| Summary: | 碩士 === 長庚大學 === 電子工程學系 === 102 === Although wireless communication products become more and more matured, however, RF wireless modules still play an important role. The system requires the RF circuits with better performance for satisfying the systems adopting the data transformation method. The RF power amplifier (PA) is one of the RF blocks that consumed the most of power of the system and affects the performance of the transceiver module directly.
In general, the power amplifier has to be maintained its linearity for working properly when the output power goes to the high power state, thus it has to maintain the higher back-off to have good performance as the output power is slight lower than the power saturation state. There have been a variety of technical methods proposed to improve the efficiency of PA, but Doherty power amplifier became the popular technical method for it having the relatively simple structure and been proposed to have various methods of performance improving design and low production costs.
In this paper, we proposed a new structure for designing the Doherty PA. Firstly, we replace the traditional power divider with the trans-directional (TRD) coupler to divide the power of the input signal into the different power ratio. Then, TRD coupler is adopted to design a new type of impedance converter and then use as adjustable power dividers to improve the efficiency.
This paper uses commercial PCB material and ADS electromagnetic simulation software to develop a Doherty power amplifier which is working in 2GHz. In the case of using 3.5V power supply, the PA can deliver the output power of 25dBmassociate with the gain of 10dB and the power efficiency of 52%. In the case of power back-off 5dB, this Doherty amplifier power efficiency can still reach 44%.
Then we use the previously mentioned the new type converter and adjustable power dividers to realize an adjustable input power ratio and different output matching networks of Doherty amplifiers to improve the characteristics of PA. It is found the new type of PA can still deliver the output power of 25dBm and 53%power efficiency, that are almost same as that using traditional structure, but the new Doherty PA can increase the output power to 5dBmat back-off region and thus increase the power efficiency of this Doherty PA up to 52% that is 8% improvement as compared with the traditional type. On the other hand, the adjustable Doherty power amplifier can reach the best efficiency by adjusting the input power ratio of carry amplifier and peaking amplifier.
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