ESD試験器のケーブル共振による接触放電波形のリンギング発生と検証

抄録

The ringing due to cable resonance in contact discharge waveforms is verified by contrasting the frequencies of variations in the “transfer impedance” of an ESD generator, which is newly defined in this paper as the rate to a test voltage in the Laplace domain of the complex spectrum of the contact discharge current waveform, with those calculated from an IEC specified simplified equivalent circuit of the ESD generator using the measured return cable impedance Z_R and charging cable impedance Z_C at one end grounding in the IEC calibration environment. The transfer impedances obtained from the contact discharge measurement waveforms with and without the 2 m return cable present are compared with those from the measured impedances Z_R and Z_C of the one end grounded return cables under the IEC specified arrangement and the same arrangement as the charging cable, respectively. The result shows that the transfer impedances are confirmed to have impedance variations in the frequency range from 40 MHz to 200 MHz, which fairly correspond to the frequencies of variations in the transfer impedance calculated from the parallel impedance between the return cable and the charging cable with one end grounded. Furthermore, comparison of the transfer impedances for the measured impedances of return cables shorter than 2 m length, which are not specified by the IEC standard, with the corresponding transfer impedances for the measured contact discharge waveforms, indicates that both frequencies of the first resonance peaks are in good agreement and ringing reduces in the subsequent frequency range. In view of the fact that the transfer impedance from 40 MHz to 200 MHz can approximately be expressed as (R_B+Z_R//Z_C) where R_B having a typical value of 330 Ω is the IEC specified discharge resistance of the ESD generator, the above finding validates that the transfer impedance variations causing ringing mainly result from the parallel resonance between the return cable and the charging cable.