[SI-LIST] Re: AC Coupled Signals
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "Scott McMorrow" <scott@xxxxxxxxxxxxx>
- Date: Mon, 24 Sep 2007 13:19:40 -0700
Doing thie requires some pretty good simulations. Some out there can do
them. I can't due to lack of the righ ttools, so I contract that work when
I am near the limits. How do you know when you are near the limits? Good
question. Takes some experience with real circuits.
> [Original Message]
> From: Scott McMorrow <scott@xxxxxxxxxxxxx>
> To: <leeritchey@xxxxxxxxxxxxx>
> Cc: npatel@xxxxxxxxxx <npatel@xxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> Date: 9/24/2007 12:51:37 PM
> Subject: [SI-LIST] Re: AC Coupled Signals
>
> Lee is mostly correct. There are some degenerate cases where the
> position of an AC coupling capacitor can cause unwanted resonances which
> can reinforce other resonances, cause insertion loss troughs, and peak
> crosstalk coupling in the interconnect. If you are close to either
> insertion loss or crosstalk margin limits, or if you have an extremely
> high density differential interconnect, with large numbers of signals,
> it may make sense to perform some AC coupling capacitor engineering.
> Design of the capacitor mounting solution, and location, does matter in
> systems pushing the limits.
>
>
> Scott McMorrow
> Teraspeed Consulting Group LLC
> 121 North River Drive
> Narragansett, RI 02882
> (401) 284-1827 Business
> (401) 284-1840 Fax
>
> http://www.teraspeed.com
>
> Teraspeed® is the registered service mark of
> Teraspeed Consulting Group LLC
>
>
>
> Lee Ritchey wrote:
> > I meant to add that this would imply that location is relatively
> > unimportant. Others may have data that says otherwise.
> >
> >
> >
> >> [Original Message]
> >> From: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
> >> To: npatel@xxxxxxxxxx <npatel@xxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> >> Date: 9/24/2007 11:37:12 AM
> >> 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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