This document covers negative feedback amplifiers, including the concept of feedback, different feedback topologies, and analysis of feedback amplifiers. It discusses four main feedback topologies: voltage series, voltage shunt, current series, and current shunt. For each topology, it explains the feedback mechanism, provides an approximate h-parameter equivalent circuit, and analyzes how feedback affects characteristics like gain, input and output resistance, bandwidth, and distortion. The document is intended to guide students through key topics relating to negative feedback amplifiers.

1. Negative Feedback Amplifiers Guided by : Prof. S. S. Patil Presentation by: Vinay Jasud (52) Vinod Arote (54)

2. TOPICS TO BE COVEREDIntroductionConcept of FeedbackFeedback TopologiesGeneral Characteristics of Negative Feedback AmplifiersAnalysis Of Feedback AmplifiersVoltage Series FeedbackVoltage Shunt FeedbackCurrent Series FeedbackCurrent Shunt Feedback

3. IntroductionFeedback (Definition) It is the process in which part of the output signal is returned back to the input.Types of Feedback 1.Positive Feedback 2. Negative Feedback

4. Difference Between Positive &Negative Feedback

5. CONCEPT OF FEEDBACK

6. Amplifiers Without FeedbackAmplifier“A”ViVo

7. Amplifiers With FeedbackSampling NetworkAmplifier“A”MixerVoVsViVoFeedbackSignalVfFeedback NetworkFeedback factor

8. Transfer characteristics with feedback (Af )Stabilization of GainEffect on input resistanceEffect on output resistanceEffect on BandwidthEffect on nonlinear distortionEffect on noiseGeneral Characteristics Of Negative Feedback Amplifiers

9. Transfer characteristics with feedback (Af )A = Transfer gain without feedbackA = Transfer gain with feedbackff oWhere X = Feedback SignalX = output signalfoTransfer gain with feedback is given by

10. Stabilization of GainFractional Change in amplification with feedback is given by Factors affecting stability are aging, temperature changes, replacement of component. ff

11. Sensitivity and Desensitivity

12. Effect on input resistance and output resistance

13. Analysis Of Feedback AmplifiersStep 1: Identify the topology.Step 2: Draw the basic amplifier circuit without feedback.Step 3: Use Thevenin’s theorem for voltage source and Norton’s theorem for current sou.rce.Step 4: Replace each device by it’s h-parameter.Step 5: Indicate Xo and Xf and evaluate .Step 6: Calculate open loop gain A.Step 7: Calculate D, Af, Rif and Rof.

14. Voltage Series FeedbackMake V0=0 If Vf=0 then voltage sampling.Feedback voltage Vf is in series with the input voltage Vs .Therefore series mixing. voltage sampling + series mixing =Voltage series feedbackTransistor emitter follower circuit

15. Approximate h-parameter equivalent circuit

17. Current Series FeedbackSet output current Io=0 if Vf=0 then current sampling.Feedback voltage Vf is in series with the input voltage Vs .Therefore series mixing.Therefore current series feedback. CE transistor amplifier with unbypassed Re

18. h-parameter equivalent circuit

19. -Re

20. Current Shunt FeedbackSet output current Io=0 if Vf=0 then current sampling.

21. Feedback signal is in parallel . Hence it is current shunt feedback. Current shunt feedback

22. h-parameter equivalent circuit

24. Voltage Shunt FeedbackMake V0=0 If Vf=0 then voltage sampling.

25. Is= Ii +If .It is series mixing.

26. Feedback is voltage shunt feedback.Voltage shunt feedback

27. h-parameter equivalent circuit