ADC

Discussion in 'Homework Help' started by Cerkit, Jan 19, 2009.

  1. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
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    What is the use of multiple channels on an ADC.I'm trying to understand how it works. Is the number of bits per channel to do with the resolution hence meaning it can sample along a larger scale of values?? Also does more channels mean more samples from one signal input or more samples from different signal inputs??
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    More analog inputs means you can select which input you want to sample at a time. Thus you can sample many analog signals with the same ADC but not at the same time (each one input individually).
     
  3. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
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    So would I be able to sample a varying voltage signal simply with one channel?
     
  4. davebee

    Well-Known Member

    Oct 22, 2008
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    yep.

    The ADC itself is designed to convert a signal to some number of bits resolution. You give the ADC a "convert" signal, wait until it signals you that it is finished, then you read some number of bits out of it. You can repeat this continuously if you want.

    Usually you use the smallest number of bits as you need, because all else being equal, more bits cost more and convert more slowly.

    Some ADCs can convert really fast, like less than a microsecond, and some are really slow, like a tenth of a second per conversion.

    Multiple channels are like a switch in front of one converter. First you tell the ADC which channel to use, then you perform a conversion and read the results. Each channel is connected to a separate pin on the chip. You're free to connect more than one pin to a single source but it wouldn't do anything extra for you. Usually the channel pins are connected to different sources.

    Some converters are able to configure multiple pins as differential inputs, where one conversion converts the difference between two pins.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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  6. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
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    Very helpful. So from what I understand a flash ADC would be the most appropriate for very fast sampling?
     
  7. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
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    So how many bits do you suggest for sampling a dc signal varying from 0 to 5V. Or can I calculate a minimum/optimum??
     
  8. mik3

    Senior Member

    Feb 4, 2008
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    What is the minimum variation in the input voltage (0-5V) you want to detect?
     
  9. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
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    Minimum variation to be detected is 0.01V
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
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    Guess you don't like to do math. 8 bits resolves 256 levels. 9 bits would resolve 512, but isn't standard. So 10 bits gives 1024 levels. 5/1024 = 4.8 mv per bit.
     
  11. Cerkit

    Thread Starter Active Member

    Jan 4, 2009
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    Thanks, sounds good!
     
  12. italo

    New Member

    Nov 20, 2005
    205
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    where do you get 4.8mv I don't get it unless i asume that you use a 10v reference supose there is a 5 v ref then you are wrong in essence. I know he calls it channels but i better understand the word mutiplexing. there such things as dual ramp A/D too.
     
  13. beenthere

    Retired Moderator

    Apr 20, 2004
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    It's called math - 5/1024 = .0048828.
     
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