chap3and6part1 - AdvanceddifferentialamplifiersandCurrent

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Adaptive Integrated Microsystems Advanced differential amplifiers and Current  Mirrors (Chapter 3: section 3.7 and Chapter 6:  section 6.1) 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 Symmetry in differential pair If Q1 and Q2 are matched (equal small signal parameters) the differential amplifier can be split along the point of symmetry (Very important !!!!!). Circuits are equivalent ONLY for small signal modeling
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Adaptive Integrated Microsystems Symmetry in differential pair ) ( - + - + - = - in in d m out out V V g g V V ) ( ) ( - + - + - + - - - = - out out d in in m out out V V g V V g I I d m in in out out g g V V V V = - - - + - +
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Adaptive Integrated Microsystems MOS Loads A v = - g mN ( g mP - 1 || r oN r oP ) ≈ - g mN g mP A v = - g mN ( r r )
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Adaptive Integrated Microsystems MOS Loads (cont.) A v g m 1 [( g m 3 r o 3 r o 1 ) || ( g m 5 r o 5 r o 7 )]
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Adaptive Integrated Microsystems MOS Loads (cont.)
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Adaptive Integrated Microsystems Active Current Mirror
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Adaptive Integrated Microsystems Conceptual operation The gate of Q2 increases 1 Q 2 Q - in V + in V b I 2 s V dd V dd V 3 Q 4 Q out V Two things can happen: either Vs can change or V1 can change. 1 V But at the same time gate of Q1 decreases. Since Q2 and Q1 are matched, Vs will not change (approximation). Therefore Vs can be replaced by a constant potential for differential operation
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Adaptive Integrated Microsystems Conceptual operation The gate of Q2 increases 1 V Because Q3 and Q4 are mirrors, the current through Q4 will increase.
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chap3and6part1 - AdvanceddifferentialamplifiersandCurrent

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