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ISRO 2015 Electronics Question Paper with Answers

ISRO 2015 Electronics
1. Electron mobility of the following intrinsic elements in descending order is
a. GaAs, Ge, Si
b. GaAs, Si, Ge
c. Si, Ge, GaAs
d. Ge, Si, GaAs
Answer: A

2. A sample of Si is doped with 1017 donor atoms/cm3. Considering electron mobility in the doped Si as 700 cm2/V-sec, the approximate resistivity of the doped Si is
a. 1 Ω-cm
b. 10 Ω-cm
c. 0.1 Ω-cm
d. 100 Ω-cm
Answer: C

3. Common base current gain of a PNP bipolar transistor is 0.99. The common emitter current gain of the transistor is
a. 101
b. 0.01
c. 99
d. 1.0
Answer: C

4. The electrical conductivity of a semiconductor increases when a radiation of wavelength shorter than 1000 nm is incident on it. The band gap of the semiconductor is
a. 2.4 eV
b. 1.2 eV
c. 3.4 eV
d. 4.0 eV
Answer: B

5. The voltage across the resistor R is
Answer: D

6. The effective resistance faced by the voltage source is

a. 4 Ω
b. 12 Ω
c. 3 Ω
d. 16 Ω
Answer: C

7. Common emitter DC current gain of the transistor is 100. The current through the Zener diode (assuming VBE of the transistor is 0.7 volts) is
a. 10.3 mA
b. 19.3 mA
c. 20 mA
d. 40 mA
Answer: A

8. The circuit is with an ideal operational amplifier with ±10 volts supply. The output voltage is

a. – 200 mV
b. – 400 mV
c. – 600 mV
d. – 300 mV
Answer: B

9. A step voltage of 10 volts applied to the circuit at t=0. The current through the resistor R just after t=0 and at steady state are
a. 100 mA, 50 mA
b. 50 mA, 50 mA
c. 100 mA, 100 mA
d. 75 mA, 75 mA
Answer: A

10. which of the following addressing mode is not usable in XCH instruction of 8051 microcontroller?
a. Direct Addressing
b. Indirect Addressing
c. Register Addressing
d. Immediate Addressing
Answer: D

11. In a binary source, 0’s occur three times as often as 1’s. What is the information contained in the 1’s?
a. 0.415 bits
b. 0.333 bits
c. 3 bit
d. 2 bit
Answer: D

12. Spectrum of a signal x(t), sampled at period T, is given by
Answer: A

13. A bandpass signal occupies the bandwidth 390 kHz to 410 kHz. What minimum sampling frequency would you use from the options given below, so as to avoid aliasing?
a. 40 kHz
b. 820 kHz
c. 41 kHz
d. 800 kHz
Answer: C

14. A 12 bit ADC has input signal range of ± 1 volt. The signal to quantization noise ratio if a sine wave signal with 0.25 volts peak voltage is given as input is:
a. 62 dB
b. 72 dB
c. 74 dB
d. 48 dB
Answer: A

15. Identify the modulation schemes for the signal constellation diagram shown
a. ASK
b. MSK
c. FSK
d. QAM
Answer: B

16. Which of the following modulating scheme requires minimum power for transmission?
b. 8 – PSK
c. 16 – QAM
d. 64 – QAM
Answer: A

17. Which of the following channel coding scheme helps in correcting burst errors?
a. CRC
b. Convolution Coding
c. Viterbi
d. Reed-Solomon
Answer: D

18. A 70 MHz carrier is QPSK modulated by a 1.544 Mbps T1 data stream. The transmitter employs a raised cosine filter with α = 0.2. What is the transmitted bandwidth of the signal?
a. 3705.6 kHz
b. 1852.8 kHz
c. 308.8 kHz
d. 926.4 kHz
Answer: D

19. If two tones f1 and f2 are amplified by a non-linear amplifier, which frequency components would be present in output?
a. f1, f2
b. f1, f2, f1+ f2, f1- f2
c. f1+ f2, f1- f2
d. nf1± m f2, where n and m are intergers
Answer: D

20. A phase locked loop with a first order loop filter can track
a. phase offset
b. frequency offset
c. frequency offset rate
d. amplitude variation
Answer: B

21. The noise figure of a device is 2. If input SNR is 37 dB, what would be output SNR?
a. 18.5 dB
b. 34 dB
c. 40 dB
d. 74 dB
Answer: B

22. What is the limit of Eb/No, below which reliable communication is not possible?
a. – 10 dB
b. – 1.6 dB
c. 0 dB
d. 1.6 dB
Answer: B

23. A satellite communication link has uplink C/No of 50 dB-Hz and downlink C/No of 47 dB-Hz. What would be overall link C/No?
a. 44 dB-Hz
b. 45 dB-Hz
c. 48. dB-Hz
d. 53 dB-Hz
Answer: B

24. A signal transmitted from an Earth station bounces back from a geostationary satellite, with an altitude of 35864 km from the Earth surface. The range from the Earth station, is 38200 km. The round trip time is about (excluding processing delays and assuming C = 3x108 m/s)
a. 255 ms
b. 127 ms
c. 239 ms
d. 120 ms
Answer: A

25. 1 mW in dBm is
a. 0 dBm
b. – 30 dBm
c. 30 dBm
d. 1 dBm
Answer: A

26. Which of the following is not true?
a. MPEG-4 is a source coding technique
b. Channel coding gives coding gain at the expense of bandwidth
c. source coding/decoding is done to remove errors
d. concatenated coding gives usually good performance
Answer: C

27. The following finite state machine (FSM) is used to detect a particular pattern in input data stream. Whenever the pattern is matched at input, output is set to ‘1’ or else output is cleared to ‘0’. For which of the following data stream, output goes to ‘1’ twice?
Answer: C

28. A digital signal processing system is described by the expression:
Y(n) = 2x(n) + x(n-1) + 2y(n-1). The system is
a. A stable FIR filter
b. A stable IIR filter
c. An unstable FIR filter
d. An unstable IIR filter
Answer: D

29. The rectangular window has relative side-lobe level:
a. – 13 dB
b. – 27 dB
c. – 32 dB
d. – 43 dB
Answer: A

30. Consider the discrete time signal x(n) = {1,1,1,1,0.5,0.5}. y(n) = conv(δ(n-1), x(n)) is
a. 1
b. δ(n-1)
c. x(n-1)
d. 5
Answer: C

31. Consider a sequence x(n) = [2,4,6,8,0,1,3,5,7,9]. Down-sample the sequence by 3 and then up-sampling by 2. The resulting sequence is
Answer: C

32. Power consumed in a CMOS circuit operating at frequency f is proportional to
a. Vcc
b. Vcc.f
c. Vcc2.f
d. Vcc2f2
Answer: C

33. The phase velocity of a plane wave given by Ex = Eocos(ωt-βz) with a frequency of 5 GHz and a wavelength in the material medium of 3 cm is
a. 3 x 108 m/sec
b. 1.5 x 108 m/sec
c. 5 x 108 m/sec
d. None
Answer: B

34. If the reflected wave at the load of a transmission line is 20 dB below the incident wave, the SWR at the load is
a. 1.5
b. 1.22
c. 3.0
d. 4.0
Answer: B

35. The highest frequency for which a circular coaxial transmission line having outer diameter = 3.1 mm and inner diameter = 1.3 mm can be operated in pure TEM mode (assuming free space medium between the two conductors) should be less than:
a. 12.2 GHz
b. 18.6 GHz
c. 26.5 GHz
d. 43.4 GHz
Answer: D

36. In a communication system at 300 MHz, the receiving antenna gain is 8 dBi, the transmitting antenna gain is 10 dBi and the transmitting power level is 25 watts, the distance between the transmitter and the receiver is 1 km, the power received at the receiving antenna port (assuming the propagation medium is loss less)
a. 1 mW
b. 9.97 µW
c. 99.7 nW
d. 0.0997 nW
Answer: B

37. A rectangular waveguide with air medium has dimensions a=22.86 mm and b=10.6 mm is fed by 3 GHz carrier from a coaxial cable, which of the following is false statement for TE01 mode?
a. Propagating mode
b. Non-propagating mode
c. Propagating mode in case filled fully with dielectric material of proper dielectric constant
d. None of the above
Answer: A

38. TM01 mode in rectangular perfect metallic waveguide is
a. Propagating mode
b. Evanescent mode
c. Non-existent mode
d. None of the above
Answer: C

39. The directivity of a prime-focal parabolic reflector antenna is 30 dBi. If the efficiency of the antenna is 50%, the gain of the antenna is
a. 27 dBi
b. 33 dBi
c. 25 dBi
d. 80 dBi
Answer: A

40. Ratio of skin depths of an electromagnetic wave inside the conductor for the corresponding frequencies at 4 GHz and 9 GHz, considering the same material properties for both the frequencies is:
a. 9:4
b. 4:9
c. 3:2
d. 2:3
Answer: C

41. A cassegrain reflector antenna has a sub-reflector whose geometric shape is
a. paraboloid
b. Hyperboloid
c. Ellipsoid
d. Spherical
Answer: B

42. The beam-width and the directivity of an antenna are
a. directly proportional
b. Indirectly proportional
c. Independent of each other
d. Equal
Answer: B

43. A lossless transmission line with characteristic impedance Zo = 50 ohm is 30 m long and operates at 2 MHz. The line is shorted at the load, if the phase velocity = 0.6 times the velocity of light, the input impedance of the line is

Answer: Question omitted for valuation

44. Two microwave sub-systems having respective return loss of 10 dB and 20 dB are cascaded together, the return loss at the input of the integrated system is
a. 9.63 dB
b. 15.36 dB
c. 21.12 dB
d. 25.23 dB
Answer: A

45. A parabolic reflector antenna used for reception of data is 1 meter in diameter and operates at 30 GHz. The far field distance of this antenna for a quadratic phase error of 22.5 degree is
a. 200 meter
b. 50 meter
c. 100 meter
d. 150 meter
Answer: A

46. A potential field is given by Φ = 2xy2 – 3y2z.

Answer: C

47. The VSWR of a microwave unit is 1.5, the return loss is
a. 14 dB
b. 16 dB
c. 18 dB
d. 11 dB
Answer: A

48. In two wire transmission line, two consecutive voltage minima and found at 20.6 cm and 25.6 cm. The operating frequency is
a. 3.5 GHz
b. 3 GHz
c. 1 GHz
d. 2.5 GHz
Answer: B

49. A TEM mode transmission line is having distributed circuit parameters as R = 1 Ω/m, L = 200 nH/m, G = 300 µS/m, C = 60 pF, the line is
a. Loss less
b. Lossy
c. Distortion less
d. None of the above
Answer: C

50. A plane wave E = 100sin(ωt-10x) V/m in a loss less medium with µ = 4µo, ε = εo, the reflection co-efficient is
a. 0.5
b. 0.25
c. 0.1
d. 0.2
Answer: D

51. What is the functionality of following digital circuit? A is input data, CLK is system clock and Y is output.
a. Falling edge detection of input A
b. Clock division by 2
c. Rising edge detection of input A
d. Clock division by 4
Answer: A

52. A loss less transmission line has the distributed circuit parameters of inductance and capacitance per meter as 625 nH/m and 64 pF/m respectively, the phase constant of the lien at 100 MHz is
a. 3.97 rad/m
b. 18.42 rad/m
c. 1.56 rad/m
d. 9.21 rad/m
Answer: A

53. In the circuit if C1 = 2 µF and C2 = 3 µF, the equivalent capacitance between points A and B is
a. 4 µF
b. 3 µF
c. 1 µF
d. 2 µF
Answer: C

54. If n number of MOSFETs with identical W/L is connected in series, then equivalent W/L is given by
a. (W/L)*n
b. (W/L) / n
c. (W/L)* n2
d. (W/L)/ n2
Answer: B

55. Which resource of FPGA implements combinational logic functionality?
a. Block RAM
b. Configurable Logic Block (CLB)
c. Routing Switch Matrix
d. All of the above
Answer: B

56. What will be the content of accumulator, register B and overflow flag (OV) after execution of following 8051 micro-controller assembly code?
Answer: B

57. Average value of the waveform is

a. 8 volts
b. 20 volts
c. 10 volts
d. 4 volts
Answer: D

58. Main function of Helix structure in a Travelling Wave Tube (TWT) amplifier is
a. To reduce axial velocity of RF field
b. To reduce noise figure of TWT
c. To properly focus electron beam
d. To reduce axial velocity of electron
Answer: A

59. Which of memory has constraint of minimum operating clock frequency?
b. Static RAM (SRAM)
c. Dynamic RAM (DRAM)
d. Magneto – resistive RAM (MRAM)
Answer: C

60. Equivalent circuit of a FET is shown in the figure below, where rg = 100 Ω, Cgs = 0.1 pF and gm = 0.1 mho. For load resistance rL = 500 Ω, the voltage gain at 1 GHz is

a. 50
b. 30
c. 20
d. 100
Answer: A

61. Which of the following is TRUE for an NMOS transistor operating in linear region?
a. VDS < (VGS – VT)
b. VDS > (VGS – VT)
c. VGS < VT
d. VGS = 0
Answer: A

62. Gain and NF of a single stage amplifier is 10 dB and 3 dB respectively. When two such amplifiers cascaded then gain and NF of the cascaded amplifier will be:
a. 20 dB, 3.2 dB
b. 20 dB, 6.0 dB
c. 13 dB, 3.6 dB
d. 13 dB, 3.7 dB
Answer: A

63. Magnitude of input impedance of a λ/8 lossless 50Ω transmission line terminated with 25 Ω is
a. 100 Ω
b. 25 Ω
c. 50 Ω
d. None of the above
Answer: C

64. Pipelining technique is used in microprocessor to improve which of the following parameter?
a. Power dissipation
b. Interrupt Latency
c. Die size
d. Maximum clock frequency
Answer: D

65. In case of an ideal Class-F microwave power amplifier, time domain voltage and current waveform of the device have
a. 50% overlap
b. Maximum overlap
c. No overlap
d. Less than 80% overlap
Answer: C

66. Reason for superior high frequency performance of metal – semiconductor diode compared to PN junction diode is
a. Higher conductivity of metal compared to semiconductor
b. No minority carrier storage effect in metal-semiconductor diode
c. Metal semiconductor junction does not rectify RF signal
d. Hole is the majority carrier in Schottky barrier diode operation
Answer: B

67. Which of the following diodes is most suitable for detection of microwave signal?
a. PIN diode
b. Schottky barrier diode
c. Varactor diode
d. PN junction diode
Answer: B

68. Which device is suitable for higher order RF frequency multiplier?
a. PIN diode
b. PN junction diode
c. BJT
d. Step recovery diode
Answer: D

69. Input reflection coefficient ‘S11’ of the 2-port network for 50 Ω system is
Answer: C

70. The graph below shows operating load line and I-V characteristics of a Schottky diode at two different RF power levels. Under this bias condition RF resistance of the diode
a. Remains constant with the RF power level
b. Decreases with the increase of RF power level
c. Increases with the increase in RF power level
d. None of the above
Answer: C

71. A BJT is having common emitter current gain 100. Considering 10 volts supply and VBE = 0.7 volts, what will be the value of RC and RB to set the quiescent point at IC = 10 mA and VCE = 8 volts?
Answer: A

72. Which statement is false about microstrip line over stripline?
a. Less radiative
b. Easier for component integration
c. One sided grounded plane
d. More interaction with neighbouring circuit element
Answer: A

73. A high gain MESFET packaged device of case to channel thermal resistance f the device is 4.5 oC/Watt provides 8Watt RF output power taking 20 Watt DC power. What will be the channel temperature of the device, if the case temperature of the device maintained at 55oC?
a. 109 oC
b. 145 oC
c. 59.5 oC
d. 91 oC
Answer: A

74. For a class-A FET power amplifier with 10 volts drain supply and 2 Amp drain current bias providing RF load current of 1 Amp amplitude. What is the DC to RF efficiency for load resistance of 5Ω?
a. 50%
b. 25%
c. 35%
d. 12.5%
Answer: D

75. DC to RF efficiency of an ideal class-F amplifier is
a. 100%
b. 78.4%
c. 50%
d. < 80%
Answer: A

76. A unilateral transistor has an output impedance Zout = (10 – j10)Ω. Value of the series and shunt components of the matching network for complex conjugate match at the output of the device to 50Ω load are
Answer: A

77. A communication channel is having a bandwidth of 3000 Hz. The transmitted power is such that the received signal to noise ratio is 1023. The maximum data rate that can be transmitted error free through the channel is
a. 3 kbps
b. 30 kbps
c. 3 Mbps
d. 300 kbps
Answer: B

78. A CDMA system requires Eb/Io of 10 dB. Each of the transmitters in the network transmits data at the rate of 1 Kbps with a PN chip rate of 1 Mbps. The maximum number of such users that the network can support is
a. 20
b. 30
c. 1000
d. 100
Answer: D

79. Laplace transform of eθtsin(ωt) is
Answer: B

80. Under steady state condition, the energy stored in the circuit is
Answer: C