USN 10ELN15/25

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First/Second Semester B.E. Degree Examination, Dec.2013 /Jan.20l4Basic Electronics

Time: 3 hrs. Max. Marks: I00

Note: I. Answer any FIVE full questions, choosing at leust two from each part.2. Answer all obiective type questions only on OMR sheet page 5 of the answer booktet.3. Answer to objective type questtons on sheets other than OMR witt not be valuecl.

PART _ A

I a. Choose the correct answers for the following :

i) The knee voltage of a silicon diode isA) 0.3V B) 0.5V c) 0.7v

ii) The efficiency of full waves rectifier is about %c) 1.21

iii) The missing terms inthe forward diode current is I, = Io[e\'1v. -11A) Vn B) rl C) Vs

iv) The zener diode is mainly used in :

A) Comparator B)Regulatorb. Discuss the behaviour of p-n junctions under:

i) No bias: ii) Forward bias: iii) Reverse bias.

C) Multivibrator D) None of these

(06 Marks)c. Explain the operation of full wave bridge rectifier with neat circuit diagram ,"0 *A1eff;p;

d. A zener diode has a breakdown voltage of 10V. It is supplied from a voltage source varyingbetween 20-40V in series with resistance of 820er, using an ideal zener diode model obtainminimum.and maximuryZener currents. (04 Marks)

2 a. Choose the correct answers for the following :

i) When transistor operated in cut offand saturation. it acts likeB) a switchD) a variable resistor

A) a linear amplifierC) a variable capacitor

iD Ifthe base emitter junction is open, what is the collector currentA)lmA B) 2mA C) l0mA D)0

iii) The _ transistor is used for impedance matchingA) C-B B) C-E C) c-C

iv) cr of a transistor is 0.99 calculate pD) None

A) p :0.9 B) B :90 C) B:99 D) B:0.09

Draw the common emitter circuit and sketch the output characteristics, explain active region,cutoff region and saturation region by indicating them on the characteristic curve. (08 Marks)With a neat circuit diagram explain the working of transistor used as voltage amplifier.

For a certain transistor, gg.6%of the carriers injected into the base cross th. "oil::1#ff]junction. If the leakage current is 5pA and the collector current is 20mA, calculate: i) Thevalue of oc; ii) the emitter current.

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(04 Marks)

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10ELN15/2s

3 a. Choose the correct answers for the following : (04 Marks)i) The best biasing stability is achieved by using biasing method.

A) Fixed B) Collector to base

C) Voltage divider D) None of these

ii) In self bias or emitter bias circuit _ is connected between emitter and ground.

C) Resistor D) Zener diodeiii) The stability factor is given by

dr _ dL,A) "'co B) *'u'dt, dl.uc

dlu r\. dl"c) - D) --'' dl.o dl.oiv) The operating point must be _ for the proper operation of transistor

A) High :: B) StableC) Increasing ,r D) Decreasing

ii',,.b. With a neat circuit diagraq explain the working of an collector-to-base bias circuit using an

npn transistor and derive the equation for In. ''- ,,, (06 Marks). .. ':,-

c. Determine the operating point for a'silioon transistor biased by base bias method with

B : 100, Rs:500KfJ, Rc:2.5KO anqVis:20V. Also drawthe load line. (06 Marks)

d. Derive the stability factor S for base bias circ,uit. (04 Marks)

4 a. Choose the correct answers for the following : (04 Marks)i) With gate opeq ifih; supply voltage exceeds the'break over voltage of SCR, then

SCR will con(u0tA) False B) True :

C) Onlv for D.C D) Only for A.bii) The SCR is a device

A) NPN B) PNP

..., c) PJ\PN D) PNNiiD A relaxation oscillator uses _

A) MOSFET B) SCRC) UJT D) BJT

iv) FET is a _controlled deviceA) VoltageC) Power

B) CurrentD) None of these

b. Explain the construction of n-channel JFET and give its symbol.

c. Write and explain the equivalent circuit of UJT.

d. Explain the two transistor model of SCR.

(06 Marks)

(05 Marks)

(05 Marks)

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PART - B

5 a. Choose the correct answers for the following :

i) Oscillator uses _ type of feedbackA) Positive B) NegativeC) Reverse D) None of these

ii) The total phase shift around a loop must be _ for the sustained oscillationsB) 360'D) 270"

B) frequency v, voltage gainD) liequency vs input voltage

is blocked by,,,,,

B) Couplihg capacitor, C6D) The transistor

A) 180.c) 90"

iii) The frequency response is a graph ofA) freouency v, current gainC) frequency v, output voltage

iv) In RC coupled amplifier the d.c componentA) Load reiistance Rr.

C) Re ,,,

With a neat circuit diagram, explainamplifier.

tOELN15/25

(04 Marks)

the workireg of a two stage capacitor coupled CE

,, (08 Marks)

(02 Marks)

(04 Marks)

B).90" ,

D) 360"

B)1D) Negative

B) Triangular waveD) Step

c. Explain with the help of circuit diagram the working of an RC phase shift oscillator usingtransistor. (06 Marks)

d. Find the frequency of the oscillations of transistorized Colpitts oscillator having tank circuitparameters as Cr : 150pF, Cz= 1.5nI and L:50prH.

6 a. Choose the correct answers for the lollowing :

i) In an inverting amplifier there is _ phase shift between input and output.A) 0'c) 180.

ii) Ideally open loop gain of op-amp is _A)0c)*

A) RampC) Cosine wave

iv) Lissajous figures are used to measureA) Phase

C) Frequency

iii) When op-amp used as integrator with input as square wave the output w

difference between sinusoidal signalsB) AmplitudeD) None of these

b.

d.

c.

Write the ideal op-amp characteristics.

Show with a circuit diagram how an op-amp can be used as differentiator.

Explain how current measurement is done using CRO.

(06 Marks)

(06 Marks)

(04 Marks)

CEUTRALLBts$T*F'V

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7 a. Choose correct answers for the following :

i) Which of the following is invalid BCD code?A) 0011c) 0101

B) 1101

D) 1001

B) 2s6D) 8192 :

)

B)111101100 :: :

D) l r00il0

t0ELN15/25

(04 Marks)

(06 Marks)

(04 Marks)

(04 Marks)

(06 Marks)

ii) Given the number (8BF)r6, what is the positional weight of the 8?

iv) The relation between carrier power and total power in an AM wave

A) 16

c) 40e6iii) (64)rc- (a6)s in binary is

A) 111101101c),111110

A) Pc=r,[,.+)

c) P, = *[,.+)

B) P. =*('.T)

D) P. =p.(t* -')t.)t\ .J

b. Determine the value of base x, if i; {225)*: $al)s; ii) (211),: (152)s. (06 Marks)c. Perform subtraction using 2's complement method I l0l - 1010. (04 Marks)d. Draw the block diagram of super helerodyne receiver and explain the functions of each

block.

8 a. Choose the correct answers fo. ti" following: '

i) De Morgan's theorem siates that A + B isAt a+ec)AB

,i, Universal gate,s are _ andA) NOT and NORC) NAND and NOR

B);A;B':-D) A+B

B) AND and 0RD) XOR and XNOR

B) NORD) EXOR

iii) For.which gate when the two inputs A and B are equal the output is zero and otherwiseone?A) NAND

iv) An half adder has two inputs and _ outputsA) ONE B) TWOC) THREE D) None of these

b. Implement EX-NOR gate using only NOR gates.

c. Simpliiy AB+AC+AeClen+C1.d. Implement fulI adder using two half adders and one OR gate. Write the equations for sum

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and Cnr1. (06 Marks)

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