Build 1 bit comparator using 2 to 4 decoder?

1. Mar 14, 2013

asdf12312

build 1 bit comparator using "2 to 4" decoder??

1. The problem statement, all variables and given/known data

3. The attempt at a solution
worked out truth table:
Code (Text):
A     B    A>B   A<B   A=B
0     0     0     0     1
0     1     0     1     0
1     0     1     0     0
1     1     0     0     1
prty sure thats right. just need part B now. now i have a 2 by 4 decoder, know wat it is, just confused because the outputs is different from what i have in the truth table. also, there is only 3 outputs in my truth table, the decoder has 4 outputs. so how does that work :\

Last edited: Mar 14, 2013
2. Mar 14, 2013

Staff: Mentor

You need to make a circuit with the Decoder plus gates to generate those three outputs. What does the raw output of the decoder look like (what is its truth table given A and B as inputs)?

BTW, nice change to code tags on your table!

3. Mar 14, 2013

asdf12312

decoder outputs are from minterms. so a'b' outputs 1 in the 0 output, a'b outputs 1 in the 1 output, and so on. so all i have to do is change the output of ab input to match the output of a'b'? so that and gate will be an or instead: ab + a'b' ??