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Elec Circuits & Comm Fundamentals : Question Paper Dec 2015 - Computer Engineering (Semester 3) | Mumbai University (MU)

## Elec Circuits & Comm. Fundamentals - Dec 2015

### Computer Engineering (Semester 3)

TOTAL MARKS: 80
TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.
(2) Attempt any three from the remaining questions.
(3) Assume data if required.
(4) Figures to the right indicate full marks.
1 (a) Give reasons for the following:
i) FET is called as a square law device
ii) Barkhausens criteria should be satisfied to get oscillations.
(5 marks)
1 (b) With neat diagram explain any one application of Zero-Crossing Detector.(5 marks) 1 (c) With neat circuit diagram explain the use of PLL as a phase shifter.(10 marks) 1 (d) Explain with suitable example what do you understand by signal multiplexing?(10 marks) 2 (a) Draw and explain JFET characteristics. Also show that for a JFET $$9m = \dfrac {2}{|V_p|}\sqrt{l_{DSS}\cdot l_{DS}}$$(5 marks) 2 (b) With respect to op-amp explain the ideal characteristics and concept of virtual aground. Explain how op-amp can be used as an averaging amplifier in inverting configuration. Also draw neat circuit diagram to
i) Convert sine wave to square wave using op-amp.
ii) detect the crossing of zero's in the generated square wave.
(5 marks)
3 (a) Explain how operating amplifier can be used for addition of two AC signals with one DC signal.(5 marks) 3 (b) Explain fly wheel effect in Class C amplifier.(5 marks) 3 (c) What is sampling theorem and state its significance in communication. What is the standard frequency for speech signal?(5 marks) 3 (d) Determine the magnitude of gm for a JFET with lDSS=8 mA and VP=-4 V at the following dc bias points:

a) VGS=-0.5 V.
b) VGS=-1.5 V.
c) VGS=-2.5 V.
(5 marks)
4 (a) Explain generation of SSB using phase shift method.(10 marks) 4 (b) Discuss the operating principle of PLL and explain its use as frequency translator.(10 marks) 5 (a) With neat diagram explain the circuit for FM detection.(10 marks) 5 (b) Explain amplitude modulation for more than one modulating signal in the following cases
i) Mathematical equation
ii) AM waveform
iii) AM amplitude and power spectrum
iv) modulation Coefficient
v) Transmission Power
(10 marks)
6 (a) Explain application of PLL as frequency synthesizer.(5 marks) 6 (b) With block diagram explain TDM-PCM system?(5 marks) 6 (c) Write short note on generation of FM by Armstrong method.(5 marks) 6 (d) Compare different biasing techniques for JFET.(5 marks)