[SI-LIST] : Re: Charge moving from decoupling capacitors

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From: Barry Ma ([email protected])
Date: Thu May 18 2000 - 09:25:28 PDT

Vinu,

I am glad to hear of different opinion to my second question:
"Do we really have to limit the distance letting the charge have enough time to move from the cap to the chip during the rise time interval?"

You said: "The decap should be much closer than 0.5 Tr to be of use."

If Tr = 1 ns, the corresponding distance is approximately equal to 14 cm in FR4. There's no problem to locate decaps much closer than 7 cm, following your opinion. If Tr = 0.2 ns (likely happens in 5 - 10 years), it might be difficult to implement it - much closer than 1.4 cm. Then further Tr = 0.1 ns, ... much closer than 0.7 cm, and so on ... That's why I raised the question.

Can you detail your opinion? Thanks.

Barry Ma
[email protected]

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