Q.
If $V _{ A }$ and $V _{ B }$ are the input voltages (either $5 V$ or $0 V$ ) and $V _{ o }$ is the output voltage then the two gates represented in the following circuit (A) and (B) are:-
Solution:
$V _{ A }=5 V \Rightarrow A =1$
$ V _{ A }=0 V \Rightarrow A =0 $
$ V _{ B }=5 V \Rightarrow B =1 $
$ V _{ B }=0 V \Rightarrow B -0$
If $A = B =0$, there is no potential anywhere here $V _{0}=0$
If $A=1, B=0$, Diode $D_{1}$ is forward biased, here $V _{0}=5 V$
If $A=0, B=1$, Diode $D_{2}$ is forward biased hence $V _{0}=5 V$
If $A =1, B =1$, Both diodes are forward biased hence $V _{0}=5 V$
Truth table for $I ^{ st }$
A
B
Output
0
0
0
0
1
1
1
0
1
1
1
1
$\therefore $ Given circuit is OR gate
For $II ^{\text {nd }}$ circuit
$V _{ B }=5 V , A =1 $
$V _{ B }=0 V , A =0$
When $A=0, E-B$ junction is unbiased there is no current through it
$\therefore V _{0}=1$
When $A =1, E - B$ junction is forward biased
$V _{0}=0$
$\therefore $ Hence this circuit is not gate.
| A | B | Output | |
|---|---|---|---|
| 0 | 0 | 0 | |
| 0 | 1 | 1 | |
| 1 | 0 | 1 | |
| 1 | 1 | 1 |