Blumlein-Generator with a GaN-HEMT in gate-boosted Operation as Closing Switch

Gate-boosted operation of a GaN-HEMT allows for an operation with a rise time significantly faster than listed in the data sheet. For a GaN-HEMT having a rise time of
approximately 4 ns under normal operating conditions a rise time of less than 1 ns in gate-boosted operation has been demonstrated. The employed gate boosting circuit compensates for the inductance in the gate circuit and the voltage drop across the inductance in the source path of the GaN-HEMT in such a way that the resonant frequency of the input circuit increases significantly and the gate can be charged more quickly. The voltage reduction due to the resulting capacitive voltage divider formed by the added series capacitor and the input capacitance of the GaN-HEMT is compensated by a sufficiently high driver voltage. A three-stage Marx circuit equipped with avalanche-rated bipolar transistors as closing switches has been used as voltage source for the driver. The gate-boosted GaN-HEMT has been tested as switch in a Blumlein configuration set up with 50-Ohm-cables as transmission lines. The contribution describes selected design details and presents measurement results
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obtained with the described test setup.