Electronic Circuits II 4th AM10 EC2251

B.E./B.Tech. DEGREE EXAMINATION, APRIL/MAY 2010
Fourth Semester
Electronics and Communication Engineering
EC2251 — ELECTRONIC CIRCUITS – II
(Regulation 2008)

PART A — (10 × 2 = 20 Marks)

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

PART B — (5 × 16 = 80 Marks)

11. (a) (i) Explain how negative feedback acts on bandwidth, distortion, Input Impedance and Output Impedance of a circuit. (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 1 MHz? (8)
Or
(b) (i) Explain voltage series and voltage shunt feedback connections. (8)
(ii) Explain Nyquist criterion to analyse the stability of feedback amplifiers. (8)

12. (a) (i) Explain Armstrong oscillator and derive its frequency of oscillation. (8)
(ii) A Colpitts oscillator is designed with pF C 100 1 = and pF C 7500 2 = . The inductance is variable. Determine the range of inductance values, if the frequency of oscillation is to vary between 950 KHz and 2050 KHz. (8)
Or
(b) (i) Explain Wien bridge oscillator and derive its frequency of oscillation. (10)
(ii) Write a note on frequency stability of oscillators. (6)

13. (a) (i) Discuss about double tuned voltage amplifier. (8)
(ii) Discuss the effect of bandwidth on cascading single tuned amplifiers. (8)
Or
(b) (i) Explain class C tuned amplifier and derive its efficiency. (10)
(ii) Explain Hazeltine Neutralization Method. (6)

14. (a) (i) Sketch and define transistor switching times. (8)
(ii) What is a clipper? Explain the operation of positive and negative diode clippers with waveforms. (8)   Or
(b) (i) Explain astable multi vibrator with neat sketch of waveforms at collector and base of transistors used in the circuit. (10)
(ii) Determine the value of capacitors to be used in an astable multi vibrator to provide a train of pulse s Âµ 2 wide at a repetition rate of 100 KHz if = = k R R 20 2 1 . (6)

15. (a) (i) Explain about astable blocking oscillator with base timing. (10)
(ii) The diode controlled astable blocking oscillator has the parameters 10 = CC V V, V VB 5 . 0 = , 2 = n , = K R 5 . 1 , =10 f R , V Vr 9 = , mH L 3 = and pF C 100 = . Calculate the frequency of oscillation and duty cycle. (6)
Or
(b) Write about Miller Integrator and Current-Time Base Circuit with waveform. (16)