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Homework Help: How to calculate this 4 bit DAC

  1. Jun 29, 2017 #1
    < Mentor Note -- thread moved to HH from the technical forums, so no Homework Help Template is shown >

    please can somebody help me, how to calculate this 4 bit dac,
    i know this one if input 5/2, 5/4 5/8 5/16 voltage

    i dont understand nothing i search on the internet but i dont find some useful example,
    my english is not so good....
    please one more time can somebody explain me how to calculate, for formula thanks
    Last edited by a moderator: Jun 29, 2017
  2. jcsd
  3. Jun 29, 2017 #2


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    Staff: Mentor

    Try again, using the search terms R-2R ladder DAC.

    After you have done that reading, try again to work your schoolwork problem and post your work here so we can check it.
  4. Jun 29, 2017 #3


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    Homework Helper
    Gold Member

    BTW, can you check your circuit, as I think the op-amp has the inputs reversed.

    Berkeman beat me to the rest of the comment.
  5. Jun 29, 2017 #4


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    Staff: Mentor

    Good catch!
  6. Jun 29, 2017 #5
    thank you a lot , it help me, thanks...
    have nice night.
  7. Jun 29, 2017 #6


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    Staff: Mentor

    Also, you show the output component as a Comparator. It should be a Op-Amp, not a Comparator.
  8. Jun 29, 2017 #7
    You really should look up another version of the R 2R ladder.
    -1 if key A is closed, the positive supply is short circuited to the output of the op-amp. That won't end well.
    2 R1 shouldn't be there.
    3 The ampiflier you connect the R-2R ladder to should have infinite (much larger than R) imput resistance.
    4 The inputs should be connected to either 0 or 5 volts, and not left unconnected.

    The last point is essential to make make the superposition principle work. If you have a network of resistors and voltage sources, you can calculate the effect of a single voltage source by replacing all the other voltage sources with a wire. You can than sum those indivudual effects to get the output voltage. Replacing the voltage sources by open circuits won't work.
  9. Jun 30, 2017 #8
    Good Morning

    i solve all the problme with voltage divider i find all the values.
    but the problem is, when i push key D, the voltage of D is the same(like i find it with voltage divider), but the voltage on c,b,a they have other value?
    how do i calculate ?because i draw the circuit in gsm (every circuit)
  10. Jun 30, 2017 #9


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    Science Advisor

    The circuit in post #1 is a weird mix of several ideas.
    Please post your revised circuit diagram.

    Attached Files:

    Last edited: Jun 30, 2017
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