雪崩管Marx电路波形振荡影响因素分析

Analysis of factors causing waveform oscillation in avalanche transistor-based Marx circuit

基于雪崩晶体管的Marx电路常用于产生高压纳秒脉冲,输出波形通常具有前沿时间百ps量级、指数型放电后沿、kV级输出电压等特征。然而这种电路结构的典型输出波形后沿通常存在振荡或畸变;Marx电路的储能电容较大时,波形前沿还会出现尖峰振荡;已有研究对此关注较少或将其归因于电路杂散参数、阻抗匹配的影响。从雪崩晶体管动态导通过程的角度进行了仿真分析,并对储能电容取值、Marx电路级数、充电电压等因素的影响开展了实验研究。结果表明,雪崩晶体管自身过压导通状态是引起波形振荡的关键因素;储能电容越大、Marx级数越低、充电电压越小,则振荡的现象越明显,振荡幅值甚至能够高于晶体管雪崩击穿形成的快前沿尖峰,此时快前沿尖峰即体现为波形前沿上的振荡。通过调整Marx电路储能电容大小、优化微带线结构等方式可改善输出波形振荡。

The avalanche transistor-based Marx circuit is often used to generate high-voltage nanosecond pulses,its output waveform usually has a rising time about hundreds of picoseconds,an exponential discharging falling edge,and an output voltage in kV-level.However,the typical output waveform falling edge of this circuit structure usually has oscillation or distortion.Meanwhile,as long as the main capacitance of Marx circuit is large enough,the spike oscillation would emerge in the rising edge of the output waveform.Previous studies have paid less attention to this or attributed it to the influence of circuit stray parameters and impedance matching.In this paper,the simulation analysis was carried out from the perspective of the dynamic switching process of the avalanche transistor,and the influences of the main capacitor,the number of Marx circuit stages and the charging voltage were studied experimentally.The results show that the operating state of the avalanche transistor in voltage ramp mode caused the waveform oscillation.The oscillation would be more obvious when the circuit has larger main capacitance,fewer Marx stages and lower charging voltage.Moreover,the amplitude of the pulse oscillation could even be higher than the fast front edge,at this time,the fast front edge could be regarded as the spike oscillation in the output waveform rising edge.The output waveform oscillation can be reduced by adjusting the main capacitance of Marx circuit and optimizing the structure of microstrip line.