Building blocks for future dual-channel GaN gate drivers: Arbitrary waveform driver, bootstrap voltage supply, and level shifter

Capitalising on the high-speed switching capability of 650 V GaN FETs in power-electronic bridge-legs is challenging. Whilst active gate driving has previously been shown to help overcome adverse switching behaviour, the best results are likely to be achieved through a combination of uncompromised circuit layout and active gate driving. A fully integrated dual-channel driver would minimise external circuitry and allow power devices to be placed as close together as possible. This would facilitate simultaneous minimization of parasitic inductances in the gate-drive and power-circuit loops. Other benefits would include ease of use, lower BOM cost, and providing a step towards full integration of driver and power stage. This paper presents three circuit blocks vital to the implementation of a fully integrated dual-channel gate driver – A 100 ps resolution, digitally-controlled active gate driver IC, a sub-ns propagation delay level shifter with 200 V/ns slew-rate immunity, and a regulated bootstrap supply that maintains its output voltage regardless of any switch-node undershoot during switching events. Measurement results show the efficacy of the high-resolution active gate driver in a GaN bridge leg, and the sub-ns propagation delay of the level shifter, both fabricated in a 50 V CMOS process. Simulation results demonstrate the slew-immunity of the level shifter, and operation of the bootstrap supply. It is also inferred how to increase the voltage rating of the level-shifter and bootstrap without adversely affecting performance.