Nanosecond pulse generator based on cascaded avalanche transistors and Marx circuits

Abstract

Avalanche transistors have been widely used in nanosecond pulse generators because of high switching speed, low jitter, small size, low intrinsic inductance, and high-frequency operation. Marx circuits based on cascaded switches are often used to increase the voltage amplitude. In this paper, some current-limiting resistors in traditional Marx circuits were replaced by diodes to speed up the charging speed, to reduce the energy loss, and to increase the repetitive frequency. The influence of capacitance and the current limiting resistor on the output voltage amplitude and frequency were analyzed. The minimum on-resistance of a single BJT was calculated to be about 2.5 Ω, and the equivalent internal resistance of the Marx circuit based on cascaded switches reduced the output voltage amplitude over the load, so multiple Marx circuits in parallel were used to increase the output voltage amplitude. By changing the number of Marx modules in parallel, the influence of the equivalent internal resistance of the circuit on the output pulse was studied. By changing the load resistance, it verified that the Marx circuit in parallel had a better boosting effect over low-resistance loads. The experiments show that nanosecond pulses with a rise time of 3.4 ns, an amplitude of 2.5 kV and a repetitive frequency of 15 kHz were obtained over a 50 Ω resistor load with four Marx circuits in parallel.