Modeling Methods Fundamentals, and Why What You Learned in School About Transistor Capacitances is Wrong!
| Presenter: |
Colin McAndrew |
NXP Semiconductors |
| Start: |
16:00 (60 minutes) |
Abstract
This tutorial will address two aspects of modeling: fundamentals of how to develop good models; and why the small-signal model for transistors (MOS and BJT) presented in every design textbook, and taught in all EE design classes, is wrong. We will start by reviewing how SPICE works, then show how this defines the best way to formulate models and how to get SPICE to solve equations, both algebraic and differential, for you “inside” your model. Fundamental model requirements, and benchmarks to verify if your model meets these requirements, will be reviewed. The four basic formulation approaches for MOS transistor models will be detailed. Do you know what the difference is between Cdg and Cgd? Which is more important in analog design? Are they Miller-multiplied, like we were taught as undergraduates, or not? Why are Csd and Cds negative? Did you know that even the gm and go in text-book representations of the hybrid-p model are wrong? This tutorial will answer those questions and will also present a new small-signal representation, not (yet) in text books, that gives the most intuitive and useful of the 11,440 possible small-signal model topologies for 4-terminal devices.
Biography
This tutorial will address two aspects of modeling: fundamentals of how to develop good models; and why the small-signal model for transistors (MOS and BJT) presented in every design textbook, and taught in all EE design classes, is wrong. We will start by reviewing how SPICE works, then show how this defines the best way to formulate models and how to get SPICE to solve equations, both algebraic and differential, for you “inside” your model. Fundamental model requirements, and benchmarks to verify if your model meets these requirements, will be reviewed. The four basic formulation approaches for MOS transistor models will be detailed. Do you know what the difference is between Cdg and Cgd? Which is more important in analog design? Are they Miller-multiplied, like we were taught as undergraduates, or not? Why are Csd and Cds negative? Did you know that even the gm and go in text-book representations of the hybrid-p model are wrong? This tutorial will answer those questions and will also present a new small-signal representation, not (yet) in text books, that gives the most intuitive and useful of the 11,440 possible small-signal model topologies for 4-terminal devices.
