| Modern communication systems adopt different modulation technique such as WCDMA, CDMA-2000 and OFDM, so signals in the communication system are mostly high-rate and high dynamic range with the high peak-to-average ratio (PAR). To satisfy those requirements, base station power amplifier should be equipped with high efficiency, especially high efficiency at the point of back-off power. Unfortunately, ascribing to the deeper back-off power, the efficiency of common power amplifier would drop off quickly.To solve this problem, this dissertation adopts Doherty power amplifier technology. In addition, to enhance the efficiency at the deeper back-off power, uneven Doherty power amplifier basing on RF impedance-match technology is employed. On the theory, this dissertation introduces three different work conditions and its corresponding efficiency of Doherty, and then analyzes the reason that Doherty power amplifier can get high efficiency at the back-off point, and detailedly introduce all power-match technology and the method of calculating impedance. On the implementation, the index of system is analyzed in this dissertation, and the basis for choice on the chips is provided, and uneven Doherty is designed by two different LDMOS chips with 30W and 50W output power respectively. Then, from the design of single-chip amplifier, this dissertation introduce the progress of even and uneven Doherty power amplifier, especially the simulation of all power-matched technology and method of computing matched impedance. Finally, make two different single-chip amplifier and Doherty power amplifier system.This dissertation provides the plan of testing power amplifier. The result of test basically matches the design index, including power added efficiency (PAE) of Doherty power amplifier is beyond 30% at the point of 8.5dB back-off power. |
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