MMIC Thermal Simulation Is Part Of Design Flow

For designers of monolithic microwave integrated circuits (MMICs), thermal simulation has generally been done using an esoteric piece of mechanical-engineering software. Such simulation can now be part of an integrated RF/ microwave design flow, howeverthanks to SYMMIC's template-based approach, simulation speed, and scripted integration to AWR's Microwave Office. This capability is the focus of a six-page application note from AWR titled, "AWR Connected for CapeSym SYMMIC."

SYMMIC, which is a template-based thermal simulator from CapeSym, has been integrated with Microwave Office via a script-based flow. With its template-based approach, SYMMIC relieves the engineer from having to create robust thermal simulations. Of course, issues like thermal boundary conditions and material properties still must be understood. Yet their particulars can be investigated as part of the design process, rather than as a precursor to it. SYMMIC also runs quickly and efficiently. The simulations in the application note were run on a personal computer (PC) with an eight-core microprocessor and 16- GB random-access memory (RAM) with a 64-b Windows XP operating system.

In the application note, AWR demonstrates the integration of Microwave Office and SYMMIC by using an actual MMIC high-power-amplifier (HPA) example. The document breaks the amplifier example into three multi-part steps. First, the MMIC is designed in typical fashion. Once the layout contains thermal sources, the SYMMIC script can be run. The MMIC-level schematic is annotated for conditions of total dissipated power (TOT_PWRA) to provide information for SYMMIC regarding the heat source(s). For this application, the HPA_MMIC. emp file is then opened. A low-noise amplifier (LNA) is added to the circuit design by copying two of the field-effect transistors (FETs) in the design and re-biasing them so their drain current is about 10% that of FETs in the PA stage(s).

The next major step is to prepare and run the Microwave Office SYMMIC script. Essentially, the SYMMIC data is created in Microwave Office and then prepared for exporting to SYMMIC. Detailed, step-by-step directions are provided for this task. In the final step, the layout is imported into SYMMIC and analyzed. Steps also are included for this process. Because SYMMIC is a standalone application that runs separately from the AWR software, it can be used anytime after the SYMMIC layout data file is exported from Microwave Office as an XML file. For each device in the desired thermal analysis, the total dissipated power (from the TOT_PWRA annotation) is required as additional input data for the SYMMIC simulation. Through this example, the application note illustrates that more accurate device simulation is possible for electrical circuit design.

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