*8235*
8235
(Pages : 3)
Reg. No. : .................................... Name : .........................................
Third Semester B.Tech. Degree Examination, November 2009 (2008 Scheme) 08.304 : ELECTRONIC CIRCUITS (RF) Time : 3 Hours
Max. Marks : 100 PART – A
Answer all questions. Each question carries 4 marks. 1. Explain the terms ripple factor, PIV, TUF and regulation as reffered to rectifier circuits. 2. Draw the circuit of a positive clipper and explain its working. 3. Show that the output of a RC differentiating circuit is the derivative of the input signal. 4. What is transistor biasing ? What are the basic conditions which are to be necessarily fulfilled for achieving faithful amplification of input signal in transistor amplifiers ? 5. Differentiate between positive and negative feedback. How does negative feedback modify the gain of an amplifier ? 6. What are the Barkhausen conditions of oscillations in electronic systems ? What are the factors which affect the frequency stability of an oscillator ? 7. What is the concept of virtual ground in opamp ? Find the gain of a non-inverting opamp amplifier. 8. Draw and explain an opamp as an adder. 9. Differentiate between low pass, high pass, band pass and band reject filters, sketching the frequency plots. Give one application of each category. 10. Explain the operation of a high pass filter employing opamp with a neat circuit diagram. P.T.O .
8235
-2-
*8235*
PART – B Answer any one question from each Module. Each question carries 20 marks. MODULE – I 11. a) Draw the circuit of a full wave rectifier circuit with shunt capacitor filter and explain its working. Derive the equation for its ripple factor. b) Draw the block diagram and explain the principle of operation of an inverter. 12. a) Draw the circuit of a low pass RC circuit. Explain its response to a square wave input. Under what conditions it acts as an integrator. Draw the input and output waveforms of the integrator when a 10V p-p square wave is given as the input. b) A halfwave rectifier has a load resistance of 3.5 k Ω . If the diode and the secondary of the transformer have a total resistance of 800 Ω and the input voltage is an ac signal of 230V, 50Hz determine i) peak, average and rms values of current flowing. ii) dc and ac power output. iii) rectification efficiency and iv) ripple factor. MODULE – II 13. a) A CE amplifier employing an NPN transistor is shown in figure. Calculate the values of R1 and Rc and the stability factor if VBE = 0.2 V, IE = 2mA, α = 0.985, VCE = 6 V, VCC = 12 V, R 2 = 30 k Ω and RE = 1k Ω .
b) Explain the working of an emitter follower circuit and show how it performs the functions of impedance matching.
*8235*
-3-
8235
14. a) Draw the circuit of a Wein bridge oscillator and explain its working. Give the equations for the frequency of oscillation and the condition for oscillation. b) Draw the internal block diagram of IC 555 timer and explain its operation. MODULE – III 15. a) Draw the circuit diagram of a opamp differential amplifier and find out its gain and CMRR. b) Explain what do you understand by offset voltage and offset current of an opamp. Discuss with a neat circuit diagram the technique for minimizing offset voltage and offset current in an inverting amplifier. 16. a) Design a band stop filter. Draw the circuit diagram and frequency response and explain its working. b) Why are active filters prefered over passive filters. Draw the schematic of a second order low pass filter and explain the cut off characteristics. _____________