15 - 1 ECSE334 Introduction to Microelectronics ECSE 334...

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Unformatted text preview: 1 ECSE334 Introduction to Microelectronics ECSE 334 Introduction to Microelectronics Roni Khazaka Lecture #15 ECSE334 Introduction to Microelectronics 2 Khazaka - 2008 Feedback Feedback a very powerful mechanism for precise control. Feedback exists in nature in many physical and biological systems. The theory of negative feedback was developed by electronics engineers 2 ECSE334 Introduction to Microelectronics 3 Khazaka - 2008 Advantages of Feedback in Amplifiers Desensitize the Gain to variations in circuit components. Reduce nonlinear distortion. Reduce the effect of noise. Control the input and output impedances. Extend the bandwidth of the amplifier Tradeoff: Reduction in Gain ECSE334 Introduction to Microelectronics 4 Khazaka - 2008 Signal Flow Diagram + Source Load A s x o x o x 2 x s o Ax x = 1 x 2 1 x x x o = Each variable is either a voltage or a current. No loading effect. 3 ECSE334 Introduction to Microelectronics 5 Khazaka - 2008 Negative Feedback System + Source Load A s x i x o x f x Output is fed back into the input with a feedback factor of . The feedback is subtracted from the input signal negative feedback. Negative Feedback ECSE334 Introduction to Microelectronics 6 Khazaka - 2008 Negative Feedback System + Source Load A s x i x o x f x i o Ax x = o f x x = f s i x x x = ( ) ( ) o s f s o x x A x x A x = = s o o Ax x A x = + s o x A A x + = 1 4 ECSE334 Introduction to Microelectronics 7 Khazaka - 2008 Negative Feedback System + Source Load A s x i x o x f x A A x x A s o f + = 1 ( ) A + 1 Amount of feedback A Loop Gain / Open Loop Gain (should be positive) Closed loop gain ECSE334 Introduction to Microelectronics 8 Khazaka - 2008 Negative Feedback System + Source Load A s x i x o x f x A A x x A s o f + = 1 1 >> A The gain is determined by the feed back network only! (as long as A is large) 1 = f A 5 ECSE334 Introduction to Microelectronics 9 Khazaka - 2008 Negative Feedback System + Source Load A s x i x o x f x s o x A A x + = 1 s s o f x x A A x x + = = 1 Tracking behaviour. x i often referred to as error signal x e ....
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15 - 1 ECSE334 Introduction to Microelectronics ECSE 334...

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