[SI-LIST] Re: AC Coupled Signals

I will elaborate a bit on what I have seen. I have measured (time domain) in 
the lab some effects that appears to be location specific in the placement of 
the AC coupling caps at the rcvr.  Now this may be due in part to the fact that 
I am using 50-ohm resistor termination in each lead as well and the combination 
(cap plus rcvr reflection) is giving some imbalance depending on distance.  The 
best rcvr eye that I am seeing is when I can move the AC/term as close to the 
rcvr as I can.  By the way these are 5Gb/s signals.
If I have time I will try and isolate what I am seeing and even simulate it, 
has anyone else seen or simulated this?
-Jory

----- Original Message ----
From: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
To: "npatel@xxxxxxxxxx" <npatel@xxxxxxxxxx>; si-list@xxxxxxxxxxxxx
Sent: Monday, September 24, 2007 1:06:06 PM
Subject: [SI-LIST] Re: AC Coupled Signals

Nikil,

I have made measurements on test PCBs and the location is not all that
important.  In identical pairs, one with AC coupling capacitors and the
other without, the loss vs. frequency is virtually identical at leas out to
6 GHz.  That would be 12 Mb/S.

Lee Ritchey


> [Original Message]
> From: <npatel@xxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Date: 9/24/2007 10:21:37 AM
> Subject: [SI-LIST] AC Coupled Signals
>
> Hi all,
> In case of AC coupled signals does anyone know of an optimum placement
> for the caps? I mean should they be placed near the source, receiver,
> middle of  the transmission line?
> How much difference does it make in the opening of the eye?
> The signals are differential CML running at 3.0Gbps
>
> Thanks,
> Nikhil 
>
>
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