Biasing Control and Protection System for GaN HEMT Power Amplifier Measurements

Depletion mode transistors, such as GaN HEMTs, are widely used in high-power RF applications. High-power RF amplifiers using GaN HEMTs are biased with large drain-source voltage, and a high current flows during its operation. Proper control of large voltage and current require precise biasing sequence and protection circuits for a reliable operation. In this study, a compact system to bias and protect high-power amplifiers is presented. It also has monitoring and data logging features. The system controls biasing sequence to turn the amplifier on/off, monitors the drain voltage, drain current, gate voltage, temperature, reflected or transmitted power, and protects the amplifier against overcurrent, high RF power, and high temperature. A microcontroller manages the biasing sequence, sensors, user interfaces, and settings. In addition to a keypad, monitoring and controlling is possible with a computer and Android device. The system is tested and verified with a 10W GaN HEMT power amplifier.