Rr210401 Electronic Circuits Analysis

Set No. 1

Code No: RR210401

II B.Tech I Semester Supplimentary Examinations, November 2007 ELECTRONIC CIRCUITS ANALYSIS (Electronics & Communication Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Calculate voltage gain AV = VO /VS at 1kHz for the circuit shown Figure1a. FET parameters are gm =2mA/V and rd =10k. Neglect capacitances.

Figure 1a (b) Repeat part (a) if capacitance 0.003µf is taken under consideration.

[8+8]

2. (a) Define fβ and fT and derive the relation between fβ and fT . (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] 3. (a) Explain about different methods of Inter stage coupling in amplifiers. (b) Two transistor amplifier circuits are cascaded as shown in figure3b. The hparameter values are as given under. Determine the overall voltage gain Av. [6+10] hie =2.2k hf e =40 hre =5×10−4 hoe =25µ mho hie =1.8k hf e =-50 hre =1 hoe =25µA/V

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Set No. 1

Code No: RR210401

Figure 3b 4. (a) Define about class A, class B, class AB and class C operation of power amplifiers. (b) Design a class B power amplifiers to deliver 25w to a load resistor RL =8Ω, using transformer coupling. Vm =Vcc =25V. Assume reasonable data wherever necessary. [6+10] 5. (a) Explain why the complimentary symmetry power amplifier has become more popular in modern circuits. (b) Draw a practical circuit of a complimentary symmetry push pull amplifier circuit? Explain its function. [8+8] 6. (a) Explain the principle of stabilizing the double-tuned transformer coupled amplifier response against the internal feedback (b) Tuned amplifier has an internal feedback capacitance of 10 Pf, which has to be neutralized. It operates at 10MHz and the output transformer is connected with a tapped primary at Na : Nb =1:4. Its primary inductance is 5 µH. If, Hazeltine neutralization is to be used, calculate the size of the neutralizing capacitor needed. Draw the Hazeltine neutralization circuit also. [8+8] 7. (a) Draw the circuit diagram of a series voltage regulator circuit and explain its operation. (b) In the given circuit 15 volts, 2 watts Zener is used. The minimum current required is 5ma for Zener to conduct. Find the value of Rs , RLmin and RLmax . {As shown in the Figure7b} [8+8]

Figure 7b 8. (a) What are the draw backs of three terminal regulators

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Set No. 1

Code No: RR210401

(b) Draw the circuit diagram of a dual power supply using three terminal regulators to obtain ±15 V output voltage and explain the operation of the circuit. [6+10] ⋆⋆⋆⋆⋆

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Set No. 2

Code No: RR210401

II B.Tech I Semester Supplimentary Examinations, November 2007 ELECTRONIC CIRCUITS ANALYSIS (Electronics & Communication Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Calculate voltage gain AV = VO /VS at 1kHz for the circuit shown Figure1a. FET parameters are gm =2mA/V and rd =10k. Neglect capacitances.

Figure 1a (b) Repeat part (a) if capacitance 0.003µf is taken under consideration.

[8+8]

2. (a) Define fβ and fT and derive the relation between fβ and fT . (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] 3. (a) Explain about different types of distortions that occur in amplifier circuits. (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 expression for efficiency of a transformer coupled class A power amplifier. (b) In the case of a class A Power Amplifiers circuit, RL =5Ω. Transistor ratings are PC(M ax) =10w, VCE(sat) =1V,VCE(M ax) =60V. Transformer coupling is used with n=2. Determine the efficiency of the amplifier. [8+8]

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Set No. 2

Code No: RR210401

5. (a) Explain the reasons for harmonic distortion in push pull power amplifiers. (b) Derive the expression for the power of output signal having distortion. (c) For harmonic distortions of D2 =0.1; D3 =0.02 and D4 =0.01 with fundamental component of output signal I1 =4 A and RL =8Ω. Calculate the total harmonic distortion, fundamental power component and total power. [5+5+6] 6. (a) Draw the circuit of single tuned amplifier and explain its operation. (b) Draw the ideal and actual response characteristics of single tuned amplifiers (c) Discuss the significance of the pass band characteristic of tuned amplifiers when they are used in Radio receivers. [6+6+4] 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. [8+8] 8. (a) Draw the circuit of 7805 voltage regulator IC and explain its working. (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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Set No. 3

Code No: RR210401

II B.Tech I Semester Supplimentary Examinations, November 2007 ELECTRONIC CIRCUITS ANALYSIS (Electronics & Communication Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Draw the circuit diagram of CE amplifier and its h-parameter equivalent circuit. Give typical values of h-parameters of a transistor in CE configuration. (b) Findout Ai , AV , Ri and Ro of CE, self-bias amplifier circuit, given R1 = R2 = 100 KΩ , RE = 2.93Ω, Rc = 2.1KΩ, RS = 50Ω, RL = 1KΩ. The h-parameters of the transistor are hf e = 100, hie = 2KΩ, hre = 0, hoe = 10−5 mhos. Neglect capacitive reactance’s of coupling and bypass capacitors. [8+8] 2. (a) Derive the expressions for feedback conductance and base spreading resistance of CE amplifier using hybrid-π model. (b) Given the following transistor measurements made at Ic=5mA; VCE =10V and at room temperature hf e =100; hie =600Ω; [Aie ]= 10 at 10 mHz , Cc =3pf. Find fβ , fT , ce , rbe and r bb′ . [6+10] 3. (a) Obtain the theoretical expressions for f1 n and f2 n when n-stages of identical amplifiers are cascaded. (b) For a given transistor (BJT), hf e = 100. fB = 5 KHzs. Determine the Bandwidth of the transistor. If the lower cut off frequency f1 = 100 Hzs and upper cut off frequency f2 = 100 KHzs, then determine the midband frequency f0 of the amplifier circuit. [10+6] 4. (a) Draw the circuit for class A transformer coupled amplifiers and explain the operation graphically. (b) A power transistor working in class A operation has zero signal power dissipation of 5 watts. If A.C. power is 2 watts, find collector efficiency and power rating of transistor. [8+8] 5. (a) Derive the expression, with necessary diagrams, to calculate the total harmonic distortion ‘D’ in power amplifiers using the five-point method of analysis. (b) State the expression relating the total output power ‘P’; total harmonic distortion ‘D’ and the fundamental power ‘P1 ’ in power amplifiers. If total distortion in the amplifier is 9%; calculate its contribution to the total power . (c) Discuss the effect of the increase in the order of harmonic frequency in power amplifier stage used in an instrument for listening to music. [8+4+4] 6. (a) Draw the circuit of FET tuned Voltage amplifier. Derive the necessary expression to draw the universal resonance curve with all necessary details.

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Set No. 3

Code No: RR210401

(b) Design the single stage FET tuned amplifier for the following specifications, fo =12 M Hz. Bandwidth B=10 KHZ and midband voltage gain Avm = -15. The FET parameters are gm =4 ms rd =25K ohms; CGS = 30pf; CGD =CDS =5pf. [8+8] 7. (a) What is a regulated power supply. Explain the terms i. Stability factor ii. Output Resistance iii. Load regulation (b) Explain the working of a simple Zener regulator circuit and also state the limitations of this circuit. [9+7] 8. (a) Explain how current boosting can be achieved in three terminal regulators. Derive necessary expressions. (b) Draw the circuit of 78xx voltage regulator circuit and explain. (c) Modify the circuit to boost the current and explain how it works. ⋆⋆⋆⋆⋆

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[5+5+6]

Set No. 4

Code No: RR210401

II B.Tech I Semester Supplimentary Examinations, November 2007 ELECTRONIC CIRCUITS ANALYSIS (Electronics & Communication Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) For the circuit shown in figure1a. Calculate Ai , AV , Ri , AV S . The hparameters are hie = 1.1K, hre = 2.5 x 10−4 , hf e = 50, hoe =25µA per volt.

Figure 1a (b) Derive the expressions, for CS amplifier with voltage divider biasing for Ri , Ro and AV . [8+8] 2. (a) Derive the expression for fT and fβ of CE amplifier using HF model. (b) If β = 150 , what are the cut off frequencies of the input and output of the given circuit? {As shown in the Figure2b} [8+8]

Figure 2b 3. (a) How is the High frequency gain of a single stage amplifier dependent on frequencies f1 and f2 . (b) In an RC-coupled BJT amplifier, we have RL =6.8k, effective ac load after Cc is Rac =1k, Cc =1 µ f, CE=24µF, RE =2.2k, hf e =49, RS =5k and hie =1k, find the low frequency cut off point. [8+8] 4. (a) Explain why a power amplifier is always preceded by a voltage amplifier? (b) Draw the circuit diagram of a single ended power amplifier? Explain the function of each component used in the circuit? [8+8] 1 of 2

Set No. 4

Code No: RR210401

5. (a) Derive the expression, with necessary diagrams, to calculate the total harmonic distortion ‘D’ in power amplifiers using the five-point method of analysis. (b) State the expression relating the total output power ‘P’; total harmonic distortion ‘D’ and the fundamental power ‘P1 ’ in power amplifiers. If total distortion in the amplifier is 9%; calculate its contribution to the total power . (c) Discuss the effect of the increase in the order of harmonic frequency in power amplifier stage used in an instrument for listening to music. [8+4+4] 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) List out the limitations of unregulated power supplies over linear regulators. (b) Write short notes on i. Zener regulator ii. Series Voltage regulator

[6+10]

8. (a) What are the draw backs of three terminal regulators (b) Draw the circuit diagram of a dual power supply using three terminal regulators to obtain ±15 V output voltage and explain the operation of the circuit. [6+10] ⋆⋆⋆⋆⋆

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