GaN-HEMT in Gate-Boosted Operation as Closing Switch in a Blumlein Generator With Adjustable Pulselength

Capacitively coupled gate-boosted operation allows for a fast turn-on of a GaN HEMT. However, as part of the gate drive circuit, a voltage source exhibiting a short rise time is crucial. A three-stage Marx circuit based on avalanche transistors acting as fast closing switches has been employed as a voltage source for the driver. It has been operated at a stage voltage of approximately 280 V. The Marx circuit is connected to the capacitor inserted for compensating the inductance in series to the gate. It forms a capacitive voltage divider in combination with the gate’s voltage-dependent input capacitance, limiting the gate-source voltage. The circuit has been set up and tested successfully connected to an essentially resistive load up to a drain-source voltage of 600 V at the GaN-HEMT. With a load of 50 Ω, when operating the device at 600 V a fall time of 0.6 ns was measured for the drain-source voltage. A test with a load impedance of 16.6 Ω resulted in a respective fall time of 0.7 ns. For the generation of fast-rising voltage pulses, the closing switch has been implemented into a Blumlein generator connected to a matched load. The use of one switch at the end of each of the two transmission lines of the Blumlein configuration allows for a control of the polarity and the length of the voltage pulse applied to the matched resistive load connected to the generator.
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With a delay line in Blumlein configuration for the generation of pulses of 10 ns pulselength the generation of pulses having an adjustable pulselength of between 1 and 5 ns has been shown for positive and negative polarity of the output pulse.