A Proposal for Adopting the Frequency Response of an Envelope Amplifier with Memoryless DPD EER PA Model

Takayuki KATO  Yoshinori KOGAMI  Yuuki FUNAHASHI  Atsushi YAMAOKA  Keiichi YAMAGUCHI  Yasuhiko TANABE  Jiafeng ZHOU  Kevin MORRIS  Gavin T. WATKINS  

IEICE TRANSACTIONS on Electronics   Vol.E95-C    No.7    pp.1163-1171
Publication Date: 2012/07/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E95.C.1163
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Recent Trends of Microwave Systems and Their Fundamental Technologies)
EER,  power amplifier,  memoryless DPD,  envelope amplifier,  frequency response,  

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Recently, dynamic power supply voltage techniques, such as an Envelope Elimination and Restoration power amplifier (EER-PA) or Envelope-Tracking Power amplifier (ET-PA), have been attracting much attention because they can maintain high efficiency in large back-off region [1]-[6]. The dynamic power supply voltage techniques cause strong nonlinearity compared to a conventional power amplifier, hence a memoryless Digital Predistortion (DPD) technique is indispensable for these efficiency enhancement techniques. However, the performance of the memoryless DPD is degraded due to the frequency response of the envelope amplifier in the dynamic power supply voltage techniques [7]-[9]. In this paper, we clarify the degradation mechanisms of the memoryless DPD for the EER-PA due to the frequency response of the envelope amplifier based on the results of two-tone tests, and propose an analytical model for improving the performance of the memoryless DPD developed for the EER-PA. In addition, a prototype EER-PA is developed and we demonstrate that the residual distortion of the developed EER-PA with conventional memoryless DPD algorithm is compensated by the new algorithm based on the proposed analytical model. In the two-tone test, third-order intermodulation distortion (IMD3) with a tone spacing from 100 kHz to 4 MHz is improvement by up to 25 dB by the memoryless DPD algorithm based on the proposed model. Measured adjacent channel leakage power ratio (ACPR) of the developed EER-PA is improved from -22.5 dBc to -42.5 dBc in the OFDM signal test with 1.08 MHz bandwidth.