140
Question
Write the truth table for circuit given in the figure, consisting of NOR gates and identify the logic operation (OR, AND, NOT) which this circuit is performing.
(Hint: A = 0, B = 1 then A and B inputs of second NOR gate will be 0 and hence Y=1. Similarly work out the values of Y for other combinations of A and B. Compare with the truth table of OR, AND, NOT gates and find the correct one).
(Hint: A = 0, B = 1 then A and B inputs of second NOR gate will be 0 and hence Y=1. Similarly work out the values of Y for other combinations of A and B. Compare with the truth table of OR, AND, NOT gates and find the correct one).
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Solution
A and B are the inputs of the given circuit. The output of the first NOR gate is ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯A+B. It can be observed that the inputs of the second NOR gate become the output of the first one.Hence, the output of the combination is given as:
Y=¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯A+B+¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯A+B=A+B
The truth table for this operation is given in the table. A B Y (=A+B) 0 0 0 0 1 1 1 0 1 1 1 1
A and B are the inputs of the given circuit. The output of the first NOR gate is ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯A+B. It can be observed that the inputs of the second NOR gate become the output of the first one.
Hence, the output of the combination is given as:
Y=¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯A+B+¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯A+B=A+B
The truth table for this operation is given in the table.
| A | B | Y (=A+B) |
| 0 | 0 | 0 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
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