Class17_18_IBIS_io_buffer_class

Class17_18_IBIS_io_buffer_class - I /O Buffe Mode C r ling...

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1 I/O Buffer Modeling Class 2 lectures Prerequisite Reading – Chapter 7 IBIS spec will be used as reference Additional Acknowledgement to Arpad Muranyi, Intel Corporation
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2 Additional Information URLs IBIS home page: http://www.eigroup.org/ibis/ibis.htm IBIS 3.2 spec: http://www.vhdl.org/pub/ibis/ver3.2/ IBIS-X: http://www.eda.org/pub/ibis/futures/ Tools Golden Parser: http://www.eda.org/pub/ibis/ibischk3 Visual IBIS editor, SPICE-to-IBIS tool on IBIS web site. We will use this free tool. http://www.mentor.com/hyperlynx/visibis.cfm
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3 Key Topics What is a model? Importance of accurate models Types of buffer models IBIS and the portions of an IBIS model How model data is generated How to calculate V OL and V OH from a model Package modeling in IBIS IBIS HSPICE example Bergeron diagrams
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4 Theories, Modeling, and Reality “I take the positivist viewpoint that a physical theory is just a mathematical model and that it is meaningless to ask whether it corresponds to reality. All that one can ask is that its predictions should be in agreement with observation. “ 1 1 Steven W. Hawking, September 30 1994, Public Lecture on “Time and Space” Electrical models can be derived in two ways From physical structures and properties From observed behavior It is irrelevant whether the electrical models correspond to physical reality. It only needs to predict behavior. Hence all models are behavioral
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5 What is a Model? Electrical representation of a physical device For example, a transmission line can be modeled as: A package can be modeled as a combination of transmission lines and lumped elements. An input or output buffer can be modeled in various ways as well. ? ?
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6 Importance of Accurate Models T-lines, package, connectors, vias, return paths, etc. can all be modeled to extreme detail, but if the input (stimulus) is not accurate, it’s wasted. Garbage in, garbage out. It is extremely important for engineers to understand the origins of model data, be familiar with modeling types and limitations, and double-check models, whether they create them or they receive them from someone else! Also, know how your tool uses model data!
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7 How do we model I/O buffers? Linear Models Description More detail Behavioral Models Linear or non-linear I-V and V-t data Transistor Circuit / Netlist Simulation Speed All buffer details including driving transistors, pre-driver circuitry, receiver diff. amp, etc. Intellectual Property “Sweep-ability” R S Slowest Fast Fast Very Somewhat limited Very Little Little Lots R High R Low
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8 Basic C-MOS Buffer Model Pad Capacitance Output / Driver Input / Receiver ESD Diodes + Inherent Diodes in Transistors Pull-up Device Pull-down Device
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9 Review Lattice Diagram Analysis V(source) V(load) V launch source ρ load V launch load V launch 0 V launch (1+ load ) V launch (1+ load + load source ) Time 0 2N ps 4N ps V launch load source V launch 2 load source V launch load source V launch (1+ load + load source + load Time N ps 3N ps 5N ps Vs Rs
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Class17_18_IBIS_io_buffer_class - I /O Buffe Mode C r ling...

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