The frequency response of a BJT amplifier is limited at high frequencies primarily by:

The correct answer is B: Base-collector parasitic capacitance C_bc (Miller effect). The base-collector capacitance C_bc exhibits the Miller effect, appearing as (1+|A_v|)C_bc at the base, creating a dominant pole that limits bandwidth. This is the primary high-frequency limitation in BJT amplifiers, with f_T ≈ g_m/(2π(C_bc(1+A_v) + C_be)).

A voltage-controlled voltage source (VCVS) has transconductance gm = 50 mS. If the input voltage is 10 mV, what is the output current?

The correct answer is A: 0.5 mA. Output current Id = gm × Vgs = 50 mS × 10 mV = 50 × 10⁻³ × 10 × 10⁻³ = 0.5 × 10⁻³ A = 0.5 mA

A signal has autocorrelation R_x(τ) = Ae^(-2|τ|). What is its bandwidth (3dB) approximately?

The correct answer is A: 2 rad/s. Power spectral density S_x(ω) = Fourier transform of R_x(τ) = 4A/(4+ω²). At 3dB point: 4+ω² = 8, so ω ≈ 2 rad/s.

In a Colpitts oscillator, the feedback network consists of:

The correct answer is A: Two capacitors in series across the inductor. Colpitts oscillator uses capacitive voltage divider with two capacitors in series across an inductor for frequency-determining feedback.

The energy of signal x(t) = e^(-2t)u(t) is:

The correct answer is B: 0.25 J. E = ∫₀^∞ e^(-4t)dt = [-e^(-4t)/4]₀^∞ = 1/4 = 0.25 J

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Electronics (ECE)

Analog/digital electronics, communication

135 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 91–100 of 135

Topics in Electronics (ECE)

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

Q.91 Easy Digital Electronics

Which of the following is NOT a characteristic of ROM (Read-Only Memory)?

A Non-volatile storage

B Programmable by user after manufacture

C Permanent data storage

D Used for storing control sequences

Correct Answer: B. Programmable by user after manufacture

EXPLANATION

Standard ROM is programmed during manufacturing and cannot be reprogrammed by users. PROM, EPROM, and EEPROM allow user programming, but basic ROM does not

Test

Q.92 Easy Digital Electronics

In VHDL, what does the 'rising_edge' function detect?

A High logic level

B Transition from 0 to 1

C Transition from 1 to 0

D Clock frequency change

Correct Answer: B. Transition from 0 to 1

EXPLANATION

'rising_edge' detects a transition from LOW (0) to HIGH (1) on a signal, commonly used in synchronous designs to trigger actions on positive clock edges

Test

Q.93 Easy Digital Electronics

A 3-to-8 decoder has how many output lines, and what is the number of active outputs for any single input combination?

A 8 lines, 1 active output

B 3 lines, 1 active output

C 8 lines, 3 active outputs

D 3 lines, 8 active outputs

Correct Answer: A. 8 lines, 1 active output

EXPLANATION

A 3-to-8 decoder has 2³ = 8 output lines. For any valid input combination, exactly 1 output line is activated (HIGH), while others remain LOW

Test

Q.94 Easy Digital Electronics

The Gray code for decimal 5 is:

A 0101

B 0111

C 0110

D 1001

Correct Answer: B. 0111

EXPLANATION

Decimal 5 = Binary 0101. Gray code is obtained by: G0=B0=1, G1=B0⊕B1=0⊕1=1, G2=B1⊕B2=1⊕0=1, G3=B2⊕B3=0⊕0=0. Result: 0111

Test

Q.95 Easy Digital Electronics

A SR flip-flop with S=0, R=0 results in:

A Set state

B Reset state

C No change in state

D Indeterminate state

Correct Answer: C. No change in state

EXPLANATION

When S=0 and R=0, the SR flip-flop holds its previous state. No change occurs because neither set nor reset is activated

Test

Q.96 Easy Digital Electronics

Which logic gate produces HIGH output only when both inputs are different?

A AND gate

B XOR gate

C NAND gate

D NOR gate

Correct Answer: B. XOR gate

EXPLANATION

XOR (Exclusive OR) gate produces HIGH output when inputs are different (01 or 10). When inputs are same (00 or 11), output is LOW

Test

Q.97 Easy Digital Electronics

In a 4-bit ripple counter using negative edge-triggered flip-flops, if the input frequency is 16 MHz, what is the frequency at the output of the third flip-flop?

A 2 MHz

B 4 MHz

C 8 MHz

D 1 MHz

Correct Answer: A. 2 MHz

EXPLANATION

In a ripple counter, each flip-flop divides the frequency by 2. The third flip-flop output frequency = 16 MHz / 2³ = 16 / 8 = 2 MHz

Test

Q.98 Easy Digital Electronics

A JK flip-flop with J=1, K=1 performs:

A No change

B Set operation

C Reset operation

D Toggle operation

Correct Answer: D. Toggle operation

EXPLANATION

JK flip-flop truth table: J=0,K=0 (No change), J=1,K=0 (Set), J=0,K=1 (Reset), J=1,K=1 (Toggle). When both are 1, output toggles.

Test

Q.99 Easy Digital Electronics

A full adder has how many inputs and outputs?

A 2 inputs, 1 output

B 3 inputs, 2 outputs

C 4 inputs, 2 outputs

D 3 inputs, 3 outputs

Correct Answer: B. 3 inputs, 2 outputs

EXPLANATION

Full adder has 3 inputs (A, B, Cin) and 2 outputs (Sum, Cout). It differs from half adder which has 2 inputs and 2 outputs.

Test

Q.100 Easy Digital Electronics

The BCD equivalent of decimal 47 is:

A 0100 0111

B 0101 0110

C 0100 0101

D 0110 0111

Correct Answer: A. 0100 0111

EXPLANATION

In BCD, each decimal digit is converted separately to 4-bit binary. 4 = 0100, 7 = 0111. So 47 in BCD = 0100 0111.

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