[SI-LIST] Re: Bypass vs Decoupling capacitors

Zhangkun, using English units and the telegrapher's equations we get:

31.9E-9H * height / area for inductance and 225E-15*Er/Height for capacitance
Consequently, we have sqrt(31.9E-9/( Er*225E-15)) * height or 377 * height 
/ sqrt( Er )

Regards,


Steve.
At 10:20 AM 8/28/2004 +0800, Zhangkun wrote:
>Steve
>
>Maybe we are different on the defination of the impedance of plane pair. 
>What is your defination? I use 2D transmission line theory to define the 
>impedance of plane pair.
>
>Best Regards
>
>Zhangkun
>2004.8.28
>----- Original Message -----
>From: "steve weir" <weirsp@xxxxxxxxxx>
>To: "Zhangkun" <zhang_kun@xxxxxxxxxx>; <istvan.novak@xxxxxxxxxxxxxxxx>
>Cc: <si-list@xxxxxxxxxxxxx>
>Sent: Friday, August 27, 2004 10:34 PM
>Subject: [SI-LIST] Re: Bypass vs Decoupling capacitors
>
>
> > Zhangkun, the issue is what connects the capacitors to the IC.  If it is
> > traces the inductance will be very high, and that is not what I 
> propose.  A
> > 4 mil board in FR-4 should come in at about 0.75 ohms.
> >
> > Regards,
> >
> >
> > Steve.
> > At 09:25 PM 8/27/2004 +0800, Zhangkun wrote:
> > >Steve
> > >
> > >If the thickness of dielectric is about 4mil, the impedance of plane pair
> > >could be about 5-10 ohm. With good fanout tech, the inductance could be
> > >controlled below 0.5nH. By the way, carefully selecting decoupling
> > >capacitor is also helpful.
> > >
> > >Best Regards
> > >
> > >Zhangkun
> > >2004.8.27
> > >----- Original Message -----
> > >From: "steve weir" <weirsp@xxxxxxxxxx>
> > >To: "Zhangkun" <zhang_kun@xxxxxxxxxx>; <istvan.novak@xxxxxxxxxxxxxxxx>
> > >Cc: <si-list@xxxxxxxxxxxxx>
> > >Sent: Friday, August 27, 2004 9:10 PM
> > >Subject: Re: [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
> > > >
> > > >
> >
> >
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