2. Combining gates (1)
Let us consider combining three logic gates to end up with a single output Q. This is the drawing:
This has an AND gate feeding an OR gate that then goes through a NOT gate for output Q. It has three inputs A,B,C. Intermediate values are labelled z,y.
Task: Write down the boolean expression for this.
Step 1: The output of the AND gate is $$ z = A.B$$ which becomes an input to the OR gate
Step 2: The input to the OR gate is $z$ (from above) and input $C$. Apply an OR operation to both of these inputs, thus
$$ y = (A.B) + C$$
Step 3: Value y is fed through the NOT gate and so negation needs to be applied to get the final output Q :
$$Q= \overline{(A.B) + C}$$
which is the answer.
Challenge see if you can find out one extra fact on this topic that we haven't already told you
Click on this link: How to build boolean expressions