J.L. Dawson

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

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Publications (4)0 Total impact

  • Source
    P.A. Godoy · S. Chung · T.W. Barton · D.J. Perreault · J.L. Dawson
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    ABSTRACT: A 1.95-GHz asymmetric multilevel outphasing (AMO) transmitter with class-E GaN power amplifiers (PAs) and discrete supply modulators is presented. AMO transmitters achieve improved efficiency over envelope tracking (ET) transmitters by replacing the continuous supply modulator with a discrete supply modulator implemented with a fast digital switching network. Outphasing modulation is used to provide the required fine output envelope control. A 4-level supply modulator is implemented that allows for fast and efficient discrete envelope modulation with up to 28-V supply voltages using low-voltage gate drivers and time-alignment logic. With two class-E GaN PAs that achieve 62.5% power-added efficiency (PAE) at 40- dBm peak output power, the AMO transmitter delivers 42.6- dBm peak output power at 1.95-GHz. For a 16-QAM signal at 36-dBm output power, the transmitter achieves 44.2/42.8/41.4% average system efficiency and 2.0/2.1/3.1% EVM for 10/20/40-MHz channel bandwidth, respectively.
    Preview · Conference Paper · Jul 2011
  • S. Chung · J. L. Dawson
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    ABSTRACT: form only given, as follows. A low-power, low-complexity adaptive digital predistortion system is presented for linearizing WLAN PAs. Second-order quadrature delta-sigma modulation is employed with phase alignment and gain normalization for maintaining modulator stability. An experimental system linearizes a 2.4-GHz PA transmitting a 20.2-dBm WLAN signal with 10-MHz bandwidth. After 523-millisecond background adaptation, the experimental predistortion system improves the EVM of the unlinearized PA from 5.90% to 0.96%.
    No preview · Article · Jan 2011 · IEEE MTT-S International Microwave Symposium digest. IEEE MTT-S International Microwave Symposium
  • T.W. Barton · SungWon Chung · P.A. Godoy · J.L. Dawson
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    ABSTRACT: A digital-to-RF phase modulator based on a single current-steering DAC is presented, including a carrier pre-rotation scheme that prevents phase inaccuracy due to carrier feedthrough. The phase modulator has been fabricated in a standard 65-nm CMOS process and draws 1.9 mW from a 1-V supply. The modulator achieves 12-bit resolution at a measured 200 MSamples/second, state-of-the-art performance in both resolution and sampling speed. It has sufficient speed to allow for oversampling to shape the output spectrum and therefore reduce filtering requirements, as demonstrated through a 32x oversampled 8-PSK signal at 6.25 MSymbols/second with under 6.1% EVM.
    No preview · Conference Paper · Jan 2011
  • Source
    SungWon Chung · Jack W. Holloway · Joel L. Dawson
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    ABSTRACT: We present a new adaptive power amplifier (PA) linearization technique. We leverage analog Cartesian feedback (CFB) to train a Cartesian look-up table, reducing DSP and power amplifier modeling requirements to a minimum and eliminating model convergence as a design issue. Because the CFB system does not continuously operate, we overcome the bandwidth limitation traditionally associated with this technique. In addition, we exploit sample averaging to greatly relax the noise requirements of the analog feedback path. We implemented a prototype 900-MHz direct-conversion transmitter with a class-A PA. We measured a 10-dB reduction of out-of-band distortion products with no noise floor degradation for 40-MHz-bandwidth, 16-QAM test signals.
    Preview · Conference Paper · Jul 2007