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

  • From: Marc-André Filion <mfilion@xxxxxxxxxxxxxxx>
  • To: <si-list@xxxxxxxxxxxxx>
  • Date: Mon, 4 Feb 2013 07:04:18 -0500

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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