[SI-LIST] Re: Decoupling for PLL (continued)
- From: "Charles Grasso" <cgrassosprint1@xxxxxxxxxxxxx>
- To: "steve weir" <weirsp@xxxxxxxxxx>, <zhang_kun@xxxxxxxxxx>
- Date: Sun, 5 Sep 2004 21:35:59 -0700
Hi Steve,
Yes I see that but typically don't you want a low
ESR cap for low power distribution imedance after
\the ferrite. This isn't an issue with plane resonance
(I think!)
20nH and 4.5uF have a resonance at 500kHz or so.
So its possible that the bulk cap is reonating with
the ferrite and its connections?
-----Original Message-----
From: steve weir [mailto:weirsp@xxxxxxxxxx]
Sent: Sunday, September 05, 2004 6:55 PM
To: zhang_kun@xxxxxxxxxx; cgrassosprint1@xxxxxxxxxxxxx
Cc: si-list
Subject: Re: [SI-LIST] Re: Decoupling for PLL (continued)
Charles and Zhangkun, if this is a series LPF somewhere in that network you
need enough resistance to damp out the reactive impedance. If you just
have a ferrite bead and a low ESR ceramic then Zhangkun is right, that
network will have a high Q. If this is a filter constructed as a shunt
notch ( unusual ), then depending on the external network, it may or may
not peak.
Steve.
At 08:59 AM 9/6/2004 +0800, Zhangkun wrote:
>Chas
>
>Ceramic cap is of no use. It is easy to resonate when low ESR caps are
used.
>
>Best Regards
>
>Zhangkun
>2004.9.6
>----- Original Message -----
>From: "Charles Grasso" <cgrassosprint1@xxxxxxxxxxxxx>
>To: <zhang_kun@xxxxxxxxxx>
>Cc: "si-list" <si-list@xxxxxxxxxxxxx>
>Sent: Monday, September 06, 2004 9:36 AM
>Subject: [SI-LIST] Re: Decoupling for PLL (continued)
>
>
> > Dear Zhangun,
> >
> > It just so happens that I have just been fighting a
> > noise problem witha ferrite bead /capacitor combo.
> > In my case it turned out that a low ESR ceramic cap
> > was required rather than a large electrolytic.
> >
> > Could this be the problem..
> >
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of zhangkun 29902
> > Sent: Saturday, September 04, 2004 4:25 PM
> > To: cgrassosprint1@xxxxxxxxxxxxx
> > Cc: si-list
> > Subject: [SI-LIST] Re: Decoupling for PLL (continued)
> >
> >
> > Chas
> >
> > I used bead. It resonated below 1MHz for the capacitor is too many.
> >
> > Best Regards
> >
> > Zhangkun
> > 2004.9.5
> >
> > ----- Original Message -----
> > From: Charles Grasso <cgrassosprint1@xxxxxxxxxxxxx>
> > Date: Sunday, September 5, 2004 6:33 am
> > Subject: [SI-LIST] Re: Decoupling for PLL (continued)
> >
> > > Hi Zhangkun,
> > >
> > > Its very important to differentiate between an inductor and a
> > > ferrite bead.
> > > A ferrite bead typically has minimal impedance in the kHz range
> > > and really
> > > only
> > > starts to kick in in the 10s of MHz range. An inductor, on the
> > > other hand,
> > > can
> > > exhibit LARGE reative impedance in the kHz range (depending on the
> > > value) -
> > > but
> > > will also exhibit resonances that need to be damped.
> > >
> > > Chas
> > >
> > > -----Original Message-----
> > > From: si-list-bounce@xxxxxxxxxxxxx
> > > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Zhangkun
> > > Sent: Thursday, September 02, 2004 10:53 PM
> > > To: si-list
> > > Subject: [SI-LIST] Decoupling for PLL (continued)
> > >
> > >
> > > Dear all
> > > Recently, I have done some measurement. It is found that when the
> > > bead(inductor) is used, the power ground noise at 333KHz from VRM
> > > is larger.
> > > There is some noise near the clock frequency points.
> > >
> > > For example, the output clock of PLL is 50MHz. At 50.333MHz and
> > > 49.667MHz,there is noise, which is in proportion to the noise at
> > > 333KHz. Maybe the PLL
> > > modulates the noise of VRM into the output clock.
> > >
> > > Is there any SPICE model for PLL?
> > >
> > > Best Regards
> > >
> > > Zhangkun
> > > 2004.9.3
> > >
> > >
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