Question

You are given the two circuits as shown in Fig. Show that circuit (a) acts as OR gate while the circuit (b) acts as AND gate.

Answer 1

(a) The left half acts as NOR gate and the right half as NOT gate.

Output from left half for inputs A and B is $\overline{A+B}$

This output is fed in the right half to produce $\overline{\overline{A+B}}=A+B$

Hence the combination acts as OR gate.

(b) The two left halves act as NOT gates.

Thus the outputs from the two gates are $\overline{A}$ and $\overline{B}$

They are fed into the NOR gate.

Thus $Y=\overline{\overline{A}+\overline{B}}=\overline{\overline{A}}.\overline{\overline{B}}=A.B$

Hence the combination acts as AND gate.