Equation 6 · When the Substrate Became the Product
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This mathematical expression combines the displayed quantities; its precise role follows from the surrounding article text. Read the equation part by part below; each part has a contextual explanation and a link to its mathematical background.
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Symbol C_fix
ix is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.
subscript
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What the article says around this equation
where collects driver, receiver, bump and pad capacitance, is capacitance per unit length of the conductor, is the reach, and is the signalling swing. Two assumptions are doing the work and both deserve stating. First, this treats the link as a lumped capacitance rather than a transmission line — reasonable for a few millimetres of on-package wire at moderate rates, wrong once the link is long or fast enough to need equalisation, retiming and serialisation, at which point the fixed circuit overhead dominates and the linear term stops being the whole story. Second, it ignores clocking and idle power, which for real links are not negligible.
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