[SI-LIST] Re: LVPECL standard ?
- From: "Ingraham, Andrew" <a.ingraham@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 14 Aug 2003 11:35:50 -0400
Well, there is JEDEC standard JESD8-2, a somewhat outdated standard that
includes "Low Voltage Emitter-Coupled Logic (ECL)". However, it seems to be
unique to Motorola's 300K logic family, which apparently used a 3.5V (not
3.3V) supply voltage.
As for the use of ECL/LVECL with a positive supply voltage ... perhaps there
is no standard for PECL or LVPECL because there doesn't need to be one. You
just redefine which voltage you want to call "ground" or "0V" and everything
else is the same, just offset by that amount.
I could use TTL with a -95V supply (Vcc) and -100V return (Vss) and it would
work just fine. It's just a matter of one's frame of reference. The IC
can't tell the difference.
JEDEC and other standards often lag what the industry is doing. In this
case I think the industry found it desirable to migrate toward 3.3V and then
2.5V, but with *ECL being in somewhat less common usage than other logic
families, perhaps the standards organizations such as JEDEC haven't gotten
around to creating new standards yet to reflect what the industry is
actually doing. The continual trend to lower voltages makes it a moving
target and more difficult to attempt to standardize.
As for incompatibilities between different vendors' offerings, that's a risk
we sometimes take. Compare the specs carefully to see how much they
actually differ. Watch for things like different temperature ranges, which
might account for the differences. Differential signaling helps offset
vendor differences.
Regards,
Andy
----- Original Message -----
From: "Henrik G. Madsen" <hgm@xxxxxxxxxxx>
To: "dan bostan" <dbostan@xxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
Sent: Thursday, August 14, 2003 05:10 AM
Subject: [SI-LIST] Re: LVPECL standard ?
> Thanks for the answer, but it did not answer my question.
>
> What I'm looking for is a DC specification (official and approved) if it =
> exist for PECL and LVPECL.
>
> I.e. a document which states
> Voh(min) =3D
> Voh(max) =3D
> Vol(min) =3D
> Vol(max) =3D
>
> Vdiff_out(min) =3D
>
> and so forth
>
> Like the JEDEC JESD8-B for the LVTTL interface or ANSI/TIA/EIA-644 for =
> the LVDS.
>
> I have looked in several component datasheet and the different vendors =
> have different specifications. Additionally, they use the 'LVPECL' term =
> for both 3.3V and 2.5V powered PECL.
>
> Regards
> /Henrik G Madsen
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