Manchester encoded bandpass sigma–delta modulation for RF class D amplifiers

T. Johnson; R. Sobot; S. Stapleton

Manchester encoded bandpass sigma–delta modulation for RF class D amplifiers

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Manchester encoded bandpass sigma–delta modulation for RF class D amplifiers

Author(s): T. Johnson ; R. Sobot ; S. Stapleton
DOI: 10.1049/iet-cds:20060054

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Author(s): T. Johnson ¹ ; R. Sobot ² ; S. Stapleton ³
- Affiliations: 1: PulseWave RF, Austin, USA
  2: Department of Electrical and Computer Engineering, The University of Western Ontario, London, Ontario, Canada
  3: School of Engineering Science, Simon Fraser University, Burnaby, Canada
Source: Volume 1, Issue 1, February 2007, p. 21 – 26
DOI: 10.1049/iet-cds:20060054 , Print ISSN 1751-858X, Online ISSN 1751-8598

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An analysis of a continuous-time bandpass sigma–delta modulator in a configuration with an upconverter is given for a RF class D amplifier application. The upconverter multiplies the modulator pulse train with a synchronised clock signal and maps each modulator bit to an integer multiple k of a (+1, −1) or (−1, +1) pattern depending on the sign of the modulator bit. The upconversion is equivalent to an extension of Manchester encoding, which is usually defined for k=1. The analysis focuses on evaluating the impact of upconversion on the modulator coding efficiency and the average pulse period. A design equation is derived, which shows that coding efficiency is dependent only on the upconversion frequency ratio, while the average pulse period depends only on k. The equations provide a designer with a way of evaluating the trade-offs in the amplifier system and show that encoding with k=1 is the most efficient configuration for maximising coding efficiency and minimising switching power loss.

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