Broadband Distortion Cancellation Technique in GaAs HJFET and GaN FET Cascode Amplifier

This paper describes broadband distortion cancellation technique in the cascode configuration composed of GaAs heterojunction field-effect transistor (HJFET) for the first stage and AlGaN/GaN heterojunction FET (HJFET), for the final stage to realize broadband low-distortion cable television (CATV) power amplifier. The device structures of GaAs HJFET and GaN FET were optimized using the Volterra distortion analysis on a load-line. The transconductance gm-profile on a load-line of the first-stage GaAs HJFET was designed to obtain the gain expansion at near Class-A operation to cancel the gain compression of the final-stage GaN FET. The gate-orientation of GaAs HJFET was optimized to achieve low distortion at lower current condition. The field-plate electrode structure of the final-stage GaN FET was optimized to improve the high-frequency distortion characteristics by reducing the capacitance nonlinearity on a load-line. The developed CATV power amplifier demonstrated low composite triple beat characteristics less than -72 dBc at low drain current condition of 380 mA under 53.7 dBmV at 865 MHz, 11.7-dB tilt, and 132 channels.