Logic Gates — Practice MCQs for CCAT

Correct Answer: C — NAND

NAND and NOR are universal - any circuit can be made using only them.

Correct Answer: B — All inputs are 1

AND gate: output is 1 only when ALL inputs are 1.

Correct Answer: B — At least one input is 1

OR gate: output is 1 when at least one input is 1.

Correct Answer: B — Inverter

NOT gate inverts the input - also called inverter.

Correct Answer: B — Inputs are different

XOR (Exclusive OR): output is 1 when inputs are different.

Correct Answer: B — Both inputs same

XNOR: output is 1 when both inputs are same.

Correct Answer: A — AND followed by NOT

NAND = NOT AND (AND gate output inverted).

Correct Answer: B — OR followed by NOT

NOR = NOT OR (OR gate output inverted).

Correct Answer: B — Output equals input

Buffer: output = input (used for signal strengthening).

Correct Answer: A — Connect both inputs together

NAND with both inputs same: A NAND A = A' (NOT A).

Correct Answer: B — AND gate

AND gate outputs 1 only when all inputs are 1. If any input is 0, output is 0.

Correct Answer: B — OR gate

OR gate outputs 1 when at least one input is 1. Output is 0 only when all inputs are 0.

Correct Answer: B — 0

NAND is NOT-AND. When all inputs are 1, AND gives 1, then NOT inverts it to 0.

Correct Answer: B — 1

NOR is NOT-OR. When all inputs are 0, OR gives 0, then NOT inverts it to 1.

Correct Answer: B — 0

XOR (exclusive OR) outputs 0 when both inputs are same (both 0 or both 1), and 1 when inputs differ.

Correct Answer: B — 1

XNOR outputs 1 when both inputs are same, and 0 when inputs differ. It is the complement of XOR.

Correct Answer: B — 2

AND = NAND followed by NOT. Use one NAND gate, then another NAND as NOT (inputs tied). Total: 2 gates.

Correct Answer: C — A'·B + A·B'

XOR can be expressed as A'·B + A·B', which gives 1 when inputs differ and 0 when same.

Correct Answer: C — XOR gate

XOR can act as controlled inverter. If control input is 0, output = input. If control is 1, output = complement of input.

Correct Answer: B — Time for output to change after input changes

Propagation delay is the time taken for the output of a gate to change in response to a change in input.

Correct Answer: B — Maximum number of gate inputs it can drive

Fan-out is the maximum number of gate inputs that a gate output can reliably drive without signal degradation.

Correct Answer: A — Number of inputs the gate can accept

Fan-in is the number of inputs a gate can accept. Higher fan-in gates may have slower operation.

Correct Answer: B — CMOS

CMOS (Complementary Metal-Oxide-Semiconductor) has the lowest static power consumption.

Correct Answer: B — Logic with 0, 1, and high-impedance states

Tri-state outputs can be 0, 1, or high-impedance (Z), allowing multiple outputs to share a bus.

Correct Answer: B — CMOS switch that passes signal when enabled

A transmission gate is a CMOS analog switch that passes an input signal when the control is active.