自积分式电容分压器的频率响应特性

Frequency response characteristics of self-integralting capacitive divider

为了测量电缆中传输的ns量级脉冲高电压,设计了自积分电容分压器并开展了频率响应特性分析。为分压器设计了不同的补偿电阻,并使用含有杂散参数的等效电路进行分析。仿真结果表明:分压器低频特性的主要影响因素是等效取样电阻与低压臂电容乘积得到的时间常数;高频特性主要受电容的杂散电感和取样电阻的杂散电容影响。增大时间常数扩展低频特性时,会导致杂散参数的影响加剧而使分压器高频特性变差。采用方波实验和扫频测量两种方法实测了不同参数分压器的频响特性。结果表明:补偿电阻为550Ω的电容分压器频响上限超过2GHz;但是低频特性不足,频率下限约为1.8 MHz;而补偿电阻为6.6kΩ,且调整结构的电容分压器带宽为0.17~700 MHz,能够满足测试需求。

A self-integrating capacitive divider has been designed to measure the high voltage pulse transmitting in a cable with rising time of 1 ns.The frequency characteristics have been analysed by the equivalent circuit that comprises stray parameters of capacitive divider.The main factor affecting the lower limiting frequency is the time constant,i.e.,the product of the capacitance of the low-voltage arm capacitor and the resistance of the equivalent load.The upper limiting frequency is chiefly impacted by some stray parameters which stem from the stray inductance of the low-voltage arm capacitor and the stray capacitance of the compensated resistor.To extend the lower limiting frequency the time constant should be increased by enhancing the capacitance or the resistance,however,this often results in the debasement of the upper limiting frequency.Different compensating resistors have been designed.The amplitude-frequency response of the capacitive dividers were measured by network analyzer,meanwhile,experiment with square pulse response was also performed as a contrast.The results indicate that the upper limit of frequency response for capacitive divider with 550Ω compensating resistance exceeds 2 GHz,however the lower limit is insufficient and about 1.8 MHz.If the compensating resistor is tuned to 6.6 kΩ,the corresponding capacitive divider will have a bandwidth of 0.17-700 MHz which satisfies the demand of measurement.