High-efficiency Doherty power amplifiers

High-efficiency Doherty power amplifiers

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This chapter discusses the power amplifier technique for amplitude-modulated (AM) radio-frequency signals was invented by William H. Doherty in broadcasting in the mid-1930s as a more efficient alternative to both conventional amplitude-modulation techniques and Chireix outphasing [4]. The amplifier was configured in a grounded-cathode structure where two vacuum tubes were connected in parallel, one as a Class B carrier tube and the other as a Class C peaking tube, and the tubes were split and combined through þ90° and -90° phase shifting networks. This novel power amplifier architecture removed limitation of low efficiency inherent in a conventional power amplifier circuit, permitting efficiencies of 60% to 65% to be realized, while retaining the principal advantages associated with low-level modulations systems and linear power amplifiers.

Chapter Contents:

  • 2.1 Basic Doherty amplifier structure
  • 2.2 Asymmetric Doherty amplifiers
  • 2.3 Multistage Doherty amplifiers
  • 2.4 Inverted Doherty amplifiers
  • 2.5 Integrated Doherty amplifiers
  • 2.6 Broadband Doherty amplifiers
  • References

Inspec keywords: vacuum tubes; radiofrequency power amplifiers; amplitude modulation; radio broadcasting

Other keywords: vacuum tubes; linear power amplifiers; conventional power amplifier circuit; low-level modulations systems; amplitude-modulated radio-frequency signals; grounded-cathode structure; high-efficiency Doherty power amplifiers; power amplifier architecture; Chireix outphasing

Subjects: Radio and television broadcasting; Vacuum tubes; Amplifiers

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