RE: [SI-LIST] : RE: RC terminations on multidrop busses

Alok Tripathi (alok@ece.orst.edu)
Sat, 14 Nov 1998 16:28:33 -0800 (PST)


Hello,

The RC termination is to decrease the DC loss. The resistance
in such a case provides a match during the transition (of driver). The
capacitance blocks a DC path such that during the steady state (of
driver) there is no flow of currents in the termination resistance,
thereby reducing the losses. Also such type of
termination is often used in bipolar type of technology.

Regards,

Alok

On Fri, 13 Nov 1998, Bob Davis wrote:

> Magnus,
>
> The RC termination is usually the same as the AC termination that you think
> about. It does not matter which is first in the R - C coupling to
> ground(signal return). When this is designed, the Resistor is the energy
> absorption terminating element and the Capacitor is for the DC isolation.
> The Resistor is chosen to match the line impedance at the point of
> termination and the capacitor is chosen to couple the resistor for the high
> frequencies of the edge and discharge prior to the next edge.
>
> I like the resistor at the ground(signal return) end to make the observation
> of the termination voltage more easily seen. The circuit still works the
> same with either order of R and C.
>
> Using this termination on stubs has worked for me to reduce multiple
> reflections back to the normal line provided the stub is long enough to
> adopt a transmission line propagation mode at the frequencies.
>
> Good luck.
>
> Bob Davis, Consulting Engineer.
> Summit Computer Systems, Inc
> Signal Integrity Specialists - High Speed, Critical PCB Design
> 408-353-2706
> bob@scsi.com , www.scsi.com
>
>
> -----Original Message-----
> From: owner-si-list@silab.Eng.Sun.COM
> [mailto:owner-si-list@silab.Eng.Sun.COM] On Behalf Of Magnus Homann
> Sent: Friday, November 13, 1998 8:37 AM
> To: Roy_Leventhal@mw.3com.com
> Cc: Si-list@silab.Eng.Sun.COM
> Subject: Re: [SI-LIST] : RE: RC terminations on multidrop busses
>
>
> > Abe,
> >
> > Thanks for your reply.
> >
> > If I read it correctly, you are talking about RC terminations at each end
> > of the backplane line. Have you ever looked into RC terminations at the
> > receivers / drivers on the daughter board stubs?
>
> I have to ask,
>
> Is the RC termination you mentioned the same as an AC-termination (cap+res
> to ground from signal) or is it a low-pass filter (res in series with
> signal,
> cap to ground). I've seen both used, but have never found a reason to use
> either in my designs. Yet.
>
> Magnus Homann
> Ericsson Mobile Data Design AB
>
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