COPLAN is a numerical simulation tool which is implemented as a library of Coplanar Elements into the environment of HP-EEsof Series IV. All elements are calculated as real 3D-elements using field-theoretical calculations and the numerical results are used for the extraction of an equivalent circuit. Since the numerical computations take place at the background, the user does not need to take care of anything regarding the field calculations and can handle the library quite similar to other libraries (like Microstrip Elements) within Libra. The implementation of COPLAN in HP-EEsof Series IV is shown in Figure 3-1.
Figure 3-1: Implementation of COPLAN in HP-EEsof Series IV
After the installation of COPLAN, the user can design the circuit within schematic window and default window of Series IV using the coplanar data items and elements which are available in the library palette. A test-bench can be defined in the test window of Series IV and the analysis can be started. During a frequency independent pre-analysis the equivalent circuit parameters for each element are calculated by the FDM-solution of Laplace´s Equation. The number of iterations, the residual error and the name of the model are displayed inside the Libra Status Window. Input parameters and the results (equivalent circuit parameters) are stored by the cache management in a data base file. During simulator startup this file is loaded into memory and works then like a cache. Based on these results a frequency dependent analysis is started and the S-parameters are calculated.
The COPLAN for Libra consists of two palettes of coplanar elements and a palette of special data items. Each element represents a specific coplanar structure like tee-junction, bend, spiral inductor etc. Special data items are introduced in order to reduce the number of input parameters for each model. These data items have a similar function as the well known data items like MSUB item of the microstrip library or the general UNIT item. The list of implemented data items and coplanar elements as well as their use will be described in the next pages.
The COPLAN for Libra comes along with eight special data items (see table 3-1) which are available in the palette "Coplanar Data Items". These items are described in detail under topic Coplanar Data Items.
|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)|
|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 3-1. Coplanar Data Items used in COPLAN for Libra
One of the problems during the implementation of the CPW-Library into HP-EEsof Series IV environment was the fact that a very large number of material and geometrical parameters was necessary for the definition of some coplanar elements like junctions or coupled lines. Furthermore, many of the necessary input parameters are common for a lot of models in a given design. This problem could be solved using data items. The common parameter are stored in data items and can be referred by all modules without the need to enter the information again and again.
Besides the Substrate Data Item (C-SUB) for the specification of parameters of three possible layers, there are three other data items for the definition of connected lines and bridges as well as some simulation control parameters. For the specification of the line parameters at ports, the so called Line Type Data Items (C_LINTYP) are used. In these data items, the line and slot width as well as the metal level used for both center line and ground plane can also be specified. Each data item represents the data for a line connected at one port of an element. The air bridge construction at each port of a coplanar junction can be defined using an Air Type Data Item (C_AIRTYP). Three types of air bridges are possible. Any combination of different line types and air types can be used. The parameters for controlling the numerical process are put down in the so called Grid Data Item (C_GRID). Here, the user can select the box and grid size as well as the error boundary for the iteration procedure.
In addition the library supports process-related layout generation. This means, all necessary information (oversizes, layer configurations, etc.) are stored in two data items. Technological data such as material constants of layers (dielectric constants, loss factors and resistivity) and layer height are put down in the C_TECH data item. A second data item C_LAYER is intended for layer data such as layer number and oversizes of each layer. In case of DEFAULT-foundry, these data items should be identified as C_TECH_DEFAULT and C_LAYER_DEFAULT. The DEFAULT-foundry is a standard feature of the COPLAN for Libra and several parameters can be adjusted to the used process by the user. Nevertheless, adaptations to other foundries are available as a special service of the IMST.
COPLAN for Libra supports the use of several foundries and processes simultaneously. In order to specify the current used foundry, the name of foundry (i.e. DEFAULT) has to be selected in C_PROCES data item. The C_PROCES data item and the foundry data items (C_TECH and C_LAYER) have to be always defined inside the "defaults" window.
Using data items, the entry of parameters is considerably simplified. Another advantage of data items is the fact that the elements which are connected together would have always compatible line parameters by selecting the same line type at connected ports.
Figure 3-2: Coplanar Data Items as used during the simulation and layout generation
The library of COPLAN for Libra consists of three types of elements: Coplanar Transmission Lines, Coplanar Discontinuities and Coplanar Lumped Elements.
In the Group of Coplanr Transmission Lines, there is a Coplanar Transmission Line (C_LIN) with arbitrary geometrical dimensions and substrate parameters. The effect of finite ground planes as well as back side metallization is considered. The conductor as well as dielectric losses are taken into account and the line attenuation is calculated for both DC and RF. The next element is the Coplanar Inter Metal Via (C_METVIA) which is used for connecting different metal levels. This element is calculated as a coplanar transmission line where the conductor thickness is the sum of the metallization thickness of two utilized metal levels. C_LINE and C_METVIA are available in the palette "Coplanar Elements".
Figure 3-3a: Coplanar Transmmision Lines in COPLAN for Libra
A set of coupled coplanar lines with 2 to 10 coupled center lines (C_2COUP . . . C_10COUP) and finite ground planes are also implemented into COPLAN for Libra and can be used for the realization of couplers or filters. The matrices of distributed parameters are calculated using quasi-static FDM and the scattering parameters are calculated for the given length of the coupled lines. These elements are available in the palette "Coplanar Coupled Elements".
The Group of Coplanar Discontinuities consists of all usual discontinuities which are needed for the design of modern (M)MICs. From one port Coplanar Opens (C_OPEN) and Shorts (C_SHORT) over two port elements like Coplanar Gaps (C_GAP), Coplanar Steps (C_STEP), Coplanar Tapers (C_TAPER) and Coplanar Air-bridge (C_AIR) to more complicated junctions like Coplanar Bend (C_BEND), Coplanar Tee-Junction (C_TEE) and Coplanar Cross-Junction (C_CROSS) are available. All junctions can have arbitrary arrangement and combination of feed lines and air-bridge types. These elements are available in the palette "Coplanar Elements".
Figure 3-3b: Coplanar Discontinuities in COPLAN for Libra
The group of Coplanar Lumped Elements contains the most used elements. These are: Coplanar Interdigital Capacitor (C_IDC), Coplanar Rectangular Spiral Inductor (C_RIND), Coplanar Thin film Resistor (C_TFR and C_TFG) and Coplanar MIM-Capacitor (C_MIM and C_CAPLIN). These elements are also available in the palette "Coplanar Elements".
Figure 3-3c: Coplanar Lumped Elements in COPLAN for Libra
A smart cache memory management is implemented in order to speed up the statistical analysis and optimization process. The calculated parameters of coplanar elements are stored in cache during the first analysis run and will be then actualized, if the structure data are changed. The calculated parameter are stored in some kind of look-up tables in binary format. The look-up table files have the name "CPW_element.CDB" (or "cpw_element.cdb" for windows95/98 and windowsNT), where "element" is the name of corresponding coplanar element (for example CPW_LINE.CDB, CPW_AIR.CDB etc.). Each file contains the input parameters and output equivalent circuit parameters of all coplanar elements of the same kind in the circuit as well as the characteristic line parameters of coplanar lines connected at the ports of these elements. The user can define an environment variable as follows in order to put down the look up table files in a desired directory (path):
setenv COPLAN_TABLE_PATH path
In order to enable the user to have an access to the calculated equivalent circuit parameter, a so called C_DEBUG element is implemented. Using this element, the user can activates flags which forces the simulator to create ASCII-Files containing input and output parameters of all elements used in the circuit. This element is available in a separate palette named "IMST-Utilities".