Code: D-08                                                                           Subject: ANALOG ELECTRONICS

Time: 3 Hours                                                                                                     Max. Marks: 100

NOTE: There are 11 Questions in all.

· Question 1 is compulsory and carries 16 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

· Answer any THREE Questions each from Part I and Part II. Each of these questions carries 14 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1       Choose the correct or best alternative in the following:                                           (2x8)

a. For faithful amplification by using a NPN germanium transistor, the base-emitter junction voltage  should not fall below

(A)  0.3 V.                                          (B)  0.5 V.

(C)   0.7 V.                                         (D)  0.1 V.

             b.   The bandwidth of an RC-coupled amplifier is limited by

(A) Coupling capacitors at the low-frequency end and bypass capacitors at the high-frequency end.          

(B) Coupling capacitors at the high-frequency end and bypass capacitors at the low-frequency end.

(C) Bypass and coupling capacitors at the low-frequency end and shunt capacitors at the high-frequency end.                                            

(D) Shunt capacitors at the low-frequency end bypass as well as coupling capacitors at the high-frequency end.

             c.   The upper 3-dB frequency in a common emitter amplifier is given in terms of the Hybrid- parameters as

(A) .                                         (B) .

(C) .                                          (D) .

             d.   The dissipation at the collector is zero in the quiescent state and increases with excitation in the case of a

(A)  Class A series-fed amplifier.        

(B) Class A transistor coupled amplifier.

(C)  Class AB amplifier.                      

(D)  Class B amplifier.

             e.   The circuit shown in Fig.1 represents a

(A) Low-pass filter.                            (B)  High-pass filter.

(C)  Band-pass filter.                           (D)  Band-stop filter.

             f.    The application where one would most likely to find a quartz oscillator would be

(A) Radio Transmitter.                        (B)  Radio Receiver.

(C)  Digital clock.                                (D)  Audio signal generator.

             g.   For an input of [assuming ideal diode], the circuit shown in the Fig.2 will behave as a

(A) Clipper, sine wave top clipped at –2 V.         

(B) Clamper, sine wave top clamped at –2 V.

(C) Clamper, sine wave top clipped at zero volt.  

(D) Clipper, sine wave top clipped at 2 V.

             h.   The given Fig.3 shows the application of 555 timer circuit as an astable multivibrator.  The charging and discharging time constants are respectively

(A) .                           

(B) .

(C)  .               

(D)  .

PART I

Answer any THREE Questions. Each question carries 14 marks.

Q.2     a.   Taking the example of a CE amplifier, explain the criterion for selection of a suitable operating point and factors affecting its stability.  Hence define stability factor.                                                   (10)

             b.   Determine the Q-Point for a fixed bias circuit with  and .  Assume  to be very small as compared to .                                                        (4)

  Q.3     a.   Why are the h-parameters preferred to analyse a circuit using bipolar transistor?  Draw h-parameters equivalent circuit of a CE transistor amplifier.  Find out its voltage gain and current gain taking into account the source resistance.                                                                                         (9)

b.   A CE transistor amplifier with h-parameters given by .  If load resistance  and source resistance , calculate:

                   (i)   (Current gain)                          (ii)  (Input resistance)                          

                   (iii) (Voltage gain)                         (iv) 

                   (v)  .                                                                                                           (5)

Q.4     a.   Describe the effect of negative feedback on :

(i)  Voltage gain.                                  (ii)   Stability.

                   (iii) Distortion & Noise.                        (iv)  Bandwidth of the amplifier.               (8)

             b.   Draw the circuit diagram of a Double-tuned amplifier.  Explain how the frequency response of this amplifier is better than that of a single-tuned amplifier.                                                                          (6)

Q.5     a.   Draw the circuit diagram of a single ended class-A Power amplifier and explain its operation.  Show that the Maximum theoretical efficiency for a single-ended class-A Power amplifier is 50%. (11)

b.   A transformer coupled class-A large signal amplifier has maximum and minimum values of collector-emitter voltages, respectively, are 25V and 2.5V.  Determine its collector efficiency.       (3)

  Q.6     a.   Draw the self-bias circuit for a N-channel JFET and explain, how stabilization of operating point is achieved by this biasing method.                         (6)

             b.   What is a power amplifier?  In what respects does it differ from a voltage amplifier?  Why heat sinks are needed in power amplifiers?                 (8)

PART II

Answer any THREE Questions. Each question carries 14 marks.

Q.7     a.   What is an Op-amp and draw the block diagram representation of a typical Op-amp.                     (3)

b.   List the characteristic parameters of an Ideal Op-amp.                                        (6)

c.   Draw the circuit of Zero-Crossing Detector using OP-AMP and explain its operation with suitable waveforms.                                                                                                        (5)

Q.8     a.   What is meant by Piezoelectric effect?  Draw the equivalent circuit of a crystal. Why is Quartz Crystal commonly used in crystal oscillators?    (6)

             b.   Explain the operation of Series Resonant Crystal Oscillator, with the help of a neat circuit diagram.  Mention its advantages and disadvantages.         (8)

Q.9     a.   Draw the circuit of shunt biased positive clipper and explain its working, when the input waveform is a 20V (P-P) sinusoidal signal and a biasing voltage of 7 V.  Draw its output waveform.  Assume the diode to be ideal.                                                   (6)

             b.   Draw the circuit of a Pulse generator using an OP-AMP.  Explain its operation with the help of input and output waveforms.                               (8)

Q.10           a.                                                        Explain how an op-amp can be used as a Time Marker Generator with the help of circuit diagram.  Draw the waveform for this circuit and mention its applications.                                                                (6)

             b.   With the help of a neat sketch, explain the working of Armstrong Oscillator.  Also explain, why this Oscillator Circuit makes use of either FETs (or ) Vacuum tubes.                                         (8)

Q.11                                                                      Write short notes on any TWO of the following :

(i) Transistor as a switch.

(ii) Source Follower.

(iii) Logarithmic Multiplier.                                                                       (7 x 2)