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    Final Final Presentation Transcript

    • Negative Feedback Amplifiers
      Guided by : Prof. S. S. Patil
      Presentation by: Vinay Jasud (52)
      Vinod Arote (54)
    • 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
    • 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
    • Difference Between Positive &Negative Feedback
    • CONCEPT OF FEEDBACK
    • Amplifiers Without Feedback
      Amplifier
      “A”
      Vi
      Vo
    • Amplifiers With Feedback
      Sampling Network
      Amplifier
      “A”
      Mixer
      Vo
      Vs
      Vi
      Vo
      Feedback
      Signal
      Vf
      Feedback Network
      Feedback factor
    • 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
    • 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
    • Stabilization of Gain
      Fractional Change in amplification with feedback is given by
      Factors affecting stability are aging, temperature changes, replacement of component.
      f
      f
    • Sensitivity and Desensitivity
    • Effect on input resistance and output resistance
    • 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.
    • 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
    • Approximate h-parameter equivalent circuit
    • 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
    • h-parameter equivalent circuit
    • -Re
    • Current Shunt Feedback
      • Set output current Io=0 if Vf=0 then current sampling.
      • Feedback signal is in parallel . Hence it is current shunt feedback.
      Current shunt feedback
    • h-parameter equivalent circuit
    • Voltage Shunt Feedback
      • Make V0=0 If Vf=0 then voltage sampling.
      • Is= Ii +If .It is series mixing.
      • Feedback is voltage shunt feedback.
      Voltage shunt feedback
    • h-parameter equivalent circuit
    • Questions ???
    • Thank You