Crosstalk suppression in a 650-V GaN FET bridgeleg converter using 6.7-GHz active gate driver

With switching transients as fast as 100 V/ns and a low threshold voltage of 1-2 V, GaN FETs in bridge-leg topologies are potentially vulnerable to crosstalk and the resultant unwanted partial turn-on, noise interference, and increased losses. Constant-strength gate drivers for GaN FETs limit switching speed to suppress crosstalk. In this work, active gate driving is shown to permit faster switching, whilst still suppressing crosstalk. This is demonstrated in a GaN FET bridge-leg converter. The control device transients are shaped to reduce crosstalk, whilst the synchronous device's gate impedance is actively varied to increase its immunity to crosstalk. This is carried out using two 6.7-GHz active gate drivers that can dynamically vary their output resistance from 0.12 Ω to 64 Ω every 150 ps during the sub-10-ns switching transients. It is demonstrated that unwanted turn-on is suppressed without incurring undershoot and oscillation in the gate, that negative spurious gate voltages can be greatly reduced, and that oscillations in the transient drain current are damped, without incurring additional loss.