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Buses- Only Digital Signals?

  1. Feb 21, 2007 #1
    Are busses mostly used to carry digital signals?

    If yes, then why so? Why aren't buses a popular means of carrying an analog signals?
     
  2. jcsd
  3. Feb 21, 2007 #2

    berkeman

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    Staff: Mentor

    Crosstalk between the multiple lines would corrupt the analog signals enough to generally cause problems. With digital signals, you can still recover the content, even with some noise added in from crosstalk.

    For analog signals, you will generally keep them isolated from each other with coax or some other shielding method.
     
  4. Feb 21, 2007 #3
    How exatly do buses corrupt analog signals? Don't they have some kind of shielding?
     
  5. Feb 21, 2007 #4

    berkeman

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    Staff: Mentor

    A typical bus of digital signals will be parallel traces run over a ground plane (like the traces are on the outer layer of a multi-layer PC board, with the adjacent inner PCB layer being the ground plane). The closer the traces are to each other, the more crosstalk you get. You can reduce the crosstalk by spreading out the bus traces, by decreasing the distance to the inner ground plane layer, and by running ground "guard" traces between each of the bus lines. But you will still get plenty of crosstalk, even with those measures.
     
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