RE: [SI-LIST] : Decoupling capacitors (again!)

From: Istvan Novak - Board Design Technology ([email protected])
Date: Thu Aug 17 2000 - 16:09:19 PDT

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Larry,

If my math is correct, 0.02 ohms at 200MHz represents about 15pH of inductance. Not
easy, but today we can measure such low values with vector network analyzers. With
two-port measurements, the limit is really due to the probe configuration and
connection. With nothing fancy, you can go down to a few picohenrys with the residual
inductance.

Regards

Istvan Novak
SUN Microsystems

        X-Unix-From: [email protected] Thu Aug 17 17:34:42 2000
        From: "Larry Miller" <[email protected]>
        To: Martin J Thompson <[email protected]>, si-list
<[email protected]>
        Subject: RE: [SI-LIST] : Decoupling capacitors (again!)
        Date: Thu, 17 Aug 2000 13:51:49 -0700
        MIME-Version: 1.0
        
        Twenty milli-ohms. 0.02 ohm. At 100 MHz. How does one measure such a
        curiosity?
        
        Thanks,
        
        Larry Miller
        (Not the other Larry)
        
> -----Original Message-----
> From: Martin J Thompson [SMTP:[email protected]]
> Sent: Wednesday, August 16, 2000 11:58 PM
> To: si-list
> Subject: RE: [SI-LIST] : Decoupling capacitors (again!)
>
> Larry, another question on buried capacitance...
> What is it about Hadco's material that allows you to get 2mils separation?
> Can this not be achieved with straight FR-4?
>
> Thanks,
> Martin
>
> <snipped for context>
> >>> Larry Smith <[email protected]> 16 August 2000 23:55:52 >>>
> It turns out that the spreading inductance of power planes
> spaced 4 mils apart will give you roughly 20 mOhms at 100 MHz. We are
> using Hadco 'buried capacitance' planes that are 2 mils apart in many
> of our products to get lower impedance.
>
>
>
>
> TRW Automotive Advanced Product Development,
> Stratford Road, Solihull, B90 4GW. UK
> Tel: +44 (0)121-627-3569
> mailto:[email protected]
>
>
>
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Istvan Novak Sun Microsystems, Inc.
[email protected] Workgroup Servers, BDT Group,
                        One Network Drive, Burlington, MA 01803
                        Phone: (781) 442 0340

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• Next message: Chris Bobek: "[SI-LIST] : Awkward analog power filtering"
• Previous message: Larry Smith: "RE: [SI-LIST] : Spreading Inductance?"
• Maybe in reply to: Martin J Thompson: "[SI-LIST] : Decoupling capacitors (again!)"
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