Elec Circuits & Comm. Fundamentals - Dec 2014

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) Mention five important specifications of ADC/DAC that are looked at while selecting them for any application.(5 marks) 1 (b) Discuss the factors that influence modulation index of an FM wave.(5 marks) 1 (c) Draw FET based Hartley and Colpitt Oscillator. What is the frequency of oscillation if
i) L1=10 mH, L2=10 mH and C=0.1 ?F for Hartley tank circuit.
ii) L=10 mH, CI=0.1 ?F and C2=0.1 ?F for Colpitt tank circuit.(5 marks) 1 (d) A public address system is connected to a microphone that has a maximum output voltage of 10mV. The microphone is connected to a 10 watt audio amplifier system that is driving an 8 Ohm speakers. The voltage amplifier is non-iverting op-amp circuit. Calculate the maximum voltage gain for the voltage amplifier stage and determine the resistor values to obtain the desired gain. Assume the power amplifier stage has a voltage gain of 1.(5 marks) 2 (a) With proper circuit diagrams and transfer characteristics indicating Q-points do comparison of JFET bias circuit in detail.(10 marks) 2 (b) Find R1 and R2 in the lossy integrator so that the peak gain is 20 dB and the gain is 3dB down from its peak when ?=10,000 rad/s. Use capacitance of 0.01 ?F.(10 marks) 3 (a) Sketch a block representation for an n-channel JFET, showing bias voltages, depletion regions, and current directions. Label the devices= terminals and explain its operation. Explain the effect of increasing levels of negative gate source voltage. Also sketch a typical drain characteristics for V_OS=0 for an n-channel JFET. Explain the shape of the characteristics, identify the regions, and indicates the important current and voltage levels.(10 marks) 3 (b) Draw the spectrum of an amplitude modulated wave and explain its components.(5 marks) 3 (c) Draw and explain OP-amp non inverting comparator. Draw input and output waveforms for Vref positive and also for Vref negative.(5 marks) 4 (a) Explain the working of a superheterodyne receiver with the help of a neat block diagram. Show the waveform at the ouput of each block.(10 marks) 4 (b) What is DSBSC wave? Explain its generation using balanced modulator.(10 marks) 5 (a) Draw the PAM, PWM and PPM waveforms in time domain assuming a sinusoidal modulating signal. Explain them in brief.(10 marks) 5 (b) The maximum deviation allowed in a FM broadcast system is 75 kHz. If the modulating signal is a single tone sinusoidal of frequency 15 kHz, find the bandwidth of the FM signal. How does the bandwidth change if the modulating frequency is doubled?(5 marks) 5 (c) How is adaptive delta modulation superior to delta modulation?(5 marks) 6 (a) What do you understand by signal multiplexing? Explain TDM and FDM with suitable examples.(10 marks) 6 (b) With neat circuit diagram explain the use of PLL as phase shifter.(5 marks) 6 (c) Give advantages and disadvantages of SSB over full carrier DSB amplitude modulated wave.(5 marks)