JNTU
JNTU B.Tech II ANALOG ELECTRONICS Previous Question Paper (February - 2024 - R16)
Note: i) Question paper consists of Part A, Part B. ii) Part A is compulsory, which carries 25 marks. In Part A, answer all questions. iii) In Part B, Answer any one question from each unit. Each question carries 10 marks and may have a, b as sub questions.
Part A
Write about the causes of distortion in amplifiers.
Answer
Distortion in amplifiers is primarily caused by non-linear characteristics of active devices (transistors), which introduce harmonics, and frequency-dependent components (coupling capacitors, bypass capacitors, and parasitic capacitances) that cause frequency distortion. Additionally, phase shift across the frequency range leads to phase distortion.
What is the principle of Darlington transistor? When it is preferred?
Answer
The Darlington transistor principle involves connecting two bipolar junction transistors in a cascade configuration such that the emitter of the first transistor drives the base of the second, resulting in an overall current gain equal to the product of the individual gains (β1 × β2). It is preferred in applications requiring extremely high input impedance and high current gain, such as in power amplification stages or sensitive sensor interfaces.
Why the h parameter model is not suitable to analyze transistor at high frequencies?
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Define fβ and fT.
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State the advantages and disadvantages of the source follower.
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Define JFET parameters and mention its relation.
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What are the factors that affect the frequency stability of an oscillator?
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An amplifier has a midband gain of 125 and a bandwidth of 250KHz. If 4% negative feedback is introduced, find the new bandwidth and gain.
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What is Harmonic distortion?
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What are the different kinds of power amplifiers?
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Part B
A CB transistor amplifier uses voltage source of internal resistance RS= 200 Ω and the load resistance is RL= 1200 Ω. The h-parameters are hib = 24 Ω, hrb = 4 × 10⁻⁴, hfb = – 0.98 and hob = 0.6 µA/V. Calculate the Ri , Ai , Av and output admittance.
Answer
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Draw the circuit of two stage R-C coupled CE transistor amplifier and explain the working of it.
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Describe the need for coupling and bypass capacitors in transistor circuits. Also, draw AC equivalent circuit of CE amplifier.
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Draw the circuit for CASCODE amplifier and then explain its working. Also, obtain overall values of the circuit in terms of h-parameters.
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Derive the expression for the CE short circuit current gain Ai as a function of frequency using Hybrid - π model.
Answer
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A single stage CE amplifier is measured to have a voltage gain bandwidth of 5 MHz with RL=500 Ω. Assume hfe=100, gm=100 mA/V, rbb'=100Ω, CC=1pF and fT=400 MHz. (i) find the value of source resistance that will give the required bandwidth. (ii) with the value of Rs found in (i), find the mid band voltage gain V0/Vs.
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In hybrid ‘pi’ model of a transistor at high frequencies, show that the gm is proportional to the collector currents.
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The data sheet of N channel JFET gives the following details. IDSS=10mA and pinch off voltage of -4.8V. Determine (i) VGS corresponding to drain current of 3.5 mA. (ii) Determine transconductance gm at this drain current.
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Draw and explain the CS stage with diode connected load.
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With the help of a diagram explain the operation of an n-channel enhancement MOSFET.
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Discuss the input and output characteristics of a folded cascode amplifier with NMOS input.
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Derive the expressions for input and output resistances of a current series feedback amplifier.
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In a transistorized Hartley oscillator, the two inductances are 2mH and 20μH while the frequency is to be changed from 950KHz to 2050KHz. Calculate the range over which the capacitor is to be varied.
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Derive the expression for frequency of oscillations and condition for sustaining oscillations of Wein bridge oscillators with BJT.
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Derive the expression for conversion efficiency of Class B push pull power amplifier.
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Draw the circuit of single tuned capacitance coupled amplifier and explain its operation.
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Draw the circuit of Direct coupled class-A power amplifier and explain its operation.
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Define a Q-factor of a resonant circuit. What is the need for tuned amplifiers?
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