Design Of The Doherty Power Amplifier Based On LDMOS

With the development of current wireless communication technology, the products of wireless communication have been widely appeared and the effects are getting more and more important in people's life. As a main of energy consumption device in wireless communication system, the performance of RF power amplifier is getting more and more attention impacted on the terminal system. The standard of wireless communication system has been changed form the traditional standard of GSM to 3G standard of WCDMA,TD-SCDMA. CDMA2000,as well as to the future 4G standard of LTE(Long Term Evaluation).The mode of signal modulation also has been changed form constant-envelope signals to envelope-varying signals. For instance, the transmit powers of wireless communication system which using OFDM on WCDMA carried high peak-to-average power ratio signals, so that signals can be strength to maximize system capacity. Owing to such a system requirement, it is common for power amplifiers operating at output power back-off from peak power under keeping linearity. Unfortunately, the consequence of this requirement is that the traditional power amplifier which operating in regions of back-off from peak power has low efficiency. So it is very important for power amplifier in base station that to enhance higher efficiencies at back-off power in these applications. The way to enhance efficiency is not just a few. Owing to such advantage as simply structure and high performance-to-price ratio, the Doherty power amplifier technology becomes hotspot at base station.This dissertation describes the basic theoretical knowledge of power amplifier and focused on the basic principle and working condition analysis of Doherty power amplifier as well as the principle of asymmetric Doherty amplifier and N series Doherty amplifier. Also the design progress of Doherty power amplifier is described and the offset lines & the bias voltage of peak power amplifier impacted on the performance of Doherty power amplifier are analyzed. This design uses the RF simulation software ADS and combined with the LDMOS, model MRF6S21140H from Freescale Company, the Doherty power amplifier in WCDMA band was designed. The simulation results are presented to demonstrate the Doherty power amplifier advantage in power added efficiency by comparing with the balanced class AB amplifier. In order to remedy the drawback of traditional Doherty amplifier, I design asymmetric Doherty amplifier with inequality input power structure which making the linearity and output power of Doherty amplifier improved.