| By the wide use of wireless communication system, spectrum resources are more and more valuable. The third and Fourth generation wireless communication system(WCDMA, TD-SCDMA, CDMA2000and LTE) all use Orthogonal Frequency Division Multiplexing (OFDM) modulation technology. The OFDM technology improves the spectrum utilization efficiency and data transfer speed, but it needs the power amplifier to be fit for high peak to average ratio and high linear requirements. Huge energy will be wasted by using power back off sheme. It not only causes heat problems to the system, but also reduces the reliability. In recent years, by the rapid development of Digital Pre-Distortion technology and the wide research of Doherty amplifier, Doherty amplifier plus digital pre-distortion technology is becoming mainstream solution of the major manufacturers.According to the above requirements of high peak to average ratio, high linear and high efficiency, this paper researched the characteristics of asymmetrical Doherty power amplifier(ADPA). Firstly, it introduced the load modulate theory of Doherty amplifier and derivated the efficiency formula of it. Secondly, it adopted ADS to simulate and analyse the symmetrical and asymmetrical Doherty amplifier, and used offset lines to improve the efficiency. It also studied the memory effects of amplifier and presented several methods to reduce it. Then it introduced two assistant circuit usually used in Doherty amplifier. At last, it implemented a55W asymmetrical Doherty amplifier using100W and140W LDMOS. It introduced how to layout, debug and test the Doherty amplifier.The test results shows:For a2.65GHz four carrier W-CDMA signal, the measured average output power of the amplifier is47.5dBm, the measured peak power is55dBm, and the measured power added efficiency (PAE) is41%. After the digital pre-distortion (DPD) calibration, the measured adjacent channel leakage ratio (ACLR) is lower than-55dBc. It basically meets the requirements of the system. |
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