Research On Broadband And Tunable Efficient RF Power Amplifiers

With CMCC firstly popularized the TD-LTE(Time Division Long Term Evolution) commercially i2013, China has now entered the era of 4G. Voice, video and other multimedia services would show blowout type growth. The commercial usages of 4G would lead to the coexistence of multiplcommunication standards in 2G, 2.5G, 3G and 4G. The coexistence of Multi-standards,Multi-bancommunication modes would inevitably become a trend of the wireless communication systems in thfuture.Doherty amplifier circuit structures had been widely used in a lot of base stations due to its higefficiency for high PAPR signals. However,the traditional Doherty structures cannot satisfy thcommunication requirements of modern multi-mode multi-band because of its relatively narrow operatinbandwidth. Thus, how to expand the conventional Doherty amplifier operating bandwidth would becoman urgent problem.In order to solve the problems above, the combiner structure of the traditional Dohertpower amplifier was improved, so as to expand its operating bandwidth.This thesis was divided into four parts:The the first Part, The frequency response of the structure of the conventional Doherty Combiner wainvestigated. It was found that the operating bandwidth was affected by narrow-band characteristics of λ/4 impedance conversion lines. To expand the bandwidth, the impedance conversion ratio of λ /impedance transformation lines should be reduced.The the second Part, The broadband matching structures were studied and a 1.7-2.7GHz broadbanpower amplifier was designed by using broadband impedance matching. The original combiner structurewere then substituted by two 70.7 ohm λ /4 impedance transformation lines. A broadband bandwidtbalanced Doherty power amplifier, with its bandwidth 1.85-2.65 GHz, was designed. The results showethat the drain efficiency was higher than 38% in the band of 1850-2650 MHz with 5-6 d B of output poweback-off.The the third Part, several concurrent multi-band impedance transformation networks were analyzedThe effects of different phase compensations to achieve optimal efficiency for different frequencies werthen analyzed. Based on the above analysis, the traditional combiner structure and compensation line werimproved by using concurrent structure. A concurrent dual-band Doherty amplifier with its bandwidth iboth 2.1GHz and 2.5GHz, was successfully designed. The test results showed that with the drain efficienchigher than 33% in the dual-band at 6d B of output power back-off, the maximum power was obtainehigher than 41.5d Bm.The the fourth Part, the adjustable devices and adjustable circuits were investigated. The tunabldevices of PIN switches and varactor diodes were practically tested. On the basis of the characteristics obalanced broadband Doherty’s Combiner structure, its compensation line is further optimized by analyzinthe impact of the compensation line for broadband Doherty structure and the concurrency impedancmatching characteristics. According to the series and parallel access ways, two tunable broadband Dohertamplifiers with bandwidth of 1.85-2.65 GHz, were designed through the regulation of PIN switch. The twadjustable ways were verified through ADS simulation to demonstrate its effective enhance on the back-ofefficiency in the entire band.