[SI-LIST] Re: Ferrite Beads on Differential Signal Lines?

  • From: Randy Dawson <rdawson16@xxxxxxxxxxx>
  • To: "weirsi@xxxxxxxxxx" <weirsi@xxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
  • Date: Fri, 12 Sep 2014 14:41:03 -0700

'The National Ferrite Bead Association'
I will have to put little Gina onto that resource, she has several bead 
projects, different color ferrites, she is all over the spectrum.
> Date: Fri, 12 Sep 2014 14:30:16 -0700
> From: weirsi@xxxxxxxxxx
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Ferrite Beads on Differential Signal Lines?
> 
> While often abused, ferrite beads are a tool that have legitimate 
> purposes.  What makes no sense is to either:
> 
> 1) "Solve" a problem that doesn't exist, or
> 2) Solve a problem with inappropriate means.
> 
> Ferrite beads are very useful in these sorts of situations:
> 
> 1) As  part of a properly decoupled high insertion loss filters.
> 2) As components in EMI filters.
> 
> Places where they should not be used, or at least not used alone:
> 
> 1) As power feeds to broadband amplifiers.  (All digital logic devices 
> qualify as broadband amplifiers.)
> 2) In circuits where their low to medium frequency behavior of a high Q 
> linear inductor has not been fully considered.
> 
> Unfortunately, there have been many times that people have misused 
> ferrite beads creating bigger problems than the beads were intended to 
> solve.
> 
> The National Ferrite Bead Association reminds us:
> 
> "Ferrite beads don't kill designs.  Lazy engineers do."
> 
> Best Regards,
> 
> 
> Steve
> 
> On 9/12/2014 8:15 AM, Lee wrote:
> > It makes no sense to put ferrite beads in any signal line.  How did this get
> > started?
> >
> > -----Original Message-----
> > From: Craig Francis
> > Sent: Thursday, September 11, 2014 4:11 PM
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Ferrite Beads on Differential Signal Lines?
> >
> > SI-List,
> > I haven't seen any literature concerning using ferrite beads on each signal
> > line of a differential pair.
> > Usually only a common-mode choke is used to reduce common-mode EMI.
> >
> > Can ferrite beads be used on a differential pair to increase the the rise
> > time of the signal and reduce unnecessary high-frequency content that may
> > radiate?
> >
> > The two ferrite beads would be sized to allow the bandwidth necessary for
> > the differential signal's highest data rate.
> >
> >
> > Thanks,
> > Craig Francis
> >
> >
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> 
> -- 
> Steve Weir
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