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Institute of Korean Electrical and Electronics Engineers (한국전기전자학회)
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Extraction of Optimal Operation Condition of QAM Envelope Tracking System using Combined Cost Function of Bandwidth and Efficiency

  • Kim, Changwook (Dept. of Electronics Engineering, Hankuk University of Foreign Studies) ;
  • Park, Youngcheol (Dept. of Electronics Engineering, Hankuk University of Foreign Studies)
  • Received : 2018.12.06
  • Accepted : 2018.12.24
  • Published : 2018.12.31
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Abstract

In this paper, we suggest a combined cost function to find out the optimal operation of an envelope tracking system, and evaluated its performance with Quadrature Amplitude Modulation (QAM) waveform, with which envelope tracking coefficients for the peak drain efficiency and the bandwidth of power amplifiers are determined. Based on the classical envelope tracking theory, the operation of the supply modulator, which is a key part of the envelope tracking process, is modeled and analyzed mathematically. Then characteristics of the modulator by setting envelope shaping function as a cubic polynomial and sweeping the coefficients of this function was analyzed. By sweeping the coefficients, efficiency and bandwidth at each condition with 64-QAM signal was used to obtain optimal point of the supply modulator. Compared to the conventional shaping functions, the optimized function showed the bandwidth reduction by 12.7 percent point while the efficiency was maintained.

Keywords

JGGJB@_2018_v22n4_1019_f0001.png 이미지

Fig. 1. Block diagram of an Envelope Tracking Power Amplifier[7].

JGGJB@_2018_v22n4_1019_f0002.png 이미지

Fig. 2. Envelope shaping functions[10].

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Fig. 3. Probability density function of 64-QAM signal (average power is set to 0 dB).

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Fig. 4. Employed 64-QAM signal in frequency domain.

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Fig. 5. Envelope Tracking figure of merit.

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