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B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2011.
B.E – Electronics and Communication Engineering
147304 — ELECTRONICS CIRCUITS — 1
Time : Three hours Maximum : 100 marks
Answer ALL questions.
PART A — (10 ´ 2 = 20 marks)
1. What is quiescent point?
2. Define stability factor.
3. Compare gain characteristics of CB and CC transistor circuits.
4. What is the advantage of Darlington circuit?
5. Mention the importance of the resistor rbb’ in the transistor hybrid p model.
6. If two amplifiers of voltage gains 50 and 100 are cascaded, what is overall gain
of the circuit in decibels?
7. What is second harmonic distortion?
8. Mention the application of class C amplifiers.
9. Define voltage regulation.
10. What is the principle of operation of an inductor filter in a rectifier circuit?
PART B — (5 ´ 16 = 80 marks)
11. (a) Draw a voltage divider bias circuit using npn transistor and explain its
operation. Analyze the circuit and obtain the stability factor of the
circuit. Discuss the advantages of this circuit with respect to other
biasing circuits. (16)
(b) (i) What is the need for bias compensation? Describe the method of
bias compensation using diodes. (9)
(ii) Explain the use of thermistor and sensistor for bias compensation.
12. (a) (i) Draw the small signal equivalent model of CE amplifier circuit and
analyze the circuit to obtain its gain, input and output impedance.
(ii) Explain the effect of removing the bypass capacitor from the
emitter resistor of the CE amplifier circuit. (4)
(b) Draw the circuit of a emitter coupled differential amplifier and explain
its operation. Analyze the circuit and obtain its transfer characteristics.
13. (a) With the help of the high frequency model of the transistor, analyze the
current gain of CE transistor amplifier with a short circuit load and
obtain its gain-frequency response. (16)
(b) (i) Draw and explain the high frequency equivalent circuit of a FET. (8)
(ii) Explain the effect of cascading transistor stages on the bandwidth
of a cascaded amplifier. (8)
14. (a) (i) Distinguish class A, class B and class C amplifiers. (6)
(ii) Explain with a neat diagram, the operation of a class A push pull
amplifier. Explain the how the circuit eliminates second harmonic
(b) (i) Explain with a neat diagram the operation of a complementary
symmetry Class B amplifier. (6)
(ii) Derive the conversion efficiency of a class B amplifier circuit. List
the advantages and disadvantages of the circuit. (10)
15. (a) (i) Explain the operation of a Capacitor filter in a full wave rectifier
circuit. Derive the equation for ripple factor for the circuit and
explain the advantages of the capacitor filter. (12)
(ii) Mention the important characteristics of a LC filter in a rectifier. (4)
(b) (i) Describe the operation of a shunt voltage regulator. (8)
(ii) Explain how SCR can be used for power control. (8)