microw. Theory Tech., Vol. 57, No. 8, 1936-1947, 2009.
doi:10.1109/TMTT.2009.2025433

6. Moon, J., J. Kim, I. Kim, and B. Kim, "Efficiency enhancement of Doherty amplifier through mitigation of the knee voltage effect," IEEE Trans. Microw. Theory Tech., Vol. 59, No. 1, 143-152, 2011.
doi:10.1109/TMTT.2010.2091207

7. Darraji, R. and F. M. Ghannouchi, "Digital Doherty amplifier with enhanced efficiency and extended range," IEEE Trans. Microw. Theory Tech., Vol. 59, No. 11, 2898-2909, 2011.
doi:10.1109/TMTT.2011.2166122

8. Kim, B., J. Kim, J. Kim, and J. Cha, "The Doherty power amplifier," IEEE Microwave Mag., Vol. 7, No. 5, 42-50, 2006.
doi:10.1109/MW-M.2006.247914

9. Bathich, K., A. Z. Markos, and G. Boeck, "Frequency response analysis and bandwidth extension of the Doherty amplifier," IEEE Trans. Microw. Theory Tech., Vol. 59, No. 4, 934-944, 2011.
doi:10.1109/TMTT.2010.2098040

10. Sun, G. and H. Rolf, "Broadband Doherty power amplifier via real frequency technique," IEEE Trans. Microw. Theory Tech., Vol. 60, No. 1, 99-111, 2012.
doi:10.1109/TMTT.2011.2175237

11. Akbarpour, M., M. Helaoui, and F. M. Ghannouchi, "A transformer-less load-modulated (TLLM) architecture for efficient wideband power amplifiers," IEEE Trans. Microw. Theory Tech., Vol. 60, No. 9, 2863-2874, 2012.
doi:10.1109/TMTT.2012.2206050

12. Rubio, J. M., J. Fang, V. Camarchia, R. Quaglia, M. Pirola, and G. Ghione, "3-3.6-GHz wideband GaN Doherty power amplifier exploiting output compensation stages," IEEE Trans. Microw. Theory Tech., Vol. 60, No. 8, 2543-2548, 2012.
doi:10.1109/TMTT.2012.2201745

13. Ye, D., Y. Wu, and Y. Liu, "A tradeoff design of broadband power amplifier in Doherty configuration utilizing a novel coupled-line couple," Progress In Electromagnetics Research C, Vol. 48, 11-19, 2014.
doi:10.2528/PIERC14011702

14. Guan, L. and A. Zhu, "Green communications: Digital predistortion for wideband RF power amplifiers," IEEE Microwave Mag., Vol. 15, No. 7, 84-99, 2014.
doi:10.1109/MMM.2014.2356037

15. Takenaka, I., K. Ishikura, H. Takahashi, K. Hasegawa, K. Asano, and N. Iwata, "Improvement of intermodulation distortion asymmetry characteristics with wideband microwave signals in high power amplifiers," IEEE Trans. Microw. Theory Tech., Vol. 56, No. 6, 1355-1363, 2008.
doi:10.1109/TMTT.2008.923365

16. Aaen, P. H., J. H. Pla, and J. Wood, Modeling and Characterization of RF and Microwave Power FETs, Cambridge University Press, New York, 2007.
doi:10.1017/CBO9780511541124

17. Brinkhoff, J., A. E. Parker, and M. Leung, "Baseband impedance and linearization of FET circuits," IEEE Trans. Microw. Theory Tech., Vol. 51, No. 12, 2523-2530, 2003.
doi:10.1109/TMTT.2003.819208

18. Feng, Y., Y. Liu, C. Yu, S. Li, J. Li, and X. Zheng, "Design of linearity improved asymmetrical GaN doherty power amplifier using composite right/left-handed transmission lines," Progress In Electromagnetics Research B, Vol. 53, 89-106, 2013.
doi:10.2528/PIERB13060502

19. Giofre, R., P. Colantonio, and F. Giannini, "A Doherty architecture with high feasibility and defined bandwidth behavior," IEEE Trans. Microw. Theory Tech., Vol. 61, No. 9, 3308-3317, 2013.
doi:10.1109/TMTT.2013.2274432

20. Colantonio, P., F. Giannini, R. Giofre, and L. Piazzon, "The AB-C Doherty power amplifier. Part I: Theory," International Journal of RF and Microwave Computer-Aided Engineering, Vol. 19, No. 3, 293-306, 2009.
doi:10.1002/mmce.20350

21. Kurokawa, K., "Power waves and the scattering matrix," IEEE Trans. Microw. Theory Tech., Vol. 13, No. 2, 194-202, 1965.
doi:10.1109/TMTT.1965.1125964

22. Haedong, J., P. Roblin, and C. Quindroit, "Adjustable load-modulation asymmetric Doherty amplifier design using nonlinear embedding," IEEE MTT-S Int. Microw. Symp., 1-4, 2014.

23. Moon, J., J. Kim, I. Kim, Y. Woo, S. Hong, J. Lee, and B. Kim, "GaN HEMT based Doherty amplifier for 3.5-GHz WiMAX applications," Proc. 37th Eur. Microw. Conf., 1193-1196, 2007.

24. Yang, M., J. Wang, J. Xia, Y. Sun, and X. Zhu, "High efficiency GaN wideband Doherty amplifier for LTE-advanced applications," Proc. Microw. Conf. 2011, 510-513, 2011.

Dr. Chuanhui Ma

Dr. Wensheng Pan

Dr. You-Xi Tang