In a complex digital system, what does 'Setup time' refer to?

The correct answer is B: Minimum time data must be stable before clock edge. Setup time is the minimum duration that the input data must be stable and valid before the active clock edge arrives at the flip-flop.

What is the maximum frequency operation for a circuit with total propagation delay of 50 ns?

The correct answer is A: 20 MHz. Maximum frequency = 1 / (propagation delay) = 1 / 50 ns = 1 / (50 × 10^-9 s) = 20 MHz.

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.

Which of the following is a non-volatile memory type commonly used in embedded systems?

The correct answer is C: Flash memory. Flash memory is non-volatile (retains data without power), widely used in embedded systems, SSDs, and microcontrollers as program storage.

In a synchronous counter design, what is the main advantage over an asynchronous counter?

The correct answer is B: Elimination of timing skew and glitches. Synchronous counters have all flip-flops clocked simultaneously, eliminating propagation delay issues and glitches present in asynchronous counters.

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Electronics (ECE)

Analog/digital electronics, communication

78 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 61–70 of 78

Topics in Electronics (ECE)

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

Q.61 Hard Electronic Devices

In a MOSFET differential amplifier, the common-mode gain is reduced by using:

A Larger channel length (L)

B Larger width-to-length ratio (W/L)

C Current mirror load and larger source degeneration

D Smaller output impedance

Correct Answer: C. Current mirror load and larger source degeneration

EXPLANATION

Current mirror loads increase output impedance, while source degeneration resistors provide common-mode feedback, both reducing common-mode gain.

Test

Q.62 Hard Electronic Devices

The noise figure of a BJT amplifier at low frequencies is primarily determined by:

A 1/f noise in base region

B Shot noise in base current

C Thermal noise in base resistance

D Flicker noise only

Correct Answer: B. Shot noise in base current

EXPLANATION

At low frequencies, shot noise associated with base current (IB) dominates, following Poisson statistics: i²n = 2q×IB×Δf.

Test

Q.63 Hard Electronic Devices

In practical MOSFET applications for RF circuits, which parasitic effect limits frequency response most?

A Substrate capacitance only

B Gate-drain capacitance (Miller effect)

C Source resistance variations

D Bulk resistance

Correct Answer: B. Gate-drain capacitance (Miller effect)

EXPLANATION

The gate-drain capacitance (Cgd) creates Miller effect, which effectively multiplies the capacitive reactance in feedback, severely limiting high-frequency gain.

Test

Q.64 Hard Electronic Devices

A JFET in pinch-off condition means:

A Gate-source junction is reverse biased and channel is closed

B Drain current equals zero regardless of drain voltage

C Gate voltage equals source voltage

D Drain current is maximum and independent of VDS

Correct Answer: A. Gate-source junction is reverse biased and channel is closed

EXPLANATION

At pinch-off, VGS reaches VP (pinch-off voltage), channel closes, and further VDS increase has minimal effect on ID (saturation region).

Test

Q.65 Hard Electronic Devices

When a BJT is used as a switch in saturated condition, the overdrive factor is defined as:

A Ratio of actual base current to minimum base current needed

B Ratio of collector current to base current

C Ratio of VCE(sat) to VBE(sat)

D Ratio of collector voltage to emitter voltage

Correct Answer: A. Ratio of actual base current to minimum base current needed

EXPLANATION

Overdrive factor β = IB(actual) / IB(min) ensures transistor stays saturated even with parameter variations.

Test

Q.66 Hard Electronic Devices

The avalanche breakdown voltage (BV) in a reverse-biased junction approximately follows:

A BV ∝ ND (doping concentration)

B BV ∝ √ND

C BV ∝ ND^(-3/4)

D BV is independent of doping concentration

Correct Answer: C. BV ∝ ND^(-3/4)

EXPLANATION

Breakdown voltage BV ∝ ND^(-3/4) approximately; lower doping increases depletion width, requiring higher field and higher voltage for breakdown.

Test

Q.67 Hard Electronic Devices

The Miller effect in a common-emitter BJT amplifier causes:

A Decrease in input impedance

B Effective multiplication of base-collector capacitance by (1+Av) at input

C Increase in voltage gain

D Phase shift of 180°

Correct Answer: B. Effective multiplication of base-collector capacitance by (1+Av) at input

EXPLANATION

Miller effect: CBE capacitance reflected to input = CμC·(1+|Av|); dominates high-frequency response and limits bandwidth in CE configuration.

Test

Q.68 Hard Electronic Devices

In a Gunn diode, negative resistance occurs due to:

A Impact ionization breakdown

B Differential mobility in different valley structures of semiconductor

C Tunneling phenomenon

D Avalanche multiplication

Correct Answer: B. Differential mobility in different valley structures of semiconductor

EXPLANATION

Gunn effect: electrons transfer from high-mobility Γ valley to low-mobility L valley at threshold field, causing dI/dV < 0 (negative resistance).

Test

Q.69 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.70 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

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