Lect2UP130_(100325) - Lecture130 Computer Models and...

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Lecture130 – Computer Models and Extraction of Simple Large Signal Model (3/25/10) Page 130-1 CMOS Analog Circuit Design © P.E. Allen - 2010 LECTURE 130 – COMPUTER MODELS AND EXTRACTION OF THE SIMPLE LARGE SIGNAL MODEL LECTURE ORGANIZATION Outline • Computer Models • Extraction of a large signal model for hand calculations • Extraction of the simple model for short channel MOSFETs • Summary CMOS Analog Circuit Design, 2 nd Edition Reference Pages 92-97 and 744-753 Lecture130 – Computer Models and Extraction of Simple Large Signal Model (3/25/10) Page 130-2 CMOS Analog Circuit Design © P.E. Allen - 2010 COMPUTER MODELS FET Model Generations • First Generation – Physically based analytical model including all geometry dependence. • Second Generation – Model equations became subject to mathematical conditioning for circuit simulation. Use of empirical relationships and parameter extraction. • Third Generation – A return to simpler model structure with reduced number of parameters which are physically based rather than empirical. Uses better methods of mathematical conditioning for simulation including more specialized smoothing functions. Performance Comparison of Models (from Cheng and Hu, MOSFET Modeling & BSIM3 Users Guide ) Model Minimum L ( μ m) Minimum Tox (nm) Model Continuity i D Accuracy in Strong Inversion i D Accuracy in Subthreshold Small signal parameter Scalability MOS1 5 50 Poor Poor Not Modeled Poor Poor MOS2 2 25 Poor Poor Poor Poor Fair MOS3 1 20 Poor Fair Poor Poor Poor BSIM1 0.8 15 Fair Good Fair Poor Fair BSIM2 0.35 7.5 Fair Good Good Fair Fair BSIM3v2 0.25 5 Fair Good Good Good Good BSIM3v3 0.15 4 Good Good Good Good Good
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Lecture130 – Computer Models and Extraction of Simple Large Signal Model (3/25/10) Page 130-3 CMOS Analog Circuit Design © P.E. Allen - 2010 First Generation Models Level 1 (MOS1) • Basic square law model based on the gradual channel approximation and the square law for saturated drain current. • Good for hand analysis. • Needs improvement for deep-submicron technology (must incorporate the square law to linear shift) Level 2 (MOS2) • First attempt to include small geometry effects • Inclusion of the channel-bulk depletion charge results in the familiar 3/2 power terms • Introduced a simple subthreshold model which was not continuous with the strong inversion model. • Model became quite complicated and probably is best known as a “developing ground” for better modeling techniques. Level 3 (MOS3) • Used to overcome the limitations of Level 2. Made use of a semi-empirical approach. • Added DIBL and the reduction of mobility by the lateral field. • Similar to Level 2 but considerably more efficient. • Used binning but was poorly implemented. Lecture130 – Computer Models and Extraction of Simple Large Signal Model (3/25/10) Page 130-4 CMOS Analog Circuit Design © P.E. Allen - 2010 Second Generation Models BSIM (Berkeley Short-Channel IGFET Model) • Emphasis is on mathematical conditioning for circuit simulation
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Lect2UP130_(100325) - Lecture130 Computer Models and...

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