Used For Wimax 20w Doherty Power Amplifier Research And Design

The power amplifier, which performance determines the entire systems' performance directly, is the largest consumption energy component in communication systems. Recently, with the rapid development of wireless communications, the radio spectrum has become tighter and tighter, appearing a variety of non-constant envelope modulation systems, such as TD-SCDMA, WCDMA, CDMA2000, WIMAX and so on. These modulated systems have very high PAR, even up to 10dB. Therefore, the higher requirement is proposed to the linearity of the power amplifier. In order to improve linearity, the power amplifiers are degraded and used in the power back off region. At present, although there are many ways to improve the linearity, for example, digital pre-distortion (DPD) and feed forward and so on, the efficiency of the amplifiers is still low. The Doherty amplifier adopted in this article can solve these problems effectively. The efficiency of the power amplifier can be greatly improved by the peak value and the average value respectively amplified without impacting the linearity. Recently the research on the Doherty power amplifier has become a central issue at home and abroad and has achieved fruitful results. Currently, the amplifier with this structure has become the mainstream scheme of the 3G communication system and the next generation of communication system (LTE). Therefore the research on Doherty amplifier has very important theoretical and practical significance.This paper mainly introduces the research and design of the 20W Doherty amplifier (DPA) that used for WIMAX from the 2.5GHz to 2.7GHz. The working principle and design procedure of the DPA are described in detail;The layout and the practical circuit are completed;Finally, a simple test is made to the circuit. The results show that the efficiency of the DPA increases 33% at 6dB back off from saturation compared with the balance conventional class AB amplifier;The average gain is above 12dB and the gain flatness is less than 1dB. By analyzing and optimizing the gate voltage of the peak amplifier, the batter linearity can be achieved.