Parametric-Cells Implementation in Expert

Introduction

A parameterized cell (P-Cell) is a cell with user-specified parameters. It is possible to create customized p-cell instances with different composition according to parameter values. Using P-Cells gives a considerable memory reduction in the case of multiple instancing of a cell. Expert layout editor creates temporary ordinary cells for each set of parameter values. All instances of a P-Cell with the same parameter values refer to the same ordinary cell. P-Cells are stored in the Expert database in the form of LISA procedure. Temporary cells are not stored in the database file.

Moreover, P-Cells add enormous flexibility to design and increase designer productivity. The notion of cells allows the designer to avoid repetitive drawing of identical pieces of layout. P-cells provide an additional benefit: a user can quickly introduce changes into the layout by modeling the parameters of an instance of P-Cell rather than redrawing the geometry.

Creating and using P-Cells in the Expert environment is extremely easy.

Creation of P-Cell involves three actions described below:

• write the XI script that actually generate the P-cell


• specify parameters


• compile the definition of P-cell.

There are two ways to create and modify P-Cell XI script: automatically using menu commands "PCell >> Parameters ..." and "PCell >> Compile" or manually through menu command "Cell >> New ...". The first method allows the user to create simple P-Cells. To create complex P-Cells the user can use powerful features of LISA/XI language that are impossible to generate automatically.

Automatic Generation of P-Cell

For automatic generation of P-Cell the user must open any ordinary cell from the processed project or activated libraries and select "PCell >> Parameters ..." menu command. The "Cell Parameters" panel appears, see Figure 1.

Figure 1. Main dialog for parameter insertion
into the master cell: Stretch parameter.

The button "Add new parameter" selects and adds new parameter to the P-Cell. Various parameter definitions are associated with specific parameters (stretch, repetition, conditional inclusion, and so forth). "Parameter definition" group of "Cell Parameters" panel is to specify parameter definitions for the selected parameter. As a rule, parameter definition has a name and default value which are used in the instancing dialog when you want to place an instance of the P-Cell.

Stretch parameters change the size and position of layout objects that are included in the specific stretch group. The name of the stretch group must be either an ordinary name or XI expression. Stretch line is used to select objects and determine the stretch direction. The horizontal stretch line controls up and down direction and the vertical stretch line controls left and right direction. Directions are indicate using "Direction" combo box. Default dimension will be used in the instancing dialog as default parameter value. Minimum and maximum value is used to control value in stretching the cell.If the "Stretch Repeated Object" box is checked, then objects included into stretch and repetition groups will be stretched.

Repetition parameters are to repeat objects from repetition group in x direction, y direction, or both directions, see Figure 2. User?s can add or remove objects from the repetition group by using the "Include/Exclude" button. The main repetition parameters are "Stepping Distance" (distance between repeated objects) and "Number of Repetition". Any name or valid XI expression can be used to specify this parameters. If the "Dependent Stretch" edit field name of the previously defined stretch group is typed in then objects from repetition group will be stretched after repetition.

Conditional inclusion parameters define the group of objects that are included or excluded from the cell depending on the condition, see Figure 3. The name of the condition group must be any name or valid XI expression.

Figure 2. Repetition parameters.	Figure 3. Conditional inclusion

When parameter definitions are complete, the P-Cell must be complied before the user can place instances of this cell.

Textual Creation of P-Cell

To create a P-cell by coding its xi-procedure, the "Parameterized cell" option in the "New Cell" panel must be checked, in addition to cell name and library selection. After the "OK" button is clicked, the user will see the "Parameterized Cell Panel" and the empty layout window for this cell, see Figure 4. This panel has its own menu.

The P-Cell Panel has a large editing field for typing a P-Cell XI script. This editor has the same standard features as a typical Windows editor. The following common editing commands are available for editing in the P-Cell Panel from its Edit menu: cut (Ctrl-X), copy (Ctrl-C), paste (Ctrl-D), clear selection ([Del] key), delete all, find, replace. Pieces may be cut from other scripts and pasted into the P-Cell Panel. The difference from the ordinary XI-script panel is that of the "Define Command" statement, can not be edited i.e., the beginning and the end of the script. It is generated automatically by Expert. The non-editable text is gray in color. All other necessary commands may be typed inside the outermost Do Begin...end statement.

The "PCell>>Compile" command of the P-Cell Panel menu compiles the definition of the P-cell into Expert database. If compilation passed without errors, the compiled P-cell is stored in the library and is ready to use. The layout window shows the drawing of the P-cells with default values of its parameters, see Figure 6.

Figure 6. Completed P-cell definition

Instancing of P-Cell

If a parameterized cell is activated for instancing, then the Create Instance dialog assumes the form shown in Figure 7. The values of the parameters may be edited by after clicking them with the mouse.

Figure 7. Instancing of a P-cel