[SI-LIST] Re: symmetry vs length matching for diff signals

Dear Jeff,

Maintaining symmetry (or constant edge-to-edge separation between the two
traces) and achieving length
matching are among important considerations when routing high-speed
differential pairs.

However, when both conditions can not be satisfied simultaneously, the
latter requirement (i.e.
length matching) proves more critical.

This is because the purpose of uniform distance between the pair is for
impedance control, whereas,
length matching relates to prevention of common mode signals, EMI and
optimum timing margins.

Subsequently, there are numerous cases in which one trace length is
increased (to meet length matching)
at the price of violating equal separation/symmetry especially for the
loosely coupled pairs.

Best Regards,

Abe Riazi
ServerWorks

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of handw0522
Sent: Thursday, November 25, 2004 8:45 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] symmetry vs length matching for diff signals



Hello all,
 
If a choice has to be made between matching lengths and fixing 
symmetry for differential signals, which one is your choice and why ?
 
Thanks,
Jeff


 


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