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MIT6_012S09_lec19

# MIT6_012S09_lec19 - Lecture19 Transistor Amplifiers(I...

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• Common-source amplifier with current-source Lecture 19 Transistor Amplifiers (I) Common-Source Amplifier Outline • Amplifier fundamentals • Common-source amplifier Common-source amplifier with current-source supply 6.012 Spring 2009 Lecture 19 1 Reading Assignment: Howe and Sodini; Chapter 8, Sections 8.1-8.4

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Amplifier Fundamentals Source resistance R S is associated only with small signal sources Choose I D = I SUP DC output current – I OUT = 0 – V OUT = 0 Input� sources Intrinsic� Amplifier V + Load 6.012 Spring 2009 Lecture 19 2 + + v s i s R S v IN = V BIAS + v s i IN = I BIAS + i s V BIAS I BIAS R S Voltage Input Current Input Supply� Current � I SUP Active � Device i D = f (input) I SUP R L i OUT = i d i D + V V Input v OUT
2. Common-Source Amplifier: Consider the following circuit: V + = V DD i R R D signal source v s R S signal i D + load R L v OUT V BIAS - V BIAS , R D and W/L of MOSFET selected to bias transistor in saturation and obtain desired output bias point (i.e. V OUT = 0). • Consider intrinsic voltage amplifier - no loading •R S = 0 •R L ---> ∞ • V GS = V BIAS - V SS V - = V SS 6.012 Spring 2009 Lecture 19 3 Watch notation: v OUT (t)=V OUT +v out (t)

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Transfer characteristics of amplifier: Load line view of amplifier: V OUT V OUT 0 I R =I D V SS V DD V DD -V SS R D load line V BIAS - V ss = V DD - V SS V BIAS - V ss V BIAS - V ss = V T Bias point calculation; Limits to signal swing Small-signal gain; Frequency response [in a few days] Want: 0 - V DD -V SS V T V DD V SS V BIAS - V ss 6.012 Spring 2009 Lecture 19 4
W 2 V Bias point: choice of V BIAS , W/L, and R D to keep transistor in saturation and to get proper quiescent V OUT .

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