Test: Logic Gates & Switching Circuits- 1 - Electronics and Communication Engineering (ECE) MCQ

• Positive logic AND gate is equivalent to bubbled NOR gate.
• Positive logic OR gate is equivalent to bubbled NAND gate.
• Positive logic NAND gate is equivalent to bubbled OR gate.
• Positive logic NOR gate is equivalent to bubbled AND gate.

 can be implemented using 4 NAND gates as shown below:

Thus, we see that after interchanging all 1’s and 0’s of inputs in the truth table of positive logic AND gate, the resulting truth table obtained is the truth table of negative logic OR gate. Similarly, we can prove that if all 0’s and 1's inputs in the truth table of NAND gate are interchanged, then the gate becomes negative logic NOR gate. Hence, both assertion and reason are true and reason is the correct explanation of assertion.

• EX-OR gate can be used as a controlled inverter as shown below:

For control input = 1 , 

For control input = 0, Y = A

• NOT gate is basically used as an inverter or for complementation purposes.
• EX-NOR gate can be used as even-odd parity checker because the output of EX- NOR gate is 1 if the number of 1’s in its inputs is even; if the number of 1’s is odd, the output is 0.
• NOR gate is an universal gate.

An important property of the EX-NOR gate is that it can be used for bit comparison. The output of an EX-NOR gate is 1 (high) if both the inputs are similar, i.e. both are 0 or 1 (not necessarily even no. of high inputs); otherwise its output is 0 or low (not necessarily odd number of high inputs). Hence, EX-NOR gate can be used as a “one-bit comparator” . Thus, assertion is a correct statement. Reason is also a true statement but not a correct explanation of assertion.

Here, (0, 1, 1) gives the output X = 1

The code where all successive numbers differ from their preceding number by single bit is gray code. It is an unweighted code. The most important characteristic of this code is that only a single bit change occurs when going from one code number to next. BCD Code is one in which decimal digits are represented by a group of 4-bits each, whereas, in Excess-3 Code, the decimal numbers are incremented by 3 and then written in their BCD format.

AND, OR, NOT are three basic gates which follow both commutative and associate law. However, the universal gates NAND and NOR don't follow associate law.

It is a D-type of flip-flop and stores one bit of data.