| With the development of wireless communication technologies, the design demand of wireless communication system is growing. Power amplifier is the backend of radio frequency transmitter. As one of the most important blocks and large cost elements, it plays a very important role in radio frequency transmitter. Its consumption is the greatest in wireless communication system. The performance of power amplifier is critical and affects the overall performance of communication system. The nonlinearity of power amplifier is the main source of wireless communication system’s nonlinearity. In order to improve the linearity and efficiency and decrease the cost, high linearity and efficiency is the goal and also the issue in the design procedure of power amplifier. This paper proposes a K-Band high performance two-stage power amplifier in 0.15μm Ga As PHEMT process. The matching network was designed to satisfy the design demand. The power added efficiency(PAE) of conventional PA has been improved greatly by the technology of Doherty.Firstly, the performance and various types of power amplifiers were introduced. Then many technologies to improve linearity and efficiency of power amplifier were discussed. Power back off, Feedforward and pre-distortion could improve the linearity of PA effectively. Kahn EER(Envelope Elimination and Restoration) technology, Envelope Tracking technology, LINC(Linear Amplification Using Nonlinear Component) and Doherty technology could improve efficiency effectively. The optimum impedance was obtained by the method of Load-pull. The maximum power transmission was achieved by matching network. K-Band power amplifier consists bias circuit, stable circuit and matching network. A 2-stage power amplifier at 24-GHz in 0.15μm Ga As PHEMT process was implemented and the layout was completed. The simulation results show that the power amplifier achieved a small signal gain of 16.85 d B at 24-GHz, a saturation output power of 25 d Bm, and an area of 2*1.2mm2 was occupied. The output power of the PA at 1-d B compression point was 24.2d Bm with a PAE of 36.9%. Doherty power amplifier is made up of a main power amplifier, an auxiliary power amplifier and a Wilkinson power divider. The main power amplifier operates at AB class while the auxiliary power amplifier operates at C class. Compared to conventional AB class power amplifier, Doherty power amplifier increased the PAE by 16%,which is a great improvement. |
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