Electronic devices and circuits ec

[aayush_005]

Note: Section A is compulsory. Attempt any Four questions from Section B and two from Section C

1.
Why the 3-dB frequency for current gain not same as fH for voltage gain?
What is base width modulation in transistors?
What is alpha cut off frequency, fa?
What is thermal runway?
What is phase shift distortion and frequency distortion?
Why is capacitive coupling used to connect a signal source to an amplifier?
Sketch a two input NOR gate and verify that it satisfies the Boolean NOR equation.
Hoe FET is used as voltage variable resistor?
What is the order of magnitude of each resistance in hybrid-p transistor model?
What are the advantages of Hartley oscillator over Collpitt oscillator?

Section B Marks 5 each

2. Discuss the effect of cascading on the gain and bandwidth of multistage amplifier quantitatively.

3. What are the four basic requirements of an audio frequency range harmonic oscillator that is to provide a flow distortion sinusoidal output? Explain each.

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

5. Draw and explain 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%?

Section C Marks 10 each

7. Explain 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 resultant upper 3 dB frequency fH* equals to fH √(21/n-1), where fH is upper 3 dB frequency for each 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? Explain.