[SI-LIST] Re: nonlinear in power ground noise of clock driver

Taking what I said "This gives a rough inductance
number" to indicate that I was not aware of the
loss may not be exactly what I was getting at.
What I may have been getting at is that the bead
is not a resistor.  Yes there is loss.  Yes there
is inductance.  I guess that rough may not be 
interpreted as having a lack of accuracy.  Perhaps
I should have used a more precise term.  The 
results, as observed in a situation that was
quite similar to the original post, happen to
have occurred.  Using a bead with some capacitance
and loading the result with a clock chip that 
has a little bit of SSO at a frequency near the
resultant resonant frequency, even if there is
some loss, will cause some problems.  

I am sorry if I caused you some concern.  I
will try to implement better descriptive language
in the future.

dav0

--- Brent DeWitt <bdewitt@xxxxxxxxxxxxx> wrote:
> David,
> 
> I think you may have started with a bad assumption by modeling the bead as
> equivalent L only to get Z.  The manufacturer should have curves for the
> loss tangent of the bead at various frequencies. Filter beads are designed
> to have the loss component dominant in the optimum design frequency range.
> 
> Brent DeWitt
> Datex-Ohmeda
> Louisville, CO
> 
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Dav0 Lieby
> Sent: Thursday, December 04, 2003 11:55 AM
> To: Glick, Gene (IndSys, Interlogix); SI-LIST
> Subject: [SI-LIST] Re: nonlinear in power ground noise of clock driver
> 
> 
> I understand that the bead is  a little
> lossy.  It is also an inductor.  In the
> instance that I talked about I calculated
> the inductance by using the impedance at
> frequency numbers associated with the
> bead.  This gives a rough inductance
> number.  The inductance is much higher
> than the package would indicate alone.
> Take a look at some curves.
> 
> dav0
> David Lieby
> Siemens Medical Systems, Ultrasound Division
> 
> 
> 
> --- "Glick, Gene (IndSys, Interlogix)" <gene.glick@xxxxxx> wrote:
> > I'm no expert in beads, but I thought they exhibit a frequency dependent
> > resistance (as opposed to Z, like an inductor).  If you are correct about
> a
> > resonance between the bead and the capacitor, in theory, it would be due
> to
> > the package inductance of the bead, right?  If that's true, wouldn't a
> > resistor have the same problem?  Maybe the package size you used was
> > different, and the resonant frequency moved elsewhere out of the trouble
> > zone.
> >
> > If beads do exhibit inductance, then how much so?
> >
> > gene
> >
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Dav0 Lieby
> > Sent: Thursday, December 04, 2003 12:42 PM
> > To: SI-LIST
> > Subject: [SI-LIST] Re: nonlinear in power ground noise of clock driver
> >
> >
> > 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.
> >
> > dav0
> > David Lieby
> > Siemens Medical Systems, Ultrasound Division
> >
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