Importance of Impedance Matching

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With regards to ringing. Usually ringing is an effect caused by the other issues (reflections due to impedance mismatch, improper terminations, improper trace layout, uncompensated inductance or capacitance, etc.) Actually in my experience the largest contributor to ringing is improper grounding. A weak current return path is guaranteed to give you ringing.

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Excellent description, thank you. I can now say that I understand what ringing looks like, how to prevent it, and what bad layout practices can lead to it.

What I don't understand is the physics behind it. I know that an impedance mismatch can cause it, but why? Is it something to do with reflections? Also, how does this explanation on Wikipedia fit in with the idea of ringing resulting from an impedance mismatch?

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[...ringing] happens when an electrical pulse causes the parasitic capacitances (http://en.wikipedia.org/wiki/capacitor) and inductances (http://en.wikipedia.org/wiki/inductor)[citation needed (http://en.wikipedia.org/wiki/wikipedia:citation_needed)] in the circuit (i.e. those that are not part of the design, but just by-products of the materials used to construct the circuit) to resonate (http://en.wikipedia.org/wiki/resonance) at their characteristic frequency (http://en.wikipedia.org/wiki/frequency).

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Thanks again,

Jon