Design of a High-Efficiency and High-Power Inverted Doherty Amplifier

In this paper, we present a design method for a compact inverted Doherty power amplifier (IDPA), which has high-efficiency and high-power characteristics. An optimum load matching network and an additional offset line, after the matching network of the carrier amplifier, dynamically modulate the load impedance according to the input power drive, while the conventional Doherty power amplifier uses a quarter-wave line to do it. The operational principles and design guide are provided. For experimental verification, a 50-W Doherty amplifier was designed for the pi/4 differential quadrature phase-shift keying application at the 860-MHz band. The measured performance of the IDPA was compared with that of the balanced class-AB amplifier with the same output matching network. At an output power of 50 W, the IDPA performs with 3.16 dB better adjacent channel power ratio (-28 versus -24.84 dBc) and 6.15% higher power-added efficiency (59.02 versus 52.87%) than the class-AB amplifier does.

[1]  W.H. Doherty,et al.  A New High Efficiency Power Amplifier for Modulated Waves , 1936, Proceedings of the Institute of Radio Engineers.

[2]  Frederick Raab,et al.  Efficiency of Doherty RF Power-Amplifier Systems , 1987, IEEE Transactions on Broadcasting.

[3]  D. M. Upton,et al.  A new circuit topology to realize high efficiency, high linearity, and high power microwave amplifiers , 1998, Proceedings RAWCON 98. 1998 IEEE Radio and Wireless Conference (Cat. No.98EX194).

[4]  P. Asbeck,et al.  An extended Doherty amplifier with high efficiency over a wide power range , 2001, 2001 IEEE MTT-S International Microwave Sympsoium Digest (Cat. No.01CH37157).

[5]  Jaehyok Yi,et al.  Optimum design for linearity and efficiency of a microwave doherty amplifier using a new load matching technique , 2001 .

[6]  Robert H. Caverly,et al.  HF, VHF, and UHF systems and technology , 2002 .

[7]  C. Weitzel,et al.  RF power amplifiers for wireless communications , 2002, 24th Annual Technical Digest Gallium Arsenide Integrated Circuit (GaAs IC) Symposiu.

[8]  F. Raab,et al.  Power amplifiers and transmitters for RF and microwave , 2002 .

[9]  Youngoo Yang,et al.  A microwave Doherty amplifier employing envelope tracking technique for high efficiency and linearity , 2003, IEEE Microwave and Wireless Components Letters.

[10]  Bumjae Shin,et al.  A fully matched N-way Doherty amplifier with optimized linearity , 2003 .

[11]  L.F. Cygan.  A high efficiency linear power amplifier for portable communications applications , 2005, IEEE Compound Semiconductor Integrated Circuit Symposium, 2005. CSIC '05..

[12]  Youngwoo Kwon,et al.  A new "series-type" Doherty amplifier for miniaturization , 2005, 2005 IEEE Radio Frequency integrated Circuits (RFIC) Symposium - Digest of Papers.

[13]  Jangheon Kim,et al.  Highly linear three-way Doherty amplifier with uneven power drive for repeater system , 2006, IEEE Microwave and Wireless Components Letters.

[14]  M. Iwamoto,et al.  Linearity Improvement of HBT-Based Doherty Power Amplifiers Based on a Simple Analytical Model , 2006, IEEE Transactions on Microwave Theory and Techniques.