Influence of Return Current Cable Arrangement on Ringing Damped Oscillations in Contact Discharge Calibration Waveform from ESD Generator

We measure contact discharge current waveforms from an ESD generator with a test voltage of 4 kV in different arrangements of a 2 m long return current cable in order to clarify the effect of ringing damped oscillations that appear in the contact discharge calibration waveforms. The spectral features of ringing are investigated based on the spectral characteristics of composite waveforms of the measured contact discharge waveform combined with the ideal contact discharge current waveform without ringing (IEC specified waveform) given in IEC 61000-4-2, in view of the measured input impedances of one-ended grounding cable. The result shows that the ringing damped oscillations of contact discharge waveforms cause the spectra from 20 MHz to 200 MHz, but the spectra in the frequency range from 40 MHz to 200 MHz differ greatly depending on the measurement environment and cable arrangements, which hardly affect the spectra from 20 MHz to 40 MHz and over 200 MHz. The frequencies of the multiple peaks and dips alternately appearing in the spectra from 40 MHz to 200 MHz roughly correspond to the resonance frequencies of the measured cable input impedances. This concludes that the ringing damped oscillations should mainly come from the distributed resonances of the return current cable.