Susceptibility of digital ICs to ringing EMI events

This study examines the susceptibility of idealized digital devices subjected to nondamaging rings at microwave frequencies. The device considered is a CMOS inverter whose susceptibility is linked to ring time of occurrence, frequency, amplitude and attenuation. The treatment considers unwanted excursions across the logic threshold as single logic breaches. In this paper, the device is considered to be in the logic input low state. Pulse overdrive specifications for commercial type AC devices are quantified via curve-fitting and the results extended to the case of the ring. It is shown that the voltage amplitude of the first positive ring peak required to cause a logic breach is approximately linear with increasing ring frequency. As ring frequency decreases, this susceptibility curve is shown to be asymptotic to the threshold voltage V_t.