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# Visvesvaraya Technological University (VTU) 2005 B.E Basic Electronics - exam paper

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Second Semester B.E Degree Examination, Feb/March 2005
Common to all Branches
Basic Electronics

Full ques. Paper in attachment

Page No... 1    ELN15/25 t fl) I 0 E 6 0 t

USN First/Second Semester B.E Degree Examination, February/March 2005

Common to All Branches

Basic Electronics

Time: 3 hrs.]    [Max.Marks : 100

Note: i. A nswer any FIVE full questions.

2.    All questions carry equal marks.

3.    Assume missing data if any suitably.

1,. (a) Explain the mechanism of conduction in semiconductors due to electrons & holes.    (6 Marks)

(b)    Derive an expression for conductivity in a semi-conductor in terms of electron and hole concentrations.    (8 Marks)

(c)    Estimate the value of resistivity of intrinsic Germanium at 300A' given :

2.5    x 1013cm 3 3800cm2 I V - s 1800cm2 I V - s'

1.6    x 10--19G\

Intrinsic concentration Electron mobility Hole mobility Electron charge

(6 Marks)

2.    (a) With a neat sketch explain the phenomenon of HALL-EFEECT in

semiconductors.    (6 Marks)

(b) A germanium diode is used in a rectifier circuit & is operating at a temperature of 25C with a reverse saturation current of lOOOju.,4. Calculate the value of forward current if it is forward biased by 0.22V. Assume the value of 17 = 1 for Ge.    18 Marks)

fc) WiLh a neat figures clearly explain the concepts of Zener and avalanche breakdown phenomena.    (6 Marks)

3.    (a) WiLh a neat sketch, clearly show the various current components in a PNP

transistor and hence establish the relevant equations.    (10 Marks)

(b)    A bridge rectifier is driving a load resistance of lOOfi. It is driven by a source voltage of 230F, 50/Tz. Neglecting diode resistances. Calculate: (6 Marks)

i)    Average DC voltage

ii)    Average Direct current

iii)    frequency of output wave form.

(c)    Define a (Alpha) and 3 (Beta) of a transistor.    (4 Marks)

Corifei.... 2

4.    (a) Clearly explain the effect of temperature and 3 6n the operating point stability.

'    " :    (8 Marks)

(b)    A transistor amplifier is driven by an input voltage of lOmV. The amplifier has a voltage gain of 60dB, Estimate the value of output voltage.    (6 Marks)

(c)    Explain the need for cascading of amplifier. Write an expression for total voltage gain of a cascaded amplifier,    "    (6 Marks)

5.    What is Bark Hausen criterion for oscillations?    (6 Marks)

(b) Design the value of an inductor to be used in a Colpitts oscillator to generate a frequency of 10MHz. The circuit is using a value of

C1 lOOp1 & C9 = 50pF.    [6 Marks)

(p) Listout the properties of an ideal Opamp and with the circuit symbol explain the significance of inverting & non inverting inputs.    (sMarks)

6.    (a) Show with a derivation and circuit diagram, how an opamp can be used as an

integrator.    (6 Marks)

(b)    An opamp is used as an inverting amplifier to amplify an input sine wave of amplitude 100mV(peak to peak). The input resistance Ri = 1ATI and feed back resistance Rj = lOkfl, Calculate the voltage gain and sketch the output wave form to scale. .    __(8 Marks)

(c)    Compare the performance of AM & FM communication systems, (6 Marks)

7.    (a) Derive an expression for the instantaneous value of an AM signal in terms of

carrier and side band frequencies.    (a Marks)

(b)    Carryout the following conversion

i) (F9AC 5D8B)i6 = (?)io

H) (457 245)3 = COlO    (6 Marks)

(c)    Carryout subtraction using :

U ls complement for (101101 - 11001)2

fi) 2s complement for (11001 - 101101)2.    (6Marks)

8.    (a) Explain the operation of a two input TTL NAND gate using a neat circuit

diagram.    (8 Marks)

(b)    With truth tabie explain how a R - S Hip flop can be realised using NOR gates,

(6 Marks)

(c)    Show how amplitude, frequency and phase can be measured using a CRO.

(6 Marks) 