Efficiency Enhancement of a Digital Predistortion Doherty Amplifier Transmitter Using a Virtual Open Stub Technique

Kenichi HORIGUCHI  Satoru ISHIZAKA  Masatoshi NAKAYAMA  Ryoji HAYASHI  Yoji ISOTA  Tadashi TAKAGI  

IEICE TRANSACTIONS on Electronics   Vol.E90-C    No.9    pp.1670-1677
Publication Date: 2007/09/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e90-c.9.1670
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Microwave and Millimeter-Wave Technology)
Category: Active Devices/Circuits
power amplifier,  microwave Doherty amplifier,  efficiency,  orthogonal frequency division multiplexing (OFDM),  predistortion,  

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This paper proposes a design method of a Doherty amplifier, which can determine the most efficient backed-off point of the amplifier by adjusting a load modulation parameter. The parameter is defined through the design of output transmission line of a carrier and a peak amplifier using a virtual open stub technique. This paper describes the design results using the technique to optimize efficiency of a Doherty amplifier for an orthogonal frequency division multiplexing (OFDM) signal, and parameter adjustment for a linearized Doherty amplifier using an adaptive digital predistortion (ADPD). Applying this method, the developed 250 W ADPD Doherty amplifier has achieved drain efficiency of 43.4% and intermodulation (IM) distortion of -48.3 dBc with output power of 44.1 dBm (10.1 dB output backed-off) at 563 MHz using an OFDM signal for integrated services digital broadcasting-terrestrial (ISDB-T).