[SI-LIST] : AC Impedence / Buried Cap Question

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From: Dill, Franz @ Celerity (@)
Date: Wed Dec 06 2000 - 17:31:56 PST


All,

A fellow co-worker mentioned: with buried capacitance the location of bypass
capacitors (for that buried capacitance plane) does not matter (i.e. an IC's
bypass cap. could be 6 inches away). Is this true?

My Thoughts:
At relatively low frequencies (say 5MHz) you cannot consider buried
capacitance an AC short which would be required in allowing you to deem its
impedence negligable. With a non-negligable BC impedence bypass caps cannot
be as effective, say 6 inches away, from the IC. I forsee the potential of
a low frequecy noise being injected on a power supply in such a bypassing
configuration. Am I mistaken?

Franz.

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