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Calculating resolution.

Discussion in 'Electronics Homework Help' started by Mymla, Nov 9, 2016.

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  1. Mymla

    Mymla

    37
    3
    May 4, 2015
    Hey everyone,
    could anyone point me in the right direction to working out this question. I have the answer but not sure how to work it out of the question.

    Calculate the resolution the following convert given that Vref=5V.

    8 Bit


    Answer: 19mV

    Is this a correct formula to use? (Vin/Vref) * 2^bitdepth
     
  2. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    Hello. How I do it is this 5/((2^8)-1) and that gets me pretty much the same answer as you. :)
    Thanks
    Adam
     
  3. Mymla

    Mymla

    37
    3
    May 4, 2015
    Thankyou!:)
     
  4. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    No probs.
     
  5. AnalogKid

    AnalogKid

    2,327
    653
    Jun 10, 2015
    Divide, not multiply.

    ak
     
  6. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Adam,
    You shouldn't subtract 1.
    To convince yourself check the case of 1 bit ;)
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,258
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    Jan 21, 2010
    Oddly enough that was the same argument I used to convince myself that you must subtract 1.
     
  8. dorke

    dorke

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    Jun 20, 2015
    I can understand why.

    For 1 bit we have 2 states "0" and "1".
    How do we decide which state are we in?
    "0" if we are below 1/2
    "1" if we are above 1/2

    What is the resolution than?
    I would say 1/2 not 1...;)

    untitled.JPG
     
  9. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    Um I used to do it the other way and then I read on some website a time a go you should subtract 1. I am not saying your wrong...let me see if I can find the website.
    Cheers
    Adam
     
  10. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    Not the website I saw but he mentions -1. But I think where I might be wrong is the maximum value FSD is Vref -1bit of resolution? Is that correct?
    Adam
     
  11. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Adam,
    Actually you are correct my bad.

    The definition of resolution is "the value that 1LSB equals to".
    In the case of 1bit it is indeed 1.
    so ,subtraction of 1 is the correct way to calculate the resolution.

    Another value is the "error" of a converter this is 1/2 LSB
    no -1 here.
     
  12. Arouse1973

    Arouse1973 Adam

    5,164
    1,078
    Dec 18, 2013
    Phew, thought I was going mad :)
    Cheers
    Adam
     
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