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Keywords:

  • Doherty Amplifier;
  • power amplifier;
  • high efficiency;
  • main;
  • auxiliary;
  • active load modulation

Abstract

In this article, the complete theoretical analysis of a Doherty amplifier employing a Class AB bias condition for the Main and a Class C one for the Auxiliary devices, respectively, is presented. Starting from the simplified model of an active device, the analysis of the AB-C Doherty behavior is carried out as a function of the input signal. In particular, the proposed approach is based on the analysis of the output drain current waveforms generated by the two active devices, while assuming a Tuned Load configuration (i.e., short circuit condition) for higher harmonic terminations. A closed form formulation is derived in order to directly design an AB-C Doherty amplifier, while fully understanding the basis of its physical behavior. Finally, which Doherty parameters can be chosen by the designer or have to be implicitly fixed are discussed and clarified. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.