Elec Circuits & Comm. Fundamentals - May 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) Draw and explain FET based Hartley and Colpitt Oscillator. (5 marks)

1 (b) Comment on the following ADC/DAC specifications
i) Resolution
ii) Linearity
iii) Accuracy
iv) Settling Time
v) Stability. (5 marks)

1 (c) How is adaptive data modulation superior to delta modulation? (5 marks)

1 (d) Discuss the factors that influence modulation index of an FM Wave. (5 marks)

2 (a) A sketch a block representation for an n-channel JFET, showing bias voltage, depletion regions, and current directions. Label the device terminals and explain its operation. Explain the effect of increasing levels of negative gate-source voltage.
Also sketch a typical drain characteristics for VGS-0 for an n-channel JFET. Explain the shape of the characteristics, identify the regions, and indicate the important current and voltage levels. (10 marks)

2 (b) Design an op-amp differentiator that will differentiate an input signal with t_max=100 Hz. Draw the output waveform for a sine wave of 1V peak at 100 Hz applied to the differentiator. Also repeat it for square wave input. (10 marks)

3 (a) Explain the different methods of biasing JFET along with their characteristics in detail. (10 marks)

3 (b) Explain any one technique used of conversion of analog signal to digital with ADC. (5 marks)

3 (c) Draw and explain op-amp inverting comparator. Draw input and output waveform for V_ref>0 and also for V_ref<0. (5 marks)

4 (a) Draw Foster Seeley Descriminator with circuit diagram and explain its working with phasor diagrams? (10 marks)

4 (b) What is DSBSC wave? Explain its generation using balanced modulator. (10 marks)

5 (a) Draw the PAM, PWM and PPM waveform in time domain assuming a sinusoidal modulating signal. Explain them in brief. (10 marks)

5 (b) In an AM radio receiver the loaded Q of the antenna circuit at the input to the mixer is 100. If the intermediate frequency is 455 Khz, calculate the image frequency and its rejection at 1MHz. (5 marks)

5 (c) With neat circuit diagram explain the use of PLL in frequency translator. (5 marks)

6 (a) What do you understand by signal multiplexing? Explain TDM and FDM with suitable example. (10 marks)

6 (b) Draw the spectrum of an amplitude modulated wave and explain its components. (5 marks)

6 (c) Compare class A and Class C power amplifiers. (5 marks)