I don't know your circumstances but I can understand why in some situations adding a resistor help. In many circuits a driver side series termination is part of the circuit design to match the driver impedance to the trace impedance for source termination. The effect of this is that any reflections are absorbed by the driver when it is reflected back and therefore preserve the signal integrity at the receiving end. A side effect could be that there is less ringing which results in less EMI. You need to look closely at your design to under the mechanics of your problem and device a solution.
Alfred On February 5, 2016 1:00:25 AM PST, Amund Westin <am...@westin-emission.no> wrote: >A resistor will cause a voltage drop, and that could make problems for >the functionality. Ferrite bead will not make a DC voltage drop. > >For higher frequencies (above 100MHz) the bead is more precise >described (Z, X and R), while the impedance of a resistor is maybe not >defined. > > > >#Amund > > > > > >Fra: Amund Westin [mailto:am...@westin-emission.no] >Sendt: 5. februar 2016 09:38 >Til: 'EMC-PSTC@LISTSERV.IEEE.ORG' <EMC-PSTC@LISTSERV.IEEE.ORG> >Emne: Ferrite bead vs. resistor > > > >Had some EMI issues, caused by a LVDS line. > >By inserting CM chokes, the radiation seemed to lower significant. > >Inserting resistors as well (aprox 22 ohm) made it even better. I can’t >check the eye curve, but 22ohm makes no problem with the EUT operation. > > > > > >But, should the series resistor be replaced by ferrite beads instead? >Will it make any really differences? > >The LVDS clock is approx 40MHz and data rate 160Mbps. > > > >#Amund > > > > > > >- >---------------------------------------------------------------- >This message is from the IEEE Product Safety Engineering Society >emc-pstc discussion list. To post a message to the list, send your >e-mail to <emc-p...@ieee.org> > >All emc-pstc postings are archived and searchable on the web at: >http://www.ieee-pses.org/emc-pstc.html > >Attachments are not permitted but the IEEE PSES Online Communities site >at http://product-compliance.oc.ieee.org/ can be used for graphics (in >well-used formats), large files, etc. > >Website: http://www.ieee-pses.org/ >Instructions: http://www.ieee-pses.org/list.html (including how to >unsubscribe) >List rules: http://www.ieee-pses.org/listrules.html > >For help, send mail to the list administrators: >Scott Douglas <sdoug...@ieee.org> >Mike Cantwell <mcantw...@ieee.org> > >For policy questions, send mail to: >Jim Bacher: <j.bac...@ieee.org> >David Heald: <dhe...@gmail.com> -- Sent from my Android phone with K-9 Mail. Please excuse my brevity. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
