Gate-driver for Gate-boosted Operation of a GaN­HEMT as fast Closing Switch

Commercially available GaN-HEMTs are known to be fast semiconductor switches operating at rise-and fall times of a few nanoseconds. Recently, it has been shown in a test setup, that such a GaN-HEMT is able to switch on at a fall-time for the drain-source voltage ofwell below one nanosecond when employing a gate driver featuring capacitive coupled gate­boosted operation of the GaN-HEMT. This technique compensates partly the parasitic inductance in the gate circuit by means of a series capacitor in order to increase the resonance frequency of this circuit to allow for faster gate charging. In order to compensate for the voltage drop across this capacitor the circuit uses a three-stage Marx circuit equipped with avalanche transistors as fast closing switches, which is operated at a charging voltage of approximately 280 V per stage. The fast GaN-HEMT switch is used as closing switch in a Blumlein circuit to generate short rectangular pulses having pulse lengths of only a few nanoseconds. For this design a conservative dimensioning of the circuit has been applied. For an improved version of the driver, measures for an operation with Iess damping have been implemented. ... mehrAs a result, when operating the GaN-HEMT connected to a resistive load at a drain-source-voltage of 600 V, fall times for the drain-source voltage of approximately 0.55 ns and 0.60 ns have been measured for a load impedance of 50 ohm and 16.66 ohm, respectively. However, the measurements also showed an increase in the voltage drop along the current path through the GaH-HEMT's channel with increasing amplitude and steeper rise of the drain current, which may limit the use of this gate driving technique for a specific device or setup.