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The models that SYMMIC analyzes are described in XML-formatted files having filenames that end with .xml extensions. Two different XML formats are used: single device template files and layout template files. A device template describes the parametrized finite element model of a single device such as a Field Effect Transistor (FET). Layouts describe the geometric arrangement of a set of devices in a MMIC or module having a common substrate. Details on the XML format can be found in the Appendices.
Single FET device template.
Layout template containing 4 FET devices.
Either type of template file is opened by the Open... command from the File menu. A shaded solid model of the device or layout is displayed in the main window after the template is successfully loaded. Colors in the model indicate the materials of different components. For example, the gold color is indicative of gold metal components in the template images shown above. When a layout is opened, all of the devices are rendered and the additional base layers are extended to create the entire MMIC or module.
A template file can also be opened by dragging and dropping the file onto the SYMMIC application icon on the desktop, on the Windows Start Menu, or onto the SYMMIC.exe file. A template can be opened and solved by xSYMMIC using this type of drag and drop. A template file cannot be dropped into the main application window after SYMMIC is already running.
If errors are encountered while reading or interpreting a template file, error messages will be displayed in the console window. In some cases, the template model may still be displayed, but in cases of severe errors the template will not be loaded and the main window of the GUI will remain blank. When the device template files comprising a layout cannot be located, the Device Layout Table dialog will be displayed with the problematic files highlighted in red. The browse buttons in the Device Layout Table can be used to locate the files, after which the layout can be reloaded using the Retry button. Use the Ignore button to load the layout without the missing devices. If all device files are missing, the layout will be abandoned and the main window will resume the blank startup screen.
There are several ways to modify templates. Since the templates are XML files written in plain text with a prescribed format they may be edited using any plain text editor such as Notepad. To avoid tedious editing of XML syntax, however, device templates can be modified by accessing the appropriate menu items from the main window. The Device menu allows parameters in a device template to be changed, as described in detail in the Devices chapter. The parameters set in the Configure Run submenu of the Solve menu are also part of the device template. Layout templates are edited through the Device Layout Table dialog, which is accessed from the File menu. Creation and editing of layouts is discussed in the Layouts chapter.
To delve into more details of the templates, a couple of other editors are also available within SYMMIC. A device template can be edited using the Edit device template... item from the File menu, as described in the Devices chapter. This Device Template Editor allows most values to be changed without dealing with the XML syntax. In addition, the Device Template Editor has utilities for deleting and inserting feature points into the device geometry, and for making other global modifications. For details see the Device Template Editor section of this manual.
Knowledge of both device template syntax and finite-element thermal analysis is a requirement to successfully use the Device Template Editor.
Changes made through the Device menu will always produce valid finite-element models, for well-designed device templates, but not so for changes made through the Device Template Editor. The user must verify that any edited template is still a valid, complete and accurate model.
The XML syntax can be directly edited and validated in SYMMIC using the Validate XML file... option from the File menu. This option is detailed in the section on XML Validation in the Devices chapter. Due to the limitations of the browser-based editor, a syntax-aware text editor such as EditPlus or Notepad++ would probably be a better option for direct XML editing.
Changes to template parameters can be retained between sessions by saving the device template file(s). The current device template is saved to its original file by selecting Save device from the File menu. To give the device a new filename or browse to a new folder, use the Save device as... command, as shown below. The device can also be given a new title by typing the string at the bottom of the Save dialog. This title string will also be used to designate the device in the Device Selection list and in the Device Layout Table.
Because template files are in XML format they normally have the .xml file extension. Starting in version 3, xSYMMIC requires that the template listed on the command line have the .xml extension. Since it is desireable to solve problems using xSYMMIC through the Background Run and Remote Run dialogs, we highly recommend sticking with the .xml filename extension. Entering a template filename without an extension in any of the Save dialogs will result in the .xml extension being automatically added. Otherwise, the .xml extension is not strictly enforced by SYMMIC, so it is possible to open and save template files that have extensions other than .xml.
Both the Save device and Save device as... commands save a single device. When working in a layout, each device would need to be saved separately to be given a new, unique filename. Be aware that Save device as... will convert an absolute filepath to one which is relative to the layout filepath. For example, saving a device to C:\Temp\devices\FET.xml while in layout file C:\Temp\layout\mmic.xml, will result in the path to the device being simplified to ..\devices\FET.xml in the layout file. SYMMIC automatically converts absolute device filepaths to relative ones when ever a new file reference is generated within a layout.
When devices in a layout are given new filenames, this also changes the filename strings in the layout template. The layout template will also need to be saved to remember these new device filenames. Layout template files are saved using the Save layout and Save layout as... commands of the File menu. Save layout overwrites the original layout file without prompting. Save layout as... allows the user to enter a new filename and title for the layout. Note that the Save layout and Save layout as... commands do not save any device templates, nor do they check for changes in the device templates and recommend that the changed devices be saved.
To save all of the devices in the layout to their original files, use the Save all devices command. This command checks for changed devices that have the same filename as devices occurring later in the layout, before writing any files. The existence of non-unique filenames means that the changes in one device would be saved to a file, but the file could later be overwritten to erase the changes. When this potential problem is detected, the user is warned as shown in the following screenshot. To avoid any conflicts, it would be best to cancel the save operation, locate the differences in the devices sharing a filename, and either replicate the changes between devices or save some of the devices to new filenames. To locate the differences, the devices in memory may be compared to the device files on disk by using the command Compare values to > template from the File menu. By selecting the original layout file as the template for comparison, each device in the layout will be compared with each device file stored on disk, and a report will be generated listing all the differences for the whole layout.
Before closing a layout, SYMMIC will check for unsaved changes to the device and layout files and ask the user if the files should be saved. If the user says Yes, the Save all devices command will then be applied. Detection of changed devices with non-unique filenames will result in the above warning message, and the user would again be given the option to continue or cancel. Continuing the operation will write all the device files in the order that they occur in the layout. Devices with repeated filenames will be written multiple times, with the final set of saved parameters being those of the last device in the layout.
Some device templates may come with complied HTML help files that explain the geometry and parameters of the devices. Help for the currently open device template can be accessed, if it is available, from the Device template? item of the Help menu. If no help file is found, a No Help Found message box will be displayed instead. If the Help window opens but is blank, the .chm file might be blocked by Internet Explorer. To remove the block, right click on the .chm file in the Windows file viewer/manager, select Properties and then press the Unblock button at the bottom of the General tab. If there is no Unblock button present, the file has already been unblocked for the local machine, but make sure that it is not being accessed over the network where it might still be blocked on other machines.
Tip: To make it easier to find individual help files for device templates, copy the .chm files to the SYMMIC program folder (e.g. C:/Program Files/SYMMIC). If SYMMIC does not find a help file locally, it will also look in the folder of the SYMMIC executable.
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