Research On High Efficiency High Power GaN Semiconductor Amplifier

Nowadays, wireless communication is everywhere. The aerospace and radar communication systems, wireless routers and Bluetooth communication are all results of applications of wireless microwave communication. With the development of the communication systems, increasing demand is proposed to microwave power amplifiers. Both the first generation of semiconductor which represented by Si and the second generation of semiconductor which represented by Ga As can not fully meet the high frequency high power requirements of the system. However, the third generation of semiconductor materials which represented by Ga N has the excellent characteristics of high working frequency, high power density and high power added efficiency at the same time, and is the most important choice of microwave power device and microwave monolithic integrated circuit applications.Under this research background, thorough research on the Al Ga N/Ga N HEMT power amplifier is presented in this dissertation, including the electrical characterization of the device, establishment of the small signal and large signal models of the device. The key point is the study on high efficiency high power microwave amplifier. S-band and C-band high efficiency and high power Ga N-based solid state amplifiers are designed and realized. The main research results of the thesis are as follows.1. Device characterization and analysis of Al Ga N/Ga N HEMT are carried out. Thorough characterization and analysis of Al Ga N/Ga N HEMT with 1.25 mm gate-width are performed, including the output characteristic, transfer characteristic, Schottky characteristic, breakdown characteristic, small signal S-parameters and power characteristics are all measured. A comprehensive evaluation of the capability of a device in high frequency and high power applications is proposed. The variation of the frequency characteristics of the device with the bias conditions is studied to optimize the bias point for applications.2. An improved EEHEMT model and a new device model for HEMT are established. A new 19 elements small signal equivalent circuit model is set up. The parasitic parameters and intrinsic parameters of the device are extracted by using the measured multi bias S-parameters. A highly fitting accuracy for S-parameters is obtained. At the same time, it is found that the fitting accuracy of output characteristic is poor by substitution the transfer characteristic and parasitic parameters into the EEHEMT model developed by By combining the test results of output characteristic and tanh function, a Kink current item is introduced to improve the fitting accuracy of output characteristic and power-added efficiency at the same time.3. A research on S-band high efficiency high power amplifier is carried on. A class-AB power amplifier operating from 1.8GHz~2.2GHz is designed and fabricated by using the established device model on the self-developed Al Ga N/Ga N HEMT with 10 mm gate-width. To improve the power-added efficiency of the amplifier, microstrip open stub lines are used to form harmonic tuning networks. The networks control the second-harmonic of the device effectively and improve the efficiency and linearity of the amplifier. To realize wide-band design of the amplifier, a method of multi-stage impedance transformation networks is proposed and an ideal band-width is obtained. The developed amplifier operates at a bias voltage of 40 V. In the whole frequency range, the output power is larger than 80 W and the power-added efficiency is over 70% in pulse mode. In CW mode, the output power is larger than 50 W and the power-added efficiency is over 60%.4. A C-band internally-matched high efficiency high power amplifier is realized. Thorough research on internally-matched method is carried out. The impedances at fundamental frequency and second harmonic frequency are obtained by model simulation. Matching networks with harmonic tuning circuits are brought out by internally-matched technology inside the package. To make the circuit as simple as possible, a λ/4 transmission line at fundamental frequency is introduced into the harmonic tuning network to make the second harmonic short. At fundamental frequency, the harmonic tuning network performs as open. The amplifier working from 3.7GHz~4.2GHz is designed based on an Al Ga N/Ga N HEMT chip with 10 mm gate-width developed by the Key Lab. The bias voltage is 40 V.In pulse mode, the amplifier exhibits an output power over 100 W, a power-added efficiency over 65% and a power gain larger than 17 d B. At 4GHz, the amplifier achieves an output power of 107.4W and a power-added efficiency of 72.1%, which is the highest power-added efficiency among the C-band power amplifiers with over 100 W output power. In CW mode, the output power is larger than 60 W with the power-added efficiency over 63%.5. A research on C-band internally-matched synthetic high efficiency high power amplifier is carried on. Two Al Ga N/Ga N HEMTs with 10 mm gate-width are synthesized of chip level by further combining the internally-matched technology and the power synthesis technology. By doing this, the insertion loss caused by power synthesis can be reduced as much as possible. The power combining circuit is realized by Wilkinson power divider. While working as a power combining circuit, the power divider transfers the impedances of the devices. The method of harmonic tuning and the network topology are same as those of the single chip internally-matched amplifier. The developed amplifier operates from 5.2GHz to 5.8GHz and the bias condition is Vds=40V, Vgs=-2.4V. The pulse output power of the amplifier is larger than 155 W, the power-added efficiency is over 65% and the power gain is higher than 12.9d B. At 5.6GHz, a performance of 166 W output power, 69.4% power-added efficiency and 13.2d B power gain is obtained. In CW mode, the amplifier exhibits an output power over 85 W and a power-added efficiency over 50%.In summary, thorough researches on large signal model and parameter extraction of Ga N device, harmonic tuning method of amplifier, realization of S-band and C-band high efficiency high power amplifiers are carried out in this dissertation. The performances of the amplifiers have reached the high level in the world. The research findings establish the important foundation and clear directiondesign direction for the design and realization of amplifiers with higher efficiency and higher power.