What is the phase shift introduced by a first-order RC low-pass filter at the cutoff frequency (fc)?

The correct answer is B: -45°. At cutoff frequency, the impedances of R and C are equal, resulting in a phase shift of -45° for a single RC low-pass filter.

In practical MOSFET applications for RF circuits, which parasitic effect limits frequency response most?

The correct answer is B: Gate-drain capacitance (Miller effect). The gate-drain capacitance (Cgd) creates Miller effect, which effectively multiplies the capacitive reactance in feedback, severely limiting high-frequency gain.

In Gray code, how many bits change when transitioning from 5 (0101) to 6 (0110)?

The correct answer is A: 1 bit. Gray code for 5 is 0111 and for 6 is 0101. Only 1 bit changes between consecutive numbers, which is the main advantage of Gray code.

In a 4:2 encoder, if input line 5 is active, what is the output?

The correct answer is C: 101 (3-bit output). A 4:2 encoder has 4 inputs and 2 outputs. However, for 8 inputs, a 3:8 encoder or 8:3 decoder is needed. Input line 5 would give binary 101.

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

The correct answer is A: Avalanche multiplication. Low doping leads to wide depletion region favoring avalanche breakdown (impact ionization) rather than direct Zener tunneling.

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Electronics (ECE)
Signals & Systems

Analog/digital electronics, communication

49 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 49

Topics in Electronics (ECE)

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

Q.11 Medium Signals & Systems

A discrete signal x[n] = cos(π n/6) has a period of:

A 6

B 12

C 24

D 3

Correct Answer: B. 12

EXPLANATION

For x[n] = cos(2πk n/N), the period N = 6/(1/2) = 12 samples.

Test

Q.12 Medium Signals & Systems

For a signal x[n] = cos(πn/4), the fundamental period N is:

A 4

B 8

C 16

D 2

Correct Answer: B. 8

EXPLANATION

For x[n] = cos(ω₀n), period N = 2π/ω₀ = 2π/(π/4) = 8.

Test

Q.13 Medium Signals & Systems

A first-order discrete filter y[n] = 0.8y[n-1] + 0.2x[n] has DC gain (at z=1) of:

A 0.2

B 1

C 0.8

D 2.5

Correct Answer: B. 1

EXPLANATION

Transfer function H(z) = 0.2/(1-0.8z⁻¹). DC gain H(1) = 0.2/(1-0.8) = 0.2/0.2 = 1.

Test

Q.14 Medium Signals & Systems

A discrete signal undergoes 16-point FFT computation. The frequency resolution is Δf = 1 kHz. The sampling frequency fs is:

A 16 kHz

B 8 kHz

C 32 kHz

D 4 kHz

Correct Answer: A. 16 kHz

EXPLANATION

Frequency resolution Δf = fs/N, where N=16. Therefore, fs = Δf × N = 1 × 16 = 16 kHz.

Test

Q.15 Medium Signals & Systems

A system has step response s(t) = 1 - e^(-2t)u(t). Its impulse response h(t) is:

A 2e^(-2t)u(t)

B e^(-2t)u(t)

C -2e^(-2t)u(t)

D δ(t) - 2e^(-2t)u(t)

Correct Answer: A. 2e^(-2t)u(t)

EXPLANATION

h(t) = ds(t)/dt = d/dt[1 - e^(-2t)u(t)] = 2e^(-2t)u(t).

Test

Q.16 Medium Signals & Systems

For a finite impulse response (FIR) filter of length M=5, the maximum linear phase is achieved when:

A h[n] is symmetric about n=2

B h[n] is antisymmetric about n=2

C h[n] has odd symmetry

D h[n] is random

Correct Answer: A. h[n] is symmetric about n=2

EXPLANATION

Linear phase FIR filters require symmetric (even) or antisymmetric (odd) impulse responses about the center. For length 5, center is n=2.

Test

Q.17 Medium Signals & Systems

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

A cos(2πf₀t)

B 2cos(2πf₀t)

C sin(2πf₀t)

D e^(j2πf₀t)

Correct Answer: A. cos(2πf₀t)

EXPLANATION

IFT{δ(f-f₀)} = e^(j2πf₀t) and IFT{δ(f+f₀)} = e^(-j2πf₀t). Sum = 2cos(2πf₀t), but accounting for delta properties, result is cos(2πf₀t).

Test

Q.18 Medium Signals & Systems

The pole-zero diagram of a causal system shows poles at z = 0.3 and z = 0.7, with a zero at z = 0. The system is:

A Low-pass filter

B High-pass filter

C Band-pass filter

D All-pass filter

Correct Answer: B. High-pass filter

EXPLANATION

Zero at z=0 (DC) causes attenuation at low frequencies. Poles near z=1 allow high frequencies to pass, characteristic of a high-pass filter.

Test

Q.19 Medium Signals & Systems

A real continuous-time signal has Fourier transform X(f) with magnitude |X(f)| symmetric about f=0. Which property is satisfied?

A Even symmetry of x(t)

B Odd symmetry of x(t)

C X(f) is always real

D x(t) is complex

Correct Answer: A. Even symmetry of x(t)

EXPLANATION

For a real signal, X(f) exhibits Hermitian symmetry: X(-f) = X*(f). Magnitude symmetry |X(-f)| = |X(f)| indicates even symmetry in x(t).

Test

Q.20 Medium Signals & Systems

For a causal discrete-time LTI system with H(z) = 1/(1-0.5z⁻¹), the system is:

A Stable and FIR

B Stable and IIR

C Unstable and FIR

D Unstable and IIR

Correct Answer: B. Stable and IIR

EXPLANATION

Pole at z=0.5 (inside unit circle) makes the system stable. The denominator has z⁻¹ term, making it IIR (infinite impulse response).

Test

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Electronics (ECE) Signals & Systems

Electronics (ECE)
Signals & Systems