Modelling the closely-coupled cascode switching process

摘要

The cascode combination of transistors is a simple and interesting way of turning a normally-on device into a normally-off one. Cascodes are usually used with wide bandgap materials such as gallium nitride (GaN) and silicon carbide (SiC) in which a wide bandgap normally-on device is connected to a silicon MOSFET. Integration of the different transistors to form a closely-coupled cascode, leads to an improvement in switching characteristics. By undertaking a detailed analysis of the closely-coupled cascode switching behaviour under constant current drive conditions, an insight into the role of the different parasitic capacitances and the current capability (related to the size) of the transistors used can be obtained. This is of great importance when designing all-GaN die-integrated cascodes. Also it provides a basis for comparing cascodes with single devices in terms of the Qg · Ron figure of merit.