Gallium nitride based transistors for high-efficiency microwave switch-mode amplifiers

Highly-efficient switch-mode power amplifiers are key elements in future fully-digital base stations for mobile communication. This novel base station concept reduces system energy consumption, complexity, size and costs, while the flexibility in terms of multi-band/multi-standard operation improves. In this work, innovative integrated core circuits for digital high-efficiency class-D and class-S power amplifiers based on gallium nitride technology were developed for the application in digital base stations. Therefore, high power heterostructure field effect transistors are investigated and optimized for switch-mode operation in close relation to physical device parameters like gate capacitances and on-resistance. In combination with an improved circuit design for high-speed, high-power digital switching applications, the operation of the amplifier core circuits at mobile communication frequencies between 0.45 and 2 GHz has been enabled with high circuit efficiency at the same time. Moreover, advanced technology options such as gate-recess to achieve normally-off device operation and integrated Schottky-diodes have been successfully implemented in order to improve the over-all circuit properties. Integrated circuits developed in this work enabled the realization of the worldwide first 2 GHz class-S power amplifier module.