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

  • From: Dave Cuthbert <telegrapher9@xxxxxxxxx>
  • To: weirsi@xxxxxxxxxx
  • Date: Fri, 12 Sep 2014 06:37:39 -0600

One must be careful applying DM ferrites to signal lines. As mentioned, if
the DM chokes are no identical there will be mode conversion and CM noise
can increase. A fix for this is to add a CM ferrite after the DM ferrites.
Another gotcha is line matching. The DM chokes will increase the driver
impedance above some frequency and load reflections will not be properly
terminated. If the load is resistively terminated this is not as much of an
issue.

All of this can be simulated in SPICE. LTSpice has many ferrite bead models
and one can experiment in simulation.

     Dave Cuthbert
     EMC, Analog, Power Electronics, SI consulting (presently doing power
design and EMC on an 8 kW power supply)

On Thu, Sep 11, 2014 at 6:34 PM, steve weir <weirsi@xxxxxxxxxx> wrote:

> Mode conversion is not a happy thing.
>
> Steve
> On 9/11/2014 4:11 PM, Craig Francis wrote:
> > 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
> >
> >
> > ------------------------------------------------------------------
> > To unsubscribe from si-list:
> > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >
> > or to administer your membership from a web page, go to:
> > http://www.freelists.org/webpage/si-list
> >
> > For help:
> > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >
> >
> > List forum  is accessible at:
> >                 http://tech.groups.yahoo.com/group/si-list
> >
> > List archives are viewable at:
> >               http://www.freelists.org/archives/si-list
> >
> > Old (prior to June 6, 2001) list archives are viewable at:
> >               http://www.qsl.net/wb6tpu
> >
> >
> >
>
>
> --
> Steve Weir
> IPBLOX, LLC
> 1580 Grand Point Way
> MS 34689
> Reno, NV  89523-9998
> www.ipblox.com
>
> (775) 299-4236 Business
> (866) 675-4630 Toll-free
> (707) 780-1951 Fax
>
> All contents Copyright (c)2013 IPBLOX, LLC.  All Rights Reserved.
> This e-mail may contain confidential material.
> If you are not the intended recipient, please destroy all records
> and notify the sender.
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> http://www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>
> List forum  is accessible at:
>                http://tech.groups.yahoo.com/group/si-list
>
> List archives are viewable at:
>                 http://www.freelists.org/archives/si-list
>
> Old (prior to June 6, 2001) list archives are viewable at:
>                 http://www.qsl.net/wb6tpu
>
>
>


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field


List forum  is accessible at:
               http://tech.groups.yahoo.com/group/si-list

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
 
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu
  

Other related posts: