Re: [SI-LIST] : [SI-LIST] Positive ECL (PECL) voltage swings, but

Jim Freeman (freeman@mavericknetworks.com)
Thu, 29 Jul 1999 11:25:34 -0700

Hi Salvador,

The main reason for the capacitors is to hold a voltage that is the diffe=
rence
between
the thresholds of the receiver and driver signalling systems. e.g. if PEC=
L is
driving LVDS,
The capacitor holds the voltage difference between the switching threshol=
d
between LVDS and
PECL. A second reason is that this allows terminations to the thresholds =
on
either end to be
different values.

Jim Freeman

Salvador Aguinaga wrote:

> All,
>
> Will some one shed some light on why differential lines (to and from) a=
ECL
> device are AC coupled? I've been unsuccessful at finding an answer fro=
m my
> internet searches.
>
> I am speaking specifically to the AC coupling that is found in fibre-ch=
annel
> ser-des transmitters.
>
> (P)ECL C1
> |\-------------o-----||---
> | \ |
> | / | C2
> |/o------o-----------||---
> | |
> | |
> < R1 >R2
> > <
> | |
> | |
> _|_ _|_
> GND GND
>
> Where C1=3DC1=3D0.01uF
>
> Why is the capacitor needed? What is the theory behind this implementa=
tion?
>
> Thanks,
>
> --------------------------------------------------------
> _ __ Salvador Aguinaga Jr.
> /_/ )/ _| Carrier Systems Group
>
> ---------------------------------------------------------------------=

---
>
> =B7 R&D
> __ |( (_  _  _   Mt. Prospect, Illinois
> \ \_)\__|(_)|))  (847) 222=B72833

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