[SI-LIST] Re: AC coupling placement
- From: Ben Rothchild <benrothchild@xxxxxxxxx>
- To: vinu@xxxxxxxxx
- Date: Fri, 1 Feb 2002 06:25:28 -0800 (PST)
Vinu,
Thanks for the input. I forgot to mention
in my last mail that all these links are
differential PECL. Any idea what is run length
for 155-STM1 and 622-STM4. The 1.25G and
2.5G are 8B/10B coded so run lengths should not
exceed 8.
The value recommended for the AC coupling cap
is 0.01uF. Now with an ESL of say 4nH
we have w=1/(0.01uF X 4nH)^0.5=500Mhz
for the case of series resonance,
or f=79Mhz. How is this going to work
for even 155M leave alone 1.25G/2.5G.
I seem to have got something wrong. Could
you or somebody correct me.
Thank you once again,
Ben
--- Vinu Arumugham <vinu@xxxxxxxxx> wrote:
>
> Usually the AC coupling capacitor would need a
> couple of vias to connect
> to the lines. Reflections from this structure can be
> lowered by placing
> it near the receiver where the edge rate is slower
> than at the
> transmitter.
>
> If you do not have very long run lengths (>100
> bits), a 0.01uF will
> work.
>
> Thanks,
> Vinu
>
> Ben Rothchild wrote:
>
> > Hello Experts,
> >
> > I have a question on AC coupling.
> > While AC coupling a high speed serial
> > link to match levels, where should
> > the AC coupling capacitor be placed.
> > Close to transmitter/close to receiver/
> > or doesn't matter, can be placed
> > anywhere on the link.
> >
> > What should be the value of the AC
> > coupling capacitor or rather how
> > do I calculate it. Is it dependent on
> > frequency. I am trying to AC couple
> > signals of 155M, 622M, 1.25G and 2.5G.
> > Any special care to be taken at these
> > different frequencies.
> >
> > Thanks for any advice.
> > Ben
> >
> > __________________________________________________
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>
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