Annamalai University question paper december 2014 B.Sc.(physics):Semiconductor device and electronic circuits

Annamalai University question paper december 2014
B.Sc. DEGREE EXAMINATION December 2014
(PHYSICS)
(THIRD YEAR)
(PART-III)
730. SEMICONDUCTOR DEVICE AND ELECTRONIC CIRCUITS
Time: Three hours Maximum: 100 marks
 SECTION – A
 Answer any TEN questions
(10×2=20)
 1. Resistance of a wire is γ ohms. If the wire is stretched to double its
length, what is its resistance in ohms?
2. What are the disadvantages of using laser diode?
3. Which photodiode parameter tells about the lower limit of detection of
light intensity?
4. Name the MOSFET types that is better suited for small signal
amplification of AC signals.
5. Define BJT.
6. Mention two important characteristics of CC circuit.
7. Which feedback increases the gain of the amplifier?
8. Describe the cross over efficiency of class-B push –pull amplifier. How it
can be minimized?
9. When negative voltage feedback is applied to an amplifier of gain 60 the
overall falls to 50. Calculate the feedback factor.
10. What do you mean by Oscillator?
11. Draw the circuit diagram for basic triangular square wave generator.
12. What are the conditions for sustained oscillator?
13. Define hybrid parameter.
14. CMRR for the differential amplifier should be high- comment.
15. What do you mean by summing amplifier?
 SECTION – B
 Answer ALL questions
(5×7=35)
16. a) Describe the working of photodiodes.
(OR)
 b) Write short notes on multi colour LED.
2
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17. a) Draw the following MOSFET.
i) N channel enhancement MOSFET
ii) P channel Enhancement MOSFET
iii) N channel Depletion MOSFET
iv) P channel Deletion MOSFET
(OR)
 b) Draw the biased n channel and p channel JFET’S with JFET
symbol and indicate all voltages and currents.
18. a) Derive the expression for gain –bandwidth product of the amplifier
and show that the gain –bandwidth product is constant.
(OR)
 b) Explain the operation of a complementary symmetry class B
amplifier and explain its advantages.
19. a) Explain Barkhausen criterion.
(OR)
 b) With a neat diagram of Astable multivibrator deduce the formula
for frequency.
20. a) Explain why mathematical operations can be performed using opamp?

(OR)
 b) What is Voltage follower? Explain in detail.
 SECTION – C
 Answer any THREE questions
(3×15=45)
21. Describe the construction and working of a zenea diode and give its
characteristics in detail.
22. Draw the circuit of an emitter coupled BJT differential amplifier and
explain the operation of the circuit. Explain how the differential with a
constant current stage improves the CMRR.
23. Prove that the maximum efficiency of Push pull class B amplifier is
78.5%.
24. What are the factors that affect the frequency stability of an oscillator?
How frequency stability can be improved in oscillators? Derive an
expression for frequency oscillation of Hartley oscillator using transistor.
25. What are the methods to improve the CMRR of differential amplifier?
Detail any two of them.
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