lec21 - 6.012 - Microelectronic Devices and Circuits - Fall...

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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 21-1 Lecture 21 - Multistage Amplifiers (I) Multistage Amplifiers November 22, 2005 Contents : 1. Introduction 2. CMOS multistage voltage amplifier 3. BiCMOS multistage voltage amplifier 4. BiCMOS current buffer 5. Coupling amplifier stages Reading assignment: Howe and Sodini, Ch. 9, §§ 9.1-9.3
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 21-2 Key questions How can one build a wide range of high-performance amplifiers using the single-transistor stages studied so far? What are the most important considerations when assembling mulstistage amplifiers: regarding interstage loading? regarding interstage biasing?
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 21-3 1. Introduction Amplifier requirements are often demanding: must adapt to specific kinds of signal source and load, must deliver sufficient gain Single-transistor amplifier stages are very limited in what they can accomplish multistage amplifier . V DD v s V S R S V SS signal source v OUT R L + - signal load Issues: What amplifying stages should be used and in what order? What devices should be used, BJT or MOSFET? How is biasing to be done?
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 21-4 2 Summary of single stage characteristics: stage A vo ,G mo ,A io CS G mo = g m CD A ± g m g m + g mb CG A io ±− 1 R in 1 g m + g mb R out key function r o //r oc transcond. amp. 1 voltage buffer g m + g mb r oc // [ r o (1 + g m R S )] current buffer CE G mo ± g m r π CC A ± 1 r π + β ( r o //r oc //R L ) CB A io 1 1 g m r o //r oc transcond. amp. 1 + R S voltage buffer g m β r oc // { r o [1 + g m ( r π //R S )] } current buffer 2 Key differences between BJT’s and MOSFETs: BJT MOSFET I B = I C β ² I G =0 g m = qI C kT >g m = 2 W L µC ox I D r o = V A I C >r o = 1 λI D
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 21-5 2. CMOS multistage voltage amplifier 2 Goals: high voltage gain high R in low R out 2 Good starting point: CS stage + - + - v in v s R S + - v out -g m (r o //r oc )v in r o //r oc + - R L R in = A vo = g m ( r o //r oc ), probably insufficient R out = r o //r oc , too high
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 21-6 2 Add second CS stage to get more gain: + - + - v in1 v s R S + - v out1 =v in2 -g m1 (r o1 //r oc1 )v in1 r o1 //r oc1 + - + - + - v
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This note was uploaded on 07/20/2009 for the course ELECTRICAL 6.012 taught by Professor Prof.jesúsdelalamo during the Fall '05 term at MIT.

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lec21 - 6.012 - Microelectronic Devices and Circuits - Fall...

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