Digital Logic - Combinational Circuits

1. In which of the following gates, the output is 1, if and only if at least one input is 1?

  • Option : C
  • Explanation : In OR gate we need atleast one bit to be equal to 1 to generate the output as 1 because OR means any of the condition out of two is equal to 1 which means if atleast one input is 1 then it shows output as 1 . Number of 1's in input may be more than one but the output will always be 1 in OR gate. So the answer is 'C'.
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2. The time required for a gate or inverter to change its state is called

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3. The time required for a pulse to change from 10 to 90 percent of its maximum value is called

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4. The maximum frequency at which digital data can be applied to gate is called

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5. What is the minimum number of two-input NAND gates used to perform the function of two input OR gate ?

  • Option : C
  • Explanation : Y=A+B. This is the equation of OR gate. We require 3 NAND gates to create OR gate. We can also write After 1st NAND operation Y = (A AND B)' Y= A' + B' (Demorgan's Law) After 2nd NAND operation Y= ( A' + B')' Y= A . B (Demorgan's Law) After 3rd NAND operation Y= ( A . B )' Y= A' + B ' (Demorgan's Law) So we need 3 NAND gates.
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