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  • 1. Negative Feedback Amplifiers
    Guided by : Prof. S. S. Patil
    Presentation by: Vinay Jasud (52)
    Vinod Arote (54)
  • 2. TOPICS TO BE COVERED
    Introduction
    Concept of Feedback
    Feedback Topologies
    General Characteristics of Negative Feedback Amplifiers
    Analysis Of Feedback Amplifiers
    Voltage Series Feedback
    Voltage Shunt Feedback
    Current Series Feedback
    Current Shunt Feedback
  • 3. Introduction
    Feedback (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 Feedback
    Amplifier
    “A”
    Vi
    Vo
  • 7. Amplifiers With Feedback
    Sampling Network
    Amplifier
    “A”
    Mixer
    Vo
    Vs
    Vi
    Vo
    Feedback
    Signal
    Vf
    Feedback Network
    Feedback factor
  • 8. Transfer characteristics with feedback (Af )
    Stabilization of Gain
    Effect on input resistance
    Effect on output resistance
    Effect on Bandwidth
    Effect on nonlinear distortion
    Effect on noise
    General Characteristics Of Negative Feedback Amplifiers
  • 9. Transfer characteristics with feedback (Af )
    A = Transfer gain without feedback
    A = Transfer gain with feedback
    f
    f
    o
    Where X = Feedback Signal
    X = output signal
    f
    o
    Transfer gain with feedback is given by
  • 10. Stabilization of Gain
    Fractional Change in amplification with feedback is given by
    Factors affecting stability are aging, temperature changes, replacement of component.
    f
    f
  • 11. Sensitivity and Desensitivity
  • 12. Effect on input resistance and output resistance
  • 13. Analysis Of Feedback Amplifiers
    Step 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 Feedback
    Make 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 feedback
    Transistor emitter follower circuit
  • 15. Approximate h-parameter equivalent circuit
  • 16.
  • 17. Current Series Feedback
    Set 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 Feedback
    • Set 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
  • 23.
  • 24. Voltage Shunt Feedback
    • Make 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
  • 28.
  • 29. Questions ???
  • 30. Thank You