Electronic Circuit Analysis Feb 2007

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Set No. 1

Code No: RR210401

II B.Tech I Semester Supplementary Examinations, February 2007 ELECTRONIC CIRCUITS ANALYSIS (Electronics & Communication Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆

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1. The small signal h-parameter ac equivalent circuit of a certain transistor connected in CE configuration is shown in figure1. Calculate current gain, voltage gain , input impedance and output impedance by deriving the expressions for the above [16]

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Figure 1:

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2. (a) Prove that (i) hf e =gm rb′e for a Hybrid π model of CE amplifier.

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(b) How does a Ce and Cc vary with | Ic | and | VCE |. (c) How does gm vary with | Ic | and | VCE |, T.

[5+6+6]

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3. An RC coupled FET Amplifier has the following circuit values: RL =10k, RG =500k, Cc =0.01 µF, Csh =150 pf, µ=25, rd =10k and gm =2.5mA/V, find Am , f1 and f2 and also derive the three parameter expressions. [16] 4. (a) Draw the circuit diagram of a push pull amplifier and explain its working. (b) Derive the equation for efficiency of a class B amplifier.

[8+8]

5. (a) Draw the complementary - symmetry class-B power amplifier circuit with single power supply and explain its working . (b) In complementary - symmetry class-B power amplifier circuit, VCC =25 Volts; RL =16Ω and Imax =2 Amps. Determine the input power, output power and efficiency. [8+8] 6. (a) Explain the operation of a Double tuned amplifier. (b) Explain the advantages of double tuned circuit over single tuned circuit. [8+8] 7. (a) What is the function of voltage regulator circuit? How it is different from unregulated power supply. 1 of 2

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Set No. 1

Code No: RR210401 (b) Define the following terms. i. Line input regulation ii. Load regulation

(c) Draw the circuit of a simple Zener regulator and explain its operation with the help of load characteristics. [5+6+5] 8. (a) Draw the circuit for 7805 voltage regulator along with unregulated power supply and explain its working. (b) Explain how 78XX can be used as a current source. Draw the circuit and explain. [8+8]

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Set No. 2

Code No: RR210401

II B.Tech I Semester Supplementary Examinations, February 2007 ELECTRONIC CIRCUITS ANALYSIS (Electronics & Communication Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) What are important characteristics of source follower? Derive an expression for its voltage gain. (b) For the CE transistor amplifier circuit with Rs and RL, show that

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i. (AIS )max = -hf e , if RL = 0 and Ro = ∞ ii. Ri = hie , if RL = 0.

[8+8]

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2. (a) Define fβ and fT and derive the relation between fβ and fT .

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(b) The h-parameters of a transistor at Ic = 8mA, VCE = 10v, and at room temperature are hie = 1KΩ , hoe = 2 x 10 −5 A/V, hf e = 50, hre = 2.5 x 10−4 . At the same operating point, fT = 60 MHz, and Cob = 2PF. Compute the values of hybrid - π parameters. [6+10]

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3. An RC coupled FET Amplifier has the following circuit values: RL =10k, RG =500k, Cc =0.01 µF, Csh =150 pf, µ=25, rd =10k and gm =2.5mA/V, find Am , f1 and f2 and also derive the three parameter expressions. [16]

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4. (a) Draw the circuit diagram of a push pull amplifier and explain its working. [8+8]

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(b) Derive the equation for efficiency of a class B amplifier.

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5. (a) If two transistors are employed in a push-pull amplifier with cut-off bias, or in Class-B operation of the amplifier, explain the process of generation of ‘crossover distortion’ with necessary diagrams and the reasons behind such phenomenon. (b) Suggest a suitable circuit for minimizing the above distortion.

[10+6]

6. (a) Explain about synchronous tuning of Tuned amplifiers with a block diagram for the system concept. (b) Draw the circuit of double-tuned transformer-coupled amplifier. Discuss the nature of responses of the amplifier for different values of KQ=1; KQ>1 and KQ<1. [6+10] 7. (a) Compare the merits and demerits of Zener regulator over series regulator and shunt regulator. (b) Draw the circuit of a shunt regulator circuit and explain its operation. [8+8] 8. (a) What are the limitation of three terminal regulators?

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Set No. 2

Code No: RR210401

(b) Draw the circuit diagram of a dual power supply using three terminal regulators to obtain +12 V and -15V regulated DC output voltage and explain the operation of the circuit. [8+8]

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Set No. 3

Code No: RR210401

II B.Tech I Semester Supplementary Examinations, February 2007 ELECTRONIC CIRCUITS ANALYSIS (Electronics & Communication Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Give points of similarity and difference in low frequency small signal models of BJT and FET.

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(b) The amplifier stage shown uses an N-channel FET having IDSS =1mA VD =1V. If quiescent drain to ground voltage is 10v, find R1 . {As shown in the Figure1} [6+10]

Figure 1:

2. (a) Explain how the parameters of hybrid-π model varies with IC , VCE and temperature. (b) The hybrid-π parameters of the transistor used in circuit are : gm = 50mA/V, rbb′ =100Ω, rb′ e = 1K, rb′ c = 4M, rce = 80K, Cc = 3PF, Ce = 100 PF. Using Miller’s theorem and the appropriate analysis, compute {As shown in the Figure2} i. The upper 3 dB frequency of the current gain AI ii. The magnitude of voltage gain at the frequency of part (i). 3. (a) Explain about different methods of Inter stage coupling in amplifiers.

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[6+10]

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Set No. 3

Code No: RR210401

Figure 2:

hoe =25µ mho hoe =25µA/V

[6+10]

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hie =2.2k hf e =40 hre =5×10−4 hie =1.8k hf e =-50 hre =1

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(b) Two transistor amplifier circuits are cascaded as shown in figure3. The hparameter values are as given under. Determine the overall voltage gain Av.

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4. (a) Explain about heat sinks. Explain the term Thermal Resistance. Give the sketches of heat sinks. (b) What is the Junction to ambient Thermal Resistance for a device dissipating 600 mw into an ambient temperature of 500 C and operating at a junction temperature of 1100 C? [8+8] 5. (a) If two transistors are employed in a push-pull amplifier with cut-off bias, or in Class-B operation of the amplifier, explain the process of generation of ‘crossover distortion’ with necessary diagrams and the reasons behind such phenomenon. (b) Suggest a suitable circuit for minimizing the above distortion.

[10+6]

6. (a) What is a tuned amplifier and how do you classify tuned amplifier.Briefly explain. 2 of 3

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Set No. 3

Code No: RR210401

(b) Briefly explain the capacitance coupled single tuned amplifier with its equivalent circuit. [8+8] 7. (a) What are the limitations of various Linear regulators. Explain.

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Figure 4:

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(b) In the given Zener diode regulator circuit, Zener diode conducts if the supply voltage Vi is greater than 20V. Zener diode voltage is 16V. The meter resistance is 500 ohms. Find R1 and R2 where R1 + R2 = 99.5KΩ. {As shown in the Figure4} [6+10]

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8. (a) What is meant by voltage multiplier? List out the names of four different multipliers.

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(b) Draw the circuit of a full-wave voltage doubler circuit and explain its operation. Mention the PIV of each diode. [6+10]

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Set No. 4

Code No: RR210401

II B.Tech I Semester Supplementary Examinations, February 2007 ELECTRONIC CIRCUITS ANALYSIS (Electronics & Communication Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Sketch the circuit of a CS amplifier. Derive the expression for AV at low frequencies. What is the maximum value of AV ? (b) For the CE transistor amplifier circuit with Rs and RL , show that Ro =

−hf e hie hoe − hre hf e −hie hie hoe − hre hf e

if RL = ∞ and Rs = 0. , if Rs = 0.

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i. (AV S )max =

[8+8]

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2. (a) Derive the expression for output conductance and diffusion capacitance of hybrid-π CE amplifier.

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(b) A single-stage CE amplifier is to have a bandwidth fH of 5MHz with RL = 500 Ω. Assume hf e = 100, gm = 100mA/V, rbb′ = 100Ω, Cc = 1PF, and fT = 400 MHz

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i. Find the value of the source resistance that will give the required bandwidth. ii. with the value of Rs , determined in part (i), find the mid band voltage gain Vo / VS . [6+10] 3. (a) Explain about different types of distortions that occur in amplifier circuits.

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(b) When 2-stages of identical amplifiers are cascaded, obtain the expressions for overall voltage gain, current gain and power gain. [6+10] 4. (a) Derive the equation for maximum value of efficiency of a class A transformer coupled amplifier. (b) Calculate the transformer turns ratio required to match a 8 ohms speaker load to an amplifier so that the effective load resistance is 3.2 K ohms. [8+8] 5. (a) What is thermal resistance? What is the unit of thermal resistance. (b) Explain the commonly available heat sinks.

[6+10]

6. (a) Mention the three methods of stabilization of the double-tuned transformer coupled amplifier circuit performance against the feedback path through the parasitic capacity between input and output and also mention the reasons for neutralization schemes. (b) Mention the frequency ranges of application of the double tuned amplifiers with neutralization schemes (c) Explain the method of adjusting the amplifiers for stabilization of the responses. 1 of 2

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Set No. 4

Code No: RR210401

7. (a) Design a series regulated power supply with following specifications. Unregulated input voltage Vi = 30V and r0 = 8 ohms Regulated output voltage = 12 V Maximum load current = 200 ma. Control transistor hf e = 100, hie = 200 ohms Amplifier transistor hf e = 200, hie = 1000 ohms Reference voltage VR = 6V Zener resistance Rz = 10 ohms Zener current = 20 mA (b) Also calculate its stability factor and output resistance (c) Also draw the complete circuit diagram with the designed component values.

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[8+8] 8. (a) Draw the circuit of 7805 voltage regulator IC and explain its working.

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(b) Using 7805 IC voltage regulator, design current source to deliver 0.25A current to 48 ohms, 10 watts load. [8+8]

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