If the input terminals of NOR gate are joined togather we get NOT gate. Now if the input A and B are inverted by using two NOT gates (obtained from NOR gates) and their outputs are jointly fed to the NOR gate as shown in Fig, we get the arrangement which works as AND gate.
Explaination. The output of gate I is,
`y_(1)=barA`
The output of gate II is, `y_(2)=barB`
The output gate III is
`y=bar(y_(1)+y_(2))=bar(barA+barB)=bar(barA).bar(barB)=A.B`
which is the Boolean expression for AND gate. The truth table of the arrangement will be as shown in Fig ., which is similar to truth table of AND gate (by reading the columns, A, B and y only).
