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

Farrokh Mottahedin (Farrokh.Mottahedin@quantum.com)
Thu, 29 Jul 1999 10:48:06 -0700

Differential signaling alone doesn't help the situation since we're trying
to avoid common mode offsets and noise terms. AC coupling breaks ground
loops, and allows filtering of SCR spikes, etc. To reduce DC imbalance,
8b/10b encoding is employed. Other side benefits of AC coupling are
galvanic isolation ( a safety issue), and simplified receiver design due to
filtering out the DC component.

Regards,

Farrokh Mottahedin
Quantum Corporation
(408) 324-7934
farrokh.mottahedin@quantum.com

> -----Original Message-----
> From: Salvador Aguinaga [SMTP:Salvador_Aguinaga@mw.3com.com]
> Sent: Thursday, July 29, 1999 9:28 AM
> To: si-list@silab.eng.sun.com
> Subject: [SI-LIST] : [SI-LIST] Positive ECL (PECL) voltage swings,
> but designed to be AC coupled
>
> 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 from
> my
> internet searches.
>
> I am speaking specifically to the AC coupling that is found in
> fibre-channel
> ser-des transmitters.
>
> (P)ECL C1
> |\-------------o-----||---
> | \ |
> | / | C2
> |/o------o-----------||---
> | |
> | |
> < R1 >R2
> > <
> | |
> | |
> _|_ _|_
> GND GND
>
> Where C1=C1=0.01uF
>
> Why is the capacitor needed? What is the theory behind this
> implementation?
>
> Thanks,
>
> --------------------------------------------------------
> _ __ Salvador Aguinaga Jr.
> /_/ )/ _| Carrier Systems Group << File: ATT85812.txt >>

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