EE 330 Lect 26 Fall 2011

EE 330 Lect 26 Fall 2011 - EE 330 Lecture 26 Small Signal...

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EE 330 Lecture 26 Small Signal Modeling
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Small-Signal Principle y x y Q x Q x SS y SS Q-point y=f(x)   Q Q SS x=x f y f x x x  Quiescent Output ss Gain How can a circuit be linearized at an operating point as an alternative to linearizing a nonlinear function at an operating point? V Nonlinear One-Port I Consider arbitrary nonlinear one-port network Review from Last Lecture
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Arbitrary Nonlinear One-Port y iV Q V=V defn I y V def SS = i i def SS v V V I Q I Q-point V Q i SS v SS Q SS SS V=V I iv V Linear model of the nonlinear device at the Q-point V Nonlinear One-Port I Review from Last Lecture
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y V i A Small Signal Equivalent Circuit: I V 2-Terminal Nonlinearl Device f(x) Arbitrary Nonlinear One-Port Q V=V I y V y iV The small-signal model of this 2-terminal electrical network is a resistor of value 1/y or a conductor of value y One small-signal parameter characterizes this one-port but it is dependent on Q- point This applies to ANY nonlinear one-port that is differentiable at a Q-point (e.g. a diode) V Nonlinear One-Port I Linear small-signal model: Review from Last Lecture
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Alternative Approach to small-signal analysis of nonlinear networks Must only develop linearized model once for any nonlinear device (steps 1. and 2.) e.g. once for a MOSFET, once for a JFET, and once for a BJT Linearized model for nonlinear device termed “small-signal model” derivation of small-signal model for most nonlinear devices is less complicated than solving even one simple nonlinear circuit Solution of linear network much easier than solution of nonlinear network 1.Linearize nonlinear devices 2. Obtain small-signal model from linearized device models 3. Replace all devices with small-signal equivalent 4 .Solve linear small-signal network Review from Last Lecture
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“Alternative” Approach to small-signal analysis of nonlinear networks Nonlinear Network dc Equivalent Network Q-point Values for small-signal parameters Small-signal (linear) equivalent network Small-signal output Total output (good approximation) Review from Last Lecture
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Linearized Circuit Elements Must obtain the linearized circuit element for ALL linear and nonlinear circuit elements V DC I DC R C Large C Small L Large L Small I AC (Will also give models that are usually used for Q-point calculations : Simplified dc models) Review from Last Lecture
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Small-signal and simplified dc equivalent elements Element ss equivalent Simplified dc equivalent V DC V DC I DC I DC R R R dc Voltage Source dc Current Source Resistor V AC V AC ac Voltage Source ac Current Source I AC I AC Review from Last Lecture
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Small-signal and simplified dc equivalent elements C Large C Small L Large L Small C L Simplified Simplified Capacitors Inductors MOS transistors Diodes Simplified Element ss equivalent Simplified dc equivalent (MOSFET (enhancement or depletion), JFET) Review from Last Lecture
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Element ss equivalent Dependent Sources (Linear) Simplified Simplified Bipolar
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EE 330 Lect 26 Fall 2011 - EE 330 Lecture 26 Small Signal...

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