If VA and VB are the input voltages (either 5V or V0) and Vo is the output voltage then the two gates represented in the following circuit (A) and (B) are
(1) AND and OR Gate
(2) OR and NOT Gate
(3) NAND and NOR Gate
(4) AND and NOT Gate
Correct answer: (2) OR and NOT Gate
Explanation:
VA = 5V ⇒ A = 1
VA = 0V ⇒ A = 0
VB = 5V ⇒ B = 1
VB = 0V ⇒ B = 0
If A = B = 0, there is no potential anywhere here V0 = 0
If A = 1, B = 0, Diode D1 is forward biased, here V0 = 5V
If A = 0, B = 1, Diode D2 is forward biased hence V0 = 5V
If A = 1, B = 1, Both diodes are forward biased hence V0 = 5V
Truth table for Ist
A B Output
0 0 0
0 1 1
1 0 1
1 1 1
∴ Given circuit is OR gate
For IInd circuit
VB = 5V, A = 1
VB = 0V, A = 0
When A = 0, E–B junction is unbiased there is no current through it
∴ V0 = 1 When A = 1, E–B junction is forward biased
V0 = 0
∴ Hence this circuit is not gate