[SI-LIST] Re: Capacitors and Anti-resonance

Daniel,

If you are worried about capacitor-capacitor antiresonance, it usually occurs 
at 
low enough frequencies that physical separation on the board can be neglected.  
You can try 'what-if' scenarios with the assumed capacitors using either SPICE 
or spreadsheets that plot the cumulative impedance of multiple capacitors.

Regards,

Istvan Novak
SUN Microsystems

        Delivered-To: si-list@xxxxxxxxxxxxx
        From: "Paradis, Daniel" <Daniel.Paradis@xxxxxxxxxx>
        To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
        Subject: [SI-LIST] Capacitors and Anti-resonance
        Date: Tue, 29 Jul 2003 09:57:46 -0400
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        I started to use only 0.1uF decoupling caps on our latest designs.
        This is to avoid the anti-resonance effect that occurs when using 2
        different caps near each other.
        The rule of thumb is to use the largest cap available for the package. 
        So far I got good results, but I was wondering....
        
        Is-there a simple way to determine the distance between 2 different
        decoupling caps beyond which there is no anti-resonance effect?
        
        In other words..
        Say that I stick to this general rule of using only one cap.
        It seems to me that there could be exceptions to that rule.
        In the case of a high speed clock buffer for instance; 
        I could need 0.0047uF instead of 0.1uF
        If this clock buffer is located far from other parts of the design. 
        Can I avoid anti-resonance?
        
        
        Daniel Paradis
        Staff Electrical Engineer
        Digital Subscriber Networks
        
        Scientific-Atlanta, Inc.
        5030 Sugarloaf Parkway, ATL 1.3468
        Lawrenceville, GA 30042
        Tel: (770) 236-7896
        Fax: (770) 236-2449
        
        
        
        
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Istvan Novak            Sun Microsystems, Inc.
Istvan.Novak@xxxxxxx    Workgroup Servers, BDT Group,
                        One Network Drive, Burlington, MA 01803  
                        Phone: (781) 442 0340

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