EE 330 Lect 24 Fall 2011

EE 330 Lect 24 Fall 2011 - EE 330 Lecture 24 Amplification...

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EE 330 Lecture 24 Amplification with Transistor Circuits Small Signal Modelling
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Amplification with Transistors Generally, an amplifier or simply amp , is any device that changes, usually increases, the amplitude of a signal . The "signal" is usually voltage or current. From Wikipedia: •It is difficult to increase the voltage or current very much with passive RC circuits •Voltage and current levels can be increased a lot with transformers but not practical in integrated circuits •Power levels can not be increased with passive elements (R, L, C, and Transformers) Often an amplifier is defined to be a circuit that can increase power levels Transistors can be used to increase not only signal levels but power levels to a load In transistor circuits, power that is delivered in the signal path is supplied by a biasing network Review from Last Lecture
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Consider the following MOSFET and BJT Circuits R Q 1 V IN (t) V OUT V CC V EE BJT MOSFET R 1 V IN (t) V OUT V DD V SS M 1 Assume BJT operating in FA region, MOSFET operating in Saturation Assume same quiescent output voltage and same resistor R 1 One of the most widely used amplifier architectures Review from Last Lecture
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Consider the following MOSFET and BJT Circuits R 1 Q 1 V IN (t) V OUT V CC V EE BJT MOSFET R 1 V IN (t) V OUT V DD V SS M 1 MOS and BJT Architectures often Identical Circuit are Highly Nonlinear Nonlinear Analysis Methods Must be used to analyze these and almost any other nonlinear circuit
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Methods of Analysis of Nonlinear Circuits KCL and KVL apply to both linear and nonlinear circuits Superposition, voltage divider and current divider equations, Thevenin and Norton equivalence apply only to linear circuits! Some other analysis techniques that have been developed may apply only to linear circuits as well Review from Last Lecture
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Methods of Analysis of Nonlinear Circuits Will consider three different analysis requirements and techniques for some particularly common classes of nonlinear circuits 1. Circuits with continuously differential devices Interested in obtaining transfer characteristics of these circuits or outputs for given input signals 2. Circuits with piecewise continuous devices Interested in obtaining transfer characteristics of these circuits or outputs for a given input signals 3. Circuits with small-signal inputs that vary around some operating point Interested in obtaining relationship between small-signal inputs and the corresponding small-signal outputs. Will assume these circuits operate linearly in some suitably small region around the operating point Other types of nonlinearities may exist and other types of analysis may be required but we will not attempt to categorize these scenarios in this course Review from Last Lecture
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1. Nonlinear circuits with continuously differential devices Use KVL and KCL for analysis Represent nonlinear models for devices either mathematically or graphically Solve the resultant set of equations for the variables of interest Analysis Strategy:
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EE 330 Lect 24 Fall 2011 - EE 330 Lecture 24 Amplification...

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