A measurement on electromagnetic noises from ESD generator just before and after ESD testing

It is widely recognized that electrostatic discharge (ESD) generators cause electromagnetic (EM) noises even before and after ESD immunity testing specified in the International Electrotechnical Commission (IEC) standard. This may provide inconsistent test results, whereas its mechanism is not well understood. To explain the mechanism qualitatively, the authors investigated a generation modeling of EM noises from an ESD generator in conjunction with the functional sequences of built-in relay switches and a DC high voltage power supply. To validate this model, using a magnetic field probe, the authors measure the induced noise voltages from an ESD generator just before and after ESD testing for contact and air discharges to an IEC recommended current injection target. As a result, it is confirmed that the EM noises are generated when the relay switches operate before and after ESD tests. In addition, the authors find that the noises amplitude for low voltages (Types C, D and F) are relatively smaller than the ones (Types A&B, E) induced at the testing in both the contact and air discharge modes, while these peak noises increase with charging voltages and especially the noise peaks induced after the testing reach almost the same level as the case for 4 kV ESD test in the air discharge mode. A new sequence of the built-in relay switch is also proposed for reducing the noise voltages generated after ESD testing.