ouestion for WBUT upcoming exam 4th sem ECE

Analog Electronics & Circuits
EC-401
Time:3 Hours TotalMarks-70

Group-A

Answer any ten questions 10 x 1= 10

1.i) In a full wave rectifier if the input frequency is 50 Hz then frequency at the output of the filter is
(a) 50 Hz (b)75 Hz (c) 75 Hz (d) 0 Hz

ii) To obtain high input and output impedance the type of the feedback amplifier is (a)Voltage series (b) Current series (c) Voltage shunt (d) Current shunt

iii) An OP-AMP has gain bandwidth product of 1 MHz and a voltage gain of 20 dB .Then the -3dB bandwidth of the OP-AMP will be
(a) 50 kHz (b) 100 kHz (c) 1000/17 (d) 1000/7.07

iv) Wide range of high purity sine wave can be generated by
(a) RC-phase shift oscillator (b) Crystal oscillator (c) Wein bridge oscillator d) Hartley oscillator

v) The slew rate of an OP-AMP is 0.5V/μs.The maximum frequency of a sinusoidal input of 2Vrms that can be handled without excessive distortion is
(a) 3 kHz (b) 30 kHz (c) 200 kHz (d) 2 MHz

vi) In order to generate a square waveform from a sinusoidal input signal the choice of the circuit is
(a) Schmitt trigger (b) Clipper and amplifier (c) Monostable Multivibrator (d) Both a and c

vii) An increase in the ambient temperature means that maximum power rating of the transistor
(a) will increase (b) will decrease (c) may increase or decrease (d) may increase or remain the same.

viii) The threshold voltage of an n channel enhancement mode MOSFET is 0.5 ,when the device is biased at a gate voltage of 3V,pinch of will be occur at a drain voltage of
(a) 1.5 V (b) 2.5 V (c) 3.5 V (d) 4.5 V

ix) Stability factor (S) for a fixed bias circuit is given by
(a) 1+β (b) 1-β (c) 1/β (d) β-1

x) For maximum unclipped output from a CE amplifier , the Q point should be
(a) at the centre of the DC load line.(b) at the centre of the AC load line (c) at the centre of the collector current (d)none of these.

xi) A CB amplifier has re =6 ohm, RL =600 ohm and α= 0.98.Voltage gain is
(a) 100 (b) 588 (c) 98 (d) 6

xii) For high frequency response of a transistor amplifier suitable model to use is
(a) Lattice network (b) Hybrid-π (c) T-network (d) Kelvin network


xiii) The period of oscillation of a symmetrical multivibrator depends upon the discharging time constant and is roughly given by
(a) T=1.4RC (b) T=RC/14 (c) T=1.4 √(RC) (d) T= √(1.4) RC

Group-B

Answer any three questions 3 x 5= 15

2. a) Define the term thermal resistance for a power transistor.
b) A Ge transistor has thermal resistance of its junction as 0.33oC/mW and the ambient temperature is 28 oC.Calculate : (i) maximum power dissipation that can be allowed without heat sink, and (ii) ) maximum power dissipation that can be allowed if a heat sink is used,which reduces the thermal resistance of the transistor to 0.09 oC/mW.
2+3=5
3.Draw the Ebers-Moll model of an npn transistor and find out the expression of the transistor terminal currents.
2+3=5
4.An amplifier has a gain A= 60 dB and output impedance of 12 K. It is required to reduce the output impedance to 500 ohm. Calculate the negative feedback required.
5
5.Find out the expression of the stability factor for a voltage divider biased amplifier.
5
6.a)What will be the shape of the output for the following circuit














b) Find out the expression of ripple factor for a half wave rectifier.
2+3=5


Group-C


Answer any three questions 3 x 15= 45

7.a) What are the differences between voltage and power amplifiers ? Why heat sink is used ?
b) Find out the expression of collector efficiency of a class-A amplifier.
c) An crystal has equivalent series inductance L= 3 H and series capacitance C=0.05 Pf and mounting capacitance Cm=10 pF. Calculate the series and parallel resonant frequencies for the crystal.
(4+2)+4+5=15
8.a)Draw a circuit of differential amplifier with an active load connection.
b)What are the advantages of differential amplifier ?
c)Find out the transconductance of the above amplifier.
d) Explain with diagram the operating principle of 555 timer. 3+2+4+6=15
9. a) Draw the circuit of an instrumentation amplifier and find out the expression of Vo.
b) What will be the transfer function of the following circuit. What type of filter it is ?

c) What are the applications of tuned amplifiers ?(2+4)(6+1)+2=15
10.a)Draw the I-V characteristics of a CE configuration transistor
b) What do you mean by early-effect.
c) Show that a transistor can be used as an inverter.
d) Analyze the transistor amplifier (shown below in the figure)using small signal equivalent circuit. Given β = 100.
2+1+4+8=15
11. Write short notes on any of the three from the following given below:
3x5=15
a) Photodiode
b) Wein bridge oscillator.
c) Bistable multivibrator.
d) Enhancement type MOSFET.
e) Schmitt trigger.
i am not able to post the corresponding figure of some question.
this is a question set for upcoming exam of WBUT .