People sometimes talk about "excess" inductance or capacitance. How does it apply to my signal integrity work?
Excess inductance is more of an RF/microwave term, coming from the matching network design widely used in microwaves and RF. The meaning of these parameters is that "if you decrease your inductance or capacitance by the excess inductance (capacitance) amount, your transmission line will be perfectly matched." The excess inductance (capacitance) value of your via will vary depending on the impedance of your transmission line surrounding your via. For signal integrity, we mostly use full capacitance, which is the value that can be used in SPICE/IBIS to predict the via, or die capacitance effects in the circuit simulation, and this is the value that IConnect TDR and VNA Software computes. We discuss techniques for measuring full inductance and capacitance in our application note on electrical characterization of packages - the techniques described in this application note are also applicable for via and connector characterization.
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