| Modern wireless communication system employs non-constant envelope modulation schemes for higher data rate, such as OFDM, which leads to high peak-to-average power ratio (PAPR). The average efficiency of traditional power amplifiers is low when amplifying high PAPR signals. Doherty and envelope tracking are able to improve the average efficiency of power amplifiers and meet the requirement of amplifying high PAPR signals effectively, have become hot issues in today’s research. The combination of the two technologies will make power amplifier amplify high PAPR signals more effectively. This dissertation focuses on envelope tracking technology applied to high-power radio frequency Doherty power amplifier and achieves an ET Doherty power amplifier. The major work and achievement of the thesis includes:1. The design of high efficiency and wide band envelope amplifier is the important and difficult point in envelope tracking. The bandwidth of LTE envelope signals is up to20MHz and it’s a big challenge for an envelope amplifier to amplify such wide band envelope signals. Traditional linear amplifier and switching converter can’t meet the requirement of efficiency and bandwidth simultaneously. This dissertation uses the structure of the hybrid envelope amplifier which is parallel combination of linear stage and switching stage to avoid this problem. The efficiency of the envelope amplifier is improved by improving the structure of the output circuit of the linear stage. As the experimental result shows, a maximum output voltage28V,20MHz bandwidth envelope amplifier is achieved. The peak efficiency is76.9% for single-tone envelope signals.2. This dissertation tracks the drain voltage of the main amplifier of the Doherty amplifier to broaden the back off region of the Doherty amplifier. The average of the Doherty is improved by this means. The theoretical of the efficiency of the ET Doherty PA is derived and the ET Doherty power amplifier is simulated in ADS. The result of the simulation shows that the efficiency of the Doherty PA is improved by10%at8dB BOP after envelope tracking.3. This dissertation achieves the implementation of the envelope tracking Doherty power amplifier at the foundation of the simulation. A peak output power43dBm; efficiency43.7%at6dB BOP GaN Doherty PA is achieved. Test the ET Doherty PA with single-tone signals and bandwidth signals. As the experimental result shows, the efficiency of the Doherty PA is improved by5%at8dB BOP tested with single-tone signals after envelope tracking. The efficiency of the Doherty PA is improved by6.53%at average output power34.2dBm tested with bandwidth20MHz, PAPR10.18dB LTE signals after envelope tracking. |
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