[SI-LIST] Re: What will happen if differential channel is not symmetric?

Asymmetires would also cause some of the differential signal component into 
your common signal and therefore increasse EMI.
 
Javid
--- On Thu, 23/7/09, Istvan Novak <istvan.novak@xxxxxxx> wrote:


From: Istvan Novak <istvan.novak@xxxxxxx>
Subject: [SI-LIST] Re: What will happen if differential channel is not 
symmetric?
To: "Chen Jikai" <yfgchen@xxxxxxxxxxxx>
Cc: si-list@xxxxxxxxxxxxx
Date: Thursday, 23 July, 2009, 1:07 PM


The short answer is YES for both in your case.  Skew is primarily 
dependent on the effective permittivity: in microstrip the effective 
permittivity is also geometry dependent, so skew (though small) will 
also occur. 

This kind of asymmetry shows up also in glass-reinforced laminates due 
to glass-weave effects even if the two traces are identical in cross 
section.    There have been many publications recently on this subject: 
one from the SUN team is: DesignCon2007, Santa Clara, CA, January 29-31, 
2007, Losses Induced by Asymmetry in Differential Transmission Lines, 
posted at http://www.electrical-integrity.com/ >> Paper download.

Regards,

Istvan Novak
SUN Microsystems

Chen Jikai wrote:
> Hi,
> I have been simulating some transmission line structures and one thing popped 
> up. What will happen if differential channel is not symmetric? For example, 
> suppose I have two coupled microstrips and one's width is bigger than the 
> other. Does this mean the channel will suffer from skew and will convert some 
> odd mode stimulus to even mode?
>
> Thanks a lot in advance!
>
>
>
>       
>
>   

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