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2014 MAIN PAPER – ECE-5

ECE-Electronics & Communication Engineering

Duration: Three Hours Maximum Marks: 100

Read the following papers instructions carefully:

1. There are a total of 65 questions carrying 100 marks. Questions are of multiple choice type or numerical

answer type. A multiple choice type question will have four choices for the answer with only one correct

choice. For numerical answer type questions, the answer is a number and no choices will be given. A

number as the answer should be entered by writing approximate value.

2. Q.1- Q.18 are of multiple choice type and carries 1 mark each. Q.19- Q.25 are of numerical answer type

and carries 1 mark each. Q.26- Q.38 are of multiple choice type and carries 2 marks each. Q.39- Q.47

are of numerical answer type and carries 2 marks each.Q.48-Q.51 include two pair of common data

questions which are of numerical answer type and carries 2marks each and Q.52-Q.55 include two pair

of linked answer questions which are multiple choice type and carries 2 marks each. The answer to the

second question of the linked answer questions depends on the answer to the first question of the pair. If

the first question in the linked pair is wrongly answered or is not attempted then the answer to the second

question in the pair will not be evaluated. Q.56-Q.60 are of multiple choice type and carries 1 mark each

and Q.61 –Q.65 are of multiple choice type and carries 2 marks each.

3. Questions not attempted will result in zero mark. Wrong answers for multiple choice type questions will

result in NEGATIVE marks. For all 1 mark questions, 1/3 mark will be deducted for each wrong

answer. For all 2 marks questions, 2/3 mark will be deducted for each wrong answer. However, in the

case of the linked answer question pair there will be negative marks only for wrong answer to the first

question and no negative marks for wrong answer to the second question. There is no negative

marking for questions of numerical answer type.

4. Objective questions must be answered on Objective Response Sheet (ORS) by marking (A, B, C, D)

using HB pencil against the question number on the left hand side of the ORS. For Numeric data

questions answer must be marked in form of numerical value only. Each question has only one correct

answer. In case you wish to change an answer, erase the old answer completely. More than one answer

marked against a question will be treated as a wrong answer.

5. Calculator is allowed. Charts, graph sheets or tables are NOT allowed in examination hall

6. Do the rough works in scribble pad provided/ In case of offline it can be done on paper itself?

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100K

v0

ix

10K

1M

vx

1. What is the value of i/p impedance Rin = (vx/ix) of circuit shown.

A. 100 K B. - 100 K C. + 1 M D. - 1 M

2. Two MOSFETS M1 and M2 have channel widths and lengths of W, L and 2W, L/2 and drain currents

of I1 and I2 respectively. Assuming that both M1 and M2 are ON, under the same temperatures and

biasing voltages, which one of the following is true??

A. 12

4

II B. 1

22

II C. I2 = 2I1 D. I2 = 4I1

3. If A and B are Boolean variables then which one of the following is equivalent to

A B AB:

A. A + B B. A+B C. A+B D. A+B

4. Consider the Boolean function of 4 Variables f(A, B, C, D) = (1, 3, 4, 6, 9, 11, 12, 14) Then

Function is

A. independent of one Variable B. independent of two Variable

C. independent of three Variable D. dependent on all the Variables

5. A transmission line of 50 ohm, characteristic impedance is terminated with a 100 ohm resistance

what is the value of Minimum impedance Measured on line.

A. 0 B. 25 C. 50 D. 100

6. If skin depth for a good-conductor is 1/2 meter, then what is the phase velocity of EM, wave. If

frequency of operation is 10 MHz.

A. 3 × 108 m/sec B. 10

7 m/sec

C. 1 × 108 m/sec D. 10

6 m/sec

7. Communication channel has a finite band width, but channel is extremely noisy such that signal

power is much below noise power. The capacity of channel will be.

(a) Finite and very large. (b) Nearly 0 (c) Infinite (d) insufficient data.

8. A signal contains components at 400 Hz & 2400 Hz The signal modulates a carrier of frequency 100

MHz However after demodulation it is found that the 400 Hz, signal component is present, and

channel B.W. is 15 kHz, what is the reason for higher frequency signal not to be detected properly.

(a) Modulation used is FM & Band width is insufficient.

(b) Modulation used is AM & Band width is insufficient.

(c) Modulation used is FM, but pre emphasis is not used.

(d) Modulation used is AM, but detector is for FM.

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|X(w)| |Y(w)|

1

100-100w w

3

50-50

9. A continuous time system is described by y(t) = e– | x(t) |

where y(t) is output and x(t) is input, then y(t)

is bounded.

(a) only when x(t) is bounded (b) only when x(t) is nonnegative

(c) only for t 0, if x(t) is bounded for t 0 (d) Even when x(t) is not bounded.

10. Magnitude of Fourier transform x(t) & y(t) are shown in figure. If phases of X(ω) and Y(ω) are zero

for all ω. The magnitude and frequency units are identical in both figure then relation between y(t)

and x(t) is expressed as :

2

(a) y(t) = x(t/2)

3

(b) y(t) = 2/3 x(2 t)

(c) y(t) = 3/2 x(2t)

(d) y(t) = 3/2 x(t/2)

11. If 2 2

2 2

6 1

6 5 6 5( )

5 5

6 5 6 5

s

s s s ss

s s s s

Then what is value of matrix A.

6 5 5 5 6 0 0 1( ) ( ) ( ) ( )

6 0 0 6 5 6 5 6a b c d

12. If polar plot of 2

10( )

( 1)G s

s s

intercepts real-axis at distance ‘a’ from origin then value of ‘a’ is

(a) –5 (b) –2.5 (c) 2.5 (d) 5

13. A potential difference of 5, volt is applied across a uniform wire of length 50 meter. Calculate drift

velocity of electrons through the wire. If relaxation time is 10–14

sec.

(a) 0.176 × 10–3

m/s (b) 0.95 m/s (c) 1.76 × 10–5

m/s(d) 1.5 × 10–6

m/s

14. A transistor with = 0.98 is operated as an amplifier in CB, circuit with a load resistance of 5 kΩ If

dynamic resistance of E-B, Junction is 70 ohm. Calculate value of voltage gain and Power gain

respectively

(a) 49, 40.6 (b) 70, 350 (c) 49, 350 (d) 70,68.6

15. Consider the following statements for series RLC series circuit?

1. Power factor will be unity.

2. Current in circuit will be maximum.

3. Current in circuit will be minimum.

4. Impedance will be maximum

Which of these statements are correct?

(a) 1, 2 and 3 (b) 1 and 2 only (c) 1, 2 and 4 only (d) 1, 3 and 4 only

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•

•5V

v0

T1

T2

16. In the circuit shown above the switch is open for a long time and closed at time t = 0. What is the

current through the switch after the switch is closed?

(a) Zero (b) 1 A (c) 2 A (d) 5 A

17. What is the value of given limit?

2 2 2 2

3

1 2 3limn

n

n

A. 1/3 B. 1/2 C. 1/6 D.

18. If A = then what is the value of A3 – A

2

A. A2(A – I) B. (A – I) C. (A + I) D. 2(A – I)

19. Both transistors T1 and T2 in figure have a threshold voltage of 1 Volt. The device parameters K1 and

K2 of T1 and T2 are, respectively, 36 A/V2 and 9 A/V

2. The output voltage V0 in volt is:

20. An E.M wave is propagating in a lossless region with = 0, 0 , = 160. The magnitude of

Poynting vector is 2W/m2. Find the max

m value of H field in Amp/meter:

21. A device with input x(t) and output y(t) is characterized by y(t)=x2(t). An FM signal with frequency

deviation of 90 KHz and modulating signal bandwidth 5 KHz is applied to this device. What is value

of bandwidth in KHz of the output signal?

22. In the circuit shown, what is the value of Ix in Amp:

1 3V 2

Ix 2 2V

23. An 8-bit successive approximation ADC has full scale reading of 2.55 volt and its conversion time

for an analog input of 1 volt is 20 sec, what is the conversion time in sec for 2volt input:

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C2

R2

C1vi

vo

R1

–

+

Iref IL

VDD

Q1 Q2

12V

Vo

Vin

2V

24. Determine the largest time constant in second for given characteristic equation

s3 + 4s

2 + 6s + 4 = 0

25. An AM voltage signal s(t) with a carrier freqn of 1.15 GHz has a complex envelop g(t) = Ac(1 +

m(t)), Ac = 500 V and modulation is a 1 KHz signal (Sinusoidal) test tone m(t) = 0.8 sin(2 × 103 t).

If signal appears across a 50 ohm load (resistive). What is the value of actual power delivered to load

in KW:

26. For the circuit shown in figure if 1 2

1 1 2 2

1 1&

R C R C and here 2 1

This given circuit will behave like :

(a) Low pass for 2 and high pass for << 1

(b) Low pass for 2 and high pass for 1

(c) Low pass for 2 and 1

(d) High pass for 2 and 1

27. for the given circuit shown in figure transistors Q1 and Q2 have aspect ratio as 1 2

/L & /L . The

value of current IL is given by :

If Q1 and Q2 are matched :

(a) refI

(b)

2

ref

1

/LI

/L

(b)

1

ref

2

/LI

/L

(d)

2

1ref 2

2

/LI

/L

28. For the circuit shown in figure :

What is the value of o

s

v

v ??

(a) –3.8

(b) –7.8

(c) –10.2

(d) –14.6

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100(s+5)(s+10)

Delay+

–

R(s)C(s)

a c

b d

c e

d f

+

–vo

Fig.(a)

vin +–

RR

R

Re

f

c

d

a bc d

I2

+

–

V2Vs

zg

+–

h(t) g(t)y(t)

x(t)x(t)

29. Consider the control system shown in figure :

If the value of delay is 0.2 sec then what is the value of gain margin for a stable system:

(a) 1.09 dB (b) 5.48 dB (c) –1.09 dB (d) 0 dB

30. A synchronous counter is defined as A A BJ K Q B C BJ Q K 1

C B CJ Q K 1

Here C is the MSB then MOD of counter is :

(a) MOD – 3 and self starting (b) MOD – 3 and not self starting

(c) MOD – 4 and self starting (d) MOD – 4 and not self starting

31. The z-parameters of first two port circuit shown in figure (a) are

11 21 12 22z 200 , z 1.6M , z 20 , z 40K

The circuit in second two port circuit is shown in figure (b) where R = 8 K

Calculate value of Vo if inv 15mVDC

(a) –1.46 V (b) –2V (c) 15 mV (d) –1 mV

32. What is the value of output impedance shown in figure below :

(a) g

bcd

a z

(b) g

bcd

a z

(c)

g

b cd

a z

(d) d bc

33. Evaluate az

2

c

edz

z 1 where C is the circle z 2

(a) 4 sin a (b) 2 sina (c) 2 isin a (d) 0

34. For the scheme shown below :

If impulse response 3t 3th t t 3e u t 2te u t then what is the impulse response g(t) ??

(a) 2t tt e u t 4e u t (b) 2t tt e u t 4e u t

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( )2

LPFy (t)1

y(t)s(t) Cy (t)2

C

+

–

vo

+

–

vi

3+j4(3–j4)

(3+j4)

Z = RL L

(c) 2t tt e u t 4e u t (d) 2t tt 2e u t 2e u t

35. If cs t A m t cos t

If given scheme is for demodulating an AM signal then term y(t) will be :

(a) 0.25 m2(t) (b) 20.33m t (c) 20.5m t (d) 20.75m t

36. An angle modulated wave is given by the following equation

cy t 5cos 2 f t 10sin 2000 t 4sin 4000 t what is value of bandwidth occupied by angle

modulated signal :

(a) 40 KHz (b) 44 KHz (c) 50 KHz (d) 54 KHz

37. On a resistively terminated high frequency loss less transmission line fed by a 500 MHz source, the

VSWR is found as 2 and the first voltage minima is measured at 30 cm from load end. What is the

value of normalized impedance ??

(a) 3 (b) 2 (c) 0.5 (c) 0.25

38. If

3x 0

x 1 a cos x bsin xlim 1

x

then what are the values of a & b :

(a) 3 1

,2 2

(b) 1 5

,2 2

(c) 3 5

,2 2

(d) 5 3

,2 2

39. If Si diode has 16 3

DN 10 cm and 17 3

AN 10 cm and 10 3

in 1.5 10 cm . If r 011.7 then what is

the width of depletion region in m on N-side when diode is forward bias at 0.5 volt:

40. If transfer function for following phase-lead network is

o

i

E s 1 ST

E s 1 ST

What is the maximum vale of phase of above phase lead network in degree :

41. A quarter wave loss less 100 line is terminated by a load Lz 210 . If the voltage at receiving

end is 80 volt then what is the voltage in volt at sending end :

42. Consider the following circuit :

At what value of LZ in ohm power dissipated from source to load LZ is maximum:

43. If an OPAMP has input resistance of 1 K and output resistance of 2.5 K

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Rx

CL1K

9K

1K–

+

+

–v (t)ov (t)i

1mH

What is the value of Rx in kilo ohm for sustained oscillations ??

44. A line of characteristic impedance z0 , phase velocity 8

pv 2 10 m/s and length 2 meter is

terminated by a load impedance zL ohm. The reflection coefficients at the input end and load end are

K1 & K2. So value of 1

2

K

K at a frequency of 50 MHz will be:

45. If x n 3,0,0,1, 1,1,0,0,3 then what is the value of jX e d

46. The following program segment is executed in an 8085 Microprocessor based system. Clock

frequency is 1 MHz.

XRA A

MOV H, A

MOV L, H

LXI SP, 3A00H

LOOP: DAD SP

SHLD 4000H

JC LOOP

What is the execution time of above program segment in sec:

47. Consider RLC circuit shown in figure for step input what is the value of overshoot in %

Common data for question 48 & 49:

The region z 0 r r10, 2.5 & 0 and the region z 0 r r1, 4 & 0

If EM wave 9E x, t 600cos 10 t z V/m is present in region z < 0 then

48. SWR in the region z < 0 is:

49. If value of max in region z < 0 is K. then value of K is:

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3K Ix

Rx

1KIo

Iin

Rin

Vo

–

+

iL1H 1F

Vc

– +

D Q

b7 b0

CLK

Common data for question 50 & 51:

50. What is the value of Rin in K :

51. What is the value of x 1I /I :

Statement for linked answer question 52 & 53:

Consider the network shown in figure:

Assume L Ci 0 2A & V 0 2volt

52. What is the value of 2

L

2

d iat t 0

dt

:

(a) 22 A/s (b) 22 A/s (c) 24 A/s (d) 24 A/s

53. What is the value of 2

c

2

d Vat t 0

dt

:

(a) 21 V/s (b) 21 V/s (c) 22 V/s (d) 22 V/s

Statement for linked answer 54 & 55 :

The 8-bit left shift register and D FF shown in figure is synchronized with same clock.

The D FF is initially cleared.

54. This circuit acts as a :

(a) Binary to 2’s complement convertor (b) Binary to gray code convertor

(c) Binary to 1’s complement convertor (d) Binary to excess-3 code convertor.

55. If initial value of register is 10110111 then after 4 clock pulses the contents of register will be :

(a) 73 (b) 72 (c) 7E (d) 74

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56. If the sum of five consecutive integers is S, what is the largest of those integers in terms of S ??

A. 10

5

S B.

10

4

S C.

10

5

S D.

10

10

S

57. If the product of 4 consecutive integers is equal to one of them, what is the largest possible value of

one of the integers??

A. 0 B. 3 C. 4 D. 6

58. Fill in the blank with appropriate word. He is ___ opponent, you must respect and fear him at all

times

A. A redoubtable B. A disingenuous

C. C raven D. An insignificant

59. (0.55)150

is closest to

A. 0.1 B. 0 C. 10 D. 100

60. What is the Missing term in sequence ABC, A2BC, A

2B

2C, ____, A

3B

2C

2

A. A3 B

2 C B. A

2 B

2 C

2 C. A

3 B

3 C

2 D. A

3 BC

61.

Percent – distribution of Bias – Motivated offenses in 1998 in USA

If in 1998, there were 10,000 bias motivated offenses based on ethnicity, how many more offenses

were based on religion than on sexual orientation??

A. 4 B. 40 C. 400 D. 4000

62. A person moves 8 km west, 6 km north, 3 km east, and 6 more km north. How far is this person from

his starting place

A. 13 B. 17 C. 19 D. 21

63. Fill in the blank by appropriate words??

The new computer system ________ next month.

A. is being installed by people B. is be installed

C. is being installed D. is been installed

64. Fill in the blank by appropriate words It’s _________ disappointing

A. Very Much B. Very C. Much D. Much Very

65. If Rout is related to Defeat then which pair is correctly matched

A. Grief: Loss B. Pathway: Ruin

C. Memory: Oblivion D. Ovation: Applause

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Solution of Mock test-5:

1. (B)

0 (1)1

0(2)

10 100

xx

x o x

v vi

M

v v v

K K

2. (D)

I = K (VGS - VT)2 where K = n C0x. w/2L

3. (A) Z = A B AB

By truth – table, Z = (A + B)

4. (B)

Just solve by K – Map and then one can get correct answer very easily

so it depends upon 2 variables and independent of 2 variables.

5. (B) 2 2

0 (50)25

100i

R

ZZ

Z

6. (B) For a good-conductor vp = w.

7 7 11

10 2 10 sec2

pv m

7. (B) C = B log2 (1 + S/N)

B log2 1 0

8. (C)

9. (D) | ( )|( ) x ty t e if x (t) is not bounded then | ( )|x te is bounded.

10. (D)

11. (D)

12. (A)

13. (A) v = E E = (V/d) e

m

14. (D) 0.98 5000

7070

i Lv

i

A RA

R

Power gain = volt.gain × current gain = 70 × 0.98 = 68.6

15. (B) For series RLC circuit Impedance will be minimum and current will be maximum.

Here 1R

Z R power factor cosZ

16. (C) At t=0+ voltage across capacitor will remains constant at 10 volt.

17. (A) 3 ( 1)(2 1)

6

n n nn

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3

3

3

( 1)(2 1)lim

6

2 (1 1/ )(1 1/ 2 )lim (1/ 3)

6

n

n

n n n

n

n n n

n

18. (B) Characteristic equation is

1 0 1

0 0 1 0

0 1 0

So (1-) (2-1) = 0

3 -

2 - + 1 = 0

By Cayley Hamilton Theorem

A3 – A

2 – A + I = 0

So A3 – A

2 = (A – I)

19. Ans=3 Volt

20. Ans= 0.2 A/m

21. Ans=370 KHz

22. Ans=2 A: Ix = 3/2 + 3 2

2

= 2A

23. Ans= 20 micro second

24. Ans=1 sec

3 24 6 4s s s

2

2

( 2) 2 ( 2) 2( 2) 0

( 2)( 2 2) 0

s s s s s

s s s

2 2 1

1timeconstant 1sec

n n

n

25. Ans=3.3 Kwatt

2

12

at c

mP P

26. (A) For

2 1o

1 2 v

i 1

R / RvA

v 1 j /

For

2 1

2 v

2

R / RA

1 j /

27. (C)

28. (B) Tie e

E

.Vh r

I

Tie

B

V 26mVh 1K

I 26 A

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fe cv

i

h R 100 4A 7.8

R 50 1

29. (A) Delay = 0.2 sec

So can be written as 0.2se

Now

0.2s100G s H s e

s 5 s 10

Calculate G.M.

30. (B) it is not self starting

but it has MOD – 3.

31. (A) Calculate ABCD parameters for Network [z] and then for fig. (b)

Since both are in cascaded so calculate ABCD parameters.

32. (B) Calculate parameters for T-Network.

33. (C)

34. (B)

35. (C) 2 2

1 cy t A m t cos t

2 2

c

A m t 2Am t1 cos 2 t

2

36. (B)

37. (B) 10

8

3 1060cm

5 10

min2 y n

2

2 30cm 0 260

R o

R o

z zK

z z

VSWR 2 So K 1/3

r

r

z 11

3 z 1

r r3z 3 z 1

rz 2

38. (D)

39. 0.1739 meter

o

a

2 V V 1 1

q N N

Here a Do 2

i

N NKTV n

q n

40. 19.47º

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m

1sin

1

where

20.5

2 2

41. 168 volt

LS R

0

z 210V V 80

z 100

SV 168volt

42. (8.2)

43. 2 K

44. (1)

45. –6.28

46. 55 sec

47. 16.3%

48. 4

49. 480

50. 1 K

51. 1.66

52. (A)

53. (C)

54. (B)

55. (C)

56. (C)

57. (B)

58. (A)

59. (A)

60. (B)

61. (C)

62. (A)

63. (C)

64. (B)

65. (D)