Design method of microwave Doherty power amplifiers and its application to Si power MOSFET amplifiers

Recently, much attention has been given to Doherty amplifiers as microwave power amplifiers that have the possibility of realizing high efficiency and low‐distortion characteristics with a wide dynamic range. In this paper, the configuration, operation, and characteristics of Doherty amplifiers are surveyed and challenges in their use as microwave power amplifiers are identified. The circuit condition for use as a microwave Doherty amplifier is derived. Based on this condition, a method for the design of a practical output coupling scheme for a Doherty amplifier is proposed. Also, the effects of the peak amplifier and the carrier amplifier composing a Doherty amplifier on the combining characteristics of the Doherty circuit configuration are studied and design guidelines are presented. The behavior and characteristics of the power Si MOSFET Doherty amplifier constructed with the proposed design method are discussed in detail by simulation. The evaluation results are presented for a 1‐GHz Si MOSFET Doherty amplifier designed and fabricated on the basis of the simulation results. Finally, summaries and future challenges are given. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(4): 9–17, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20137