VTU Previous Question Papers BE EC 3rd Semester Electronic Circuits January 2008

VTU Previous Question Papers BE EC 3rd Semester

Electronic Circuits January 2008

 

Note ; Answer any FIVE full questions.

1 a.  Discuss voltage doubler circuit.

b.  Define regulation and derive equation for a fullwave circuit.

c.  In the Fig. 1(c) the diodes are ideal. Write the transfer characteristic equations (V0 Vs Vi). Plot V0 Vs Vi. Indicate all intercepts, slopes and voltage levels.

1

 

Fig. 1(c)

Repeat for the case when Vr ~ 1 V Vj = 40 sin ot

 

2. a. Define three stability factors. For a self bias circuit derive the expression for Sv and S.

b.  For the circuit shown in Fig.2(b) Vcc = 24 V, Rc = 10 kO, Re = 270 Q, (3 = 45, Silicon transistor is used \mder operationing condition Vce – 5V find

i) R                                 ii) Stabiiityfector S

2

              Fig.2(b)       

c. Briefly discuss how do you provide operating point stability using compensation

technique.

 

3 a. Using small signal low frequency hybrid model for the CE amplifier with a  load of ZL and source resistance Rs derive expression for Ai, Ay, Z; and Z0 (10 Marks)

b.  For a transistor amplifier in CB configuration find Al3 Ay, Z,Ib Zout, Avs and AK given that hib = 22 Q, hfb = 2.9 x 10-4, h* = -0.98, l/h0b = 2.04 mQ.

c.  State and Prove Miller’s theorem.

 

4 a, Draw small signal high frequency CE model for transistor and explain the significance of even component in the model and prove that hfc = gm rb’e.

b.  Discuss the various types of distortion in amplifier.

c.  With suitable RC circuit calculate low frequency response of an amplifier.

 

5 a. Explain the advantages of negative feedback circuit.

b.  Draw and explain different feedback amplifier topologies.

c.  An amplifier with open loop voltage gain Av = 1000 ± 100 is available. It is necessary to have an amplifier whose voltage gain varies by no more than ± 0.1%.

i) Find the reverse transmission factor {3 of the feedback network

ii)  Find gain with feedback.

 

6 a. Show that the maximum conversion efficiency of class-B push pull amplifier is 78.5%.

b. Discuss why even harmonics are not present in push-pull amplifier.

c.  Explain:

i) Input bias current compensation in OP AMP.

ii)  Input offset voltage compensation for inverting and non inverting configuration.

 

7 a. Design a single pole LPF with-a cut off frequency of 10 kHz and mid band gain of 1.5. Draw the circuit diagram.

b.  With a neat diagram and relevant waveforms explain the following OP AMP circuits:

i) Peak detector and clamper

ii) Schmitt trigger

iii) Instrumentation amplifier

c. Explain sample and hold act.

 

8 a. With a neat diagram and relevant waveforms, explain the working of an a stable modulator

circuit using 555 timer. Obtain the expression for the time period.

b. Discuss the specifications of a DAC circuit.

Leave a Comment