A signal has autocorrelation R(0) = 10 and R(1) = 5. What is the signal's power?

The correct answer is B: 10. For a signal, power P = R(0) = autocorrelation at lag 0.

In a 4-bit binary counter, after state 1111, the next state is:

The correct answer is B: 0000. In a 4-bit binary counter, states cycle from 0000 to 1111 (0 to 15). After 1111, it wraps around to 0000 (overflow occurs).

In a Butterworth filter design, increasing the filter order primarily:

The correct answer is C: Increases roll-off rate after cutoff frequency. Higher-order filters provide steeper roll-off (slope = -20N dB/decade for Butterworth). They reduce transition width and are more complex computationally.

A filter has poles at z = 0.7 and z = 0.9. What can we infer about its stability and response?

The correct answer is B: Stable, poles inside unit circle. For discrete-time systems, stability requires all poles inside the unit circle (|z| < 1). Both 0.7 and 0.9 satisfy this, so the filter is stable.

A 4-bit binary subtractor using 2's complement method requires:

The correct answer is A: 4 full adders and complementing circuit. 2's complement subtraction (A-B) converts to addition A+2's complement of B. This requires 4 full adders (for addition) and XOR gates (for bit complementing), avoiding dedicated subtractors

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Electronics (ECE)

Analog/digital electronics, communication

187 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 81–90 of 187

Topics in Electronics (ECE)

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

Q.81 Medium Analog Circuits

The Miller effect in a Common Emitter amplifier results in:

A Increase in input capacitance

B Decrease in bandwidth

C Both A and B

D Increase in gain

Correct Answer: C. Both A and B

EXPLANATION

Miller effect causes effective input capacitance to increase by factor (1 + |Av|), reducing input impedance and bandwidth. This limits high-frequency response.

Test

Q.82 Medium Analog Circuits

In an RC phase shift oscillator, how many RC sections are typically used to achieve 180° phase shift?

A One

B Two

C Three

D Four

Correct Answer: C. Three

EXPLANATION

Three RC sections are used, each providing 60° phase shift. Total = 3 × 60° = 180°, which combined with 180° from inverting amp gives 360° (0°) for sustained oscillation.

Test

Q.83 Medium Analog Circuits

A Class B amplifier has two transistors operating in push-pull configuration. What is the maximum theoretical efficiency?

A 50%

B 78.5%

C 88.5%

D 95%

Correct Answer: B. 78.5%

EXPLANATION

Class B has maximum efficiency of π/4 ≈ 78.5%. Each transistor conducts 180° of the signal cycle, eliminating idle current waste compared to Class A.

Test

Q.84 Medium Analog Circuits

For the oscillator to sustain oscillations, the loop gain must satisfy which condition (assuming phase shift is 360° or 0°)?

A Loop gain = 0

B Loop gain ≥ 1

C Loop gain < 0.5

D Loop gain = 0.5

Correct Answer: B. Loop gain ≥ 1

EXPLANATION

Barkhausen criterion requires loop gain ≥ 1 (or |A×β| ≥ 1) for sustained oscillations; less than 1 causes damping, more than 1 causes amplitude growth until saturation.

Test

Q.85 Medium Analog Circuits

Which configuration provides the highest input impedance and lowest output impedance among op-amp circuits?

A Inverting amplifier

B Non-inverting amplifier

C Voltage follower (unity gain buffer)

D Summing amplifier

Correct Answer: C. Voltage follower (unity gain buffer)

EXPLANATION

Voltage follower has Zin ≈ infinity (determined by op-amp input impedance) and Zout ≈ 0, making it ideal for impedance transformation.

Test

Q.86 Medium Analog Circuits

A BJT amplifier exhibits thermal runaway due to increased leakage current. Which design modification can best prevent this phenomenon?

A Increase the base bias resistor value

B Use a voltage divider bias network with low impedance

C Reduce the collector supply voltage

D Increase the emitter bypass capacitor

Correct Answer: B. Use a voltage divider bias network with low impedance

EXPLANATION

Voltage divider bias with low impedance provides stiff bias independent of transistor parameters, preventing thermal runaway by maintaining stable base voltage despite temperature changes.

Test

Q.87 Medium Analog Circuits

In a saturated BJT transistor used as a switch, the voltage drop VCE(sat) is typically

A 0 V (ideally)

B 0.1 - 0.3 V

C 0.7 V

D 5 V

Correct Answer: B. 0.1 - 0.3 V

EXPLANATION

In saturation, VCE(sat) ≈ 0.1-0.3 V for silicon BJT (not zero due to residual resistance). VBE(on) ≈ 0.7V in saturation. This is used in switching applications.

Test

Q.88 Medium Analog Circuits

The gain-bandwidth product (GBP) of an op-amp is approximately constant. For a 741 op-amp with GBP ≈ 1 MHz, the open-loop gain at 100 kHz is approximately

A 10 V/V

B 100 V/V

C 1000 V/V

D 10000 V/V

Correct Answer: A. 10 V/V

EXPLANATION

GBP = Aol × f. For 741: 1 MHz = Aol × 100 kHz, therefore Aol = 1 MHz / 100 kHz = 10 V/V. GBP is approximately constant over frequency.

Test

Q.89 Medium Analog Circuits

In a Colpitts oscillator, the frequency of oscillation is determined by

A Only inductance L

B Only capacitance values

C L and the series combination of capacitors C1 and C2

D L and parallel combination of C1 and C2

Correct Answer: C. L and the series combination of capacitors C1 and C2

EXPLANATION

Colpitts oscillator frequency f = 1/(2π√(L·Ceq)) where Ceq = (C1·C2)/(C1+C2). Voltage divider is formed by C1 and C2 for feedback.

Test

Q.90 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.

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