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Wednesday, November 14, 2012

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GATE question papers: Electronics and Communication Engineering 2011

Ashok royal - 19:23

                                                           

Q. 1 - Q. 25 carry one mark each.

1
The modes in a rectangular waveguide are denoted by TEmn/TMmn where m and n are the eigen numbers along the larger and smaller dimensions of the waveguide respectively. Which one of the following statements is TRUE?
(A) The TM10 mode of the wave does not exist
(B) The TE10 mode of the wave does not exist
(C) The TM10 and the TE10 modes both exist and have the same cut-off
frequencies
(D) The TM10 and TM10 modes both exist and have the same cut-off frequencies
Answer: (A)
2
The Column-I lists the attributes and the Column-II lists the modulation systems. Match the attribute to the modulation system that best meets it

Column-I

Column-II
P
Power efficient transmission of signals
I.
Conventional AM
Q
Most bandwidth efficient transmission of voice signals
II.
FM
R
Simplest receiver structure
III.
VSB
S
Bandwidth efficient transmission of signals with Significant dc component
IV.
SSB-SC
(A) P-IV, Q-II, R-I, S-III
(B) P-II, Q-IV, R-I;S-III
(C) P III, Q-II, R-I; S-IV
(D) P-II, Q-IV, R- III, S-I
Answer: (B)
3
The differential equation  describes a system with an input x(t) and an output y(t). The system, which is initially relaxed, is excited by a unit step input. The output y(t) can be represented by the waveform
Answer: (A)

4
For the transfer function G(jw) j, the corresponding Nyquist plot for positive frequency has the form
Answer: (A)
5
The trigonometric Fourier series of an even function does not have the
(A) dc term
(B) cosine terms
(C) sine terms
(D) odd harmonic terms
Answer: (C)
6
When the output Y in the circuit below is '1', it implies that data has
(A) changed from "0" to "1"
(B) changed from "1" to "0"
(C) changed in either direction
(D) not changed
Answer: (A)
7
The logic function implemented by the circuit below is (ground implies logic "0")
(A) F = AND(P,Q)
(B) F = OR (P,Q)
(C) F = XNOR (P,Q)
(D) F = XOR (P,Q)
Answer: (D)
8
The circuit below implements a filter between the input current ii and the output voltage vo. Assume that the opamp is ideal. The filter implemented is a
(A) low pass filter
(B) band pass filter
(C) band stop filter
(D) high pass filter
Answer: (D)
9
A silicon PN junction is forward biased with a constant current at room temperature. When the temperature is increased by 10°C, the forward bias voltage across the PN junction
(A) increases by 60mV                            (B) decreases by 60mV
(C) increases by 25mV                            (D) decreases by 25mV
Answer: (D)

10
In the circuit shown below, the Norton equivalent current in amperes with respect to the terminals P and Q is
(A) 6.4 - j4.8
(B) 6.56 - j7.87
(C) 10 j0
(D) 16 j0
Answer: (A)

11
In the circuit shown below, the value of RL such that the power transferred to RL is maximum is
(A) 5W                                                                                   (B) 10 W
(C) 15 W                                                                               (D) 20 W
Answer: (C)
12
The value of the integral  where c is the circle |z| = 1 is given by
(A) 0
(B) 1/10
(C) 4/5
(D) 1
Answer: (A)
13
A transmission line of characteristic impedance 50is terminated by a 50 load. When excited by a sinusoidal voltage source at 10GHz, the phase difference between two points spaced 2mm apart on the line is found to be p/4 radians. The phase velocity of the wave along the line is
(A)  0.8 ´ 108 m / s
(B) 1.2 ´ 108 m / s
(C) 1.6 ´ 108 m / s
(D)  ´ 108 m / s
Answer: (C)
14
Consider the following statements regarding the complex Poynting vector for the power radiated by a point source in an infinite homogeneous and lossless medium. Re denotes the real part of , S denotes a spherical surface whose centre is at the point source, and  denotes the unit surface normal on S. Which of the following statements is TRUE?
(A) Re remains constant at any radial distance from the source
(B) Re increases with increasing radial distance from the source
(C).dS remains constant at any radial distance from the source
(D).dS decreases with increasing radial distance form the source
Answer: (D)

15
An analog signal is band-limited to 4 kHz, sampled at the Nyquist rate and the samples are quantized into 4 levels. The quantized levels are assumed to be independent and equally probable. If we transmit two quantized samples per second, the information rate is
(A) 1 bits / second
(B) 2 bits / second
(C) 3 bits / second
(D) 4 bits / second
Answer: (D)
16
The root locus plot for a system is given below. The open loop transfer function
corresponding to this plot is given by
(A)                (B) 
(C)      (D) 
Answer: (B)
17
A system is defined by its impulse response h(n) = 2n u(n − 2). The system is
(A) stable and causal
(B) causal but not stable
(C) stable but not causal
(D) unstable and non-causal
Answer: (B)
18
If the unit step response of a network is (1 − e−at), then its unit impulse response is
(A) ae-at
(B) a−1 e-at
(C) (1- a-1 ) e-at
(D) (1 - a)e-at
Answer: (A)




19
The output Y in the circuit below is always "1" when
(A) two or more of the inputs P, Q, R are "0"'
(B) two or more of the inputs P, Q, R are "1"
(C) any odd number of the inputs P, Q, R is "0"'
(D) any odd number of the inputs P, Q, R is "1"
Answer: (B)
20
In the circuit shown below, capacitors C1 and C2 are very large and are shorts at the input frequency. vi is a small signal input. The gain magnitude |vo/vi| 10Mrad/s is
(A) maximum
(B) minimum
(C) unity
(D) zero
Answer: (A)
21
Drift current in the semiconductors depends upon
(A) only the electric field
(B) only the carrier concentration gradient
(C) both the electric field and the carrier concentration
(D) both the electric field and the carrier concentration gradient
Answer: (C)
22
A Zener diode, when used in voltage stabilization circuits, is biased in
(A) reverse bias region below the breakdown voltage
(B) reverse breakdown region
(C) forward bias region
(D) forward bias constant current mode
Answer: (B)
23
The circuit shown below is driven by a sinusoidal input vi = Vp cos (t /RC). The
steady state output vis
(A) (Vp / 3) cos (t/RC)
(B) (Vp / 3) sin (t/RC)
(C) (Vp / 2) cos (t/RC)
(D) (Vp / 2) sin (t/RC)
Answer: (A)

24
Consider a closed surface S surrounding volume V. If is the position vector of a
point inside S, with the unit normal on S, the value of the integral dS is
(A) 3V
(B) 5V
(C) 10V
(D) 15V
Answer: (D)
25
The solution of the differential equation , y(0) =  c is
(A) x = ce-ky
(B)x = kecy
(C) y = cekx
(D) y =  ce-kx
Answer: (C)

Q.26 to Q.55 carry two marks each.

26
The electric and magnetic fields for a TEM wave of frequency 14 GHz in a homogeneous medium of relative permittivity er and relative permeability m=1 are given by
V/m
A/m
Assuming the speed of light in free space to be 3 ´ 108 m/s, the intrinsic
impedance of free space to be 120, the relative permittivity er of the medium and the electric field amplitude Ep are
(A) er = 3, Ep 120p
(B) er = 3, Ep 360p
(C) er = 9, Ep 360p
(D) er = 9, Ep 120p
Answer: (D)
27
A message signal m(tcos200p4cos pt modulates the carrier
c(t) cos2fc t where fc 1 MHZ to produce an AM signal. For demodulating the generated AM signal using an envelope detector, the time constant RC of the detector circuit should satisfy
(A) 0.5 ms < RC < 1ms
(B) 1m<< RC 0.5 ms
(C) RC << ms
(D) RC >> 0.5 ms
Answer: (B)
28
The block diagram of a system with one input and two outputs yand y2 is given below.
A state space model of the above system in terms of the state vector and the output vector is
(A)                    
(B)                   
(C)         

(D)            
Answer: (B)
29
Two systems H(z) and H2 (z) are connected in cascade as shown below. The over all output y(n) is the same as the input x(n) with a one unit delay. The transfer function of the second system H2 (z) is
(A)                                (B) 
(C)                                 (D) 
Answer: (B)
30
An 8085 assembly language program is given below. Assume that the carry flag is initially unset. The content of the accumulator after the execution of the
program is
MVI A, 07H
RLC
MOV B, A
RLC
RLC
ADD B
RRC
(A) 8CH
(B) 64H
(C) 23H
(D) 15H
Answer: (C)
31
The first six points of the 8-point DFT of a real valued sequence are5, 1 − j3, 0,
3 − j4, 0 and 3 + j4. The last two points of the DFT are respectively
(A) 0, 1 − j3
(B) 0, 1 + j3
(C) 1 + j3, 5
(D) 1 – j3, 5
Answer: (C)
32
For the BJT Q1 in the circuit shown below, b = ¥, VBEon = 0.7V, VCEsat = 0.7V, The switch is initially closed. At time t = 0, the switch is opened. The time t at which Q1
leaves the active region is
(A) 10 ms
(B) 25 ms
(C) 50 ms
(D) 100 ms
Answer: (C)
33
In the circuit shown below, the network N is described by the following Y matrix:
. The voltage gain is
(A) 1/90
(B) -1/90
(C) -1/99
(D) -1/11
Answer: (D)
34
In the circuit shown below, the initial charge on the capacitor is 2.5 mC, with the voltage polarity as indicated. The switch is closed at time t=0. The current i(t) at
a time t after the switch is closed is
(A) i(t) = 15exp(−2 ×103 t) A
(B) i(t) =  5exp(−2 ×103 t) A
(C) i(t) = 10exp(−2 ×103 t) A
(D) i(t) = -5exp(−2 ×103 t) A
Answer: (A)
35
The system of equations
x + y + z = 6
x + 4y + 6z = 20
x + 4y +lz = m
has NO solution for values of and m given by
(A) l = 6, m  = 20
(B) l = 6, m  ¹ 20
(C) l ¹ 6, m 20
(D) l ¹ 6, m ¹ 20
Answer: (B)
36
A fair dice is tossed two times. The probability that the second toss results in a value that is higher than the first toss is
(A) 2/36
(B) 2/6
(C) 5/12
(D)1/2
Answer: (C)
37
A current sheet  A/m lies on the dielectric interface x = 0 between two dielectric media with er1 5, mr1  = 1 in Region-1 (x < 0) and er2  = 2, mr2  = 2 in Region-2 (x > 0). If the magnetic field in Region-1 at x=0 is A/m, the magnetic field in Region-2 at x = 0is
(A) A/m                      (B) A/m
(C) A/m                                 (D) A/m
Answer: (A)
38
A transmission line of characteristic impedance 50 W is terminated in a load impedance ZLThe VSWR of the line is measured as 5 and the first of the voltage maxima in the line is observed at a distance of l/4 from the load. The value of ZL is
(A) 10 W
(B) 250 W
(C) (19.23 j46.15) W
(D) (19.23 - j46.15) W
Answer: (A)
39
X(t) is a stationary random process with autocorrelation function Rx(t)= exp (-pt2).  This process is passed through the system shown below. The power spectral density of the output process Y(t) is
(A) (4p2 f2 + 1) exp (−pf2)
(B) (4p2 f2 –1) exp (−pf2)
(C) (4p2 f2 + 1) exp (−pf)
(D) (4p2 f2 – 1) exp (−pf)
Answer: (A)
40
The output of a 3-stage Johnson (twisted- ring) counter is fed to a digital-to-analog (D/A) converter as shown in the figure below. Assume all the states of the counter to be unset initially. The waveform which represents the D/A converter output Vo is

Answer: (A)
41
Two D flip-flops are connected as a synchronous counter that goes through the
following QBQA sequence 00 ® 11® 01 ® 10 ® 00 ® ...
The combination to the inputs DA and DB are
(A) DA = QB, DB = QA
(B) DA = , DB = 
(C) DA = (QQB), DB = QA
(D) DA = (QA QB +), DB
Answer: (D)
42
In the circuit shown below, for the MOS transistors,mnCox = 100μA / V2 and the threshold voltage  VT = 1 V. The voltage Vx at the source of the upper transistor is
(A) 1V
(B) 2V
(C) 3V
(D) 3.67V
Answer: (C)
43
An input x (t) = exp (−2t)u(t) + d(t − 6) is applied to an LTI system with impulse response h(t) = u(t) . The output is
(A) [1 − exp (−2t)] u(t) + u(t+6)
(B) [1 − exp (−2t)] u(t) + u(t-6)
(C) 0.5 [1 − exp (−2t)] u(t) + u(t+6)
(D) 0.5 [1 − exp (−2t)] u(t) + u(t-6)
Answer: (D)
44
For a BJT the common base current gain a = 0.98 and the collector base junction reverse bias saturation current ICO = 0.6μA. This BJT is connected in the common emitter mode and operated in the active region with a base drive current
IB=20μA. The collector current IC for this mode of operation is
(A) 0.98mA
(B) 0.99mA
(C) 1.0mA
(D) 1.01mA
Answer: (D)
45
If  then the initial and final values of f(t) are
respectively
(A) 0,2
(B) 2,0
(C) 0,2/7
(D) 2/7,0
Answer: (B)
46
In the circuit shown below, the current I is equal to
(A) 1.4 Ð0°A
(B) 2.0Р0°A
(C) 2.8 Ð0°A
(D) 3.2Р0°A
Answer: (B)
47
A numerical solution of the equation f (xcan be obtained using Newton- Raphson method. If the starting value is = 2 for the iteration, the value of xthat is to be used in the next step is
(A) 0.306
(B) 0.739
(C) 1.694
(D) 2.306
Answer: (C)

Common Data Questions


Common Data Questions: 48 & 49
The channel resistance of an N-channel JFET shown in the figure below is 600 W when the full channel thickness (tch) of 10μm is available for conduction. The built-in voltage of the gate P+ N junction (Vbi) is –1 V. When the gate to source
voltage (VGS) is 0 V, the channel is depleted by 1μm on each side due to the built-in voltage and hence the thickness available for conduction is only 8μm

48
The channel resistance when VGS = 0 V is
(A) 480 W
(B) 600 W
(C) 750 W
(D) 1000 W
Answer: (C)
49
The channel resistance when VGS = -3 V is
(A) 360W
(B) 917W
(C) 1000W
(D) 3000W
Answer: (C)

Common Data Questions: 50 & 5 1
The input-output transfer function of a plant H(s) = . The plant is placed in a unity negative feedback configuration as shown in the figure below.

50
The signal flow graph that DOES NOT model the plant transfer function H(s) is
Answer: (D)
51
The gain margin of the system under closed loop unity negative feedback is
(A) 0 dB                                                (B) 2 0dB
(C) 26 dB                                               (D) 46 dB
Answer: (C)

Linked Answer Questions
Statement for Linked Answer Questions: 52 & 53
A four-phase and an eight-phase signal constellation are shown in the figure below.

52
For the constraint that the minimum distance between pairs of signal points be d
for both constellations, the radii r1, and r2 of the circles are
(A) r= 0.707d, r2 = 2.782d                    (B) r1 = 0.707d, r2 = 1.932d
(C) r1 = 0.707d, r2 = 1.545d                    (D) r1 = 0.707d, r2 = 1.307d
Answer: (D)
53
Assuming high SNR and that all signals are equally probable, the additional average transmitted signal energy required by the 8-PSK signal to achieve the same error probability as the 4-PSK signal is
(A) 11.90 dB                                          (B) 8.73 dB
(C) 6.79 dB                                            (D) 5.33 dB
Answer: (D)

Statement for Linked Answer Questions: 54 & 55
In the circuit shown below, assume that the voltage drop across a forward biased diode is 0.7 V. The thermal voltage Vt = kT/q = 25mV. The small signal input vi = Vp cos(wt) where Vp = 100mV .

54
The bias current IDC through the diodes is
(A) 1 mA
(B) 1.28 mA
(C) 1.5 mA
(D) 2 mA
Answer: (A)
55
The ac output voltage vac is
(A) 0.25cos (wt)mV
(B) 1cos (wt)mV
(C) 2cos (wt)mV
(D) 22cos (wt)mV
Answer: (C)

General Aptitude (GA) Questions:

56
Q. 56 to Q. 60 carry one marks each
The question below consists of a pair of related words followed by four pairs of words. Select the pair that best expresses the relation in the original pair:
Gladiator : Arena
(A) dancer : stage
(B) commuter: train
(C) teacher : classroom
(D) lawyer : courtroom
Answer: (D)
57
There are two candidates P and Q in an election. During the campaign, 40% of the voters promised to vote for P, and rest for Q. However, on the day of election 15% of the voters went back on their promise to vote for P and instead voted for Q. 25% of the voters went back on their promise to vote for Q and instead voted for P. Suppose, P lost by 2 votes, then what was the total number of voters?
(A) 100
(B) 110
(C) 90
(D) 95
Answer: (A)
58
Choose the most appropriate word from the options given below to complete the
following sentence:
It was her view that the country's problems had been______ by foreign technocrats, so that to invite them to come back would be counter-productive.
(A) Identified
(B) ascertained
(C) exacerbated
(D) Analysed
Answer: (C)
59
Choose the word from the options given below that is most nearly opposite in
meaning to the given word:
Frequency
(A) periodicity
(B) rarity
(C) gradualness
(D) persistency
Answer: (B)
60
Choose the most appropriate word from the options given below to complete the
following sentence:
Under ethical guidelines recently adopted by the Indian Medical Association, human genes are to be manipulated only to correct diseases for which______ treatments are unsatisfactory.
(A) Similar
(B) Most
(C) Uncommon
(D) Available
Answer: (D)

Q. 61 to Q. 65 carry two marks each.

61
The horse has played a little known but very important role in the field of medicine. Horses were injected with toxins of diseases until their blood built up immunities. Then a serum was made from their blood. Serums to fight with diphtheria and tetanus were developed this way.
It can be inferred from the passage that horses were
(A) given immunity to diseases
(B) generally quite immune to diseases
(C) given medicines to fight toxins
(D) given diphtheria and tetanus serums
Answer: (B)
62
The fuel consumed by a motorcycle during a journey while traveling at various speeds is indicated in the graph below.
The distances covered during four laps of the journey are listed in the table below
Lap
Distance (kilometers)
Average speed (kilometers per hour)
P
15
15
Q
75
45
R
40
75
S
10
10
From the given data, we can conclude that the fuel consumed per kilometre was least during the lap
(A) P                                                     (B) Q
(C) R                                                     (D) S
Answer: (A)
63
Three friends, R, S and T shared toffee from a bowl. R took 1/3rd of the toffees, but returned four to the bowl. S took 1/4th of what was left but returned three toffees to the bowl. T took half of the remainder but returned two back into the bowl. If the bowl had 17 toffees left, how many toffees-were originally there in the bowl?
(A) 38                                                   (B) 31
(C) 48                                                   (D) 41
Answer: (C)
64
Given that f(y) = | y | / y, and q is any non-zero real number,
the value of | f(q) – f(–q) | is
(A) 0                                                     (B) –1
(C) 1                                                     (D) 2
Answer: (D)
65
The sum of n terms of the series 4+44+444+.... is
(A) (4 /81) [10n+1 - 9n - 1]                     (B) (4 /81) [10n-1 - 9n - 1]
(C) (4 /81) [10n+1 - 9n - 10]                    (D) (4 /81) [10n - 9n - 10]
Answer: (C)

End of Question Paper

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