Reduction Effect on Charging Cable Arrangement of Ringing Damped Oscillations in Calibration Waveform of Discharge Current from ESD Generator

In order to investigate the influence of charging cable arrangements on contact discharge waveforms, which is not specified in the IEC calibration environment of ESD generators, we measure contact discharge waveforms by using four different models of domestic and foreign ESD generators with test voltages of 4 kV and 8 kV, including two battery-powered models, under different arrangements of around a 2 m charging cable, and analyze their spectra to clarify the effect of the charging cable arrangements on the ringing. The result confirms from the measured waveforms and their spectral characteristics that the ringing tends to be suppressed in the calibration measurement of ESD generators when the charging cable is placed floating from the metal plane compared to when the cable is placed along the metal plane. To verify this finding, we show the reduction effect of the cable arrangement change on the ringing by an energy ratio (ER) of the difference waveform between the measured contact discharge waveform and the IEC specified waveform, which corresponds to the amount of ringing generation, to reveal that the calculated values of ER are definitely reduced for the floating charging cable arrangement. Furthermore, the input impedances of a 2 m long return current cable grounded at one end under different arrangements are measured to calculate the spectra of the contact discharge waveform derived from a simplified equivalent circuit based on the IEC standard in the Laplace domain of an ESD generator, which indicates that the floating cable arrangement is more effective in reducing the spectra at frequencies below 40 MHz.