Code No: R Set No. 1

Transcription

1 Code No: R Set No. 1 II B.Tech I Semester Supplementary Examinations, February 2007 ELECTRONIC CIRCUIT ANALYSIS ( Common to Electronics & Communication Engineering and Electronics & Telematics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. (a) For a single stage transistor amplifier, R S = 10K and R L = 10K. The h- parameter values are h fc = 51, h ic =1.1KΩ, h rc 1, h oc = 25 µa/v Find A I, A V, A V S, R i, and R o for the CC transistor configuration. (b) For a single stage transistor amplifier, R S =1KΩ, and R L = 10K The h-parameter values are h fe = 50, h ie =1.1KΩ, h re = 2.5x10 4, h oe = 25 µ A/V. Find A I, A V, A V S, R i, and R o for the CE transistor configuration. [8+8] 2. A two stage FET RC coupled amplifier has the following parameters: g m = 10mA/V, r d = 5.5K and R g = 0.5 M for each stage. Assume C S is arbitrarily large. (a) What must be the value of C b in order that the frequency characteristic of each stage be flat within 1 db down to 10 Hz? (b) Repeat the above part if the overall gain of both stages is to be down 1 db at 10 Hz. (c) What is the overall mid band voltage gain? [8+4+4] 3. (a) Prove that in Hybrid - π model, the diffusion capacitance is proportional to the emitter bias current. (b) In Giacolletto model of a transistor at high frequencies, how does C e vary with I c and V CE? How does C c vary with I c and V CE? [8+8 ] 4. (a) Write short notes on requirement and types of heat sinks for power dissipation in large signal amplifiers. (b) With the help of a neat circuit diagram, explain the operation of a complementary symmetry configured class B power amplifier. (c) Compare and contrast push-pull and complementary-symmetry configurations for class B power amplifiers. [6+6+4] 5. (a) Draw and explain the circuit diagram of a Single tuned Inductively coupled amplifier using BJT? (b) Draw its High frequency circuit and explain it? [8+8] 6. Explain in detail the effect of cascading tuned amplifiers and hence derive the expression for bandwidth of n-stage amplifier. Also draw the frequency response and explain what happens as the number of stages increases? [16] 1 of 2

2 Code No: R Set No (a) Explain why voltage regulators are required for a DC power supply operating from an AC source? (b) A power supply has a voltage regulation of 1% If the no load voltage is 30V What is the full load voltage? (c) Give the differences between Load and Line Regulations. [6+4+6] 8. (a) What is catcher diode and explain the necessity of catches diode in Switch Regulator with the help of circuit diagram. (b) List the operating ratings and electrical characteristics of IC 723. [8+8] 2 of 2

3 Code No: R Set No. 2 II B.Tech I Semester Supplementary Examinations, February 2007 ELECTRONIC CIRCUIT ANALYSIS ( Common to Electronics & Communication Engineering and Electronics & Telematics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. (a) Derive the expressions for A i, A V of CE amplifier circuit. Explain how A i and A V are effected by R L. (b) Consider a single stage CE amplifier with R S = 1K, R 1 = 50 K, R 2 =2 K, R C = 1K, R L = 1.2K, h fe = 50, h ie =1.1K, h re = h oe = 0; Find A I, R i, R o, A V and power gain. [8+8] 2. (a) State Miller s theorem. Explain its significance in transistor circuit analysis. (b) For the amplifier shown in figure1, calculate R i, R I, A V, A V S and A I = - I 2 / I 1. The h-parameter values are h fe = 50, h ie = 1.1KΩ, h re = 2.5x10-4, h oe = 24 µa/v. Figure 1: 3. (a) Derive various Resistive parameters of Hybrid - π model of a transistor in terms of h parameters. (b) What is the relationship between f T and f β? Discuss the significance of f T. [12+4] 1 of 2

4 Code No: R Set No (a) Compare the series fed and transformer coupled Class - A power amplifiers. Why is the conversion efficiency doubled in transformer coupled Class-A amplifier? [8] (b) Discuss in detail the origin and effect of cross-over distortion. How do you avoid the cross over distortion in power amplifiers circuit? Discuss in detail. [8] 5. (a) What is meant by the term Tuned amplifier and briefly explain the various methods of classification of tuned amplifiers? (b) A constant generator drives a parallel tuned circuit consisting of a loss less capacitor C and a coil L (having small resistance R ). Derive the expression for the frequency of resonance? [8+8] 6. Explain in detail the effect of cascading tuned amplifiers and hence derive the expression for bandwidth of n-stage amplifier. Also draw the frequency response and explain what happens as the number of stages increases? [16] 7. (a) Explain the classification of power supplies with respect to methods of output voltage regulation. (b) What is the difference between overload and over current protection in regulators? (c) What is meant by foldback limiting in power supplies? Draw the load voltage and current characteristics and indicate the foldback limiting region. [4+6+6] 8. (a) What is catcher diode and explain the necessity of catches diode in Switch Regulator with the help of circuit diagram. (b) List the operating ratings and electrical characteristics of IC 723. [8+8] 2 of 2

5 Code No: R Set No. 3 II B.Tech I Semester Supplementary Examinations, February 2007 ELECTRONIC CIRCUIT ANALYSIS ( Common to Electronics & Communication Engineering and Electronics & Telematics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. (a) Draw the circuit diagram of CB- amplifier and its h-parameter equivalent circuit. List out the characteristics of a CB amplifier. (b) In a single stage CB amplifier circuit, R E = 20K, R C = 10K, V EE = 20V, V CC = 20V, R L = 10K and R S = 0.5K. Find A I, R i, R o, A V. [8+8] 2. (a) How are multistage amplifiers classified depending upon the type of coupling. (b) Write a note on distortions in amplifiers. (c) If eight identical amplifiers are cascaded each having f H =200 KHz, determine the overall upper 3dB frequency f h. Assume non interacting stages. [5+6+5] 3. (a) Draw the small signal equivalent circuit for an emitter follower stage at high frequencies. (b) Consider a CE stage with a resistive load R L. Using Miller s theorem Find out input capacitance at mid-band frequencies and high frequencies? [8+8] 4. (a) Define the conversion efficiency of a power amplifier. A class A power amplifier with a direct coupled load has a collector efficiency of 15% and delivers a power output of 5 Watts. Find i. The DC power input ii. Power dissipation at maximum output [6] (b) Draw the push-pull power amplifier circuit. Derive the expression for the output current in push pull amplifier with base current as i b = I bn sin wt. [10] 5. (a) Explain what happens to the gain because of the presence of feedback capacitance from collector to base in single tuned BJT amplifier circuit? (b) Explain in detail the Unilateralisation technique with the help of circuit diagram? (c) Explain the difference between Neutralization and Unilateralisation techniques? [4+8+4] 6. Explain in detail the effect of cascading tuned amplifiers and hence derive the expression for bandwidth of n-stage amplifier. Also draw the frequency response and explain what happens as the number of stages increases? [16] 7. (a) Explain the operation of a Zener diode Voltage Regulator. (b) Discuss about the stability factor of a zener diode voltage regulator 1 of 2

6 Code No: R Set No. 3 (c) Explain how overload protection is provided in Series Voltage Regulators. [6+4+6] 8. (a) What are the features of IC LM78XX, three terminal voltage regulator and also give its applications (b) Write a short notes on UPS and SMPS. [8+8] 2 of 2

7 Code No: R Set No. 4 II B.Tech I Semester Supplementary Examinations, February 2007 ELECTRONIC CIRCUIT ANALYSIS ( Common to Electronics & Communication Engineering and Electronics & Telematics) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks 1. (a) For a single stage transistor amplifier, R S =200Ω and R L = 5K. The h-parameter values are h fb = , h ib =21 Ω, h rb = 2.9 x 10 4, h ob = 0.49 µa/v. Find A I, A V, A V S, R i, and R o for the CB transistor configuration. (b) For a single stage transistor amplifier, R S =1KΩ and R L = 10K The h-parameter values are h fe = 50, h ie =1.1KΩ, h re = 2.5x10 4, h oe = 25 µa/v. Find A I, A V, A V S, R i, and R o for the CE transistor configuration. [8+8] 2. (a) How are multistage amplifiers classified depending upon the type of coupling. (b) Write a note on gain-bandwidth product of amplifiers. (c) If eight identical amplifiers are cascaded each having f H =100 KHz, determine the overall upper 3dB frequency f h. Assume non interacting stages. [5+6+5] 3. (a) In Hybrid - π model of a transistor at high frequencies, show that g m is proportional to the collector current. (b) Define f T and what is physical significance of f T? If a silicon p-n-p transistor has an f T = 400MHz. What is the base thickness? [Assume Diffusion constant as 13 cm 2 /sec. [8+8] 4. (a) In series fed Class - A power amplifier, explain the importance of the position of operating point on output signal swing. Show that the conversion efficiency is 25%. (b) Discuss the origin of various distortions in transistor amplifier circuits. [10+6] 5. In the simple BJT tuned amplifier shown in figure 1, the circuit bandwidth is 5 KHz and the voltage gain has a maximum value at 200 KHz, when the tuning capacitor is adjusted to 470pF. Assume the coil has a series resistance of r ohms. (a) Draw the small signal equivalent of the given amplifier circuit. (b) Calculate coil inductance, given the coil Q as 75. (c) Find the circuit output impedance at resonant frequency. (d) Find the internal resistance r O of the BJT used. [16] 6. Explain as to how you can increase the selectivity of single tuned amplifier. Draw the circuit diagram and explain its operation and also draw its frequency response? [16] 1 of 2

8 Code No: R Set No. 4 Figure 1: 7. (a) Draw and explain a circuit which limits the current that can be drawn from the supply to a certain specific maximum. (b) Determine the minimum and maximum values for series resistor, required for a zener diode regulator with an output voltage of 5.6V, if the supply voltage varies from 10 V to 50V. The maximum load current is 20mA and minimum zener current is 3 ma. [8+8] 8. (a) What is catcher diode and explain the necessity of catches diode in Switch Regulator with the help of circuit diagram. (b) List the operating ratings and electrical characteristics of IC 723. [8+8] 2 of 2