Research And Design Of High-efficiency Power Amplifier Based On Doherty Structure

Microwave/RF power amplifier is the key device in wireless communication system,lots of indicators of which such as linearity and efficiency directly determines the performance of the whole system. Modern wireless communication system use complex modulation technology to achieve high spectrum efficiency, as the result, the peak-to-average power ratio(PAPR) becomes higher. When amplified by the traditional power amplifier, the actual working efficiency is very low because the back-off power is far from saturated, which does not meet today's require about the concept of "green communication". The most popular way to solve this problem is the Doherty structure,which can achieve high efficiency at the back-off area.Based on the 34 th TDD-LTE band of 2010 ~ 2025 MHZ, this paper introduces two kinds of design with the Doherty structure to research the design of high-efficiency Doherty amplifier. The first design is based on the classical theory of Doherty, which can keep high efficiency in the range of 6 dB back-ff. Physical test shows that the saturation power can reach 45 dBm, and the peak efficiency is more than 60%, the efficiency at 6dB back-off is more than 40%. The second design has much better performance. With the use of GaN HEMT as the power transistor, the performance of single PA is improved.And with the use of inverse F class design, the single PA's efficiency is increased largely. The uses of different power distribution ratio and ranging bias design can meet the demand of the actual active load traction and enlarge the range of the back-off area. Through these measures, the simulation results show that the Doherty amplifier's saturation power can reach 44 dBm,the peak efficiency approaching 80%, and 8dB back-off efficiency remains above 60%.Actual test results show that its output saturation power is more than 44 dBm, the peak efficiency is above 75%, and the efficiency at 8dB back-off range is more than 50%. It's obvious to see that the second design's performance improved a lot than the classical Doherty amplifier design.Through the contrast, with the use of the new design,the the overall performance has a great enhance on the basis of the keep simple circuit structure, which may have certain engineering practical value.