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QUESTION: 1

For the Wien-bridge oscillator circuit shown below, the condition for bridge balance is

Solution:

At oscillator frequency

i.e. gain of non-inverting amplifier

⇒ R_{B} = 2R_{A}

QUESTION: 2

Find the value of inductance in (mH) in the oscillator shown below to achieve a frequency of oscillation = 100 KHz is

Solution:

*Answer can only contain numeric values

QUESTION: 3

For the circuit shown in the figure the value of R to get oscillation of 100 kHz is ________ KΩ.

Solution:

The given oscillator is Colpitts’s oscillator

The condition for oscillation is

|Aβ|=1

A = -R_{2}/R_{1}

β=C_{2}/C_{1
}

*Answer can only contain numeric values

QUESTION: 4

The figure shows a phase-shift oscillator circuit with voltage follower buffer stages.

The value of R_{2}/R required for sustained oscillations is _____.

[Assume ideal op-amps and neglect loading effect].

Solution:

- The basic amplifier of the circuit is the op-amp A
_{3}. - The output of amplifier is connected to 3 stage RC filter.
- Voltage followers eliminate loading effect of each stage.

**Transfer function of first RC network
**

RC networks are identical and no loading effect

The amplifier A

The loop gain is

Substitute real part of denominator to zero

At this frequency

QUESTION: 5

The value of R in oscillator circuit shown in a given circuit below is chosen such that it oscillates at an angular frequency of ω. The value of ω and the required value of R will respectively be

Solution:

**Hartley oscillator
**

Amp with +ve F.B

Loop again AB = 1 + j0

At oscillation

∠AB = 0 (no reactance X_{L} = X_{C})

At frequency of oscillation look lies resistive Network

For ideal op amp

Use voltage division Rule

R + 1 = 21

R = 20 kΩ

R = 2 × 10^{4}Ω

*Answer can only contain numeric values

QUESTION: 6

The frequency of oscillation of the circuit in kilohertz is ______ kHz.

Solution:

The given circuit is wein bridge oscillator.

R_{3} = R_{4} = 159 KΩ

C_{1} = C_{2} = 1 nF

= 10^{3} HZ

= 1 KHZ

QUESTION: 7

For the transistor oscillator circuit given below the frequency of oscillation is 8.5 kHz. The value of the collector resistor approximately is

Solution:

In a transistor phase shift oscillator the oscillation frequency

R, C are the resistor and the capacitor in phase shift circuit

R_{C} is collector capacitance

⇒ R_{C} = 2R = 10 kΩ

*Answer can only contain numeric values

QUESTION: 8

The oscillation frequency if the below-shown oscillator is 1 kHz then the value of ‘L’ is ______ mH

Solution:

The given oscillator is Hartley oscillator, where the oscillation frequency.

= 253.3 mH

L_{eq} = L + 5 mA

⇒ L = 253.3 – 5

= 248. 3 mH

QUESTION: 9

For the circuit shown the value of R_{1} and R_{2} such that the circuit generates oscillations of frequency 274 Hz is [Assume the time constant of the feedback RC network is 0.01 sec]

Solution:

Given figure is of A-stable multi-vibrator,

Time constant is given by

β = feedback factor

τ = time constant of feedback loop:

Option 3 satisfies the condition

*Answer can only contain numeric values

QUESTION: 10

The frequency of oscillation of the circuit shown below is ________ Hz.

Solution:

The given oscillator is Wien-bridge oscillator with R = 5 kΩ, C = 1 μF

⇒ frequency of oscillation f = 1/2πRC

= 31.8 Hz

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