Load-pull investigation of GaN-HEMT for supply modulated applications

In this paper the potential and limitations of using GaN-HEMT for increased back-off efficiency in supply modulated applications is investigated. Based on extensive on-wafer class-AB load-pull characterization at varying supply voltage and input power the possible efficiency improvement is explored and the technology and device limitations are discussed. Post-processing of the measurement data shows a possible static efficiency enhancement from 7 % to 37 % in the 10 dB back-off region. The voltage and current dependency of an extracted large-signal output capacitance have also been analyzed. It is found that the power induced shift of the output capacitance largely contribute to the overall output impedance shift in class-AB supply modulated applications thereby preventing a good match over power and voltage for the fixed output matching network present in a fabricated amplifier.