Previous Question Papers Electronic Devices and Circuits

MODEL QUESTION PAPER-1

Answer ALL Questions

PART A - (10 x 2 = 20 marks)

1. Define Pinch off Voltage.

It is the voltage at which the channel is pinched off, (i.e.,) all the free charges from the channel get removed.

2. Compare Avalanche and Zener breakdown.

3. What do you mean by Q-point?

The voltages and currents are called quiescent values and they determine the operating point or Q-point for the transistor. Since the operating point is a fixed point on the transistor characteristics, it is also called as Quiescent point or Q- point

4. What are the methods for biasing BJT?

i. Fixed Bias (or) Base Resistor Method

ii. Collector to Base Bias (or) Biasing with Feedback Resistor

iii. Self Bias or Emitter Bias

5. Write the features of differential amplifier.

i. High differential gain

ii. Low common mode gain

iii. High CMRR

iv. High input impedance and low output impedance

v. High gain

vi. Large Bandwidth

6. Define bandwidth of tuned circuit.

The bandwidth of a tuned circuit is defined as the band of frequencies between the points in the resonance curve when the impedance drops to 1/√2 of its maximum value at resonance

7. What is Barkhausen Criterion?

For getting sustained oscillations we should satisfy the following two conditions.

(i) The loop gain should be unity

(ii) The loop phase shift should be 0° or 360°. ie., β_V A_V = 1. This criterion is known as Barkausen's criterion for oscillation.

8. Why crystal oscillators are superior than other oscillator.

Crystal oscilators are superior than other oscillators because of their great mechanical strength, simplicity of manufacture and it obeys the Piezoelectric effect accurately.

9. What is power amplifier?

Power amplifier amplifies a weak signal until sufficient power to operate output device such as loudspeaker.

10. What do you mean by Buck-Boost Converter?

A Buck-Boost Regulator produces an output voltage which may be less than or greater than the input voltage. The polarity of output voltage is opposite that of input voltage. So, this regulator is also known as inverting or flyback regulator.

PART B (5 × 15 = 80 Marks)

11. (a) With necessary diagram explain the forward and reverse characteristics of PN Junction diode.

[OR]

(b) Draw the basic construction and equivalent circuit of UJT. Briefly explain the device operation.

12. (a) Explain the various techniques for biasing FET.

[OR]

(b) Explain the analysis of CE amplifier with emitter resistor.

13. (a) Explain the common mode and differential mode analysis of differential amplifier and derive its CMRR.

[OR]

(b) Explain the operation of tuned amplifiers in detail.

14. (a) With a neat block diagram, explain voltage series and current shunt feedback amplifier.

[OR]

(b) Explain with neat circuit diagram, the working of Hartely oscillator using transistor. Derive an expression for frequency of oscillation.

15. (a) Explain the operation of class A power amplifier and derive its efficiency.

[OR]

(b) Explain the operation of Buck converter in detail.

 

MODEL QUESTION PAPER-2

Answer ALL Questions

PART A-(10 x 2 = 20 marks)

1. State few applications of Zener diode.

i. Voltage regulators.

ii. Zener limiters to clip the unwanted portion of the voltage waveform.

iii. Over voltage protection.

2. Why FET is called unipolar device?

The operation of FET depends upon the flow of majority carriers only either hour or electrons and hence FET is said to be unipolar device.

3. Write the properties of common source amplifier.

i. High input and output impedance

ii. Relatively high small-signal voltage gain.

iii. Very high small-signal current gain.

4. Define biasing.

The process of giving proper supply voltages and resistances for obtaining the desired operating point is known as biasing.

5. What is cascade amplifier?

The output of one stage is fed as the input of the next stage. Two or more CE amplifier are connected together to form cascade amplifier.

6. Define CMRR.

Common Mode Rejection Ratio (CMRR) is defined as the ability of a differential amplifier to reject the common mode signal. It is the figure of merit of a differential amplifier.

7. What are the factors required to choose type of oscillators.

The factors needed to choose type of oscillators are

i. The nature of generated wave form.

ii. The frequency of generated signals

iii. The type of associated circuit of components.

iv. The fundamental mechanism involved

8. Write the advantages of negative feedback.

i. Negative feedback stabilizes the gain of the amplifier.

ii. There is a significant increase in the bandwidth of the amplifier.

iii. Distortions in the amplifier output are reduced.

iv. Input resistance increases for certain feedback configurations.

v. Output resistance decreases for certain feedback configurations.

vi. Operating point is stabilized

9. Compare voltage and power amplifiers.

10. What do you mean by Buck converter?

Buck converter is also known as step down converter and produces a lower output voltage than input voltage. The average output voltage is less than the input voltage.

 

PART B (5 × 15 = 80 Marks)

11. (a) (i) Explain the construction and operation of zener diode.

(ii) How does a zener diode operate as voltage regulator. Explain.

[OR]

(b) Draw the circuit diagram of a depletion MOSFET amplifier and explain. its operation.

12. (a) Draw the equivalent circuit for common source amplifier at high frequencies and derive expressions for voltage gain, input and output impedance.

[OR]

(b) Explain the biasing methods of BJT in detail.

13. (a) Explain the operation of differential amplifier in detail and derive its expressions.

[OR]

(b) What is neutralization? Explain its methods in detail.

14. (a) Explain the operation of voltage series and current series feedback amplifier in detail.

[OR]

(b) Explain the operation of Wien bridge oscillator in detail and derive its frequency of oscillation.

15. (a) Draw the circuit of push pull class B amplifier and explain its operation.

[OR]

(b) Write notes on

(i) Distortion in amplifiers

(ii) Compare Class A, B, AB and C amplifiers.