Andhra University 2010 B.E Electronics & Communication Engineering Ec2251 — electronic circuits – ii - Question Paper

B.E./B.Tech. DEGREE EXAMINATION, APRIL/MAY 2010
Fourth Semester

Electronics and Communication Engineering
EC2251 — ELECTRONIC CIRCUITS – II

(Regulation 2008)
Time: 3 hours Maximum: 100 Marks
ans ALL ques.

PART A — (10 × two = 20 Marks)

1. What is the impact of negative feedback on noise in circuits?
2. describe sensitivity and desensitivity of gain in feedback amplifiers.
3. Mention 2 essential conditions for a circuit to maintain oscillations.
4. In a RC phase shift oscillator, if R = R = R = 200 K  one two three and
C C C 100 pF one two three = = = , obtain the frequency of the oscillator.
5. describe tuned amplifier.
6. describe the term unloaded Q factor.
7. provide 2 applications of bistable multivibrator.
8. A 20 KHz, 75% duty cycle square wave is used to trigger continuously, a
monostable multivibrator with a triggered pulse duration of 5µ s . What will be
the duty cycle of the waveform at the output of the monostable multivibrator?
9. Mention any 2 applications of blocking oscillator.
10. What is the function of time base circuit?

PART B — (5 × 16 = 80 Marks)

11. (a) (i) discuss how negative feedback acts on bandwidth, distortion, Input
Impedance and Output Impedance of a circuit. (Marks 8)
(ii) An amplifier has a mid-frequency gain of 100 and a bandwidth
of 200 KHz.
(1) What will be the new bandwidth and gain, if 5% negative
feedback is introduced?
(2) What should be the amount of feedback, if the bandwidth is to
be restricted to one MHz? (Marks 8)
Or

(b) (i) discuss voltage series and voltage shunt feedback connections. (Marks 8)
(ii) discuss Nyquist criterion to analyse the stability of feedback
amplifiers. (Marks 8)

12. (a) (i) discuss Armstrong oscillator and derive its frequency of oscillation.
(Marks 8)

(ii) A Colpitts oscillator is designed with C 100 pF one = and
C 7500 pF two = . The inductance is variable. Determine the range of
inductance values, if the frequency of oscillation is to vary ranging from
950 KHz and 2050 KHz. (Marks 8)
Or
(b) (i) discuss Wien bridge oscillator and derive its frequency of
oscillation. (Marks 10)
(ii) Write a note on frequency stability of oscillators. (Marks 6)

13. (a) (i) explain about double tuned voltage amplifier. (Marks 8)
(ii) explain the effect of bandwidth on cascading single tuned
amplifiers. (Marks 8)
Or
(b) (i) discuss class 'C' tuned amplifier and derive its efficiency. (Marks 10)

Earning:   Approval pending.