Ultra-fast Gate Drivers with Nanosecond Propagation Delays for GaN FETs

This paper presents the design and implementation of two ultra-fast isolated gate drivers with 2-8 ns propagation delays and very high on/off slew rates, helping achieve super high control bandwidths (over 1 MHz) for applications switching at tens of MHz. The first proposed circuit uses low-voltage differential signaling (LVDS) for signal comparison/isolation to achieve a propagation delay of less than 6.8 ns and a gate-source voltage slew rate above 8 V/ns, with rise and fall times below 0.5 ns. This approach provides isolation voltage up to 1.5 kV. The second proposed gate driver achieves an even shorter propagation delay of 2.7 ns by creating a large inductive current to quickly charge a capacitive load through a very-high-frequency (VHF) isolated transformer. The gate-source voltage is clamped between a positive turn-on voltage rail and ground, using extremely fast-switching pull-up/pull-down diodes. This design has a much lower cost and lower component count, and is more compact than the first proposed design – but it offers a lower gate-source voltage slew rate (∼2 V/ns) with rise and fall times of ∼2.2 ns.