Re: [SI-LIST] : on-chip capacitance & core noise

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From: D. C. Sessions ([email protected])
Date: Wed Jul 19 2000 - 12:44:16 PDT

David Chengson wrote:
> Does anyone have some approximate numbers for
> the amount of on-chip capacitance that has been explicitly
> added to large commercial or non-commercial chips?
> I'm looking for data as it relates to explicit on-chip
> capacitance to reduce core noise.
> As an example, I heard at one point that the DEC Alpha chips
> in the mid 90's used on the order of 50nF of explicit
> capacitance for its core logic.
> If there is data on the order of magnitude
> amount of capacitance used on Sun, MIPs, Intel, Motorola, IBM
> uPs, or other large VLSI chips, I would greatly appreciate
> hearing about it.

I can only speak to the capacitance added to recent chips that
I've seen. Not CPU chips, but a customer data-path design.
We found that the chip had about 1400 mVpp of core noise on a
1.8v supply without added capacitance; the addition of about
50 nF was needed to bring it to a reasonable level. More would
have been much better.

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