[SI-LIST] Re: AC Coupled Signals
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: leeritchey@xxxxxxxxxxxxx
- Date: Mon, 24 Sep 2007 15:18:59 -0400
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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