It is confusing how pulsed signals are very different from switching EMI.
Dear Sassia,
In my opinion and although they are related, pulsed signals cannot be directly compared to switching EMI.
It can be said that Switching EMI is a product of pulsed signals and it is caused by the fast rising/falling switching edges of pulsed (switched) signals.
The reason is that fast switching edges cause high frequency ringing (oscillations) due to the parasitic inductance and capacitance in a circuit. That high frequency ringing couples to the various wires/tracks of the circuit and is emitted, either as radiated emissions or conducted emissions.
I'd say it depends on what type of pulse you're talking about and in what context, but for a simple analysis, you can look at the differences in dI/dt and dV/dt. In the switching case, the radiation impulse comes from the on/off or off/on transition. A pulse might be considered as an off/on followed quickly by an on/off, but is typically impedance limited. You'll either see an exponential rise and fall curve (critically damped case) or a decaying sinusoidal oscillation. There's no actual "on" duration associated with the pulse. Note that the derivative of the transition case will look a lot like the pulse described here, so in the end, the results from the detected emission will look very similar.
For switched signals, the di/dt is high and consequently, the frequencies generated are large in number. Stray H-fields are produced which cause strong interference in the circuit. Pulses are amplitude limited and of certain frequency and , therefore, much easier to handle in terms of EMI/EMC.
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