Punjab Engineering College 2005 B.Tech Electronic Devices & Circuits - Question Paper

EC 203 third Sem May 2005

ELECTRONIC DEVICES AND CIRCUITS
Max Marks 60
Max Time three Hours
Note: part A is compulsory. Attempt any 4 ques. from part B and 2 from part C

part A

1.(10 * 2=20)

(a) Why the 3-dB frequency for current gain not identical as fH for voltage gain?
(b) What is base width modulation in transistors?
(c) What is alpha cut off frequency, fa?
(d) What is thermal runway?
(e) What is phase shift distortion and frequency distortion?
(f) Why is capacitive coupling used to connect a signal source to an amplifier?
(g) Sketch a 2 input NOR gate and verify that it satisfies the Boolean NOR formula.
(h) Hoe FET is used as voltage variable resistor?
(i) What is the order of magnitude of every resistance in hybrid-p transistor model?
(j) elaborate the advantages of Hartley oscillator over Collpitt oscillator?

part B Marks five every
(5 *4=20)
2. explain the effect of cascading on the gain and bandwidth of multistage amplifier quantitatively.

3. elaborate the 4 basic requirements of an audio frequency range harmonic oscillator that is to give a flow distortion sinusoidal output? discuss every.

4. discuss push-pull circuit using transistors having complementary symmetry.

5. Draw and discuss the small signal equivalent circuit for an emitter follower stage at high frequencies.

6. To an amplifier of 60 dB gain, a negative feedback with b = 0.05 is applied. What would be the change in overall gain of the feedback amplifier, if the internal amplifier is subjected to a gain reduction of 12%?

part C Marks 10 every
(10 * 2=20)
7. discuss origin of cross-over distortion. Show that maximum conversion efficiency of the idealized class B push-pull circuit is 78.5%.

8. Prove that in n stage amplifier with non-interfacing stages, the resulting upper three dB frequency fH* equals to fH v(21/n-1), where fH is upper three dB frequency for every stage.

9. Draw the electrical model of a piezoelectric crystal. Sketch the reactance vs. frequency function. Over what portion of the reactance curve do we desire oscillations to take place when the crystal is used as a part of sinusoidal oscillator? discuss.

Earning:   Approval pending.