# First  Second Semester B.E. Degree Examination Dec 07  Jan 08

Time: 3 hrs.

Note : Answer any FIVE full questions.

Explain the mechanism of conduction in P and N type semiconductors using energy band diagrams.                                 (08 Marks)

With the help of diode equation, explain the VI characteristics of a PN junction. (08 Marks)

The saturation current density of a PN junction of a diode is 250 mA/m at 300°K. Find the voltage that must be applied across junction to cause a forward current density of 10 Amp/m2 to flow.  (04 Marks)

With a neat sketch explain the phenomenon of HALL EFFECT in semiconductors.    (07 Marks)

With a neat diagram explain the working of bridge rectifier.  (06 Marks)

With neat figures, explain the concepts of Zener and Avalanche Breakdown phenomena. (07 Marks)

Show that a transistor could be used as an amplifier. (05 Marks)

With a neat diagram explain, output characteristics of an NPN transistor in CE- configuration.                                 (05 Marks)

A transistor has Ib ~ 100 |iA and Ic = 2 mA. Find i) P of the transistor ii) a of the transistor iii) Emitter current Ie-

If Ib changes by +25 pA and Ic changes by +0.6 mA, find the new value of p. (10 Marks)

Clearly explain the effect of temperature and J3 on the operating point stability. (08 Marks)

A transistor amplifier is driven by an input voltage of 10 mV. The amplifier has a voltage gain of 60 dB. Estimate the value of output voltage.                          (06 Marks)

Explain the need for cascading of amplifier. Write an expression for total voltage gain of a cascaded amplifier.                 (06 Marks)

What is Bark Hausen criterion for oscillations?       (06 Marks)

Design the value of an inductor to be used in a Colpitts oscillator to generate a frequency of 10 MHz. The circuit is using a value of Ci ~ 100 pF and C2 = 50 pF.                                    (06 Marks)

List out the properties of an ideal opamp and with the circuit symbol explain the significance of inverting and non-inverting inputs.    (08 Ma rks)

Explain the need for modulation in communication systems. (04 Marks)

Explain the principle of frequency modulation. Draw the frequency spectrum of FM wave. (06 Marks)

Draw the block diagram of a super heterodyne receiver. Explain he function of each stage with necessary waveform.                (10 Marks)

Convert the following:

i)   [0.6875]10 = [?]g ii) [O.IOIOO! 10]2 =[?jg iii) [A72E]16 = [?]„

i) Add g and \$ ii) Perform using 2’s complement 48 – 23.

i)         For each of the following statements, indicate the logic gates used:

• Output is LOW if and only if all inputs are HIGH
• Output is LOW if and only if ail inputs are LOW.                                           (03 Marks)
• Output is HIGH if and only if all inputs are HIGH

ii)        Make a critical comparison of combinational circuits and sequential circuits. Give an example for each.      (09 Marks)

1. Draw the circuit of a DTC NAND gate. Explain its working.                               (06 Marks)
2. Show how amplitude, frequency and phase can be measured using CRO.                   (06 Marks)
3. Explain the working of a CRT.                                                                                  (08 Marks)