chap3part1 - Basiccurrentmirrorsandsinglestage

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Adaptive Integrated Microsystems Basic current mirrors and single stage  amplifiers (Chapter 3: Section 3.1-3.8) ECE 412 Introduction to mixed-signal circuits (Fall 2007) Class website: http://www.egr.msu.edu/classes/ece412/shantanu
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Adaptive Integrated Microsystems Large signal model ) 1 ( ) ( 2 2 DS TH GS ox n D V V V L W C I λ μ + - = I D = μ n C ox GS - V TH ) V DS - 1 2 V DS 2 ] th D G V V V < - th GS V V For Saturation: Triode region Saturation region Transistor conducts currently only when Important ! Not completely correct
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Adaptive Integrated Microsystems Small Signal Model 1 eff V 2 eff V th gd V V ds th gs V V V - eff V Condition for saturation Typical value of V V eff 4 . 0 Minimum drain to source voltage to maintain a transistor in saturation.
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Adaptive Integrated Microsystems Bias point V V g g th d m 7 . 0 10 10 1 8 1 6 = = = - - - - Bias Point Linear operation Bias point for a transistor is determined by its drain current and gate-to-source voltage o I TH GS o m V V I g - = 2 o TH GS ox n DS D D DS ds I V V L W C V I I V r λ μ 1 ) ( 2 1 / 1 2 = - = = = o d I g =
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Adaptive Integrated Microsystems Important concepts G D S Id D S G Id What happens when Vs is increased ? gs m ds V g I = ds r ds d ds V V g I ds = = 1 gs m ds V g I - = ds d ds V g I - = What happens when Vs is increased ? NMOS Transistor PMOS Transistor d m g g
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Adaptive Integrated Microsystems Small Signal Model
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Adaptive Integrated Microsystems Input and output impedance Lower the input impedance higher current the circuit will draw. Higher the output impedance implies the output current remains insensitive to changes in output voltage. in V out V in I out I t cons out V in in in I V Z tan = = t cons in V out out out I V Z tan = =
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Adaptive Integrated Microsystems Current sources and sinks Ideal current sources and sinks have infinite output/input impedance. Only in saturation/active region, nmos and pmos transistors act as a reasonable current sink or source. dp ds out g r Z / 1 = = b I dn ds in g r Z / 1 = = Is determined by the gate-to-source voltage Vb, which is constant.
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Adaptive Integrated Microsystems Current sources and sinks b I Is determined by the gate-to-source voltage Vb, which is constant. Current can be varied by changing the gate-to-source voltage. Transistors are in saturation, therefore there is a saturation voltage drop across drain to source terminal (Important !!!) eff V eff V
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Adaptive Integrated Microsystems How to improve the current source ?
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This note was uploaded on 03/01/2010 for the course ECE 412 taught by Professor - during the Fall '08 term at Michigan State University.

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chap3part1 - Basiccurrentmirrorsandsinglestage

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