Q 14.13 You are given two circuits as shown in Fig. 14.38, which consist of NAND gates. Identify the logic operation carried out by the two circuits.
a)
A and B are inputs of a NAND gate and output of this gate is the input of another NAND gate so,
Y =
Y=
Y=
Hence this circuit functions as AND gate.
b)
A is input to the NAND gate output of whose goes to the rightmost NAND gate. Also, B is input to the NAND gate whose output goes to the rightmost NAND gate.
Y =
Y = +
Y = A + B
Hence the circuit functions as an OR gate .
Alternative method
fig. a
construct the truth table by giving various input and observe the output
INPUT |
INTERMEDIATE OUTPUT |
OUTPUT |
00 | 1 | 0 |
01 | 1 | 0 |
10 | 1 | 0 |
11 | 0 | 1 |
The above truth table is the same as that of an AND gate
fig. b
INPUTS | OUTPUT |
00 | 0 |
01 | 1 |
10 | 1 |
11 | 1 |
The above truth table is the same as that of an OR gate