Data processing: structural design – modeling – simulation – and em – Simulating electronic device or electrical system – Circuit simulation
Reexamination Certificate
1999-05-04
2001-05-22
Teska, Kevin J. (Department: 2123)
Data processing: structural design, modeling, simulation, and em
Simulating electronic device or electrical system
Circuit simulation
C703S004000, C703S002000
Reexamination Certificate
active
06236956
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of computer simulation of analog and mixed-signal circuits and systems. (Modeling of components, circuits or systems generally described in terms of purely discrete time and discrete value systems, commonly known as digital systems, is outside the scope of the present invention.)
Simulation methods and apparatus are useful in increasing design productivity in a wide variety of applications because design defects can be detected prior to construction of the actual apparatus being simulated. Simulation of digital systems has progressed rapidly over the last decade. This growth has been spurred by the development of standard languages such as VHDL and Verilog for modeling digital devices at both the structural and behavioral levels. The former has gained the widest acceptance in large part due to the U.S. Defense Department's mandate that new designs be presented in VHDL form in order that the design be technologically independent. This standardization has allowed companies to invest large resources in the development of models. These models can then be reused and/or sold to allow for rapid prototyping and simulation of new designs, further increasing productivity and efficiency. The same cannot be said in the analog and particularly the mixed-signal arena.
Despite recent progress towards a standard analog hardware description language to facilitate model development, the relative paucity of analog and mixed signal models is still a major barrier to potential increases in design productivity. However, simply increasing the size of model libraries is of limited usefulness, as specific models typically lack portability and reusability. Moreover, since the effective robustness of circuit and system level simulation is determined to a large degree by the model-simulator interaction, simulation tools and modeling tools must be considered together to enable substantial improvements.
The lack of a sufficient quantity and quality of affordable models to adequately represent analog and mixed-signal systems that need to be simulated can be addressed by reducing the expertise required to create robust software components (i.e., models). Presently, model development is done manually and requires significant modeling and computer language expertise. Simulation problems presently are resolved by trial and error adjustment of simulator control settings to find a combination that works for each analysis applied to a design. Moreover, the introduction of a standard description language such as IEEE standard 1076.1 analog extension to VHDL (“VHDL-A”) will merely exacerbate these problems if no modeling tools are available and no improvements are made to the simulator. Users will be faced with issues of porting existing models from proprietary languages to VHDL-A. Also, the proposed VHDL-A standard only standardizes the description of a model, not the algorithms and methods used to perform simulation.
In the area of model robustness, intuitive tools are needed to perform model diagnostics that will help the modeler visualize both model characteristics and its interaction with the simulator. Moreover, improvement is needed in tools for configuring model-specific simulation controls. This is presently done on an ad hoc basis where availability of an experienced expert is often a prerequisite to timely success. What is needed is methodology to automate configuration of simulation controls.
When a design calls for a model that is either unavailable or inadequate, it is useful for designers who are typically model users to have modeling tools that are simple enough to create or adjust models to meet an immediate need. It is also useful for model suppliers to have adequate modeling tools to create or repair models more efficiently. Presently, the lack of adequate modeling tools makes this a labor intensive process because focus must be placed on implementation details rather than model requirements. As a result, the modeling test takes too long and the quality of the completed model is sacrificed.
The earliest model creations paradigm was strictly text based, requiring the user to specify topologies and mathematical relationships in a strictly defined syntax, for example in early versions of SPICE. Recently, others have suggested removing the language or programming barrier by developing an environment that is a purely graphical model description for analog and mixed signal models. Even this approach fails to provide the flexibility and ease-of-use necessary for efficient model creation.
In the area of simulation robustness, the need remains to provide tools that allow a non-expert user to improve simulation performance and identify and resolve simulation problems. New tools that assist in locating and analyzing the cause of simulation failures will lead to improved efficiency in the overall design process.
SUMMARY OF THE INVENTION
Present analog and mixed-signal development systems are inadequate in three, related areas: model creation, model robustness and simulation robustness.
One of the present difficulties in model creation is that it requires experience and proficiency in the underlying description language. Model creation can be facilitated by providing model creation tools that are easier to use. One object of the present invention is to streamline the process of developing analog and mixed signal models.
Another object of the invention is to create a model development environment that better supports model portability and reusability.
A further object is to reduce the user expertise required to create robust simulation models.
Yet another object is to provide intuitive tools for performing model diagnostics that will help the modeler visualize both model characteristics and its interaction with the simulator.
A further object is to improve simulation robustness, by providing tools that allow a non-expert user to improve simulation performance, identify and resolve simulation problems. New tools that assist in locating and analyzing the cause of simulation failures will lead to improved efficiency in the overall design process. In describing the invention, we will use the terms defined in the following Glossary. These brief definitions are solely for the convenience of the reader, and are subject to the more complete discussion that follows.
GLOSSARY
Analog
An analog component, circuit or system is one whose behavior is generally described as continuous in time but which may have continuous or discrete values. Examples include a motor or a switched-capacitor filter.
Condition Number Analysis
A sensitivity analysis that allows the user to trace back errors in a simulation to the model instance(s) which have the most significant contributions. This is a feature of the Matrix Viewer.
Matrix
A numerical representation of a system of equations used in simulation for executing a given model. The matrix is a rectangular array of cells, each cell having a numeric value or symbolic expression. Matrix cell values change with each iteration of the simulation algorithm.
Matrix Viewer
An interactive, graphical tool for studying a matrix. In the matrix viewer screen display, a selectable portion of a matrix is displayed, and displayed matrix cells can be selected to obtain more detailed information, e.g., an analysis of what elements contribute to the numeric value of the selected cell.
Mixed-signal
A mixed-signal component, circuit or system is one whose behavior is generally described as a combination of a discrete time circuit or system and a continuous time circuit or system. Its behavior may be expressed in terms of continuous or discrete values. Examples include an analog-to-digital converter or a digital-to-analog converter. Both analog and mixed-signal systems can exist in any technology or mixture of technologies, such as electronic, electrical, mechanical, optical, hydraulic, electromechanical, electro-optical etc.
Model Database
A set of data structures and interface protocols
Cooper Douglas K.
Mantooth H. Alan
Vlach Martin
Avant! Corporation
Broda Samuel
Skjerven Morrill & MacPherson
Suryadevara Omkar K.
Teska Kevin J.
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