A Frequency Response Test Device for Nano-Second Coaxial Resistor Divider

A resistor divider with good frequency response to nano-second signals is usually used in the calibration of VFTO sensors, serving as comparative measurement. And a coaxial cavity is usually used in the calibration process to reduce the loop inductance. In this paper, a coaxial resistor divider is developed making use of the end matching resistor of the coaxial cavity. The frequency characteristics of the resistor divider is evaluated through step-response test, in which a step signal with rise time less than 500 ps is applied. The resistor divider is designed at the end of coaxial cavity. The end matching resistor is used as the high voltage arm. And the low voltage arm is a PCB board welded with multiple low-inductance chip resistor. This structure greatly reduces stray inductance of the low voltage arm and improves the high frequency performance. To evaluate the frequency characteristics of the resistor divider, a compact square wave generator is designed. This test device is compact in structure, small in size with low stay inductance in the whole loop, resulting in a fast rising front of square wave. A wet-reed relay, as the switch of square wave generating circuit, is driven by the external magnetic field and has the advantage of fast conduction. The step response of the resistor divider has a rise time of approximately 300 ps with the overshot less than 10%.