| Along with the mature using of the third generation(3G) mobile communication technology and the rapid development of the fourth generation(4G) application, multiple modulation modes and multiple frequency bands coexist in modern mobile communication system. Multimode and multiband system coorperation inevitably becomes the development trend of the future wireless mobile communication system. Modulation methods trend to operate signals with high peak to average power ratios, multiple carriers and large signal capacity. Power amplifier designers face new and greater challenges due to more stringent requirements in functionality, performance, size and cost, so coexistence of different working modes and modulation methods on the same communication platform is attacting people’s attention, thus leading to the higher requirements on broadband power amplifiers. As the core module of a transmitter, the performance of power amplifier directly affects the transfered signal quality of the whole communication system. Moreover, further expansion of the power amplifier working bandwidth is greatly needed. This thesis focuses on the research and study of broadband and high-efficiency power amplifier.The dissertation firstly introduces the basic theory of power amplifier, including classification, performance indexes, load-line theory and loadpull technology. As followed are a few common methods for bandwidth extension and efficiency enhancement, comparison on different efficiency enhancement methods are given. Secondly, the Doherty power amplifier operating theory and active loadpull modulation process are shown. Dynamic variations of the load impedance under different Doherty operating modes are illustrated together with efficiency characteristics. In the end, some novel Doherty arthitectures are given.Based on the theories above, a handy and useful broadband and high-efficiency power amplilfier design method is shown. A simple broadband bias architecture is used, the optimum source and load impedances of transistor are obtained using source/load-pull simulation, simple matching networks are implemented with common matching architectures. Also a novel broadband inverted Doherty power amplifier design method is given by utilizing broadband matching network which matches the transistor impedance to a novel low level common load impedance and broadband impedance-invert networks.Along with the design methods given above, our studies firstly focus on low-power-level amplifiers. First step, a 10 W broadband high efficiency power amplifier was designed and implemented. Measurements showed that the PA had a saturated output power in the range of 42-42.5dBm over the frequency range 1.8-2.7GHz, while the power added efficiency reached to 56%-67.8%, the designed PA has great advantage in output power. Second step, a 20 W broadband inverted Doherty power amplifier working on 1.8-2.7GHz was proposed and characterized. Measurements under CW signal showed that the IDPA had a saturated output power in the range of 43.2-45.1dBm, over 1.8-2.7GHz. At 6.7-8.6dB output power back-off(output power of 36.5dBm), the PA had a drain efficiency of 41.5-45.3%. The linearity of the broadband IDPA was characterized using a WCDMA standard signal. Over the whole bandwidth, Adjacent Channel Power Ratio(ACPR) less than-27.4dBc was obtained with drain efficiency of 45.3-48.6% at output power of 36.5dBm, the minimum ACPR even reached to-40.3dBc at 2.1GHz under 5MHz offset. To the best of authors’ knowledge, the designed inverted DPA has the highest bandwidth reported so far.Secondly are the high-power-level amplifier design technologies. First step, a 100 W broadband high efficiency power amplifier working on 1.8-2.7GHz was simulated and implemented. Measurements showed that except the relatively bad output power performance on 2.7GHz(Psat=47.5dBm), the PA had a saturated output power in the range of 49.3-50.5dBm, the saturated power added efficiency reached to 55.3%-65.7% under the whole frequency band. Second step, another 200 W broadband inverted Doherty power amplifier circuit was designed on the basis of the design above. The measured performance showed that under the working frequency 1.8-2.7GHz, the IDPA got P-3 output power ranging from 47.5-52.93 dBm, when output power got back to 46 dBm, the circuit drain efficiency of 34.2%-45.9% was obtained.This thesis mades a more comprehensive analysis and summary on broadband and high efficiency power amplifier and broadband Doherty power amplifier design technology. Based on GaN HEMT power transistors, 10 W and 100 W power amplifier circuits, as well as 20 W and 200 W broadband Doherty power amplifiers working on 1.8-2.7GHz are designed and characterized, providing a realistic reference for modern mobile wireless communications. |
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