[SI-LIST] Re: Default tap settings for SerDes

  • From: Mario Antolos <marioantolos@xxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Tue, 2 Sep 2014 23:37:35 +0200

Steve, yes that sounds reasonable, when looking thru PCI-SIG presentations,
it's clear that the fixed  -3.5 dB de-emphasis for PCI Express Gen 1, was
made as an trade-off, with respect to target channels where it is supposed
to be used.
Are there any other SerDes interface standards besides PCI Express Gen 1 &
2, that has default tap settings?








2014-09-02 22:22 GMT+02:00 steve weir <weirsi@xxxxxxxxxx>:

> You may find that for consistently built short links that fixed EQ is
> fine.  And you may even find that the default coefficients are
> adequate.  But I don't know how you get there without doing the homework
> at least once.
>
> Steve
>
> On 9/2/2014 1:06 PM, Mario Antolos wrote:
> > For SerDes transceivers with high equalization capabilites and many
> > different tap combinations, when it's "good enough" to use default
> > settings, instead of performing extensive optimal tap settings search?
> > I know that it should boil down to how much margin (losses, receiver
> > sensitivty, etc) we have, but for example in cheap consumer electronics,
> > it's cheaper to have fixed default tap setting then to have programmable
> > tap settings.
> >
> >
> > Also what are default tap settings?
> >
> > For example in PCI Express where we have:
> >
> > -3.5 dB de-emphasis, for 2.5 Gbps & 5 Gbps
> >
> > -6.0 dB de-emphasis, for 5 Gbps
> >
> >
> > Thanks, Mario
> >
> >
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