In a heterostructure bipolar transistor (HBT), the wide bandgap material in the emitter provides which advantage?

The correct answer is A: Higher emitter injection efficiency and reduced base current. Wide bandgap emitter (e.g., AlGaAs) blocks minority carrier injection from base, improving γE and allowing lower base doping for higher β.

Which of the following logic gates has an output of 1 only when both inputs are different?

The correct answer is A: XOR gate. XOR (Exclusive OR) produces 1 when inputs are different and 0 when they are same.

A signal x[n] has Z-transform X(z) = 1 + 2z^-1 + 3z^-2 for |z| > 0. The signal values are:

The correct answer is A: x[0]=1, x[1]=2, x[2]=3. By definition, X(z) = Σx[n]z^-n. Comparing coefficients: x[0]=1, x[1]=2, x[2]=3.

The input impedance of an op-amp in an ideal configuration is assumed to be:

The correct answer is A: Infinite. Ideal op-amp assumptions include infinite input impedance (no current drawn at inputs), zero output impedance, and infinite open-loop gain.

The energy of a signal x[n] = {1, 2, -1, 0} is:

The correct answer is B: 6. Energy = 1² + 2² + (-1)² + 0² = 1 + 4 + 1 + 0 = 6.

Home

Home › Subjects › Electronics (ECE) › Electronic Devices

Electronics (ECE)
Electronic Devices

Analog/digital electronics, communication

41 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 41

Topics in Electronics (ECE)

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

Q.1 Medium Electronic Devices

In an n-channel depletion-mode MOSFET with Vto = -3 V, if VGS = 0 V, the device is in which region?

A Cutoff region

B Linear (Ohmic) region

C Saturation region

D Breakdown region

Correct Answer: C. Saturation region

EXPLANATION

For n-channel depletion MOSFET, when VGS = 0 V (which is greater than Vto = -3 V), the channel is open and device conducts. With VGS > Vto and positive VDS, the device operates in saturation. Depletion-mode devices conduct at VGS = 0.

Test

Q.2 Medium Electronic Devices

A germanium BJT has a base-emitter voltage VBE = 0.3 V in forward bias. Compared to a silicon BJT with VBE = 0.7 V, which statement is correct?

A Germanium has lower bandgap energy and requires less forward voltage to turn on

B Silicon has lower bandgap energy than germanium

C Both have identical forward voltage requirements

D Germanium BJT cannot be used in modern integrated circuits

Correct Answer: A. Germanium has lower bandgap energy and requires less forward voltage to turn on

EXPLANATION

Germanium has bandgap Eg ≈ 0.67 eV versus silicon's 1.12 eV. Lower bandgap requires less voltage to forward bias. However, silicon is preferred due to better temperature stability and lower leakage current.

Test

Q.3 Medium Electronic Devices

A device operates with reverse saturation current IS = 10^-14 A at 25°C. If temperature increases to 75°C, by approximately what factor does IS increase?

A ~10 times

B ~100 times

C ~1000 times

D ~10,000 times

Correct Answer: C. ~1000 times

EXPLANATION

IS doubles approximately every 5°C for Si. Over 50°C increase: IS(75°C) = IS(25°C)·2^(50/5) = 2^10 ≈ 1000 times

Test

Q.4 Medium Electronic Devices

In a BJT common-emitter amplifier with emitter bypass capacitor, what is the primary effect on voltage gain?

A Increases due to reduced emitter degeneration

B Decreases due to increased feedback

C Remains unchanged from uncompensated stage

D Becomes frequency-dependent only at high frequencies

Correct Answer: A. Increases due to reduced emitter degeneration

EXPLANATION

Bypass capacitor shorts RE to ground at signal frequencies, eliminating degeneration feedback and increasing Av = gm·RC approximately.

Test

Q.5 Medium Electronic Devices

A DIAC is used in a light dimmer circuit. What is its primary characteristic?

A Bidirectional switching at a fixed breakover voltage

B Unidirectional conduction with adjustable trigger voltage

C Analog voltage regulation

D Phase shift modulation capability

Correct Answer: A. Bidirectional switching at a fixed breakover voltage

EXPLANATION

DIAC is a bidirectional diode that switches in both directions when breakover voltage (typically 30V) is exceeded, used to trigger TRIACs.

Test

Q.6 Medium Electronic Devices

A thyristor (SCR) is triggered into conduction. To turn it off, which method is most commonly used in AC circuits?

A Gate reverse bias

B Anode-cathode voltage reversal (natural commutation)

C Sudden removal of gate signal

D Increasing forward bias voltage

Correct Answer: B. Anode-cathode voltage reversal (natural commutation)

EXPLANATION

SCRs turn off naturally when anode-cathode voltage reverses in AC supply. Gate signal only triggers ON, not OFF.

Test

Q.7 Medium Electronic Devices

A light-emitting diode (LED) has a bandgap of 2.5 eV. What is the approximate wavelength of emitted light?

A 450 nm

B 550 nm

C 500 nm

D 600 nm

Correct Answer: C. 500 nm

EXPLANATION

λ = hc/Eg = (1240 eV·nm)/(2.5 eV) ≈ 496 nm ≈ 500 nm (green light region)

Test

Q.8 Medium Electronic Devices

In a MOSFET, the transconductance gm depends on which parameters in saturation region?

A gm = (1/2)·(W/L)·μn·Cox·(VGS - VT)

B gm = μn·Cox·(VGS - VT)²/2

C gm = (W/L)·μn·Cox·VDS

D gm is independent of gate-source voltage

Correct Answer: A. gm = (1/2)·(W/L)·μn·Cox·(VGS - VT)

EXPLANATION

In saturation, gm = ∂ID/∂VGS = (W/L)·μn·Cox·(VGS - VT), showing linear dependence on overdrive voltage.

Test

Q.9 Medium Electronic Devices

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?

A 40 kΩ

B 4 kΩ

C 400 Ω

D 4 MΩ

Correct Answer: A. 40 kΩ

EXPLANATION

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

Test

Q.10 Medium Electronic Devices

Which of the following statements about Schottky diodes is incorrect?

A They have lower forward voltage drop compared to p-n junction diodes

B They exhibit higher reverse leakage current than p-n junctions

C They are used in high-speed switching applications

D They have higher junction capacitance than p-n diodes of same rating

Correct Answer: D. They have higher junction capacitance than p-n diodes of same rating

EXPLANATION

Schottky diodes have LOWER junction capacitance due to the metal-semiconductor junction, making them suitable for high-frequency applications.

Test

1 2 3…5

All Subjects & Topics

Govt. Exams

Entrance Exams

Teacher Exams

Subjects

Quick Links

Electronics (ECE) Electronic Devices

Electronics (ECE)
Electronic Devices