__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__

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

** ****Short Answer questions:**

- What is meant by feedback?
- What is tank circuit? How it is used in oscillators?
- State Barkhausen’s criterion.
- Differentiate positive feedback with negative feedback.
- If open loop voltage gain of feedback amplifier is 200 and feedback factor is 1/5 then find
- Gain with negative feedback.
- BW with negative feedback if open loop BW is 100 KHz.
- What are the advantages of negative feedback?
- What is the effect of negative feedback on bandwidth?
- Explain how gain stability is improved by negative feedback?
- Draw block diagrams of voltage- series and current- shunt feedback topologies?
- What are four topologies of feedback amplifiers?
- What is positive feedback .Give the advantage of positive feedback?
- Write the definition of oscillator?
- Differentiate oscillators with the frequency of operation?
- Draw under damped over damped and un-damped oscillatory signals.
- .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:**

- What is the effect of negative feedback on input and output impedances in voltage-series feedback amplifier give necessary expressions?
- Derive the general equation for LC oscillator circuits used in oscillators.
- Distinguish between positive feedback and negative feedback in amplifiers. State the advantages of negative feedback in amplifiers.
- Draw the circuit diagram of Hartley’s oscillator and explain its operation in detail. Derive the expression for frequency of oscillation.
- Draw the circuit diagram of Colpitt’s oscillator and explain its operation in detail. Derive the expression for frequency of oscillation.
- What is the effect of negative feedback on Bandwidth give explanation with necessary equations?
- Write in detail about four topologies of feedback amplifiers and compare the topologies in terms of gain, BW, input impedance and output impedance.
- 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.
- Draw a neat circuit diagram of an RC phase shift oscillator using BJT and explain its working principle
- 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**

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