UPSC Engineering Services (Main) Examination 2024 Electronics-Telecommunication Engineering Paper I & II – Previous Year Question Paper PDF Download
UPSC Engineering Services (Main) Examination 2024 Electronics-Telecommunication Engineering Paper I & II
Previous Year Question Paper PDF Download
ELECTRONICS AND TELECOMMUNICATION ENGINEERING
Paper - I
Time Allowed : Three Hours
Maximum Marks : 300
## Question Paper Specific Instructions
Please read each of the following instructions carefully before attempting questions :
There are EIGHT questions divided in TWO sections.
Candidate has to attempt FIVE questions in all.
Questions No. 1 and 5 are compulsory and out of the remaining, any THREE are to be attempted choosing at least ONE question from each section.
The number of marks carried by a question/part is indicated against it.
Wherever any assumptions are made for answering a question, they must be clearly indicated.
Diagrams/figures, wherever required, shall be drawn in the space provided for answering the question itself.
Unless otherwise mentioned, symbols and notations have their usual standard meanings.
Attempts of questions shall be counted in sequential order. Unless struck off, attempt of a question shall be counted even if attempted partly.
Any page or portion of the page left blank in the Question- cum- Answer (QCA) Booklet must be clearly struck off.
Answers must be written in ENGLISH only.
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UPSC Engineering Services (Main) Examination 2024 Electronics-Telecommunication Engineering Paper I & II
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Values of constants which may be required :
Electron charge = - 1.6 × 10⁻¹⁹ Coulomb
Free space permeability = 4π × 10⁻⁷ Henry/m
Free space permittivity = (1/36π) × 10⁻⁹ Farad/m
Velocity of light in free space = 3 × 10⁸ m/s
Boltzmann constant = 1.38 × 10⁻²³ J/K
Planck's constant = 6.626 × 10⁻³⁴ J-s
UPSC Engineering Services (Main) Examination 2024 Electronics-Telecommunication Engineering Paper I & II – Previous Year Question Paper PDF Download
1. (a) Consider an ideal pMOS capacitor of area 100 μm × 100 μm operated at T = 300 K , φ_M (work function for the metal) = 5·2 eV , x₀ (oxide thickness) = 3 nm and N_D = 10¹⁷ /cm³ . Calculate the flat band voltage V_FB and the threshold voltage V_TP . Assume E_ox = 3·43 × 10⁻¹³ F/cm , V_T (thermal voltage) = 0·026 V , n_i = 10¹⁰ /cm³ , χ_Si (electron affinity of Si) = 4·05 eV , E_G = 1·12 eV and E_Si = 10⁻¹² F/cm . 12
(b) In the circuit shown in the figure below, M₁ serves as an electronic switch. If v_in is very small, determine W/L such that circuit attenuates the signal by 5% . Assume V_G = 1·8 V and R_L = 100 Ω . μ_n C_ox = 200 μA/V² and V_TN = 0·4 V .
[Image: please refer to given pdf link for image and diagram]
(c) Find the voltage v₀ in the circuit shown in the figure using source transformation. Also, find the power developed by the 250 V voltage source. 12
[Image: please refer to given pdf link for image and diagram]
(d) An electrical load absorbs an average power of 85 kW at lagging power factor of 0·85 . If the load operates at 240 V rms, calculate the complex power and impedance of the load. 12
6 (i) Draw neat sketches of the edge and screw dislocations. Illustrate the Burger's vector on the sketches of dislocations. 6
(ii) Calculate the line energy of dislocation in BCC iron if the shear modulus and lattice parameter of BCC iron are 80·2 GN/m² and 2·87 Å , respectively. 6
Q2. (a) A p-n junction solar cell is fabricated using silicon and has the following important parameters :
N_A = 3 × 10¹⁸ /cm³ , N_D = 2 × 10¹⁶ /cm³
D_n = 25 cm²/s , D_p = 10 cm²/s
τ_n0 = 4 × 10⁻⁷ s , τ_p0 = 10⁻⁷ s
The photocurrent density J_L = 20 mA/cm² . Calculate the open circuit voltage of the solar cell at T = 300 K . Assume n_i = 1·5 × 10¹⁰ /cm³ . 20
(b) (i) What are the two functions of commutator in DC machines ? 5
(ii) Explain how the commutator keeps the armature mmf stationary in space, along the interpolar axis, even though the armature rotates. 15
(c) (i) Explain why end-centred tetragonal geometry does not exist in Bravais crystal structures. 10
(ii) Differentiate between different types of magnetic materials on the basis of magnetic dipoles and hysteresis loops. 10
Q3. (a) (i) Design a Widlar current source shown in the figure below to give I₀ = 5 μA and I_R = 1 mA . The parameters are V_CC = 30 V , V_BE1 = 0·7 V , V_T = 26 mV and β_F = 100 . 10
[Image: please refer to given pdf link for image and diagram]
(ii) Design an amplifier that has a voltage gain of 2 if V_IN < 0 and 1, if V_IN > 0 . Assume ideal diodes and ideal op amps are available. 10
10
(ii) A 10 kVA / 2500 / 250 V , single- phase transformer has the following parameters: Primary winding (h.v. side): Resistance r₁ = 2·4 Ω Leakage Reactance, x₁ = 6·00 Ω Secondary winding (l.v. side): Resistance r₂ = 0·03 Ω Leakage Reactance, x₂ = 0·07 Ω
With primary supply voltage held constant at 2500 V , calculate the secondary terminal voltage, when the low voltage winding is connected to a load impedance of 5 + j3·5 Ω and the transformer delivers its rated current at 0·8 p.f lagging on the low voltage side. 10
(c) (i) Discuss photoelectric effect and find out the number of photoelectrons emitted per unit time from a transmitter operated at a frequency of 800 kHz and 10 kW power. 10
(ii) Define dielectric strength. Discuss different types of dielectric breakdowns in solids. 10
Q4. (a) For the circuit shown in the figure below, determine the frequency of oscillation f₀ and overall voltage gain A_v . Also identify the type of oscillator. (Assume op amps are ideal) 20
[Image: please refer to given pdf link for image and diagram]
10
(b) (i) Determine the impedance Z_L that results in maximum average power transferred to Z_L for the circuit shown in the figure. Calculate the maximum average power transferred to the load impedance determined. 10
[Image: please refer to given pdf link for image and diagram]
(ii) What are the major factors that have led to the acceleration and development of solar and wind power? 10
(c) To produce a p-type semiconductor, the boron is doped in pure silicon. Doping is done through a B₂O₃ vapour phase of a surface concentration equivalent to 3·3 × 10²⁶ boron atoms/m³ . Calculate the time required to get a boron content of 10²³ atoms/m³ at a depth of 2 μm . The doping temperature is 1000°C and D_B in Si at this temperature is 4 × 10⁻¹⁷ m²/s . 20
Given: erf (0.95) = 0.8209
erf(1·0) = 0.8427
erf(2·4) = 0.9993
erf(2·6) = 0.9998
5. (a) Assume an ideal 10 bit ADC with V_REF = 5 V is used to sample 1 V_{p-p} sinusoidal signal that has a 2·5 V offset. What percent of error can be expected in the peak voltage measurement due to quantization effect of the ADC? (The error is relative to the magnitude of the sinusoid). 12
(b) A 555 IC is connected as shown in the figure below. Determine the frequency of oscillation and the duty cycle. (Assume that diode is an ideal diode). 12
[Image: please refer to given pdf link for image and diagram]
(c) (i) The network of the figure contains both a dependent voltage source and a dependent current source. Determine the y and z parameters. 6
[Image: please refer to given pdf link for image and diagram]
6
(ii) In the figure shown, a network with a steady state is reached with switch K open. At t = 0 , the switch is closed. For the element values given, determine the value of v_a (0- ) and v_a (0+).
[Image: please refer to given pdf link for image and diagram]
(d) (i) For the figure shown, find i1.
[Image: please refer to given pdf link for image and diagram]
(ii) The network of inductors in the figure below is composed of a 1 H inductor on each edge of a cube with the inductors connected to the vertices of the cube as shown. Find out the Lequivalent between the terminals A - B.
[Image: please refer to given pdf link for image and diagram]
12
(e) It is desired to measure the voltage across the 50 kΩ resistor in the circuit shown in the figure. Two voltmeters are available for this measurement: Voltmeter 1 with sensitivity of 1000 Ω/V and Voltmeter 2 with a sensitivity of 20,000 Ω/V . Both meters are used on their 50 - V range. Calculate the reading of each meter.
[Image: please refer to given pdf link for image and diagram]
Q6. (a) For the circuit shown in the figure below, MOS and BJT are operating in saturation and active mode, respectively. The capacitor C is very large and V_M is small. The parameters of the transistors are : μ_n C_ox = 100 μA/V² , V_TN = 1 V , L = 2 μm , V_T = 25 mV , β_F = 100 , V_BE = 0.7 V and quiescent output voltage is 5 V . Size the MOSFET and calculate the small signal voltage gain A_v = V_ow / V_s
[Image: please refer to given pdf link for image and diagram]
(b) (i) Prove that the true power = cosφ / (cosφ·cos(φ - β)) × actual watt meter reading for electrodynamometer type of watt meters, where, cos φ = power factor of the circuit, β = tan⁻¹ ωL / R where, L and R are the inductance and resistance of the pressure coil of the circuit. 10
(ii) Explain why errors are large when the power factor is low. 10
10
[Image: please refer to given pdf link for image and diagram]
(ii) For the ladder network determine the g parameters in the s domain. 10
[Image: please refer to given pdf link for image and diagram]
Q7. (a) The parameters of the amplifier shown in the figure below are R_C₁ = 4 kΩ , R_E = 2 kΩ , R_C₂ = 5 kΩ , R_F = 4 kΩ and R_S = 200 Ω . The DC bias currents of the transistor are I_C₁ = 0.5 mA , I_C₂ = 1 mA . The transistor parameters are h_fe = h_fe1 = h_fe2 = 150 . Use the techniques of feedback analysis to calculate the input resistance R_IF , the output resistance R_OF and the closed loop transresistance gain A_F . Assume V_T = 25 mV . 20
[Image: please refer to given pdf link for image and diagram]
10
(ii) The output of an LVDT is connected to a 5 V voltmeter through an amplifier whose amplification factor is 200. An output of 2 mV appears across the terminals of LVDT when the core moves through a distance of 0.5 mm . Calculate the sensitivity of the LVDT and that of the whole set- up. The milli voltmeter scale has 100 divisions. The scale can be read to 1/5 of a division. Calculate the resolution of the instrument in mm. 10
(c) (i) In the series RL circuit, the switch is in position 1 long enough to establish the steady state and is switched to position 2 at t = 0 . Find the current i. 10
[Image: please refer to given pdf link for image and diagram]
(ii) Obtain the overall ABCD parameters of the circuit. 10
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8. (a) (i) Determine the functional behaviour of the circuit. Assume that input w is driven by a square wave signal. 10
[Image: please refer to given pdf link for image and diagram]
Clear
(ii) In the circuit shown in the figure below, the gate voltage V_G is very small. Assume op amp is an ideal op amp, V_TN = 1 V and μ_n C_ox w / L = 200 μA/V² . Calculate output voltage. 10
[Image: please refer to given pdf link for image and diagram]
(b) (i) Describe the construction and working of a shunt type ohmmeter. Write down its design equations. 10
10
(ii) The ohmmeter shown in the figure uses a 100 Ω basic movement requiring a full- scale current of 1 mA . The internal battery voltage is 3 V . The desired scale marking for half- scale deflection is 2000 Ω . Calculate the value of R₁ and R₂ , and the maximum value of R₂ to compensate for a 10% drop in the battery voltage.
[Image: please refer to given pdf link for image and diagram]
(c) A series resonant network consists of a 50 Ω resistor, a 4 mH inductor and a 0·1 μF capacitor. Calculate values for (a) ω₀ , (b) f₀ , (c) Q₀ , (d) BW, (e) ω₁ , (f) ω₂ , (g) Z_in at 45 k rad/sec, and (h), the ratio of magnitude of the capacitor impedance to resistor impedance at 45 k rad/sec.
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UPSC Engineering Services (Main) Examination, 2024-ELECTRONICS-TELECOMMUNICATION-ENGINEERING -I
UPSC Engineering Services (Main) Examination, 2024-ELECTRONICS-TELECOMMUNICATION-ENGINEERING-II
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