Logic Gates Questions and Answers

Answer: B

Correct answer: 16

The 4049 is a hex inverting buffer, and its package has 16 pins - six inverters using twelve pins, plus supply and ground, with two pins unused.

Answer: C

Correct answer: 16

Each input can be 0 or 1 independently, so n inputs give \( 2^n \) combinations, and \( 2^4 = 16 \).

Answer: D

Correct answer: 16

Each input takes two values independently, so four inputs give \( 2^4 = 16 \) combinations.

Answer: C

Correct answer: x(y+z)

The dual of an expression is formed by exchanging AND with OR and 0 with 1, leaving the variables uncomplemented. Applying that to \( x + yz \) turns the outer OR into AND and the inner AND into OR, giving \( x(y+z) \). Complementing the variables would give the complement, not the dual.

Answer: A

Correct answer: the inputs are equal

XNOR is the complement of XOR, so where XOR detects difference, XNOR detects agreement. It is HIGH when both inputs are 0 and when both are 1.

Answer: D

Correct answer: 16

A truth table has one row for each combination of input values, and n inputs give \( 2^n \) combinations. With four inputs that is \( 2^4 = 16 \).

Answer: D

Correct answer: all inputs are LOW

NOR is the complement of OR, and OR is 0 only when every input is 0, so NOR is 1 in exactly that case.

Answer: C

Correct answer: Fan-in of a gate is always equal to fan-out of the same gate

Fan-in is the number of inputs a gate has and fan-out the number of gate inputs its output can drive; the two are independent properties and there is no reason for them to be equal. The other three statements are the standard definitions of propagation delay, noise immunity and operating speed.

Answer: B

Correct answer: X = A · B · C

AND is a product, written with dots or by juxtaposition. The plus sign denotes OR, and the other two symbols have no meaning in Boolean algebra.

Answer: A

Correct answer: input combination at the time

A combinational circuit has no memory: its output at any moment is a function of the inputs present at that moment alone. Any dependence on previous inputs or outputs makes the circuit sequential.