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Redraw Equivalent Circuit for 3-input OR gate

  1. Aug 29, 2011 #1
    How do you redraw a three-input OR gate circuit using only 2-input NAND gates?
     
  2. jcsd
  3. Aug 29, 2011 #2
    Using De Morgan's laws, you should be able to figure out how to make a 2-input OR gate using NAND gates. You can make a NOT gate by wiring the NAND inputs together.
     
  4. Aug 29, 2011 #3

    LCKurtz

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    DeMorgan's law says
    [tex]\overline{A+B}= \overline A\cdot \overline B[/tex]

    or

    [tex]A+B = \overline{\overline A\cdot \overline B}= NAND(\overline A,\overline B)[/tex]

    So start with A + (B + C)...
     
  5. Aug 29, 2011 #4

    berkeman

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    You know the rules, Deathfish. Show us your work!
     
  6. Aug 29, 2011 #5
    i've worked on this, but i seem to be going back and forth combining all combinations ie. 3C2 with no luck... difficult to explain this here. I know the equivalent of 2-input OR gates... but i am required to draw up 3-input OR gate when i am given just 2-input NAND gates. The question is to output HIGH when at least 2 out of 3 inputs are LOW.
     
  7. Aug 29, 2011 #6

    berkeman

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    A 3-input OR gate does not "output high when at least 2 out of 3 inputs are low"...
     
  8. Aug 29, 2011 #7
    its part of the question... A AND B, B AND C, A AND C then combine them together..
     
  9. Aug 29, 2011 #8

    LCKurtz

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    Part of what question? Your original post says nothing about AND gates.
     
  10. Aug 29, 2011 #9
    figured the first part out just need to combine that using three-input OR gate..
     
  11. Aug 29, 2011 #10

    LCKurtz

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    Just guessing, are you trying to implement a majority circuit where two or more of A,B, and C are true? If so, it probably will take as many NAND gates to implement the 3 input OR gate by itself as it would to do the whole problem with NANDs in the first place.
     
  12. Aug 29, 2011 #11

    berkeman

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    Thanks for being so clear in your OP. In the future, use the Homework Help Template, which asks for the exact problem statement.

    I'm out.
     
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