[SI-LIST] Re: nonlinear in power ground noise of clock driver
- From: Zhangkun <zhang_kun@xxxxxxxxxx>
- To: si-list <si-list@xxxxxxxxxxxxx>
- Date: Fri, 05 Dec 2003 17:30:55 +0800
Dear All:
We re-measured the noise of CDC2516. We made one mistake when we measure the
noise yesterday. Now the simulation and measurement agree to each other. There
is no non-linear.
Sorry for disturbing.
Best Regards
Zhangkun
2003.12.5
----- Original Message -----
From: "Rich Peyton" <p2rich@xxxxxxxxxxxxx>
To: <gene.glick@xxxxxx>; <si-list@xxxxxxxxxxxxx>
Sent: Friday, December 05, 2003 3:35 AM
Subject: [SI-LIST] Re: nonlinear in power ground noise of clock driver
> Here's an interesting article on Ferrite beads that would be of interest =
> to
> you. =20
>
> http://www.ce-mag.com/archive/02/11/may.html
>
>
> Rich
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
> On
> Behalf Of Glick, Gene (IndSys, Interlogix)
> Sent: Thursday, December 04, 2003 1:40 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: nonlinear in power ground noise of clock driver
>
>
> Can someone enlighten me on ferrite bead behaviour? My rudimentary =3D
> understanding of these non-linear devices (and I've never persued it any =
> =3D
> further) is that they act as frequency dependent resistors. Do they =3D =
> have
> inductance as well? What other non-linear stuff is going on there?
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx =
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On
> Behalf Of Raymond Anderson
> Sent: Thursday, December 04, 2003 1:23 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: nonlinear in power ground noise of clock driver
>
>
> In this particular case with the info given I can't be sure if the =3D
> difference seen is caused by just the difference in the decap ESR or by =
> the
> =3D difference in ESR combined with the LC filter design. I'd kind of =
> guess it
> is a =3D function of the ceramic cap having a much lower ESR.
>
> As Dav0 wrote, LC power filters can be very problematic is not designed
> correctly. The problem stems from the fact that the filter (be it pi, t, =
> =3D
> or L
> section) is being driven from a very low impedance source (say 10's of
> milliohms or less) and is loaded by a moderate (10's or 100's of ohms) =
> =3D
> load. The large ratio of load to source impedance can cause huge (10 or =
> 20
> dB =3D or
> more) peaking in the filter's response. A filter that you might hope has =
> =3D a
> nice low pass roll-off at about 10 kHz may have 20 dB peaking very near =
> =3D to
> that frequency. A person might think they could synthesize a proper =3D
> low-pass filter using classical synthesis methods to produce a nice
> Butterworth =3D (or
> whatever) LPF. On paper you can, but you will find the element values =
> =3D are
> essentially unrealizable. A filter that is driven from near zero =3D =
> impedance
> into say a 100 ohm load with a cutoff freq of around 10 kHz can require
> Henries of inductance and perhaps Farads of capacitance (not the sort of
> thing you want on your PCB. You can actually measure more noise on the =
> =3D
> filter output than on the input (due in part to the different impedance =
> =3D
> levels). The typical cure is to place a small amount of resistance in =
> series
> with the inductor to effectively de-Q it and limit the circulating =
> current
> or as =3D Dave mentioned, go to a RC filter instead of an LC filter. =
> Build
> yourself a =3D good=3D20 spice model of the filter and play around with =
> it to
> understand what is =3D going=3D20 on. BTW, you can generate a pretty =
> good model
> for the ferrite or =3D powdered iron=3D20 inductive element, but you =
> won't find
> it in the vendor's data sheets or =3D web site.
>
>
>
>
> -Ray Anderson
> Staff SI Engineer
> Sun Microsystems Inc.
> Menlo Park, CA
>
>
> Dav0 Lieby wrote:
>
> >I had this experience a while ago.
> >It boils down to the bead and the
> >capacitance. We found a resonant
> >circuit. Various capacitors gave
> >huge noise results, another lot of
> >them was OK. The final solution
> >we did was to replace the bead with
> >a resistor, the clock chip did not
> >eat too much current so it did not
> >go out operational range. =3D20
> >
> >dav0
> >David Lieby
> >Siemens Medical Systems, Ultrasound Division
> > =3D20
> >
>
>
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