One of the problems by the direct parameterization of the CPW elements is the great number of input parameters. For some of elements like coplanar tee-junctions more than 30 parameters are necessary for the definition of geometrical dimensions. A solution is the use of special data items (see Figure 4-1).
Figure 4-1: Definition of parameters for a coplanar tee-junction using coplanar data items
The COPLAN for Libra uses several data items to set-up geometries, substrate data and process data as well as simulation control parameters. All data items defined by COPLAN for Libra have a name beginning with "C_".
If using Series IV, some data items are well known to the user like the MSUB item (definition of a microstrip substrate) or the UNITS item. The C_SUB defines the substrate and corresponds with the MSUB data item.
A simple microstrip line is described only by its width. In case of coplanar line, the cross section is described by the widths of line, slot and ground plane width. In order to reduce the number of input parameter for each element, the cross section of coplanar lines used in each element is defined in a special data item, called C_LINTYP.
Since COPLAN for Libra uses an optimized numerical Field-solver for each component, some simulation control information have to be passed to the simulator. For this reason, the gird and control information is also stored in a special data item, called C_GRID. Because the grid depends on the dimensions of the structure, it has to be defined for each component to be analyzed. However, in most cases a few number of different C_GRID is sufficient for a complete circuit..
The same situation we have in case of the air bridges. Most of the bridges have the same structure and in COPLAN for Libra there are components with up to 4 bridges to avoid odd mode excitation. The introduction of the C_AIRTYP data item reduces the number of input parameters to be defined drastically.
An important feature is the process-related simulation and layout generation. During simulation, COPLAN for Libra takes into account process-related information like minimal lengths, permitivities and losses of dielectric layers etc. In addition, the automated generated layout of a coplanar circuit is generated with respect to a selected foundry. This means, that oversizes, layer numbers and configurations etc. can be defined by the user and are used for the layout generation.
In order to have a very flexible user interface in defining such foundry data, three data items were introduced: C_PROCES item, C_TECH item and C_LAYER item. COPLAN for Libra is potentially able to support more than only one foundry. The name of foundry being used for simulation and layout processing is specified in C_PROCES. The process data itself (layer configuration, permitivities etc.) are defined by the C_TECH and C_LAYER data items and can be edited by the user in the similar way than for other data items. In the standard package of COPLAN, a so called Default Foundry is implemented. The user of a standard package cannot define a foundry (process) other than the default foundry. However, IMST provides a special service to implement a customized foundry into the COPLAN for Libra software.
The COPLAN for Libra comes along with eight special data items which are available in the palette "Coplanar Data Items". For more information of these items, please use the links in the following table (table 4.1).
|C_SUB||Substrate definition for coplanar structures|
|C_GRID||Definition of grid and shielding sizes for finite difference approach|
|C_LINTYP||Definition of cross-sectional dimensions of coplanar line|
|C_NL_TYP||Definition of cross-sectional dimensions of coplanar coupled lines (up to 10 coupled lines)|
|C_AIRTYP||Definition of airbridge parameters|
|C_PROCES||Foundry selection for layout generation and process-related simulation|
|C_TECH||Definition of technological data for selected Foundry|
|C_LAYER||Definition of layer data for selected Foundry|
Table 4-1. Coplanar Data Items used in COPLAN for Libra