Tests

R.M.D. ENGINEERING COLLEGE

RSM NAGAR, KAVARAIPETTAI – 601 206

4^th Semester – B.E. / B.Tech.

First Internal Assessment Test – January / February 2014

Sub. Title:Electronic Circuits II                                             Date :  30.01.2014   

Sub. Code : EC2251                                                                 Branch :  ECE

Duration    : 100 minutes                                                       Max. Marks :  50

Answer all questions

Part A - (5 x 2 = 10)

1.   What is return ratio of a feedback amplifier?

2.   Compare the input and output resistance for a voltage and current shunt feedback amplifiers.

3.    Addition of negative feedback to an amplifier reduces its voltage gain from 300 to 60. Determine the feedback factor.

4.   List the characteristics of negative feedback amplifiers.

5.   Mention two essential conditions for a circuit to maintain oscillations.

Part B - (2 x 16 + 1 x 8 = 40)

 6.    (a)   (i)  Discuss the effects of negative feedback on gain, bandwidth, distortion and noise. (10)

            (ii) With a negative feedback, an amplifier gives an output of 12.5V with an input of1.5V. When the feedback is removed, it requires 0.25V input for the same output. Calculate (a) gain without feedback (b) feedback fraction b.                    (6)

Or

b) (i) Draw the circuits of voltage shunt and current series feedback amplifiers and derive the expressions for input impedance R_if and output impedance R_of.(12)

(ii) An amplifier has a mid band gain of 125 and a bandwidth 250 KHz. If 4%  negative feedback  is introduced, find the new bandwidth and gain. (4)

7.     (a) (i) With neat circuit diagram explain Colpitt’s oscillator and derive their frequency of oscillation and condition for oscillation.  (10)

(ii) A current series feedback amplifier is shown in the figure below                                    (6)      It has the following parameters:

R₁ = 20 KΩ, R₂ = 20 KΩ, h_ie = 2 KΩ, R_L = 1 KΩ, R_e = 100 Ω, h_fe = 80

Calculate G_m, β,G_mf, R_if and A_Vf .

 Or 

(b) (i) Transistors in the feedback amplifier shown in the figure are identical  and the parameters are h_ie = 1.1 K, h_fe = 50, h_re = h_oe =  Identify the feedback amplifier and calculate A_vf, R_of and R_if. (10)

 

(ii)   In a Colpitt’s oscillator, the value of the inductor and capacitors in the tank circuit are L = 40 mH, C₁ = 100 pF and C₂ = 500 pF. (6)

(1)  Find the frequency of oscillation. 

(2)  If the output voltage is 10 V, find the feedback voltage at the input side of the amplifier. 

(3)  Find the minimum gain, if the frequency is changed by changing ‘L’ alone. 

(4)  Find the value of C1 for a gain of 10 if C2 is kept constant as 500 pF. Also find the resulting new frequency.

8. (a) Explain Nyquist stability criterion to analyze the stability of feedback amplifiers. (8) Or


(b) With neat circuit diagram explain the working principle of Armstrong oscillator. (8)

4^th Semester – B.E. / B.Tech

 Retest for First Internal Assesment test – January 2014

Sub. Title         : ELECTRONIC CIRCUITS II                              Date         : 30.01.2014

Sub. Code       : EC 2251                                                                 Branch     : ECE

Time                : 100 Minutes                                                           Max. Marks: 50

           

Answer all questions

Part – A (5x 2 = 10)

1.       State the essential condition for maintaining oscillation.

2.       What is the impact of negative feedback on noise in circuit?

3.       What is ‘return ratio’ of a feedback amplifier?

4.       If L1=1mH,L2=2mH and C=0.1µf,What is the frequency of oscillation of Hartley oscillator.

5.       Addition of negative feedback to an amplifier reduces the voltage gain from 300 to 60. Determine the feedback factor.

PART – B     (3 * 12 = 36marks)

6.       (a) )(i)Draw the circuit of voltage  shunt and current series feedback amplifier. Derive the                  

                       expression for Rif & Rof.         (12)

        (ii)Discuss Nyquist criterion for stability of feedback amplifier with the help of Nyquist plot  (4)

(OR)

  (b) (i)With example prove that negative feedback increases stability                                                 (5)

        (ii)Derive expression for Avf with positive feedback and negative feedback and state the  

               condition for stability in negative feedback amplifiers.                                                                 (6)

        (iii)An RC coupled amplifier has a voltage gain of 1000, f1=50hz, f2=200Khz and a distortion of

               5%  with feedback. Find Av1,BW when β=0.01 is applied.                                                                 (5)

7.       (a)Draw the circuit diagram and explain the working of Hartley oscillator. Also derive the  

        expression for frequency of oscillation & condition for oscillation.                                               (16)    

(OR)

   (b)(i)How is a clap oscillator modified from a colpitts oscillator?                               (4)

         (ii)Derive the general condition for oscillation for a LC oscillator and derive the frequency of  

             Oscillation for a colpitt’s oscillator.                                                                               (12)

      8. (a) Derive the Expression for BW for negative feedback amplifier.      (8)                                                                               (OR)

              (b) Explain the working principles of an Armstrong oscillator.                         (8)

R.M.D. Engineering College

Rsm nagar, kavaraipettai – 601 206

4^th Semester – B.E. / B.Tech

Second internal test –February 2014

Sub. Title         : Electronic circuits – II                                          Date         : 27.02.2014

Sub. Code       : EC 2251                                                                 Branch     : ECE

Time                : 100 Minutes                                                           Max. Marks: 50

           

Answer all questions

Part – A (5x 2 = 10)

1.      List the applications of class c tuned amplifier.

2.      A quartz crystal has L=3H, C_S=0.05pF,R=2000Ω and C_M=10pF.  Calculate

the  parallel resonant frequency  f_p of the crystal.

3.      Mention the features of crystal oscillator.

4.      Define unloaded and loaded Q of tuned circuits.

5.      Compare a single tuned amplifier and a double tuned amplifier

PART – B {(2 X 16 = 32) + (1 X 8 = 8) = 40}

6.   a. i.  Draw the circuit diagram of Wein bridge Oscillator and derive the expression

for gain and frequency of oscillation.             (10)                                                                                                                  

                      ii.  Explain the circuit of a Twin-T Oscillator.                  (06)                             

                                                      (OR)

b. With the neat circuit diagram, explain how Barkhausen conditions are

  satisfied in RC Phase shift Oscillator and obtain the frequency of              oscillation.                                                                                                                                        (16)

7.      a.     Derive the gain and bandwidth of a capacitance coupled single tuned      

        amplifier.                                                                                                    (16)

                                                      (OR)

       b. i. Discuss the techniques implemented to overcome the instability of a single  

       tuned amplifier?                                          (08)

     ii. Explain the working of Stagger tuned amplifier.                    (08)

8.a.Explain the working principle of Miller Crystal Oscillator.          (08)

                                                       (OR)

b.   i    Derive the bandwidth for three stage single tuned amplifier.                       (04)

                        ii   State the advantages of Class C tuned amplifier          (12)

R.M.D ENGINNERING COLLEGE

KAVARAIPETTAI

DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING

Class Test - 1

                   SUB:EC II                                                                         DATE:20.01.14

PART A(5*2=10)

1.      What is the impact of negative feedback on noise in circuits?

2.      Define sensitivity and de-sensitivity of gain in feedback amplifiers.

3.      What is feedback ratio of a feedback amplifier?

4.      State the effect of output resistance on a input resistance of amplifier when shunt feedback amplifier is employed.

5.      Calculate the closed loop gain of a negative feed back amplifier if its open loop gain is 100000 and feed back factor is 0.01

PART B(1*10=10)

6.      Derive the input & output resistance of current series feedback (or) voltage feedback.

Previous Years'  Test Question Papers

4^th Semester – B.E. / B.Tech

First internal Retest – February 2013

Sub. Title       : ELECTRONIC CIRCUITS II               Date         : 8.02.2013

Sub. Code      : EC 2251                                               Branch     : ECE

Time               : 100 Minutes                                          Max. Marks: 50

Answer all questions

Part – A (5x 2 = 10)

1.   State the essential condition for maintaining oscillation.

2.   What is the impact of negative feedback on noise in circuit?

3.   What is ‘return ratio’ of a feedback amplifier?

4.   If L1=1mH, L2=2mH and C=0.1µf,What is the frequency of oscillation of Hartley oscillator.

5.   Addition of negative feedback to an amplifier reduces the voltage gain from 300 to 60.              Determine the feedback factor.

PART – B     (3 * 12 = 36marks)

6.   (a)  (i) Draw the circuit of voltage  shunt and current series feedback amplifier. Derive the expression for Rif & Rof.                                                              (10)

   (ii) Discuss Nyquist criterion for stability of feedback amplifier with the help of Nyquist plot                                                                                    (6)

(OR)

(b) (i)  With example prove that negative feedback increases stability       (5)

     (ii) Derive expression for A_vf with positive feedback and negative feedback and state the  condition for stability in negative feedback amplifiers.     (6)

    (iii) An RC coupled amplifier has a voltage gain of 1000, f1=50hz, f2=200Khz and a distortion of   5%  with feedback. Find Av1, BW when β=0.01 is applied. (5)

7.   (a)   Draw the circuit diagram and explain the working of Hartley oscillator. Also derive the expression for frequency of oscillation & condition for oscillation.  (16) 

                                                                  (OR)

    (b) (i) How is a clap oscillator modified from a colpitts oscillator?    (6)

   ii) Derive the general condition for oscillation for a LC oscillator and derive the frequency of   Oscillation for a colpitt’s oscillator.       (10)

8. (a)  In a Colpitt oscillator, the value of the inductor & capacitor in the tank circuit are L=40mH,C1=100pf& C2=500pf.  

      (i)    Find the frequency of oscillation

     (ii)   Find the minimum gain if the frequency is changed by charging the L alone                    

     (iii) Find the value of C1 for a gain of 10 if C2 is kept constant as 500 pf. Also find   the resulting  new frequency  (8)                                                                             

                                                                (OR)
(b) Derive the expression for BW and input impedance of a voltage series feedback amplifier.                (8)