AMIETE – ET (OLD SCHEME)

 

Flowchart: Alternate Process: DECEMBER 2009Code: AE05                                                                               Subject: BASIC ELECTRONICS

Time: 3 Hours                                                                                                     Max. Marks: 100

 

NOTE: There are 9 Questions in all.

·      Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

·      Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

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

 

 

Q.1       Choose the correct or the best alternative in the following:                                   (2x10)

       

a.       With increasing temperature, the resistivity of an intrinsic semiconductor decreases. This is because, with the increase of temperature  

 

                   (A)   both the carrier concentration and mobility of carriers decreases.                              

                   (B)  the carrier concentration increases but the mobility of carriers decreases.

(C)    the carrier concentration decreases but the mobility of carriers increases.

(D)   the carrier concentration remains the same but the mobility of carriers   decreases.

       

b.      RC coupling is popular in low-level audio amplifiers because it 

 

(A)    has better low frequency response.                                                                           

(B)    is inexpensive and needs no adjustments.

(C)  provides an output signal in phase with the input signal.                                              

(D) needs low voltage battery for collector supply.

                                                               

             c.   The voltage gain of a given common-source JFET amplifier depends on its

 

(A)  Input impedance.                          (B)  Amplification factor.

(C)  Dynamic drain resistance.             (D)  Drain load resistance.

 

             d.   The main function of a transformer employed at the output of a Power Amplifier is

 

(A)    to increase the voltage gain.        

(B)    to step up the voltage and power.

(C)  to match the load impedance with the dynamic output impedance of transistor for maximum power transfer.                                            

(D)  to safeguard the transistor against overheating.          

 

             e.   The input impedance of an amplifier can be increased from 2K to 50 K by introducing

                  

(A)     Current-Shunt negative feedback.

(B)     Voltage-Shunt negative feedback.

(C)  Current-Series negative feedback.     

(D)  Positive feedback.

 

             f.    An Oscillator which employs both Positive and Negative feedback is

 

(A)    Hartley oscillator.                         (B)  Colpitts oscillator.

(C)  R-C Phase-Shift oscillator.           (D)  Wein-Bridge oscillator
 
 


             g.   The OP-AMP circuit shown in Fig.1 is

 

                                                                                                  

(A)     Comparator.                               

(B)     Integrator.

(C)  Differentiator.                              

(D)  Summer.

                                                          

 

             h.   A Schmitt Trigger is basically

 

(A)    an Astable Multivibrator.              (B)  a Monostable Multivibrator.

(C)  a Bistable Multivibrator.                (D)  an Oscillator..

 

             i.    The output of Logic Gate is 1 when all its inputs are at Logic 0. The Gate is either

 

(A)   a NAND or an EX-OR.               (B)  an OR or an EX-NOR.

(C) an AND or an EX-OR.                 (D) a NOR or an EX-NOR.

 

             j.    A  Ring counter consisting of five Flip-Flops will have

 

(A)     5 states.                                       (B)  10 states.

(C)  32 states.                                     (D)  Infinite states.

 

 

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

 

 

  Q.2     a.   With neat diagrams, explain clearly why a Common-Base connected  Transistor can exhibit Transistor action with the Collector-Base Junction voltage reduced to zero.                                                  (8)

 

b.   A Square wave shown in Fig.2 is applied to the circuit in Fig.3. Name the circuit and explain its working. Sketch the output waveform.               (8)
 
 

 

 

 

 

 

 

 

 

 

 

 

 


  Q.3     a.   Why are the h-parameters preferred to analyse a circuit using Bipolar Transistor? Draw the h-Parameter equivalent circuit of a CB transistor amplifier and derive an expression of (i) its Voltage Gain and (ii) Current Gain.                                                                                                                (10)

 

             b.   A 3-stage Cascaded Amplifier has voltage gains of 40, 60 and 80 respectively.      

                   (i)   Calculate the overall voltage gain in dB.

                    (ii)  If the power gains of the three stages are 100, 400 and 800 respectively,    

                          what will be the overall power gains in dB.                                                   (6)          

 

  Q.4     a.   Give the schematic diagram of construction of an N-channel depletion type MOSFET and explain its operation.                                                                                                          (9)          

            

             b.   A pair of transistors operate in a Class-B Push-Pull circuit with a power supply of voltage VCC = 12 V.  If the turns ratio of the output transformer is 2 and the load resistance RL is 6, Calculate the Maximum Output Power and the Maximum DC power supplied. Hence find the efficiency of the circuit. Neglect transformer winding resistances.           (7)

 

  Q.5     a.   Explain how the Non-linear distortion can be reduced by a factor  by adding negative feedback to an amplifier, while at the same time keeping the output signal voltage unchanged.   (6)

 

             b.   In a Current-Shunt feedback amplifier, show that

                   (i)  the input impedance decreases with negative feedback.

                   (ii) the output impedance increases due to negative feedback.                            (10)

 

  Q.6     a.   A Colpitt’s Oscillator has C1 = 0.01 pF, C2 = 0.05 pF and the value of L in the tank circuit is 0.01 mH. Calculate the Frequency of oscillations.                                                               (4)          

 

             b.   What is a Sample and Hold circuit? Draw the circuit of OP-AMP Sample and Hold circuit and explain its operation by drawing its input and output waveforms.                                                         (8)

 

             c.   Define Slew rate and what causes the Slew Rate?                                               (4)

 

  Q.7     a.   Draw the circuit of a Half-wave rectifier using capacitor filter and explain its working by drawing input and output waveforms.                               (8)   

 

             b.   A  Zener diode with Zener voltage of 30 V is used in a regulator circuit with a series resistance of 200 connected across the zener diode. Over what range of input voltage will the circuit operate? Maximum and Minimum zener currents are 25 mA and 0 mA respectively.                                (8)

 

  Q.8     a.   Design an Astable Multivibrator using Silicon Transistors to produce a symmetrical square wave of frequency f = 100 Hz. Assume VCC = 6 V, = 100, IC = 2 mA and VCE(sat) = 0.2 V       (8)

 

 

             b.   Explain how the IC 555 can be used as a Monostable multivibrator with the help of circuit diagram, input and output waveforms.                               (8)                                                            

 

  Q.9     a.   Prove the following equations using the Boolean Algebraic Theorems:

                   (i)   A + .B + A.  = A + B

                   (ii) B + AC + AB+ ABC = AB + BC + CA                                      (7)

                  

      b.   Minimise the logic function F(A,B,C,D) = m(1,3,5,8,9,11,15) + d(2,13)

            Use Karnaugh map.  Draw the logic circuit for the simplified function using NAND and NOR gates.                                                                      (9)