Target influence of the calibration uncertainty of ESD simulators

Up to now the target or target along with the measurement chain has been characterized by insertion loss (S₂₁ parameter). This parameter is used in uncertainty estimation based on ANSI C63 16-7 (2000) or for recalculation of the output voltage of the target into the discharge current based on P. Glattli (1996). ANSI Standard requires a very flat insertion loss of the target and measurement chain (±0.3dB up to 1GHz and ±0.75dB between 1GHz and 4 GHz). This requirement makes it possible to estimate the corresponding uncertainty contribution making certain assumptions without any simulations or calculations. This, however, can lead to overestimation. It is obvious that the IEC target based on IEC 61000-4-2 (1999) with a strong frequency dependent insertion loss does not fulfil ANSI requirements. For laboratories which use the IEC target or another target which does not fulfill ANSI requirements, the question "how big is the target contribution in uncertainty estimation?" is relevant. The paper answers this question in a new, more precise manner. The method presented here consists in measuring S-parameters, rearranging them in Z- and Y-parameters and calculating the frequency dependent transfer impedance of the target. The transfer impedance is used to calculate the discharge current from the target output voltage. The calculation and comparison in this paper is restricted to the peak current. It is performed for two targets with different frequency characteristic: a target which slightly exceeds the ANSI requirements and the IEC target which drastically exceeds them.