[SI-LIST] Re: Loose coupling vs tight at the same time

  • From: steve weir <weirsi@xxxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Mon, 04 Feb 2013 05:48:24 -0800

Marc, using practical geometries the line to line coupling of the most 
tightly coupled differential pair on a PCB with an image plane is less 
than 15%.

Steve

On 2/4/2013 4:04 AM, Marc-André Filion wrote:
> Hi,
> Does the coupling type (tight and loose) affect the way that the return 
> current will behave? Someone told me that a tight coupled diff pair return 
> current will be more on the coupled trace than the reference plane. Since the 
> coupling is stronger with the other trace, the electron will tend to flow on 
> the trace rather than on the plane.
>
> I'm really not sure about this one, but the doubt is high enough to check how 
> urban this legend is.
>
> Regards,
>
>
>
> Marc-André Filion, ing
> Concepteur Matériel / Hardware Designer
> Brioconcept Consulting Inc.
> 450.681.2779  x2368
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
> Behalf Of steve weir
> Sent: 1 février 2013 20:27
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Loose coupling vs tight at the same time
>
> Marc, just to add a little bit to Lee's good comment:  The impedance in
> both even and odd modes is going to change.   How much this is going to
> cause S11 impairment depends on just how tightly you couple in the pin field. 
>  If the data rate is reasonably high I encourage you to put what you are 
> considering through a field solver so that you can see what is going to 
> happen to both your reflections and your cross talk.  The latter may be the 
> bigger problem with what you are trying to do.
>
>
> Steve.
> On 2/1/2013 3:33 PM, Lee wrote:
>> The big thing to worry about is the change in impedance when you go
>> from tight to loose or the reverse.  Any good 2D field solver will
>> allow you to quantify that.
>>
>> -----Original Message-----
>> From: Marc-André Filion
>> Sent: Friday, February 01, 2013 2:35 PM
>> To: SI-LIST mailing list
>> Subject: [SI-LIST] Loose coupling vs tight at the same time
>>
>> Hi,
>> We’re having a discussion here and I would like to know your thought
>> about it.
>>
>> How bad is it to transition from tight coupling diff signal to loose
>> coupling signal and vice-versa. We have a case here where we pass-thru
>> a pin field and we reduce the coupling from loose to tight for 2”and
>> get back to loose after.
>>
>>
>>
>> I’m not sure that it’s a good approach. What’s your idea on this?
>>
>>
>>
>>
>>
>>
>>
>> Marc-André Filion
>>
>>
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>
> --
> Steve Weir
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-- 
Steve Weir
IPBLOX, LLC
1580 Grand Point Way
MS 34689
Reno, NV  89523-9998
www.ipblox.com

(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax

All contents Copyright (c)2012 IPBLOX, LLC.  All Rights Reserved.
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