The group delay of a filter is defined as:

The correct answer is B: τ_g(ω) = -dφ(ω)/dω. Group delay τ_g(ω) = -dφ(ω)/dω represents the delay of signal envelope.

The punch-through effect in a BJT occurs when:

The correct answer is B: Reverse bias on collector-base junction extends depletion region to base contact. Punch-through occurs when CBJ depletion width extends to base contact, causing base resistance to vanish and uncontrolled current flow.

A MOSFET operating in triode (linear) region exhibits:

The correct answer is B: VDS < VGS - VTh. In triode region, the condition VDS < VGS - VTh allows the channel to conduct with resistance proportional to VDS.

A combinational logic circuit implements a function where output Y = (A'BC) + (AB'C) + (ABC'). After minimization using K-map, the circuit requires minimum number of gates. Which of the following is the simplified expression?

The correct answer is C: Y = C(A ⊕ B) + ABC'. Using K-map for three variables: (A'BC) + (AB'C) + (ABC') = C(A'B + AB') + ABC' = C(A ⊕ B) + ABC'. This represents XOR operation with an additional term, which is the minimal form requiring fewer gates than other options.

The input impedance of a voltage follower (common collector) amplifier is

The correct answer is B: Very high (MΩ range). CC amplifier has very high input impedance (Zin ≈ β·re) making it suitable as a buffer stage between high impedance sources and low impedance loads.

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Electronics (ECE)

Analog/digital electronics, communication

187 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 151–160 of 187

Topics in Electronics (ECE)

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

Q.151 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.152 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.153 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.154 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.155 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.156 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

Q.157 Medium Electronic Devices

The output impedance of a BJT common-collector amplifier is approximately:

A r_e = V_T/I_E (very low)

B r_o = V_A/I_C (very high)

C R_L (equal to load resistance)

D R_E || r_e (parallel combination with slight reduction)

Correct Answer: A. r_e = V_T/I_E (very low)

EXPLANATION

Common-collector (emitter follower) configuration provides very low output impedance ≈ r_e = V_T/I_E ≈ 26Ω/I_E(mA). This makes it an excellent impedance matching buffer. The low impedance comes from the emitter follower configuration.

Test

Q.158 Medium Electronic Devices

A CMOS inverter has asymmetric rise and fall times primarily because:

A Electron mobility is higher than hole mobility

B The pull-up and pull-down networks have different W/L ratios

C Supply voltage affects NMOS and PMOS equally

D The threshold voltages are identical

Correct Answer: A. Electron mobility is higher than hole mobility

EXPLANATION

Since μ_n ≈ 2-3 μ_p, NMOS transistors have higher transconductance. To achieve balanced rise and fall times, the PMOS width is typically designed larger (2-3×) than NMOS. Without this, the PMOS pull-up is slower.

Test

Q.159 Medium Electronic Devices

For an IMPATT diode oscillator, the 'IMPATT' stands for:

A Impact Ionization Transit-Time diode

B Impurity Modulated Transit Time diode

C Impact Avalanche and Transit-Time device

D Impedance Modulated Avalanche Transit diode

Correct Answer: C. Impact Avalanche and Transit-Time device

EXPLANATION

IMPATT (Impact Avalanche and Transit-Time) diodes operate by combining avalanche multiplication at the p-n junction with carrier transit time delay, producing negative resistance for microwave oscillation at GHz frequencies.

Test

Q.160 Medium Electronic Devices

A varactor diode is used in frequency modulation circuits because:

A Its junction capacitance varies with reverse bias voltage

B It has high forward conductance

C It exhibits negative resistance characteristics

D Its reverse saturation current is voltage dependent

Correct Answer: A. Its junction capacitance varies with reverse bias voltage

EXPLANATION

Varactor (variable capacitor) diodes have a depletion capacitance C_j = C_0/(1+|V_R|/V_bi)^n that varies with reverse bias. This voltage-dependent capacitance is used to modulate oscillator frequency.

Test

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