From: Kowal, Keith ([email protected])
Date: Fri Feb 25 2000 - 13:04:53 PST
I would suggest using series resistor termination, one resistor
on each end. The two resistors should be tied to a voltage
source/(plane, if permitting) and well decoupled . This works
very well for BTL/GTL type drivers.
If you are concerned about power dissipation
and resistor count you can cut the R count by half
Also avoid resistor networks at that speed...if your
Zo of the etch is 50 ohms or so then try termination
of R=40ohms on each end / simulate it - we have
done something like this with speeds up to 170mhz
> -----Original Message-----
> From: Shayle Hirschman [SMTP:[email protected]]
> Sent: Friday, February 25, 2000 9:34 AM
> To: [email protected]
> Subject: [SI-LIST] : Fast edge termination choice
> SI experts:
> I am interested in making a decision between series source termination and
> parallel termination (probably something like 100 ohms to vcc and 100 ohms
> to gnd) at the destination of a point to point route.
> I want to use the fast slew rate option of the FPGA as the clock is 150
> and there isn't much timing budget from chip to chip.
> Does series source termination defeat the purpose of selecting the fast
> slew rate option? Will it slow the edge transition time down, or will the
> signal still transition and travel as fast as if there was no termination,
> but simply be divided (thereby depending on the reflection at the
> I suspect the latter, except that I've heard people say that series source
> termination reduces EMI by slowing the edges down. Could it be that it
> reduces EMI, not by slowing the edges down, but rather just simply because
> it terminates? And that, therefore, as far as EMI goes, parallel
> termination would have a similar EMI result?
> If the edge rate does not diminish by using series source termination,
> I would prefer that method since it uses only one resistor and has no DC
> bias current as does parallel termination.
> Any suggestions?
> Thanks in advance.
> Shayle I. Hirschman, Senior Engineer
> Managing Director
> Digital Design Solutions
> [email protected]
> Phone 901/759-1802 Fax 901/759-2324
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