| The amount of global mobile subscribers exceeded 5 billion in 2010; meanwhile, the business needs of mobile users are increasingly diversified. Greater capacity and higher data rates are required for the mobile communication systems to meet the requirements of subscribers. Non-constant envelope modulation and multi-carrier technique are adopted in third generation mobile communication systems (3G), enlarging system capacity, increasing data rates, and also resulting in higher peak to average power ratio (PAPR).The power amplifier should operate in power back-off region to linearly amplify signals with high PAPR, resulting in low efficiency, which not only cause energy waste, and large numbers of thermal energy dissipation on the power amplifier, seriously affected the life of the stability and power amplifiers for mobile communication systems. Therefore, improvement of the efficiency of power amplifier is helpful to energy-saving, emission reduction and protection of the environment, and can improve the operator's competitive advantage.Among numerous techniques of efficiency enhancement, Doherty is widely accepted and adopted owing to its simple circuit structure, low cost, and excellent performance. Besides, linearity of Doherty power amplifier can be greatly improved with combination of digital pre-distortion (DPD).In this article, key techniques of high efficiency PA are first illustrated, then detailed analysis on operation of Doherty amplifier is given, and current research achievements in Doherty PA are reviewed. Uneven structure is employed to overcome drawbacks of classical Doherty PA. Circuit simulation and design of PCB are fulfilled by means of ADS and Altium Designer respectively. Finally, the uneven Doherty PA is debugged and tested.The power added efficiency is 41.1% at 43dBm average output power, tested under TD-SCDMA 9 carriers signal, ACLR and EVM are improved to–44.3dBc and 11.5% respectively after linearization of DPD. It's shown that, uneven Doherty PA is highly efficient, and applicable to TD-SCDMA system with the combination of digital pre-distortion technique. |
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