Distortion analysis of low-THD/high-bandwidth GaN/SiC class-D amplifier power stages

Power amplifiers providing an output current of high precision, high bandwidth and low distortion are required in different fields like magnetic resonance imaging or motion control systems for semiconductor production processes. This paper analyzes different power stage implementations of switched-mode (Class-D) amplifiers intended for such applications. They are preferred to linear or hybrid solutions as they feature a high output power with a good efficiency at low cost and low complexity. The advent of wide bandgap (WBG) semiconductors based on gallium nitride (GaN) or silicon carbide (SiC) enables Class-D amplifiers with unprecedented performance regarding distortion and bandwidth. Comprehensive circuit simulations incorporating detailed switch- and thermal models of all relevant components are used to compare different implementations of Class-D switching stages based on GaN and SiC semiconductors with respect to output voltage distortion. The systems´ sensitivities to various parameters such as power circuit topology or output current amplitude are derived as a performance measure. It is shown that the thermal behavior of the power devices has significant influence on the output distortion and that the dual buck topology, which requires no dead time in between the turn-off and the turn-on of the bridge leg transistors, is less sensitive to parameter variations and has a better distortion performance than the conventional half bridge topology.