High Repetition Frequency Subnanosecond Avalanche Marx Generator

Ultrawideband electromagnetic pulses have sub-nanosecond rise time and repetition frequency above 100 kHz. Ultrawideband characteristics make it increasingly used in biomedical, intentional electromagnetic interference, and other fields. Avalanche Marx circuits are an important way to generate high-voltage sub-nanosecond pulses with high repetition rates. However, traditional avalanche Marx circuits (TAMCs) are difficult to achieve a repetition rate of 100 kHz and often fail when they reach kilohertz. The second-stage transistor is extremely vulnerable to damage, which is the principal cause of circuit failure. In this article, through the analysis of its discharge mechanism, it is found that the damage to the second-stage transistor is related to the slow ON-speed of the first-stage transistor. In fact, the first-stage transistor is the last to be avalanche broken down, causing the already-opened second-stage transistor to be subjected to enormous electrical stress for an instant. This electrical stress is the passive lift voltage of the second-stage transistor, which is the direct cause of easy damage to the second-stage transistor. Therefore, an improved avalanche Marx circuit (IAMC) is proposed. By connecting a protection resistor in series with the second-stage transistor, the passive lift voltage is suppressed. In order to verify the high refrequency capability of this circuit, a 20-stage pulse generator using an IAMC is developed. It achieves a rise time of 230 ps in a 50- $\Omega $ load, an amplitude of 1.65 kV, and a repetition rate of 100 kHz. After adding the necessary cooling device, it finally achieves a stable output of 230-ps rise time, 730-V amplitude, and 700-kHz repetition rate on a 50- $\Omega $ load.