115A_1_EE115A_W10-Chap7

115A_1_EE115A_W10-Ch - Chapter 7 CMOS Amplifiers h 7.1 General Considerations h 7.2 Common-Source Stage 312 h 7.3 Common-Gate Stage h 7.4 Source

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Unformatted text preview: Chapter 7 CMOS Amplifiers h 7.1 General Considerations h 7.2 Common-Source Stage 312 h 7.3 Common-Gate Stage h 7.4 Source Follower h 7.5 Summary and Additional Examples Chapter Outline CH7 CMOS Amplifiers 313 MOS Biasing ( ) TH DD TH GS V R R V R V V V V V 2 2 1 2 1 2 1 1 - + + +-- = CH7 CMOS Amplifiers 314 h Voltage at X is determined by V DD , R 1 , and R 2 . h V GS can be found using the equation above, and I D can be found by using the NMOS current equation. S ox n R L W C V μ 1 1 = Self-Biased MOS Stage DD D S GS D D V I R V R I = + + CH7 CMOS Amplifiers 315 h The circuit above is analyzed by noting M1 is in saturation and no potential drop appears across R G . Current Sources CH7 CMOS Amplifiers 316 h When in saturation region, a MOSFET behaves as a current source. h NMOS draws current from a point to ground (sinks current), whereas PMOS draws current from V DD to a point (sources current). Common-Source Stage CH7 CMOS Amplifiers 317 D D ox n v D m v R I L W C A R g A μ λ 2- =- = = Operation in Saturation ( ) TH GS DD D D V V V I R-- < CH7 CMOS Amplifiers 318 h In order to maintain operation in saturation, V out cannot fall below V in by more than one threshold voltage. h The condition above ensures operation in saturation. CS Stage with λ =0 319 L out in L m v R R R R g A = ∞ =- = CS Stage with λ ≠ CH7 CMOS Amplifiers 320 h However, Early effect and channel length modulation affect CE and CS stages in a similar manner. ( ) O L out in O L m v r R R R r R g A || || = ∞ =- = CS Gain Variation with Channel Length CH7 CMOS Amplifiers 321 h Since λ is inversely proportional to L, the voltage gain actually becomes proportional to the square root of L....
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This note was uploaded on 01/08/2011 for the course EE 115 taught by Professor Kaiser during the Spring '09 term at UCLA.

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115A_1_EE115A_W10-Ch - Chapter 7 CMOS Amplifiers h 7.1 General Considerations h 7.2 Common-Source Stage 312 h 7.3 Common-Gate Stage h 7.4 Source

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