EE 330 Lect 27 Spring 2011

EE 330 Lect 27 Spring 2011 - EE 330 Lecture 27 Small-Signal...

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EE 330 Lecture 27 Small-Signal Models of n-terminal devices Small-signal models of MOSFET and BJT
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Small-Signal Principle y x Q-point X Q Y Q Region around Q-Point y=f(x) Review from Last Lecture
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Small-Signal Principle 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 Model of the nonlinear device at the Q-point Review from Last Lecture
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y V i A Small Signal Equivalent Circuit I V 2-Terminal Nonlinearl Device f(x) Small-Signal Principle 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 One small-signal parameter characterizes this one-port but it is dependent on Q-point Review from Last Lecture
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Solution for the example was based upon solving the nonlinear circuit for V OUT and then linear zing the solution by doing a Taylor’s series expansion Solution of nonlinear equations very involved with two or more nonlinear devices Taylor’s series linearization can get very tedious if multiple nonlinear devices are present Standard Approach to small-signal analysis of nonlinear networks 1. Solve nonlinear network 2. Linearize solution 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 Alternative Approach to small-signal analysis of nonlinear networks Review from Last Lecture
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Standard Approach to small-signal analysis of nonlinear networks Nonlinear Network dc Equivalent Network Q-point Values for small-signal parameters Small-signal equivalent network Small-signal output Total output (good approximation) Review from Last Lecture
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Nonlinear Device Linearized Small-signal Device Linearized nonlinear devices Review from Last Lecture
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Dc and small-signal equivalent elements Element ss equivalent dc equivalnet 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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Dc and small-signal equivalent elements C Large C Small L Large L Small C L Simplified Simplified Capacitors Inductors MOS transistors Diodes Simplified Element ss equivalent dc equivalnet Review from Last Lecture
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Dc and small-signal equivalent elements Element ss equivalent dc equivalnet Dependent Sources Simplified Simplified Bipolar Transistors Review from Last Lecture
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How is the small-signal equivalent circuit obtained from the nonlinear circuit? What is the small-signal equivalent of the MOSFET, BJT, and diode ? Review from Last Lecture
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y V i A Small Signal Equivalent Circuit I V 2-Terminal Nonlinearl Device f(x) Small-Signal Diode Model Q V=V I y V y iV -1 D d D Q I R V    Thus, for the diode
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Small-Signal Diode Model -1 D d D Q I R V    For the diode D t V V DS I =I e D t V V DQ D S tt Q I I 1 = I e VV t Q V    t d DQ V R= I
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EE 330 Lect 27 Spring 2011 - EE 330 Lecture 27 Small-Signal...

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