Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 96.002CIRCUITS ANDELECTRONICSMOSFET AmplifierLarge Signal AnalysisCite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 9 Amp constructed using dependent source Superposition with dependent sources:one way tleave all dependent sources in;solve for one independentsource at atime [section 3.5.1 of the text] Next, quick review of amp …Reading: Chapter 7.3–7.7+–+–a′avb′b)(vfi=a′ab′bcontrolportDSoutputportDependent source in a circuitReviewCite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 9Amp reviewLDSORiVv−=()2I1v2K−for vI≥ 1V= 0 otherwiseSVOvLR+–()2ID1v2Ki −=IvVCCSCite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 9Key device Needed:Let’s look at our old friend, the MOSFET …ABvC()vfi=voltage controlledcurrent sourceCite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 9Key device Needed:Our old friend, the MOSFET …First, we sort of lied. The on-state behavior of the MOSFET is quite a bit more complex than either the ideal switch or the resistor model would have you believe.DSGDSTGSVv<GTGSVv ≥?Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 9GraphicallyDSvDSiTGSVv ≥TGSVv <TGSVv ≥1GSvSaturationregionTriode regionS MODELDSvDSiSR MODELDSvDSiDemoTGSVv<TGSVv<2GSv3GSv+–DSv+–DSiGSv...TGSDSVvv−=CutoffregionCite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 9GraphicallyDSvDSiTGSVv ≥TGSVv <TGSVv ≥1GSvSaturationregionTriode regionS MODELDSvDSiSR MODELDSvDSiTGSVv<TGSVv<2GSv3GSv+–DSv+–DSiGSv...TGSDSVvv−=Notice thatMOSFET behaves like a current sourcewhenTGSDSVvv −≥Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 9MOSFET SCS ModelDSGDSTGSVv<G()22TGSVvK−=whenTGSDSVvv−≥()GSDSvfi=TGSVv ≥DSGWhenthe MOSFET is in its saturation region, and the switch current source (SCS) model of the MOSFET is more accurate than the S or SR modelTGSDSVvv−≥Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 9Reconciling the models…TGSDSVvv −≥TGSDSVvv −<use SCS modeluse SR modelNote: alternatively (in more advanced courses)or, use SU Model (Section 7.8 of A&L)S MODELSR MODELSCS MODELfor fun!for digitaldesignsfor analogdesignsWhen to use each model in 6.002?DSvDSiTGSVv ≥TGSVv <TGSVv ≥1GSvSaturationregionTriode regionDSvDSiDSvDSiTGSVv<TGSVv<2GSv3GSv...TGSDSVvv−=Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 9Back to Amplifierin saturationregionIvOvAMPSVSVLRIvOvGDS()22TIDSVvKi −=To ensure the MOSFET operates as a VCCS, we must operate it in its saturation region only. To do so, we promise to adhere to the“saturation discipline”Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 9MOSFET Amplifierin saturationregionSVLRIvOvGDS()22TIDSVvKi −=To ensure the MOSFET operates as a VCCS, we must operate it in its saturation region only. We promise to adhere to the“saturation discipline.”In other words, we will operate the amp circuit such that vGS≥ VTand vDS≥ vGS– VTat all times.vO≥ vI– vTCite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 9Let’s analyze the circuitFirst, replace the MOSFET with itsSCS model.forTIOVvv−≥IGSvv =GIv+–+–SVOvLRDSA()22TIDSVvKi −=Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 9Let’s analyze the circuitforTIOVvv−≥IGSvv =GIv+–+–SVOvLRDSA()22TIDSVvKi −=or()LTISORVvKVv22−−=forTIVv ≥TIOVvv−≥SOVv =forTIVv <(MOSFET turns off)LDSSORiVv −=B1Analytical method:IOvvsv(vO= vDSDSin our examplein our example))Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].6.002 Fall 2000 Lecture 92Graphical method:BFromA(),22TIDSVvKi −=:2ODSDSOTIOv2KiKi2vVvv≤⇓≥⇓−≥IOvvsvforL0LSDSRvRVi−=Cite as: Anant Agarwal and Jeffrey Lang, course materials for 6.002 Circuits and Electronics, Spring 2007. MIT
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