High Efficiency Doherty Amplifier

As an important equipment in wireless communication systems, the power amplifier(PA) is widely used in mobile communications, satellite communications, and radar systems. When the signals have an high peak to average power ratio, the PA should work backed off from P1dB in order to ensure the communication quality. This not only causes a serious waste of energy, but also gives the system a shorter life because of heat issues. Therefore, improving efficiency of power amplifier at power back-off condition can save energy and reduce power consumption. High-efficiency PA has become a hot issue at the present stage of research.In this paper, we focus on the study of Doherty power amplifier. And the Class E amplifier is used in Doherty structure to improve efficiency at the power backoff. Firstly,we analyze the working principle of Doherty PA theoretically and the factors which impact efficiency and linearity. BLF6G10-200RN which is manufactured by NXP Corporation is used to design Doherty PA which works for multi-carrier GSM communication. In the simulation, we study the impact of offset line and gate voltage on efficiency, gain and linearity of Doherty PA in details. The measurement results show the Doherty PA exhibits a drain efficiency of 45.6% at 50-dBm output power (6dB back-off ), and the IM3 is -33dBcThis paper analyzes the operation characteristics of shunt capacitor Class E, parallel circuits Class E andλ/ 4 transmission-line Class E theoretically. The shunt capacitor Class-e PA andλ/ 4 transmission-line Class E PA which used GaN power transistor NPTB0025 have been designed at 1GHz.When the output power is 42.5dBm, their efficiency are 88.17% and 84.67%,respectively. Finally, when the output power is 40dBm(5.6dB backoff), the efficiencies of two kinds of Class E Doherty PA will be 79.89% and 74.72%, respectively. They can improve the efficiency of Doherty PA in the power back-off.