Experience in simulation and measurement of GaN FET switching behavior

Due to their better figure of merits, gallium nitride field effect transistors (GaN FETs), when employed as the switching devices in power electronics applications, have better performance than conventional silicon metal-oxide-semiconductor field effect transistors (Si MOSFETs). One of the superiorities of GaN FETs is their ability to switch very fast, which results in low switching losses. However, the associated high di/dt and dv/dt can lead to severe parasitic effects in the circuit, impacting circuit operation. Therefore, the switching behavior of GaN FETs in a circuit should be investigated carefully with various circuit parasites taken into consideration. A simulation circuit model is particularly beneficial in addressing this point in that it enables observing the circuit behavior and identifying possibly existing problems before hardware implementation. In this paper, experience in building a GaN switching circuit prototype, measuring high speed switching signals, and establishing a simulation circuit model for the GaN switching circuit is presented. The prototype built involves a number of design considerations that are important in obtaining satisfactory switching behavior and measurement results. In particular, the board design conforms to certain layout rules that are especially critical for high speed switching circuits. A number of considerations about measurement and modeling are also discussed, and it turns out that probing position affects measurement fidelity enormously, and that a lumped simulation model taking critical trace inductances into consideration can predict GaN switching behavior to a reasonable extent.