Electronics and Communication Engg_Full Paper_2007.pdf

8/10/2019 Electronics and Communication Engg_Full Paper_2007.pdf

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Electronics and Communication Engg - 2007

Full Paper

1. If E denotes expectation, the variance of a random variable X is given by

1) E[X2] - E2[X]

2) E[X2] + E2[X]

3) E[X2]

4) E2[X]

2. The following plot shows a function y which varies linearly with x. The value of the integral I

= is

1) 1.0 2) 2.5 3) 4.0 4) 5.0

3. For | x |


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4) e-x2

6. For the function e-x, the linear approximation around x = 2 is

1) (3 - x)e-2

2) 1 - x

3) [3 + 22 - (1 + 2)x]e-2

4) e-2

7. An independent voltage source in series with an impedance ZS = RS + jXS delivers a

maximum average power to a load impedance ZLwhen

1) ZL= RS+ jXS

2) ZL= RS

3) ZL= jXS

4) ZL= RS- jXS

8. The RC circuit shown in the figure is

1) a low-pass filter

2) a high-pass filter

3) a band-pass filter

4) a band-reject filter

9. The electron and hole concentration in an intrinsic semiconductor are n iper cm3at 300 K.

Now, if acceptor impurities are introduced with a concentration of NAper cm3 (where NA

>> ni), the electron concentration per cm3at 300 K will be1) ni

2) ni+ NA

3) NA- ni

4) (ni2/NA)

10. In a p+n junction diode under reverse bias, the magnitude of electric field is maximum at

1) the edge of the depletion region on the p-side

2) the edge of the depletion region on the n-side

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3) the p+n junction

4) the centre of the depletion region on the n-side

11. The correct full wave rectifier circuit is

1)

2)

3)

4)

12. In a transconductance, amplifier, it is desirable to have

1) a large input resistance and a large output resistance2) a large input resistance and a small output resistance

3) a small input resistance and a large output resistance

4) a small input resistance and a small output resistance

13. X = 01110 and Y = 11001 are two 5-bit binary numbers represented in two's complementformat. The sum of X and Y represented in two's complement format using 6 bits is

1) 100111

2) 001000

3) 0001114) 101001



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14. The Boolean function Y = AB + CD is to be realized using only 2- in put NAND gates.The minimum number of gates required is

1) 2 2) 3 3) 4 4) 5

15. If the closed-loop transfer function of a control system is given asT(s) = (s - 5)/((s + 2)(s + 3)), then it is

1) an unstable system

2) an uncontrollable system

3) a minimum phase system

4) a non-minimum phase system

16. If the Laplace transform of a signal y(t) is Y(s) = 1/(s(s - 1)), then its final value is

1) -1 2) 0 3) 1 4) Unbounded

17. If R() is the autocorrelation function of a real, wide-sense stationary random process,then which of the following is NOT true?

1) R() = R(-)

2) | R() | R(0)

3) R() = -R(-)

4) The mean square value of the process is R(0)

18. If S(f) is the power spectral density of a real, wide-sense stationary random process, then

which of the following is ALWAYS true?1) S(0) S(f)

2) S(f) 0

3) S(-f) = -S(f)

4)

19. A plane wave of wavelengthis travelling in a direction making an angle 30 with positivex-axis and 90 with positive y-axis. The field of the plane wave can be represented as

(E0is a constant)

1)

2)

3)

4)

20. If C is a closed curve enclosing a surface S, then the magnetic field intensity the current



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density and the electric flux density are related by

1)

2)

3)

4)

21. It is given that X1, X2, ---- XMare M non-zero, orthogonal vectors. The dimension of the

vector space spanned by the 2M vector X1, X2, .... XM, - X1, X2, ---- - XM, is

1) 2 M

2) M + 1

3) M

4) dependent on the choice of X1, X2,---XM

22. Consider the function f(x) = x2- x - 2. The maximum value of f(x) in the closed interval [-4,4] is

1) 182) 10

3) -2.25

4) indeterminate

23. An examination consists of two papers, Paper 1 and Paper 2. The probability of failing inPaper 1 is 0.3 and that in Paper 2 is 0.2. Given that a student has failed in Paper 2, theprobability of failing in Paper 1 is 0.6. The probability of a student failing in both the papersis

1) 0.5 2) 0.18 3) 0.12 4) 0.06

24. The solution of the differential equation k2(d2y/dx2) = y - y2under the boundary conditions

(i) y = ylat x = 0 and

(ii) y = y2at x = ,

where k, y1and y2are constants, is

1) y = (y1- y2) exp(-x/k2) + y2

2) y = (y2- y1) exp(-x/k) + y1

3) y = (y1- y2) sin h(x/k) + y1

4) y = (y1- y2) exp(-x/k) + y2



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25. The equation x3- x2+ 4x - 4 = 0 is to be solved using the Newton-Raphson method. If x =2 is taken as the initial approximation of the solution, then the next approximation usingthis method will be

1) 2/3 2) 4/3 3) 1 4) 3/2

26. Three functions f1(t), f2(t) and f3(t), which are zero outside the interval [0, T] are shown in

the figure. Which of the following statements is correct ?

1) f1(t) and f2(t) are orthogonal



4) f1(t) and f2(t) are orthonormal

27. If the semi-circular contour D of radius 2 is as shown in the figure, then the value of the

integral is

1) j 2) -j 3) - 4)

28. Two series resonant filters are as shown in the figure. Let the 3-dB bandwidth of Filter 1

be B1and that of Filter 2 be B2. The value of (B1/B2) is



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1) 4 2) 1 3) 1/2 4) 1/4

29. For the circuit shown in the figure, the Thevenin voltage and resistance looking into X-Yare

1) 4/3 V, 2

2) 4 V, 2/3

3) 4/3 V, 2/3

4) 4 V, 2

30. In the circuit shown, VCis 0 volts at t = 0, sec. For t > 0, the capacitor current ic(t), where t

is in seconds, is given by

1) 0.50 exp(-25t)mA

2) 0.25 exp(-25t)mA

3) 0.50 exp(-12.5t)mA

4) 0.25 exp(-6.25t)mA

31. In the AC network shown in the figure, the phasor voltage VAB(in Volts) is



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1) 0

2) 5 30

3) 12.5 30

4) 17 30

32. A p+n junction has built-in potential of 0.8 V. The depletion layer width at a reverse bias of1.2 V is 2 m. For a reverse bias of 7.2 V, the depletion layer width will be

1) 4 m

2) 4.9 m

3) 8 m

4) 12 m

33. Group I lists four types of p-n junction diodes. Match each device in Group I with one ofthe options in Group II to indicate the bias condition of that device in its normal mode ofoperation.

Group I Group II

P. Zener Diode 1. Forward bias

Q. Solar cell 2. Reverse bias

R. LASER diode

S. Avalanche Photodiode

1) P-1, Q-2, R-1, S-2

2) P-2, Q-1, R-1, S-2

3) P-2, Q-2, R-1, S-1

4) P-2, Q-1, R-2, S-2

34. The DC current gain () of a BJT is 50. Assuming that the emitter injection efficiency is0.995, the base transport factor is

1) 0.980

2) 0.985

3) 0.990

4) 0.995

35. Group I lists four different semiconductor device. Match each device in Group I with itscharacteristic property in Group II.

Group I Group II

P. BJT 1. Population inversion

Q. MOS capacitor 2. Pinch-off voltage

R. LASER diode 3. Early effect

S. JFET 4. Flat-band voltage

1) P-3, Q-1, R-4, S-28/23 gate.edooni.com


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2) P-2, Q-4, R-3, S-2

3) P-3, Q-4, R-1, S-2

4) P-3, Q-2, R-1, S-4

36. For the Op-Amp circuit shown in the figure, Vo is

1) -2 V

2) -1 V3) -0.5 V

4) 0.5 V

37. For the BJT circuit shown, assume that theof the transistor is very large and V BE= 0.7

V. The mode of operation of the BJT is

1) cut-off

2) saturation

3) normal active

4) reverse active

38. In the Op-Amp circuit shown, assume that the diode current follows the equationI = Is exp (V/VT). For Vi = 2 V, V0 = V01, and for Vi = 4 V, V0 = V02. The relationship

between V0land V02is



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1) V02= (2) V01

2) V02= e2V01

3) V02= V01ln 2

4) V01= V02= VTln 2

39. In the CMOS inverter circuit shown, if the transconductance parameters of the NMOS and

PMOS transistor are kn = kp = n Cox (Wn/Ln) = pCox (Wp/Lp) = 40A/V 2 and their

threshold voltages are VTHn= VTHp= 1V, the current I is

1) 0 A

2) 25 A

3) 45 A

4) 90 A

40. For the Zener diode shown in the figure, the Zener voltage at knee is 7 V, the knee currentis negligible and the Zener dynamic resistance is 10. If the input voltage (V i) range is

from 10 to 16 V, the output voltage (V0) range from

1) 7.00 to 7.29 V

2) 7.14 to 7.29 V

3) 7.14 to 7.43 V

4) 7.29 to 7.43 V

41. The Boolean expression Y = D + BC + A D +AB can be minimized to

1) Y = D + B + A D

2) Y = D + BC + A D

3) Y = BC + D + A D

4) Y = BC + D + AB

42. The circuit diagram of a standard TTL NOT gate is shown in the figure. When Vi= 2.5 V,



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the modes of operation of the transistor will be

1) Q1: reverse active;

Q2: normal active;

Q3: saturation;

Q4: cut-off;

2) Q1: reverse active;

Q2: saturation;

Q3: saturation;

Q4: cut-off;

3) Q1: normal active;Q2: cut-off;

Q3: cut-off;

Q4: saturation;

4) Q1: saturation;

Q2: saturation;

Q3: saturation;

Q4: normal active;

43. In the following circuit, X is given by

1) X = A + B + C + A B C

2) X = B C + A C + A B +

3) X = A B + B C + A C



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4) X = + +

44. The following binary values were applied to the X and Y inputs of the NAND latch shown inthe figure in the sequence indicated below :X = 0, Y = 1; X = 0; Y = 0; X = 1, Y = 1The corresponding stable P, O outputs will be

1) P = 1, Q = 0; P = 1, Q = 0;P = 1, Q = 0 or P = 0, Q = 1

2) P = 1, Q = 0; P = 0, Q = 1 or P = 0, Q = 1;P = 0, Q = 1

3) P = 1, Q = 0; P = 1, Q = 1;

P = 1, Q = 0 or P = 0,Q = 14) P = 1, Q = 0; P = 1, Q = 1;

P = 1, Q= 1

45. For the circuit shown, the counter state (Q1Q0) follows the sequence

1) 00, 01, 10, 11, 00.....

2) 00, 01, 10, 00, 01.....

3) 00, 01, 11, 00, 01.....

4) 00, 10, 11, 00, 10.....

46. An 8255 chip is interfaced to an 8085 microprocessor system as an I/O mapped I/O as

shown in the figure. The address lines A0and A1of the 8085 are used by the 8255 chip todecode internally its three ports and the Control register. The address lines A3 to A7 as

well as the IO signal are used for address decoding. The range of addresses for which

the 8255 chip would get selected is

1) F8H FBH



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2) F8H FCH

3) F8H FFH

4) F0H F7H

47. The 3 - dB bandwidth of the low-pass signal e-tu(t), where u(t) is the unit step function, is

given by1) (1/2) Hz

2)

3)

4) 1 Hz

48. A Hilbert transformer is a

1) non-linear system

2) non-causal system

3) time-varying system

4) low-pass system

49. The frequency response of a linear, time-invariant system is given by H(f) = 5/(1 + j10f).The step response of the system is

1) 5(1 - e-5t)u(t)

2) 5(1 - e-(t/5))u(t)

3)1/5(1 - e

-5t

)u(t)4) 1/5(1 - e-(t/5))u(t)

50. A 5-point sequence x[n] is given asx[-3] = 1, x[-2] = 1, x[-1] = 0, x[0] = 5, x[1] = 1.

Let X(ej) denote the discrete-time Fourier transform of x[n]. The value of is

1) 5

2) 10

3) 16

4) 5 + j10

51. The z-transform X[z] of a sequence X[n] is given by X[z] = 0.5/(1 - 2z-1). It is given that theregion of convergence of X[z] includes the unit circle. The value of x[0] is

1) -0.5 2) 0 3) 0.25 4) 0.5

52. A control system with a PD controller is shown in the figure. If the velocity error constant Kv= 1000 and the damping ratio = 0.5, then the values of K

Pand K

Dare



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1) KP= 100, KD= 0.09

2) KP= 100, KD= 0.9

3) KP= 10, KD= 0.09

4) KP= 10, KD= 0.9

53. The transfer function of a plant is T(s) = 5/((s + 5)(s2 + s + 1)). The second-orderapproximation of T(s) using dominant pole concept is

1) 1/((s + 5)(s + 1))

2) 5/((s + 5)(s + 1))

3) 5/(s2+ s + 1)4) 1/(s2+ s + 1)

54. The open-loop transfer function of a plant is given as G(s) = 1/(s2 - 1). If the plant isoperated in a unity feedback configuration, then the lead compensator that can stabilizethis control system is

1) (10(s - 1))/(s + 2)

2) (10(s + 4))/(s + 2)

3) (10(s + 2))/(s + 10)

4) (1(s + 2))/(s + 10)

55. A unity feedback control system has an open-loop transfer function G(s) = K/(s(s2+ 7s +12)). The gain K for which s = -1 + j1 will lie on the root locus of this system is

1) 4 2) 5.5 3) 6.5 4) 10

56. The asymptotic Bode plot of a transfer function is as shown in the figure. The transferfunction G(s) corresponding to this Bode plot is

1) 1/((s + 1)(s + 20))



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2) 1/(s(s + 1)(s + 20))

3) 100/(s(s + 1)(s + 20))

4) 100/(s(s + 1)(1 + 0.05s))

57. The state space representation of a separately excited DC servo motor dynamics is given

as

where is the speed of the motor, i a is the armature current and u is the armature

voltage. The transfer function ((s))/(U(s)) of the motor is

1) 10/(s2+ 11s + 11)

2) 1/(s2+ 11s + 11)

3) (10s + 10)/(s2+ 11s + 11)

4) 1/(s2+ s + 1)

58. In delta modulation, the slope overload distortion can be reduced by

1) decreasing the step size

2) decreasing the granular noise

3) decreasing the sampling rate

4) increasing the step size

59. The raised cosine pulse p(t) is used for zero ISI in digital communications. The expression

for p(t) with unity roll-off factor is given byp(t) = (sin 4Wt)/(4Wt(1 - 16 W2t2)).The value of p(t) at t = (1/4W) is

1) -0.5 2) 0 3) 0.5 4)

60. In the following scheme, if the spectrum M(f) of m(t) is as shown, then the spectrum Y(f) ofy(t) will be

1)



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2)

3)

4)

61. During transmission over a certain binary communication channel, bit errors occurindependently with probability p. The probability of AT MOST one bit in error in a block of n

bits is given by1) pn

2) 1 - pn

3) np(1 - p)n - 1+ (1 - p)n

4) 1 - (1 - p)n

62. In a GSM system, 8 channels can co-exist in 200 kHz bandwidth using TDMA. A GSMbased cellular operator is allocated 5 MHz bandwidth. Assuming a frequency reuse factorof (1/5), i.e. a five-cell repeat pattern, the maximum number of simultaneous channels

that can exist in one cell is

1) 200 2) 40 3) 25 4) 5

63. In a Direct Sequence CDMA system the chip rate is 1.2288 x 106chips per second. If theprocessing gain is desired to be AT LEAST 100, the data rate

1) must be less than or equal to 12.288 x 103bits per sec

2) must be greater than 12.288 x 103bits per sec

3) must be exactly equal to 12.288 x 103bits per sec

4) can take any value less than 122.88 x 103bits per sec

64. An air-filled rectangular waveguide has inner dimensions of 3 cm x 2 cm. The waveimpedance of the TE20mode of propagation in the waveguide at a frequency of 30 GHz is

(free space impedance 0= 377 )

1) 308

2) 355

3) 400

4) 461



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65. The field (in A/m) of a plane wave propagating in free space is given by

= (5(3)/0) cos ( t - z) + (5/0) sin (t - z + (/2)).

The time average power flow density in Watts is

1)0/100

2) 100/0

3) 50 02

4) 50/0

66. The field in a rectangular waveguide of inner dimensions a b is given by

= /h2(/a) H0sin(2x/a) sin ( t - z)

where H0 is a constant, and a and b are the dimensions along the x-axis and the y-axis

respectively. The mode of propagation in the waveguide is

1) TE20

2) TM11

3) TM20

4) TE10

67. A load of 50 is connected in shunt in a 2-wire transmission line of Z 0= 50 as shown in

the figure. The 2-port scattering parameter matrix (S - matrix) of the shunt element is

1)

2)

3)

4)

68. The parallel branches of a 2-wire transmission line are terminated in 100 and 200resistors as shown in the figure. The characteristic impedance of the line is Z 0= 50 and

each section has a length of (0/2). The voltage reflection coefficient I-at the input is



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1) -j(7/5)

2) ((-5)/7)

3) j(5/7)

4) 5/7

69. A /2 dipole is kept horizontally at a height of 0/2 above a perfectly conducting infinite

ground plane. The radiation pattern in the plane of the dipole ( plane) looks

approximately as

1)

2)

3)

4)

70. A right circularly polarized (RCP) plane wave is incident at an angle of 60 to the normal.on an air-dielectric interface. If the reflected wave is linearly polarized, the relative



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dielectric constant r2is

1) 2 2) 3 3) 2 4) 3

The figure shows the high-frequency capacitance-voltage (C-V) characteristics of a

Metal/SiO2/silicon (MOS) capacitor having an area of 1 x 10-4 cm2. Assume that the

permittivities ( 0r) of silicon and SiO2 are 1 x 10-12 F/cm and 3.5 x 10-13 F/cm

respectively.

71. The gate oxide thickness in the MOS capacitor is

1) 50 nm

2) 143 nm

3) 350 nm

4) 1 m

72. The maximum depletion layer width in silicon is

1) 0.143 m

2) 0.857 m

3) 1 m

4) 1.143 m

73. Consider the following statements about the C-V characteristics plot :S1 : The MOS capacitor has an n-type substrate.S2 : If positive charges are introduced in the oxide, the C-V plot will shift to the left.Then which of the following is true ?

1) Both S1 and S2 are true

2) S1 is true and S2 is false

3) S1 is false and S2 is true

4) Both S1 and S2 are false

Two 4-ary signal constellations are shown. It is given that l and 2 constitute an



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orthonormal basis for the two constellations. Assume that the four symbols in both theconstellations are equiprobable. Let (N0/2)denote the power spectral density of white

Gaussian noise.

74. The ratio of the average energy of Constellation 1 to the average energy of Constellation 2is

1) 4a2

2) 43) 2

4) 8

75. If these constellations are used for digital communications over an AWGN channel, thenwhich of the following statements is true ?

1) Probability of symbol error for Constellation 1 is lower

2) Probability of symbol error for Constellation 1 is higher

3) Probability of symbol error is equal for both the constellations

4) The value of N0will determine which of the two constellations has a lower probability ofsymbol error

Consider the Op-Amp circuit shown in the figure.

76. The transfer function V0(s) Vt(s) is

1) (1 - sRC)/(1 + sRC)

2) (1 + sRC)/(1 - sRC)

3) 1/(1 - sRC)

4) 1/(1 + sRC)

77. If Vi= V1sin (t) and V0= V2sin (t + ), then the minimum and maximum values of



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(in radians) are respectively

1) -/2 and /2

2) 0 and /2

3) -and 0

4) -/2 and 0

An 8085 assembly language program is given belowLine1 : MVIA, B5H2 : MVI B, 0EH3 : XRI 69H4: ADD B5: ANI 9BH6 : CPI 9FH7 : STA 3010H8 : HLT

78. The contents of the accumulator just after execution of the ADD instruction in line 4 will be

1) C3H 2) EAH 3) DCH 4) 69H

79. Alter execution of line 7 of the program, the status of the CY and Z flags will be

1) CY = 0, Z = 0

2) CY = 0, Z = 1

3) CY = 1, Z = 0

4) CY = 1, Z = 1

Consider a linear system whose state space representation is x (t) = Ax (t). If the initial

state vector of the system is x (0) = , then the system response is x(t) = .

If the initial state vector of the system changes to x(0) = , then the system response

become x(t) =

80. The eigenvalue and eigenvector pairs (i, vi,) for the system are

1) (-1, ) and (-2, )

2) (-2, ) and (-1, )

3) (-1, ) and (2, )

4) (-2, ) and (1, )

81. The system matrix A is

1)



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2)

3)

4)

An input to a 6-level quantizer has the probability density function f(x) as shown in thefigure. Decision boundaries of the quantizer are chosen so as to maximize the entropy ofthe quantizer output. It is given that 3 consecutive decision boundaries are '-1', '0' and '1'.

82. The values of a and b are1) a = 1/6 and b = 1/12

2) a = 1/5 and b = 3/40

3) a = 1/4 and b = 1/16

4) a = 1/3 and b = 1/24

83. Assuming that the reconstruction levels of the quantizer are the mid-points of the decisionboundaries, the ratio of signal power to quantization noise power is

1) 152/9 2) 64/3 3) 76/3 4) 28

In the Digital-to-Analog converter circuit shown in the figure below, VR= 10 V and R = 10

k

84. The current i is

1) 31.25 A

2) 62.5 A

3) 125 A

4) 250 A

85. The voltage Vois



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1) -0.781 V

2) -1.562 V

3) -3.125 V

4) -6.250 V



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Answer Key

1) 1 2) 2 3) 3 4) 1 5) 4 6) 1 7) 4 8) 3 9) 4 10) 3

11) 3 12) 1 13) 3 14) 2 15) 4 16) 1 17) 3 18) 2 19) 1 20) 4

21) 3 22) 1 23) 3 24) 4 25) 2 26) 2 27) 1 28) 4 29) 4 30) 1

31) 4 32) 1 33) 2 34) 2 35) 3 36) 3 37) 2 38) 4 39) 4 40) 3

41) 4 42) 2 43) 1 44) 3 45) 2 46) 3 47) 1 48) 1 49) 2 50) 2

51) 4 52) 2 53) 3 54) 1 55) 4 56) 4 57) 1 58) 4 59) 3 60) 1

61) 3 62) 2 63) 1 64) 3 65) 4 66) 1 67) 2 68) 4 69) 3 70) 4

71) 1 72) 2 73) 3 74) 2 75) 2 76) 1 77) 3 78) 2 79) 3 80) 1

81) 4 82) 1 83) 2 84) 2 85) 3

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Electronics and Communication Engg_Full Paper_2007.pdf