lec20 - 6.012 Microelectronic Devices and Circuits Fall...

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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 20­1 Lecture 20 ­ Transistor Amplifers (II) Other Amplifier Stages November 17, 2005 Contents : 1. Common­source amplifer ( cont. ) 2. Common­drain amplifer 3. Common­gate amplifer Reading assignment: Howe and Sodini, Ch. 8, §§ 8.7­8.9
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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 20­2 Key questions What other amplifer stages can one build with a sin­ gle MOSFET and a current source? What is the uniqueness these other stages?
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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 20­3 1. Common­source amplifer with current­source supply V DD v s V GG v OUT i SUP i D R S R L signal source + - signal load V SS Loadline view: load line i SUP =I D V GG -V SS =V DD -V SS I SUP V GG -V SS V GG -V SS =V T 0 V SS V DD V OUT
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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 20­4 Current source characterized by high output resistance: r oc . Then, unloaded voltage gain of common­source stage: A vo | = g m ( r o //r oc ) | signiFcantly higher than ampliFer with resistive supply. Can implement current source supply by means of channel MOS±ET: V DD V B v s V GG v OUT i D i SUP R S signal source + - V SS
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± ± 6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 20­5 Relationship between circuit fgures oF merit and device parameters Remember: ± W g m = ± ² 2 µ n C ox I D L 1 L r o λ n I D I D Then: Circuit Parameters Device | A vo | R in Parameters g m ( r o //r oc ) I SU P ­ W ­± µ n C ox ­ ↑± L ­ R out r o //r oc ↓± ­± ­± ↑± adjustments are made to V GG so none oF the other parameters change CS amp with current supply source is good voltage am­ plifer ( R in high and | A v | high), but R out high too voltage gain degraded iF R L ² r o //r oc .
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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 20­6 Common­source amplifer is acceptable voltage amplifer (want high R in , high A vo ,low R out ): v s v in + + R out R S A vo v in R in R L v out + + ... but excellent transconductance amplifer (want
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lec20 - 6.012 Microelectronic Devices and Circuits Fall...

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