Andhra University BE/B.Tech Electronics Previous Paper 2008
First question is compulsory.
All questions carry equal marks.
Answer all parts of any question at one place.
1. (a) List any two applications of tunnel diode.
(b) Sketch the V-I characteristics of a UJT and mark the important parameters on it.
(c) Why does the operating point of an CE amplifier shift due to temperature?
(d) What is the role of doping of impurities in pure silicon or germanium?
(e) Define Barhausen criteria for oscillations.
(f) Define 3-dB Bandwidth of an amplifier.
(g) Prove that for any transistor amplifier configuration the I/P resistance R1=hi/1-hrAο
2. (a) Explain the diffusion and drift current for a semiconductors.
(b) Briefly explain the behavior of junction in forward and reverse bias mode for PN-diode. Derive the necessary expression.
3. (a) The capacitance of certain varactor diode can be varied from 5 pf to 50 pf. The diode used in a tunnel ckt of a radio receiver is shown below.
Determine the tuning range for circuit, if the inductance is 10 mH.
(b) What is a Zenor diode ? Draw the equivalent ckt of an ideal zenor in the breakdown region. Explain how it can be used as a voltage regulator.
4. (a) What is UJT? How does it differ from a JFET?
(b) Give a schematic diagram of SCR and derive it equivalent representation it terms of transistors. Explain any one application of SCR.
5. (a) A certain transistor has α = 0.98 and a collector leakage current ICο of 1 µA. Calculate the collector and the base currents when Ib = 1µA.
(b) List the advantages and disadvantages of FET over BJT.
6. (a) Draw the circuit diagram of a FWR with
(i) Centre-tap connection and
(ii) Bridge connection. Explain their working.
(b) A 50 Hz transformer having 50 V r.m.s. on each side of the center tap supplies a full wave rectifier circuit. The circuit load is 150 Ω with a shunt capacitor filter of 1000 µF. Find the ripple factor.
7. (a) For the collector feedback bias ckt shown in figure below, find Ic(snt), VCE and stability factor (g).
Take β = 100 and neglect VBE.
(b) Explain why CE amplifier require a form of d.c. stabilization , where as CB amplifiers are usually unstabilized.
8. (a) With the help of a suitable ckt diagram explain the working of a RC coupled amplifier . Derive the expression for voltage gain of the amplifier.
(b) A transistor is connected in common collector configuration and its h-parameter are:
hie=1100 Ω ; hre=2.5 X 10-4 Ω
hfe=50; hoe=24 µA/V.
The circuit uses RL=10kΩ and Rg=1 kΩ.
Calculate gain Ai, i/p resistance Rg and the voltage gain Av of this amplifier.http://www.stepinau.com/2013/09/26/andhra-university-beb-tech-electronics-previous-paper-2008/IT 2.1 Previous PapersCSE,CSE Previous Papers,Electronics Previous Papers,IT,IT Previous Papers