# Basic Electronics Important Questions Unit 3 (FAQ)

UNIT – 3

Unit-3:  Feedback concepts: Properties of negative feedback amplifiers, Classification, Parameters. Oscillators: Barkhausen’s Criterion, LC Type and RC type oscillators and crystal oscillator. (Qualitative treatment only)

ASSIGNMENT- UNIT3

1. Draw the basic block diagram of feedback amplifier and explain each block in detail. 10M.
2. What is the effect of negative feedback on input and output impedances of a voltage series feedback amplifier? Give necessary expressions.
3. Write a short note about RC Phase Shift Oscillator.

Short Answer questions:

1. What is meant by feedback?
2. What is tank circuit? How it is used in oscillators?
3. State Barkhausen’s criterion.
4. Differentiate positive feedback with negative feedback.
5. If open loop voltage gain of feedback amplifier is 200 and feedback factor is 1/5 then find
6. Gain with negative feedback.
7. BW with negative feedback if open loop BW is 100 KHz.
8. What are the advantages of negative feedback?
9. What is the effect of negative feedback on bandwidth?
10. Explain how gain stability is improved by negative feedback?
11. Draw block diagrams of voltage- series and current- shunt feedback topologies?
12. What are four topologies of feedback amplifiers?
13. What is positive feedback .Give the advantage of positive feedback?
14. Write the definition of oscillator?
15. Differentiate oscillators with the frequency of operation?
16. Draw under damped over damped and un-damped oscillatory signals.
17. .In the forward path of an oscillator, two amplifiers of equal gain are cascaded. If the feedback path transfer function is 1/81, find the gain of each amplifier.

Long Answer questions:

1. What is the effect of negative feedback on input and output impedances in voltage-series feedback amplifier give necessary expressions?
2. Derive the general equation for LC oscillator circuits used in oscillators.
3. Distinguish between positive feedback and negative feedback in amplifiers. State the advantages of negative feedback in amplifiers.
4. Draw the circuit diagram of Hartley’s oscillator and explain its operation in detail. Derive the expression for frequency of oscillation.
5. Draw the circuit diagram of Colpitt’s oscillator and explain its operation in detail. Derive the expression for frequency of oscillation.
6. What is the effect of negative feedback on Bandwidth give explanation with necessary equations?
7. Write in detail about four topologies of feedback amplifiers and compare the topologies in terms of gain, BW, input impedance and output impedance.
8. Write the working operation of the following circuits and derive the expression of frequency of oscillation. i. RC-Phase shift oscillator. ii. Wein-bridge oscillator. iii. Crystal oscillator.
9. Draw a neat circuit diagram of an RC phase shift oscillator using BJT and explain its working principle
10. A Hartley oscillator is designed with L1=2mH, L2=20mH, and a variable capacitance. Determine the range of capacitance value, if the frequency of oscillation is varied between 950 kHz and 2050 kHz.

ALL THE BEST

Prepared by       P.Lakshmi Prasanna

## Author: Lakshmi Prasanna Ponnala

Completed M.Tech in Digital Electronics and Communication Systems.

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