Analysis of tilting load-lines in AlGaN/GaN broadband uniform distributed amplifiers

This paper presents a general analysis of tilting load-lines in uniform distributed power amplifiers (UDPA). By means of an ideal equivalent circuit, the dependency of the load-line behavior of the first transistor on design parameters is examined. A DC-15 GHz UDPA designed in a 0.25 µm AlGaN/GaN technology is employed to verify the undertaken theoretical analysis by large-signal simulation and thermal IR-imaging results. The theoretical analysis shows that the two most effective remedies are transistor tapering and drain-line tapering to maintain the first transistor in the safe operating region. Nevertheless, in the presented AlGaN/GaN UDPA design power absorption by the first transistor at certain frequencies could not be suppressed by drain-line tapering due to design specific constraints.