Friday Free Board Quiz: Differential trace length match – Prize is USB 2.0 Flash drive 8GB


USB-Flash-8GB is low cost Flash drive for OLinuXino we recently add in stock and we give away tor this weekend Quiz winner, the winner also will receive OLinuXino paper notebook and OLinuXino keyring holder with Tux.

To participate in the Quiz is enough to re-tweet the Twitter Quiz announcement message.

To double your chances you have to answer the Quiz question :)

The Quiz question is:


Sometimes when route differential tracks one of the tracks is with shorter length and the length have to be matched. Which is the correct way to do this? Up or Down figure on the picture?

You have time to re-tweet and/or answer until Monday 30th of November.

In Monday we will post the correct answer and ask to generate random number in range then announce the winner and ship the board by post/airmail.

Good Luck!

6 Comments (+add yours?)

  1. adj
    Nov 27, 2015 @ 20:28:33

    The best way is the first way, because you want your signal to travel simultaneously as long as possible, in both differential traces.


  2. bib
    Nov 27, 2015 @ 20:31:34

    The fig. at the up side. We have to compensate the length mismatch of diff pairs early in PCB routing sequence. In other words we have to consider early the mismatch side for length compensating.



  3. LinAdmin
    Nov 27, 2015 @ 21:43:28

    Does not matter which one.


  4. indreias
    Nov 27, 2015 @ 22:12:08

    I agree that the correct way should be the one depicted in the “up” figure.
    If you look from right, and imagine to “inject” the signal from that side, only in that specific arrangement you will have the shorter track correctly compensated otherwise the noise cancellation benefit of the differential pair will be lost.


  5. LinuxUser
    Nov 28, 2015 @ 20:23:38

    Upper version is obviously better: in bottom version, signal travelling from right to left side would get delayed in the very beginning of travel, fronts of positive and negative pairs are no longer synchronized at this point. But the whole point of differential pair is to get normal and inversed versions of signal to travel synchronously, so receiver can use difference of levels between pairs rather than absolute values. Negating most of noise bursts in the process, because noise usually affects both wires in similar ways. So if receiver only cares about difference, line noise is automatically subtracted. This in turn allows to use lower voltage swing and achieve higher data transfer speeds. So virtually all high-speed buses are differential.


  6. Phuong
    Dec 08, 2015 @ 01:54:48

    The second picture is better.


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