Sensitivity and Worst-case Analysis

Step 1: Setting up the Testplan

DVM needs a sensitivity_base.testplan file to set up the circuit for simulation. Now that you have defined the scalars and tests that you want to use, you can set up the testplan that must include a label column with entries that match exactly the labels in the sensitivity_function.def file.

Step 2: Define Scalars and Tests

The sensitivity_function.def text file defines the scalars to be measured and the test(s) to run.

• The first column lists the scalar function(s) to be measured. The scalar name in this column must not contain spaces nor equal signs.
• The second column is the display name for the scalar. This display name also appears in the sensitivity_parameter.def file and is used in the output report. The name in this column can contain spaces and punctuation.
• The third column indicates the test that DVM will execute to find the scalar identified in the first column. The test specified in this column also appears in the sensivity_base.testplan file.

Each scalar is added one per line to the file. DVM automatically figures out how many tests to run in order to find the sensitivity of the scalar functions listed in the file.

The following example includes the file name and the schematic name in comments on the first and second lines.

Step 3: Defining Parameters to Vary

The sensitivity_parameter.def file specifies the parameters to vary during the sensitivity analysis.

• The first column contains the display names exactly as you entered them in the sensitivity_function.def file.
• The remaining columns are a tab-separated list of parameters.
  Note: In most cases, these parameters are component references; however, DVM can also reach down inside each hierarchical component and change parameters. In the following example,  U1.U3.C1, U1.U3.C2, U1.U3.R2 represent hierarchical components, where U1 and U3 are the first two levels, with C1, C2, and R2 as the components to be varied.

Step 4: Defining Component Tolerances

The final step is to define the tolerances of the components in the sensitivity_tolerance.def file. DVM interprets these tolerances as +/- 3 sigma limits.

The sensitivity_tolerance.def file has three mandatory columns and two optional columns.

• The names in the first column must exactly match the display names in the in the sensitivity_function.def and the  sensitivity_parameter.def  files.
• The second and third columns, NTOL and PTOL, are required and contain the tolerances from nominal. The values can be expressed in % of nominal or in absolute delta from nominal.
• The fourth column, LOT, is optional to declare components which move as a lot.
• The fifth column, MATCH, is to define a matching tolerance.

To make certain that each parameter is assigned a value, you can copy each unique parameter from sensitivity_parameter.def and paste it on its own line in the sensitivity_tolerance.def file, insert a tab and then add the tolerances with tabs between the specifications for each component. The sensitivity_tolerance.def file for this example looks like the following: