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EE 435 Lect 15 Spring 2010

# EE 435 Lect 15 Spring 2010 - EE 435 Lecture 15 Compensation...

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EE 435 Lecture 15 Compensation

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Review of Basic Concepts Consider a second-order factor of a denominator polynomial, P(s), P(s)=s 2 +a 1 s+a 0 Then P(s) can be expressed in several alternative but equivalent ways ( )( ) ( )( ) j β α s j β α s poles, conjugate complex if and p s p s ω s2 ξ 2 s ω Q ω s s 2 1 2 0 2 2 0 0 2 + + + + + + + 0 These are all 2-paramater characterizations of the second-order factor and it is easy to map from any one characterization to any other Review from last lecture
Review of Basic Concepts 2 0 0 2 ω Q ω s s + + o ω θ 1 sin θ 2Q = ω o = magnitude of pole Q determines the angle of the pole Review from last lecture

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Feedback applications of the two- stage Op Amp D(s) N(s) A(s) = β (s) A(s) 1 1 β (s) 1 β (s) A(s) 1 A(s) (s) A FB + = + = N(s) (s) N FB = β (s)N(s) D(s) (s) D FB + = Open-loop Gain Alternate Feedback Gain Often β (s) and β 1 (s) are not dependent upon frequency and in this case Standard Feedback Gain β (s) N(s) D(s) N(s) (s) β β (s) β (s) A(s) 1 1 (s) β 1 (s) A 1 1 FB + = + = In either case, denominators are the same and characteristic equation defined by Review from last lecture
Basic Two-Stage Op Amp 04 o2 od o6 o5 oo g g g and g g g + = + = m1 md g g = md mo md mo C L g g g g C C Q β β = ( ) 2 md mo md mo 2 L C β g g g g Q β C C = Right Half-Plane Zero Limits Performance where It can be shown that m5 mo g g = ( ) ( ) mo md md mo C L C 2 c m0 md FB g g β g β g sC C C s sC g g (s) A + + But what pole Q is desired? Review from last lecture

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Compensation What is “compensation” or “frequency compensation” and what is the goal of compensation? Nobody defines it or defines it correctly but everybody tries to do it ! Review from last lecture
Compensation Compensation (alt Frequency Compensation) is the manipulation of the poles and/or zeros of the open-loop amplifier so that the closed-loop amplifier will perform acceptably Note this definition does not mention stability, positive feedback, negative feedback, phase margin, or oscillation. Note that acceptable performance is strictly determined by the user in the context of the specific application Review from last lecture

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Compensation Compensation is the manipulation of the poles and/or zeros
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