Code: DE08 Subject: ANALOG ELECTRONICS

Time: 3 Hours Max. Marks: 100

NOTE: There are 9 Questions in all.

· Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1 Choose the correct or best alternative in the following: (2x10)

a. A semiconductor has a

(A) negative temperature co-efficient of resistance.

(B) positive temperature co-efficient of resistance.

(C) constant temperature co-efficient of resistance.

(D) None of above.

b. When a p-n junction is reverse biased

(A) the width of depletion layer increases.

(B) it offers high resistance.

(C) small current flows through it.

(D) All of above.

c. For faithful amplification with germanium transistor, the base emitter junction voltage should not fall below

(A) 0.3 V (B) 0.5 V

(C) 0.7 V (D) 0.1 V

d. The ideal value of stability factor is

(A) 1 (B) 5

(C) 10 (D) 100

e. A high Q tuned circuit in an amplifier permits it to have high

(A) selectivity. (B) fidelity.

(C) sensitivity. (D) frequency range.

f. The final stage of an amplifier uses

(A) R-C coupling. (B) transformer coupling.

(C) direct coupling. (D) all of above.

g. A push pull amplifier

(A) reduces odd harmonics in output.

(B) reduces even harmonics in output.

(C) is the first stage of an audio amplifier.

(D) uses single transistor.

h. The voltage gain of an amplifier is 100. When negative feedback with a factor of 0.04 is introduced, its gain will be

(A) 20 (B) 25

(C) 4 (D) 0.4

i. The loop gain of the oscillator to start with is

(A) more than 100 (B) slightly more than 1

(C) less than 1 (D) none of above

j. The gain of op-amp decreases at high frequency because of

(A) external capacitance. (B) external resistance.

(C) internal capacitance. (D) internal resistance.

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2 a. Describe the self bias method of biasing for BJT. (8)

b. For voltage divider biasing circuit given below, find emitter current, collector emitter voltage and collector voltage. (8)

Q.3 a. Find the D.C. voltages and currents for the silicon n-p-n transistor given below assuming . Determine the small signal model and voltage gain of the amplifier. (10)

b. Explain how MOSFET is biased using self bias method. (6)

Q.4 a. Derive an expression for efficiency of class-A amplifier. Show that its maximum value is 50%. (8)

b. For a power amplifier working in class A operation, the zero signal collector current is 100 mA. If dc supply voltage .

Find

(i) the maximum ac power output

(ii) power rating of transistor

(iii) the maximum collector efficiency. (8)

Q.5 a. An amplifier has gain A = 60dB and output impedance . It is required to modify its output impedance to by negative feedback. Find

(i) value of feedback factor.

(ii) the percentage change in overall gain for 10% change in gain of basic amplifier. (8)

b. What do you mean by feedback? Derive an expression for gain with feedback. (8)

Q.6 a. Explain the characteristics of an ideal op-amp. (8)

b. Draw the circuit diagram of second order low pass Butterworth filter and derive an expression for cut off frequency. (8)

Q.7 a. Describe the process of square wave generation using op-amp. (8)

b. Describe the operation of 555 timer as an astable multivibrator. (8)

Q.8 a. Draw the circuit of shunt biased negative clipper and explain its working, when the input waveform is 20V (peak to peak) and a biasing voltage of 7V. Draw output waveform. (8)

b. Draw and explain the working of UJT relaxation oscillator. (8)

Q.9 a. In a transistor Hartley oscillator if , and mutual inductance between two coils . Calculate value of capacitor of oscillatory circuit to obtain frequency of 4110 kHz. (8)

b. Explain the operation of FET as an amplifier. State its advantages. (8)