6 002 CIRCUITS AND ELECTRONICS MOSFET Amplifier Large Signal Analysis 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 9 Review Amp constructed using dependent source control a a port DS b output b port Dependent source in a circuit a b v i f v a b Superposition with dependent sources one way tleave all dependent sources in solve for one independent source at a time section 3 5 1 of the text Next quick review of amp Reading Chapter 7 3 7 7 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 9 Amp review VS RL vO VCCS vI K 2 iD vI 1 2 for vI 1V 0 otherwise vO VS iD RL K vI 1 2 2 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 9 Key device Needed v A B i f v voltage controlled current source C Let s look at our old friend the MOSFET 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 9 Key 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 D G vGS VT D S S G vGS VT 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 9 Graphically Demo iDS vGS iDS egio n iDS vGS VT vGS VT vGS VT vDS S MODEL vDS vGS VT vGS 1 Saturation region vGS 2 vGS3 vGS VT Trio de r iDS v DS vDS SR MODEL vGS VT Cutoff vDS region 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 9 Graphically iDS vGS iDS iDS egio n S MODEL vGS 2 vGS3 vGS VT Saturation region Trio de r vGS VT vDS vDS vGS VT vGS 1 iDS vGS VT vGS VT v DS vDS SR MODEL vGS VT vDS when vDS vGS VT Notice that MOSFET behaves like a current source 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 9 MOSFET SCS Model When vDS vGS VT the MOSFET is in its saturation region and the switch current source SCS model of the MOSFET is more accurate than the S or SR model D G vGS VT S D D G S vGS G VT iDS f vGS K 2 vGS VT 2 S when vDS vGS VT 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 9 Reconciling the models iDS iDS vGS VT vGS VT vDS S MODEL for fun vGS VT Saturation region vGS 2 vGS3 vGS VT Trio de r egio n iDS vDS vGS VT vGS 1 vDS SR MODEL for digital designs vGS VT vDS SCS MODEL for analog designs When to use each model in 6 002 Note alternatively in more advanced courses vDS vGS VT vDS vGS VT use SCS model use SR model or use SU Model Section 7 8 of A L 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 9 Back to Amplifier VS vI AMP vO VS RL vI G D S vO K 2 iDS vI VT 2 in saturation region 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 9 MOSFET Amplifier VS RL vI G D S vO K 2 iDS vI VT 2 in saturation region 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 VT and vDS vGS VT vO vI vT at all times 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 9 Let s analyze the circuit First replace the MOSFET with its SCS model VS RL vO G vGS vI vI D iDS S K 2 vI VT 2 A for vO vI VT 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 9 Let s analyze the circuit VS RL vO G vGS vI vI D iDS K vI VT 2 2 A for vO vI VT S vO vDS in our example 1 Analytical method vO vs vI vO VS iDS RL B K 2 or vO VS vI VT RL for vI VT 2 vO vI VT vO VS vI VT MOSFET turns off for 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 9 Graphical method vO vs vI K 2 From A iDS vI VT 2 vO vI VT 2 for 2iDS vO K iDS B iDS K 2 vO 2 VS v0 RL RL 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 9 2 Graphical method vO vs vI K 2 K 2 A …
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