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?

The correct answer is C: ~1000 times. 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

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.

The convolution of x[n] = {1, 2, 3} and h[n] = {1, 1} yields a sequence of length:

The correct answer is C: 4. Length of convolution = M + N - 1 = 3 + 2 - 1 = 4.

In a Finite State Machine (FSM) with 7 states, what is the minimum number of flip-flops required?

The correct answer is B: 3 flip-flops. Minimum flip-flops needed = ⌈log₂(number of states)⌉ = ⌈log₂(7)⌉ = 3.

In a Wien Bridge oscillator, the frequency of oscillation is determined by:

The correct answer is B: f = 1/(2πRC) where R and C are in the bridge arms. Wien Bridge oscillator has frequency of oscillation: f = 1/(2πRC), where R and C are the series and parallel RC components in the bridge network.

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Analog Circuits

Analog/digital electronics, communication

47 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 41–47 of 47

Topics in Electronics (ECE)

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

Q.41 Medium Analog Circuits

In a Class A amplifier, the maximum theoretical efficiency is

A 25%

B 50%

C 75%

D 100%

Correct Answer: A. 25%

EXPLANATION

Maximum theoretical efficiency of Class A = π/4 ≈ 78.5% when maximum swing is used, but practically 25-50% is achieved due to quiescent current and losses.

Test

Q.42 Medium Analog Circuits

For a feedback amplifier with feedback fraction β, the loop gain is defined as

A Aβ

B A/β

C A + β

D β/A

Correct Answer: A. Aβ

EXPLANATION

Loop gain = Aβ, where A is open-loop gain and β is feedback fraction. For stability, loop gain should be <1 for phase margin requirements.

Test

Q.43 Medium Analog Circuits

In an RC coupled amplifier, the lower cutoff frequency is primarily determined by

A Coupling capacitor and input impedance

B Load resistance alone

C Supply voltage

D Transistor junction capacitances

Correct Answer: A. Coupling capacitor and input impedance

EXPLANATION

Lower cutoff frequency fL ≈ 1/(2π·CC·Rin) where CC is coupling capacitor and Rin is input impedance. Larger CC gives lower fL.

Test

Q.44 Medium Analog Circuits

At what frequency does the gain of a RC coupled amplifier reduce to 70.7% of its mid-band gain?

A At DC

B At cutoff frequency (-3dB point)

C At twice the cutoff frequency

D At half the cutoff frequency

Correct Answer: B. At cutoff frequency (-3dB point)

EXPLANATION

The -3dB cutoff frequency is where the magnitude of gain reduces to 1/√2 (≈ 70.7%) of maximum gain. This defines the bandwidth of the amplifier.

Test

Q.45 Medium Analog Circuits

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

A Very low

B Very high (MΩ range)

C Equal to load impedance

D Independent of load resistance

Correct Answer: B. Very high (MΩ range)

EXPLANATION

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.

Test

Q.46 Medium Analog Circuits

In a differential amplifier, the common mode rejection ratio (CMRR) is defined as

A Ratio of differential gain to common mode gain

B Ratio of common mode gain to differential gain

C Product of differential and common mode gains

D Sum of differential and common mode gains

Correct Answer: A. Ratio of differential gain to common mode gain

EXPLANATION

CMRR = Ad/Ac, where Ad is differential mode gain and Ac is common mode gain. High CMRR (>80dB typical) is desired to reject common mode noise.

Test

Q.47 Medium Analog Circuits

The bandwidth of a common emitter amplifier can be increased by

A Increasing the load resistance

B Decreasing the emitter bypass capacitor

C Increasing the collector supply voltage

D Using emitter degeneration resistor without bypass capacitor

Correct Answer: D. Using emitter degeneration resistor without bypass capacitor

EXPLANATION

Emitter degeneration without bypass capacitor increases input impedance and reduces gain but significantly increases bandwidth due to negative feedback.

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Electronics (ECE) Analog Circuits

Electronics (ECE)
Analog Circuits