3.7.2 Amplifier with Negative Feedback

Chapter 3.7.2 Amplifier with Negative Feedback

Physics Lecture Notes – Phys 395 Electronics Book
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Physics Lecture Notes – Phys 395 Electronics Book

  • CHAPTER 3. FILTER CIRCUITS59Figure 3.13: Transfer function and phase shift for the above circuit.3.7.2Amplifier with Negative FeedbackFeedback is a widely used technique to improve the characteristics of an imperfect amplifier.A generalized amplifier with negative voltage feedback is shown in figure 3.15.The overall transfer function (closed-loop gain) can be written asH(s)=v3v1.(3.79)Realizing thatv2 = v1− v4;v2 =v3A(s)andv4 = Fv3.(3.80)we may writeH(s)=A1+ AF.(3.81)If|AF|1⇒ H(s)=1/F. The transfer function is now independent of the amplifiergain. F is the transfer function of a stable resistive network which means that H will alsobe stable.