Doherty功率放大器 英文 .docVIP

The Doherty Power Amplifier The current wireless communication systems have made significant progress toward increased bandwidth and number of carriers for high-data-rate applications. Memory effects, however, make it very difficult to design a high-power amplifier with a wide instantaneous bandwidth. In addition to bandwidth concerns, the instantaneous transmit powers of the wireless communication systems, such as CDMA-2000, wide-band code division multiple access (WCDMA), orthogonal frequency division multiplexity (OFDM) and so on, vary widely and rapidly, carrying high peak-to-average ratio (PAR) signals. The base station power amplifiers for the systems require a high linearity to amplify the high PAR signal source without distortion. To satisfy linearity requirements, the power amplifiers are usually biased at class A or AB mode and must operate at a large amount of back-off from the peak output power. Another requirement of the base station power amplifier for the modern wireless communication systems is high efficiency. As the communication systems are reduced in both size and cost, the cooling system should be simple and small, requiring a power amplifier with high efficiency. Because the base station power amplifiers have a low efficiency due to the back-off operation, efficiency enhancement techniques become very important. The design technique of the base station power amplifiers with high efficiency and linearity across a wide instantaneous bandwidth has become a hot issue. In this article, we show that the Doherty amplifier is capable of delivering the stringent requirements of the base station power amplifiers. We explain the operation principles, including both linearity and efficiency improvements, and the basic circuit configuration of the amplifier. Advanced design methods to operate across wide bandwidth and improve the linearity are also described. For verification, the Doherty amplifier is implemented using laterally diffused metal oxide semicon