In a Wien bridge oscillator, what is the condition for sustained oscillation?

The correct answer is C: Total phase shift around loop = 0° or 360°, and |Aβ| = 1. For sustained oscillation: (1) Barkhausen condition: |Aβ| = 1 (unity loop gain), (2) Phase condition: ∠Aβ = 0° or 360°. In Wien bridge, gain needed ≈ 3 to compensate losses.

Which of the following statements about Zener diodes is correct?

The correct answer is B: They are reverse biased and maintain constant voltage across their terminals. Zener diodes operate in reverse breakdown region maintaining nearly constant voltage for voltage regulation applications.

The diffusion potential (built-in potential) of a silicon p-n junction at room temperature is approximately:

The correct answer is B: 0.7 V. For silicon at 300K, the built-in potential is typically 0.7 V, determined by V_bi = (kT/q)ln(N_a*N_d/n_i²). This value is fundamental for silicon device calculations.

For a linear time-invariant system with Laplace transform H(s) = 1/(s+2), determine the response to input x(t) = e^(-2t)×u(t):

The correct answer is A: y(t) = t×e^(-2t)×u(t). X(s) = 1/(s+2). Y(s) = H(s)×X(s) = 1/[(s+2)²]. This is a repeated pole, inverse Laplace gives y(t) = t×e^(-2t)×u(t). This is a resonance condition in the system.

An asynchronous counter with n flip-flops counts from 0 to:

The correct answer is B: 2^n - 1. An n-bit counter has 2^n possible states (from 0 to 2^n - 1). For 3-bit counter: states are 0 to 7 (000 to 111).

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Electronics (ECE)
Analog Circuits

Analog/digital electronics, communication

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Difficulty: All Easy Medium Hard 31–33 of 33

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

Q.31 Easy Analog Circuits

For maximum power transfer in an amplifier circuit, the load impedance should be

A Equal to source impedance

B Complex conjugate of source impedance

C Much larger than source impedance

D Much smaller than source impedance

Correct Answer: B. Complex conjugate of source impedance

EXPLANATION

Maximum power transfer theorem states that maximum power is delivered when load impedance is the complex conjugate of source impedance (ZL = ZS*).

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Q.32 Easy Analog Circuits

The input impedance of a common base amplifier is

A Very high (MΩ range)

B Very low (Ω range)

C Moderate (kΩ range)

D Frequency dependent

Correct Answer: B. Very low (Ω range)

EXPLANATION

Common base configuration has very low input impedance (typically 20-100 Ω) because the input is at the emitter which is forward biased.

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Q.33 Easy Analog Circuits

In a common emitter amplifier, the voltage gain is maximum when the load resistance is

A Very small

B Equal to output impedance

C Much larger than output impedance

D Zero

Correct Answer: C. Much larger than output impedance

EXPLANATION

Voltage gain AV = gm × RL. Maximum gain occurs when load resistance is much larger than the output impedance of the transistor, limited only by practical considerations.

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Electronics (ECE) Analog Circuits

Electronics (ECE)
Analog Circuits