In a p-channel MOSFET, if VGS = -8 V and VT = -2 V, what is the gate-source overdrive voltage?

The correct answer is A: -6 V. For p-channel: |VGS - VT| = |-8 - (-2)| = |-6| = 6 V overdrive, or algebraically VGS - VT = -8 - (-2) = -6 V

For a Source Follower (Common Drain FET amplifier), what is the typical voltage gain range?

The correct answer is B: Voltage gain ≈ 1 but less than 1. Source follower has voltage gain Av = gm·Rl/(1 + gm·Rl) ≈ 1 for practical cases, always less than 1. It provides high input impedance and low output impedance.

For a causal LTI system with transfer function H(z) = 1/(1-0.5z^-1), the system is:

The correct answer is C: Stable. Pole is at z = 0.5, which lies inside the unit circle. For causality and stability, all poles must be inside |z| < 1.

The inverse Fourier transform of δ(f-f₀) is:

The correct answer is A: e^(j2πf₀t). IFT of δ(f-f₀) = e^(j2πf₀t) using sifting property of delta function

In a 4-bit synchronous binary counter using JK flip-flops, if the clock frequency is 10 MHz, what is the maximum counting frequency at the MSB output?

The correct answer is B: 625 kHz. In a 4-bit synchronous counter, the MSB output toggles every 2^4 = 16 clock cycles. Therefore, MSB frequency = 10 MHz / 16 = 625 kHz. This is the divide-by-16 behavior of a 4-bit counter.

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Electronics (ECE)

Analog/digital electronics, communication

187 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 161–170 of 187

Topics in Electronics (ECE)

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

Q.161 Medium Electronic Devices

In a MESFET (Metal-Semiconductor FET), compared to MOSFET:

A It has better high-frequency performance

B It is easier to manufacture due to Schottky junction formation

C It has lower parasitic capacitances

D All of the above are correct

Correct Answer: D. All of the above are correct

EXPLANATION

MESFETs use Schottky metal-semiconductor junctions instead of oxide layers, resulting in lower gate capacitance, better high-frequency response (f_T/f_max higher), and simpler manufacturing process, especially in GaAs technology.

Test

Q.162 Medium Electronic Devices

In an optocoupler (photocoupler), the coupling efficiency depends on:

A Only the LED forward current

B The spectral response match between LED emission and photodetector sensitivity

C Only the photodetector bandwidth

D The operating temperature of the LED

Correct Answer: B. The spectral response match between LED emission and photodetector sensitivity

EXPLANATION

Coupling efficiency is maximized when the LED's emission spectrum overlaps with the photodetector's spectral sensitivity. Spectral mismatch significantly reduces overall coupling efficiency.

Test

Q.163 Medium Electronic Devices

A photodiode is operated in photovoltaic mode when:

A It is forward biased with light incident on junction

B It is reverse biased and generates voltage without external bias

C It is not biased externally, with light generating open-circuit voltage

D It operates in breakdown region under illumination

Correct Answer: C. It is not biased externally, with light generating open-circuit voltage

EXPLANATION

Photovoltaic mode occurs when the photodiode is not externally biased and acts as a light-sensitive voltage source, generating an open-circuit voltage proportional to light intensity. This is used in solar cells.

Test

Q.164 Medium Electronic Devices

In a BJT, the early voltage (V_A) represents:

A The voltage at which base-collector junction breaks down

B The extrapolated voltage where I_C becomes zero with slope equal to output resistance

C The voltage drop across the base terminal

D The thermal voltage at room temperature

Correct Answer: B. The extrapolated voltage where I_C becomes zero with slope equal to output resistance

EXPLANATION

Early voltage is a measure of the output resistance of a BJT. It's the voltage extrapolated from the I_C vs V_CE characteristic where the output current would theoretically become zero, indicating the slope of the characteristic curves.

Test

Q.165 Medium Electronic Devices

Which of the following statements about tunnel diodes is INCORRECT?

A They exhibit negative resistance in forward bias region

B They have heavily doped p and n regions

C They operate at frequencies above 1 GHz

D They have lower switching time than conventional diodes

Correct Answer: C. They operate at frequencies above 1 GHz

EXPLANATION

Tunnel diodes typically operate at frequencies below 100 GHz due to parasitic capacitances and lead inductances, though they are still very fast. All other statements are correct characteristics of tunnel diodes.

Test

Q.166 Medium Electronic Devices

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

A Lower base current requirement and reduced input impedance

B Lower base current requirement and improved input impedance

C Higher base current and higher transconductance

D No change in circuit performance

Correct Answer: B. Lower base current requirement and improved input impedance

EXPLANATION

Higher β means lower IB needed for same IC, reducing loading on the driving source and improving effective input impedance (Zin ≈ β×re).

Test

Q.167 Medium Electronic Devices

In a BJT common-emitter amplifier, if input impedance needs to be increased, the preferred biasing technique is:

A Fixed base bias

B Collector feedback bias

C Voltage divider bias with emitter resistor

D Emitter bias alone

Correct Answer: C. Voltage divider bias with emitter resistor

EXPLANATION

Voltage divider bias with emitter resistor provides stability and increases input impedance through negative feedback from emitter resistor.

Test

Q.168 Medium Electronic Devices

The breakdown mechanism in a Zener diode at low doping concentrations is primarily:

A Avalanche multiplication

B Zener tunneling

C Impact ionization

D Thermal runaway

Correct Answer: A. Avalanche multiplication

EXPLANATION

Low doping leads to wide depletion region favoring avalanche breakdown (impact ionization) rather than direct Zener tunneling.

Test

Q.169 Medium Electronic Devices

A Schottky diode compared to a pn-junction diode has:

A Higher forward voltage drop

B Lower forward voltage drop and faster switching

C Slower recovery time

D Higher reverse saturation current and lower leakage

Correct Answer: B. Lower forward voltage drop and faster switching

EXPLANATION

Schottky diodes have forward voltage ~0.3-0.4V (vs 0.7V for Si) and fast switching due to no stored charge in depletion region.

Test

Q.170 Medium Electronic Devices

In a Zener diode regulation circuit, increasing load current causes:

A Zener current to increase

B Zener current to decrease

C Output voltage to increase

D Series resistor voltage to decrease

Correct Answer: B. Zener current to decrease

EXPLANATION

As load current increases, less current flows through the Zener diode to maintain constant output voltage, so Zener current decreases.

Test

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