Logic Families MCQs

Practice Logic Families MCQs with four options, answers and explanations for focused Electronics & Telecommunication Engineering revision.

Question 1

Digital ElectronicsLogic Families

Compared with classic TTL, CMOS logic is especially known for low?

AInput impedance
BStatic power consumption
CNoise margin
DFan-out in every case

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Correct Answer: B. Static power consumption

Explanation: A major advantage of CMOS logic is very low static power consumption, particularly when not switching.

Reference: Standard digital electronics: CMOS characteristics

Question 2

Digital ElectronicsLogic Families

Fan-out of a logic gate refers to?

AThe number of outputs inside the gate
BThe maximum number of standard logic inputs its output can drive reliably
CThe propagation delay through the gate
DThe number of power-supply pins

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Correct Answer: B. The maximum number of standard logic inputs its output can drive reliably

Explanation: Fan-out specifies how many compatible logic inputs one gate output can drive while maintaining valid logic levels.

Reference: Standard digital electronics: fan-out

Question 3

Digital ElectronicsLogic Families

TTL is an abbreviation for?

ATransistor-Transistor Logic
BTransfer-Timing Logic
CTri-state Transfer Logic
DTransistor-Tuned Line

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Correct Answer: A. Transistor-Transistor Logic

Explanation: TTL stands for Transistor-Transistor Logic, a family of digital integrated circuits based on bipolar junction transistors.

Reference: Standard digital electronics: TTL

Question 4

Digital ElectronicsLogic Families

CMOS is an abbreviation for?

AComplementary Metal-Oxide-Semiconductor
BCommon Mode Output System
CControlled Memory Output Switch
DComplementary Magnetic Output Stage

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Correct Answer: A. Complementary Metal-Oxide-Semiconductor

Explanation: CMOS stands for Complementary Metal-Oxide-Semiconductor.

Reference: Standard digital electronics: CMOS

Question 5

Digital ElectronicsLogic Families

A CMOS gate has a specified noise margin high NMH = VOH(min) − VIH(min). If VOH(min)=4.4 V and VIH(min)=3.2 V, NMH equals?

A0.8 V
B1.2 V
C3.2 V
D7.6 V

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Correct Answer: B. 1.2 V

Explanation: NMH = 4.4 − 3.2 = 1.2 V. It represents the allowable HIGH-level noise before the receiving input may no longer be guaranteed HIGH.

Reference: Standard digital electronics: noise margin

Question 6

Digital ElectronicsLogic Families

A logic output can sink a maximum LOW-state current of 16 mA. Each connected input requires 1.6 mA when LOW. Ignoring other limits, the LOW-state fan-out is?

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Correct Answer: C. 10

Explanation: Fan-out based on LOW-state current is IOL(max)/IIL = 16/1.6 = 10 loads.

Reference: Standard digital electronics: fan-out calculation

Question 7

Digital ElectronicsLogic Families

In ideal CMOS logic under steady DC conditions, the input current is approximately?

AVery large
BApproximately zero except leakage
CEqual to output current
DFixed at 1 mA

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Correct Answer: B. Approximately zero except leakage

Explanation: The insulated MOS gate draws essentially no DC input current ideally; practical devices have small leakage and transient charging current.

Reference: Standard digital electronics: CMOS input characteristics

Question 8

Digital ElectronicsLogic Families

For CMOS logic, dynamic power dissipation is approximately proportional to which expression?

ACL VDD² f
BCL/VDD
CVDD/f
D1/(CL f)

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Correct Answer: A. CL VDD² f

Explanation: A common approximation is Pdynamic ≈ αCLVDD²f, where α is switching activity. Thus power rises strongly with supply voltage and switching frequency.

Reference: Standard digital electronics: CMOS dynamic power