Which of the following is NOT a characteristic of ROM (Read-Only Memory)?

The correct answer is B: Programmable by user after manufacture. Standard ROM is programmed during manufacturing and cannot be reprogrammed by users. PROM, EPROM, and EEPROM allow user programming, but basic ROM does not

The thermal voltage (VT) at 300K is approximately:

The correct answer is A: 25 mV. VT = kT/q where k=1.38×10⁻²³ J/K, T=300K, q=1.6×10⁻¹⁹C gives approximately 26 mV or 25 mV.

A BJT has β = 100 and early voltage VA = 80 V. If IC = 2 mA and VCE = 10 V, what is the small signal output resistance ro?

The correct answer is A: 40 kΩ. ro = VA/IC = 80/(2×10^-3) = 40,000 Ω = 40 kΩ. Early voltage determines the output resistance.

For a given application, selecting a BJT with higher β (current gain) results in:

The correct answer is B: Lower base current requirement and improved input impedance. Higher β means lower IB needed for same IC, reducing loading on the driving source and improving effective input impedance (Zin ≈ β×re).

Which semiconductor material has the lowest bandgap at room temperature?

The correct answer is C: Germanium (0.66 eV). Germanium has Eg ≈ 0.66 eV at 300K, lowest among common semiconductors; causes high intrinsic carrier concentration and leakage current.

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Electronics (ECE)
Electronic Devices

Analog/digital electronics, communication

30 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–30 of 30

Topics in Electronics (ECE)

All Electronic Devices 100 Digital Electronics 100 Analog Circuits 100 Signals & Systems 100

Q.21 Hard Electronic Devices

The body effect in MOSFETs causes which of the following?

A Increase in transconductance

B Decrease in threshold voltage

C Increase in threshold voltage and decrease in output impedance

D No change in device characteristics

Correct Answer: C. Increase in threshold voltage and decrease in output impedance

EXPLANATION

Body effect (substrate bias) increases VT due to back-bias effect and decreases output impedance; VT = VT0 + √(2εqNa/Cox)·φt term.

Test

Q.22 Hard Electronic Devices

The punch-through effect in a BJT occurs when:

A Base-emitter junction breaks down

B Reverse bias on collector-base junction extends depletion region to base contact

C Collector current exceeds maximum rating

D Temperature exceeds junction temperature limit

Correct Answer: B. Reverse bias on collector-base junction extends depletion region to base contact

EXPLANATION

Punch-through occurs when CBJ depletion width extends to base contact, causing base resistance to vanish and uncontrolled current flow.

Test

Q.23 Hard Electronic Devices

The transconductance (gm) of a MOSFET in saturation region is given by:

A gm = μnCox(W/L)(VGS - VT)²

B gm = 2μnCox(W/L)ID

C gm = ID/(VGS - VT)

D gm = (VGS - VT)/ID

Correct Answer: C. gm = ID/(VGS - VT)

EXPLANATION

Transconductance gm = ∂ID/∂VGS = ID/(VGS - VT) at saturation, fundamental small-signal parameter.

Test

Q.24 Hard Electronic Devices

In integrated circuit design, what does the term 'aspect ratio' refer to in MOSFETs?

A The ratio of gate voltage to drain voltage

B The ratio of channel width (W) to channel length (L)

C The ratio of oxide thickness to gate length

D The ratio of drain current to gate current

Correct Answer: B. The ratio of channel width (W) to channel length (L)

EXPLANATION

Aspect ratio (W/L) is a fundamental design parameter in MOSFETs affecting current capability and switching speed. Higher W/L provides larger current capacity and faster transitions, crucial for circuit optimization and performance tuning.

Test

Q.25 Hard Electronic Devices

What is the significance of Early voltage (VA) in a BJT?

A It represents the barrier potential of the junction

B It indicates the thermal voltage of the transistor

C It characterizes the slope of output characteristics (channel length modulation effect)

D It defines the maximum frequency of operation

Correct Answer: C. It characterizes the slope of output characteristics (channel length modulation effect)

EXPLANATION

Early voltage (VA) represents the output resistance (ro = VA/Ic) of a BJT. Larger VA indicates steeper output characteristics, meaning collector current is more independent of collector-emitter voltage, indicating better current source behavior.

Test

Q.26 Hard Electronic Devices

A Schottky diode offers advantages over PN junction diodes primarily because of:

A Higher forward voltage drop

B Slower switching speed

C Lower forward voltage drop and faster switching speed

D Better reverse recovery characteristics

Correct Answer: C. Lower forward voltage drop and faster switching speed

EXPLANATION

Schottky diodes have metal-semiconductor junctions with lower forward voltage (0.3-0.5V vs 0.7V for silicon) and faster switching due to absence of minority carrier storage. This makes them ideal for high-frequency and high-speed switching applications.

Test

Q.27 Hard Electronic Devices

In a power MOSFET, the on-resistance (RDS_on) is primarily determined by:

A Gate oxide thickness

B Channel length modulation

C Drift region resistance and channel resistance

D Gate-drain capacitance

Correct Answer: C. Drift region resistance and channel resistance

EXPLANATION

RDS_on consists of channel resistance and drift region resistance. For power MOSFETs, drift region (epitaxial layer) dominates. Minimizing drift region thickness reduces RDS_on but decreases breakdown voltage, creating a design trade-off.

Test

Q.28 Hard Electronic Devices

Which of the following statements about CMOS logic is correct?

A High static power dissipation at rest

B Low static power dissipation but higher dynamic power dissipation

C Requires less substrate area than NMOS

D Cannot operate at high frequencies

Correct Answer: B. Low static power dissipation but higher dynamic power dissipation

EXPLANATION

CMOS (Complementary MOS) has very low static power dissipation because complementary P and N transistors prevent steady-state current paths. However, dynamic power dissipation increases with switching frequency due to capacitive charging/discharging.

Test

Q.29 Hard Electronic Devices

For a BJT in saturation, the relationship between base current and collector current is:

A Ic = β × Ib (normal relationship holds)

B Ic < β × Ib (actual current is less than theoretical)

C Ic > β × Ib (actual current exceeds theoretical)

D Ic is independent of Ib

Correct Answer: B. Ic < β × Ib (actual current is less than theoretical)

EXPLANATION

In saturation, both junctions are forward biased. The collector current becomes less than β × Ib because the transistor is no longer in linear region. Excess base current doesn't proportionally increase collector current.

Test

Q.30 Hard Electronic Devices

A tunnel diode exhibits negative resistance in a specific voltage range due to:

A Reverse bias condition

B Quantum mechanical tunneling effect

C High doping concentration creating a narrow depletion region

D All of the above

Correct Answer: D. All of the above

EXPLANATION

Tunnel diodes show negative differential resistance due to quantum tunneling through the narrow depletion region created by heavy doping. This occurs in forward bias and enables their use as oscillators and amplifiers.

Test

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Electronics (ECE) Electronic Devices

Electronics (ECE)
Electronic Devices