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Digital multiplexer question

  1. Jan 27, 2012 #1

    I have a question regarding digital multiplexers.

    In communication systems, when we use mux, we can combine a lot of low bandwidth channels and transmit as a high bandwidth channel and then use a demux at the receiving end to split it back to the low bandwidth channels.

    I saw the digital mux had a selector option which only sends one output at a time. So, this means that if we connect a demux to the output of the mux, it still will not get all the inputs inserted into the mux at the output of demux. But, only the SELECTED output at the mux.

    I was wondering is this the way it works or have I got it wrong. Appreciate if anyone can clarify this for me.

  2. jcsd
  3. Jan 27, 2012 #2
    Low bandwidth channels have high time periods. Now just consider N number of such channels. Then you sample each channels and reduce the duty cycle from 50 % to (50/N) %. Now you put variable offset before each channel so that they dont overlap. Then you can use mux to multiplex them and send all of them with N times bandwidth. Reverse is done at the receiver.
  4. Jan 27, 2012 #3
    So, if we send low bandwidth channel by channel at a very fast rate, then we don't even need a high bandwidth channel. Just can send channel by channel using a low bandwidth channel
  5. Jan 27, 2012 #4
    Appreciate if anyone could clarify the digital mux part.
  6. Jan 28, 2012 #5
    Can someone explain to me if we can make the digital mux output all the inputted data as in a communication mux
  7. Jan 29, 2012 #6


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    Staff: Mentor

    Could you give some specific examples of the communication systems that you are asking about?

    You can combine lower bandwidth channels into a higher bandwidth channel, but there has to be some way to keep the different data streams separate so they can be demuxed at the other end of the high bandwidth channel.

    For example, you can include addressing information in a packetized format, much like Ethernet handles lots of different low-bandwidth channels being combined into higher speed backbones.

    Or you can use time division multiplexing, where each low-bandwidth channel has a pre-set timeslot in each overall channel period.

    If you could post more specific details about your question, that would help us to try to help you out.
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