[SI-LIST] Re: Bypass vs Decoupling capacitors

Zhangkun, are you talking about trace inductance as in:

VRM => trace => decoupling => trace => loads

OR

VRM => trace => planar island w/ decoupling?

I am talking about the second case.  The first case has high impedance.

Power plane SRF is a function of geometry and Er.  The issue is what is the 
relative cost and headaches to damp the planes making them into 
transmission lines, versus chopping them up.

100 ohms sounds quite high.  We would be thinking in the low ohms or 100's 
of mohms.  The difficult part is the attachment inductance.  If I have a 
perfect resistor at 500mohms, but have to attach through 1nH of inductance, 
then at 1GHz, the inductive reactance is more than 12 times the resistance 
and the phase will be about 85 degrees.   Even using an IDC type structure 
we are not going to get close to the order of magnitude improvement needed.

Now, the one thing that I have not given too much thought to is whether we 
can get away with inductive terminations if we remain resistive through the 
first few harmonics of the board SRF.

Regards,


Steve.
At 06:25 PM 8/27/2004 +0800, Zhangkun wrote:
>istvan and steve
>
>I want to add some comments on this topic.
>
>1.The power delivery system, which uses traces not plane, will have some 
>defect for the leading inductance. We have done a lot of simulation about 
>the leading inductance of decoupling capacitor. When the trace is taken 
>placed by plane, the ESL gets less of about 6db.
>
>2.The resonance about power plane could be eliminated by means of some 
>effort. The frequency could be extended to about 1GHz or higher. However, 
>in some product PCB, there is no space for this kind of measures. The PCB 
>is too crowded. AVX has provided some high-ESR capacitor, whose ESR could 
>be as large as 100 ohm.
>
>3.Using trace for power delivery could be used for some special circuit 
>such as PLL. There are some paper in IEEE International Symposium on EMC 
>2003 on this topic.
>
>Best Regards
>
>Zhangkun
>2004.8.27


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: