Component-based analog and mixed-signal simulation model development including newton step manager

• US 6,236,956 B1
• Filed: 05/04/1999
• Issued: 05/22/2001
• Est. Priority Date: 02/16/1996
• Status: Expired due to Term

• Current Assignee: Synopsys Incorporated
• Original Assignee: Avant! Corporation (Synopsys Incorporated)
• Inventors: Mantooth, H. Alan, Cooper, Douglas K., Vlach, Martin
• Primary Examiner(s): Teska, Kevin J.
• Assistant Examiner(s): Broda, Samuel
• Application Number:
  US09/305,238
• Time in Patent Office: 749 Days
• Field of Search: 703/1, 703/2, 703/3, 703/4, 703/14, 702/12
• US Class Current: 703/14
• CPC Class Codes: G06F 30/367 Design verification, e.g. using simulation, simulation program with integrated circuit emphasis [SPICE], direct methods or relaxation methods
• CPC Class Codes: G06F 8/34 Graphical or visual programming

Abstract

The Model Editor (106) makes simulation modeling easier and more intuitive by extracting essential information and presenting it to the user, and by providing tools to investigate simulation and model robustness, in an interactive, graphical environment. The Model Editor (106) includes a Newton step manager as an interactive, graphical tool. During simulation of a model, the Newton step manager captures matrix norms. Any indications of Newton limiting are also captured. The matrix norms are plotted as a function of iteration count, and the iterations at which Newton limiting were encountered are identified. Newton step manager can also be run automatically using a functional dependency analysis.

Claims

1. A Newton step manager software tool for use in creating and revising a representation of a simulation model for modeling analog and mixed signal digital-analog physical circuits and systems in a digital computer, the Newton step manager software tool comprising:

means for measuring an indication of Newton step limiting that occurred during execution of the simulation model; and

means for graphically displaying the Newton step limiting.

2. A Newton step manager software tool according to claim 1 further comprising:

means for interactively assigning Newton steps to a selected independent variable in a graphical display independently of hardware description language; and

means for inserting the assigned Newton steps into the simulation model so that a user need not insert the assigned Newton steps into the simulation model by editing the model in a hardware description language.

3. A Newton step manager software process for use in development of a simulation model for modeling analog and mixed signal digital-analog physical circuits and systems, the process comprising the steps of:

simulating a predetermined model using a DC modified nodal analysis;

during said simulation, capturing a selected matrix norm at each iteration of the simulation algorithm;

during said simulation, capturing an indication of any Newton limiting at each iteration of the simulation algorithm;

plotting the captured matrix norms as a function of iteration count; and

identifying on the plot which iteration counts encountered Newton limiting.

4. A Newton step manager software process according to claim 3 and further comprising the steps of:

receiving a user selection of one of the iteration counts in the plot where Newton limiting is identified;

identifying which one or more of multiple independent variables within the model were Newton limiting at the iteration count selected by the user;

determining respective values of the identified independent variables at the selected iteration count; and

displaying the identified independent variables and their respective values to assist the user in further developing the model.

5. A Newton step manager method of studying and controlling Newton limiting in the iterative solution of a matrix representing a model undergoing simulation, comprising the steps of:

simulating the model in a predetermined circuit with a DC analysis in a simulator;

during the simulation, capturing the matrix norm of each iteration of the simulation algorithm;

during the simulation, capturing an indication of each Newton limit that occurs during the simulation and the iteration at which Newton limit occurred;

plotting the captured matrix norms in a screen display as a function of iteration count; and

superimposing on the screen display plot an indication of each of the indicated Newton limits.

6. A Newton step manager method according to claim 5 further comprising:

receiving a user selection of one of the Newton limits indicated in the screen display plot;

responsive to the user selection of one of the Newton limits, determining which one or more of multiple independent variables were limiting and their respective values at the time the selected Newton limit occurred; and

displaying the determined limiting independent variables and their respective values for user inspection.

7. A Newton step manager method according to claim 5 further comprising interactively assigning, in a graphical display, Newton steps to a selected independent variable that causes an indication of a Newton limit.

8. A Newton step manager method according to claim 7 further comprising inserting the assigned Newton steps into the simulation model so that the user need not do so by editing the model.

9. A Newton step manager software process for use in development of a simulation model for modeling analog and mixed signal digital-analog physical circuits and systems, the process comprising the steps of:

simulating a predetermined model using a DC modified nodal analysis, wherein the model includes multiple independent variables;

during said simulation, capturing a selected matrix norm at each iteration of the simulation algorithm;

during said simulation, determining the values of all independent variables at each iteration of the simulation algorithm;

relating the captured matrix norms and the independent variable values in order to identify those independent variables for which to apply Newton limiting;

determining what Newton limits to assign to the identified independent variables; and

updating the simulation model according to the identified independent variables, their respective values, and the assigned Newton limits.

10. A Newton step manager software process according to claim 9, wherein the step of relating the captured matrix norms and the independent variable values comprises:

plotting the captured matrix norms as a function of iteration count;

identifying on the plot which iteration counts encountered Newton limiting;

receiving a user selection of one of the iteration counts in the plot where Newton limiting is identified; and

rank-order correlating the matrix norm with the independent variable values which caused Newton limiting at the selected iteration count.

11. A Newton step manager software process according to claim 9, wherein the step of relating the captured matrix norm and the independent variable values comprises electronically correlating the captured matrix norms and the independent variable values.

12. A Newton step manager software process according to claim 9, wherein the step of determining what Newton limits to assign to the identified independent variables includes:

rank-order correlating the identified independent variables to the captured matrix norm;

selecting a most rank-order correlated independent variable;

determining all nonlinear functions of the model;

restricting the nonlinear functions to only a set of functions that depend on the most rank-order correlated independent variable;

rank-order correlating the limited set of nonlinear functions to the captured matrix norm;

selecting a most rank-order correlated nonlinear function; and

using the relationship between the most rank-order correlated nonlinear function and the most rank-order correlated independent variable to compute the Newton limit value.

13. A Newton step manager software process according to claim 12, wherein the step of using the relationship between the most rank-order correlated nonlinear function and the most rank-order correlated independent variable to compute the Newton limit value includes:

identifying an iteration at which the most rank-order correlated nonlinear function exceeds a predetermined upper bound;

identifying a prior iteration at which the most rank-order correlated nonlinear function is below the predetermined upper bound;

determining values of the most rank-order correlated independent variable at the identified iteration and the identified prior iteration; and

performing a linear interpolation on the most rank-order correlated independent variable to determine a value at which the most rank-order correlated nonlinear function reaches the predetermined upper bound.

14. A Newton step manager software process according to claim 12, wherein the step of restricting the nonlinear functions to only a set of functions that depend on the most rank-order correlated independent variable includes performing a functional dependency analysis to determine which nonlinear functions include the most rank-order correlated independent variable.

15. A Newton step manager software process according to claim 9, wherein the step of updating the model comprises:

inserting the identified independent variables and their respective values into the simulation model; and

repeating the simulating step using the updated model.

16. A Newton step manager software process for use in development of a simulation model for modeling analog and mixed signal digital-analog physical circuits and systems, the process comprising the steps of:

simulating a predetermined model using a DC modified nodal analysis, wherein the model includes an independent variable;

during said simulation, capturing a selected matrix norm at each iteration of the simulation algorithm;

during said simulation, determining the value of the independent variable at each iteration of the simulation algorithm;

determining what Newton limit to assign to the independent variable; and

updating the simulation model according to the independent variable, its value, and the assigned Newton limit.

17. A functional dependency analysis process for use in development of a simulation model in a digital computer for modeling analog and mixed signal digital-analog physical circuits and systems, the process comprising the steps of automatically:

identifying all constants, parameters, and variables of the model;

identifying which variables are dependent;

generating a dependency set for each dependent variable, where the dependency set for an individual dependent variable contains all constants, parameters, and variables on which the dependent variable depends;

updating the dependency sets for each dependent variable according to equations of the model; and

using the dependency sets in a Newton step manager in the simulation model to model the analog and mixed signal digital-analog physical circuits and systems.

18. A functional dependency analysis process according to claim 17, wherein:

the step of identifying which variables are dependent further includes identifying which variables are potential independent; and

the step of generating a dependency set for each dependent variable includes treating each potential independent variable as an independent variable.

19. A functional dependency analysis process according to claim 18, where a potential independent variable is a variable that meets the following conditions:

the variable is equal to an independent variable, the negative of an independent variable, or the difference of two independent variables;

the variable is either affine dependent on exactly two independent variables or linearly dependent on exactly one independent variable, and has no dependence on any other independent variables;

the variable depends on constants or parameters only in a varying manner;

the variable is part of a condition or an expression that defines a variable other than itself;

only one definition of the variable is used in the model for purposes other than to redefine the variable itself.

20. A functional dependency analysis process according to claim 19, where the potential independent variable meets the following further condition:

if the variable was at any point defined in a manner inconsistent with being a potential independent variable, then the variable is considered not to be a potential independent variable.