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I've designed this circuit with 4 logic gates, and did Karnaugh map's simplification and Quine McCluskey method. However I found out that actually my circuit design is already optimized and I can't really compare how the simplifications offer a less expensive circuit.

This is the original circuit

I'd like to add a few more gates to the circuit not changing the boolean function of it. Which is (X2'∙X0)+(X2∙X1)

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Are you saying something like add inverters to the inputs and outputs of the middle "AND" gate and "OR" gate and then redo the work? –  Amzoti Jul 13 '13 at 17:35
    
Aha ... I just need to make a bigger circuit to show how Quine McCluskey help to get a shorter funcion and so a smaller circuit –  diegoaguilar Jul 13 '13 at 17:44
    
Your current circuit is prone to logical hazards. Do you know what a consensus term is? –  Ataraxia Jul 13 '13 at 17:46

1 Answer 1

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You are correct in your desire to add extra gates, because as it's currently constructed it is prone to a logical hazard. Particularly there is a risk of the output briefly transitioning to a $0$ when the input changes between $111$ and $011$ when it should remain $1$.

Adding the term $X_0X_1$ will not change the logical function of the circuit, and will eliminate the hazard. So your expression will become:

$$F=X_0X_2'+X_1X_2+X_0X_1$$

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