# VTU Previous Question Papers BE EC 3rd Semester

# Analog Electronic Circuits July 2008

**Note : Answer any FIVE full questions, selecting at least two questions from each part.**

**PART-A**

1 a. Differentiate between static and dynamic resistance of a semi conductor diode.

b. Explain with the help of a circuit diagram the working of a Full Wave Rectifier. Derive expressions for i) Id_{c} ii) I_{rms} iii) V_{dc }iv) Ripple factor v) Rectifier efficiency.

c. For the circuit shown, in Fig.Q 1(c) write the transfer characteristic equations. Assume diodes are ideal. Plot V_{o} against V_{i}, indicating all slopes and voltage levels.

2 a. Design a voltage divider bias circuit with V_{cc} – 10 V, R_{c} = 1.5 K ohm, I_{C} – 2 mA, V_{CE} – 5 V, β = 50. Assume silicon transistor and stability factor S = 5.

b. Derive an expression for the stability factor S(Ico) for a voltage divider bias circuit.

c. Determine Rb and Rc for the transistor inverter of Fig.Q2(c) if Ic_{SAt} -10 mA.

3 a. For the network of Fig.Q3

(a): i) Determine r_{e } ii) Calculate Z_{i} and Z_{0 } iii) Find Av Given β = 100 S_{I} transistor.

b. Draw the emitter follower circuit Derive expressions; for:

i)Z_{i} ii) Z_{o} iii) A_{v} using r_{e} model.

c. Define h-parameters. Draw the h-parameter model of a transistor.

4 a. Determine the lower cutoff frequency for the network of Fig.Q4(a). Given p = 100, r_{0} “ oo ohm. Determine the mid band gain. If Cb_{e} – 36 pF, Cb_{c} = 4 pF, C_{w} = 6 pF, C._{v} = 8 pF. Determine f_{H}.and f_{H} and sketch the frequency response for low and high w o ^^*0frequency regions using the results.

b. Calculate the overall lower 3 db and upper 3 db frequencies for a 3 stage amplifier having an individual fj = 40 Hz and fz — 2 MHz.

**PART-B**

5 a. Draw the cascade configuration and list the advantages of this circuit.

b. Determine A;, R_{i;} A_{v} and Ro for the circuit shown in fig.Q5(b).

Given h parameters hi_{e} = 1.1 k ohm, h_{re} = 2 x 10″^{4}, ho_{e} – 25 x 1 O’^{6} U, hf_{e} = 50.

c. List the advantages of negative feedback amplifier. Derive expressions for Zjf and Z_{0}f for voltage series feedback amplifier.

6 a. Explain the working of a class B push pull amplifier. Prove that the maximum efficiency is 78.5%.

b. A single transistor amplifier with transformer coupled load produces harmonic amplitudes in the output as Bo – 1.5 mA, Bi – 120 in A, B_{2} – 10 mA, 83-4 mA, B4 = 2 mA, B5 – 1 mA.

i) Determine the percentage total harmonic distortion

ii) Assume second identical transistor is used along with suitable transformer to provide push pull operation. Using the above harmonic amplitudes, determine the new total harmonic distortion.

7 a. Explain with the help of a circuit diagram, the working of an RC phase shift oscillator.

b. With the help of Barkhousen criterion, explain the working of a BJT crystal oscillator.

Calculate the frequency of a Wien Bridge oscillator circuit when R = 12 k ohm and C = 2400 pf.

8 a. Determine Z_{h} Zq and A_{v} for the circuit shown in Fig.Q8(a), if Yf_{s} = 3000 }is and= 50 jxs.

Fig. Q8(a)

b. Determine Z_{i}, Z_{o }, and A_{v} if r_{d}= 40 k£l for fig.Q 8(b).

c. With the help of circuits and equations, show different biasing arrangements for depletion type MOSFET.