PCB Design Analysis Software Guidelines

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HyperLynx Applications


1.0 Introduction


HyperSuite EXT software is primarily for the analysis of electronic Printed Circuit Board (PCB) design as an aid in minimizing potential PCB design problems that can contribute to electromagnetic emissions. Use of the software analysis services throughout the PCB design cycle can help eliminate any circuit design revisions needed to address signal integrity, crosstalk, and emission problems. The optimization of PCB performance provides an effective means of preparing equipment for meeting applicable EMC test requirements. Proper planning for use of the software can result in lower overall development costs for most electronic equipment. HyperSuite EXT is a high-speed PCB design suite that includes signal-integrity, crosstalk, and EMC analysis tools. It provides for the analysis of high-speed designs early in the design cycle and prior to layout (LineSim); after placement but prior to routing, or after placement and routing of a few critical nets (BoardSim); and after complete PCB layout (BoardSim). Single boards and multi-board systems may be analyzed using LineSim or BoardSim. LineSim is also useful for generating the constraints needed for high speed PCB routing. Interactive simulations may be run for a quick analysis of any critical nets or the batch mode may be used for simulation of a large number of nets simultaneously.


2.0 Procedures


Application of the software design and analysis tools becomes more beneficial if the PCB design process is properly planned and tailored for their use. Plans should be made to make efficient use of the software applications throughout the PCB design process. The following is a description of the HyperLynx software suite analysis capabilities and the recommended sequence of application.


2.1 Pre-Layout Fast Analysis


A fast analysis should be used at the schematic level to identify and determine suitable what-if design alternatives. Layout files are not needed for this application. LineSim is an excellent tool for solving signal integrity and EMC problems early in the design cycle, prior to investing time in the PCB layout. Critical nets and signals with fast switching characteristics should be identified as high priority candidates for the pre-layout analysis. These are usually associated with clock signals and the devices having rapid transition times. Any applicable constraints should be determined for the critical nets and signals. Constraints may be used during the analysis for increased accuracy and as an aid when the critical nets are routed. Exact device models are not needed early in the design process since this type of information may not be available. Models may be determined and added as the design materializes.


2.2 Post-Layout Detailed Analysis


A detailed post-layout analysis should be done using the layout tool files saved in the hyp extension. There are some problems that can only be determined after PCB layout. For example, a properly designed net can be affected by the boards overall layout characteristics and geometry. If a trace length is not constrained properly during routing, or if a net overly extends itself between board layers, there can be some unanticipated problems. BoardSim is usually used after layout and routing since the analysis is based on actual details of a board's routing. However, it can also analyze a board as soon as it is placed, prior to routing, by using Manhattan Routing that BoardSim creates; or when the board is placed and only partially routed.


2.2.1 Input Files


The initial step in running BoardSim is to translate the PCB layout into BoardSim's file format (".HYP"). OrCAD is a good layout software tool for this purpose. However, board layout files are acceptable from several different layout tools and boards from different layout programs may be mixed. Some PCB layout tools contain a BoardSim translator that is available as a menu item. Other tools may require an external translator that is supplied with BoardSim. BoardSim supports the following PCB layout tools: OrCAD Layout, Protel Advanced PCB, Accel EDA / P-CAD, Cadence Allegro, Innoveda PowerPCB (formerly PADS), Mentor BoardStation and Veribest, Zuken-Redac Visula / Cadstar, Zuken CR-3000 / 5000.


BoardSim's MultiBoard option provides the capability to load multiple boards simultaneously, interconnect them, and simulate the PCBs as a system. The files for each board may be in .HYP file format, or in a type of I/O Buffer Information Specification (IBIS) board model called Electrical Board Description (.EBD). The EBD format allows for modeling of random interconnects, and it can be used to represent PCBs, complex IC packages, and custom modules. If the equipment to be analyzed consists of locally designed PCBs, it is recommended that all of the boards be made avaliable as .HYP files. Third party boards such as memory modules may be provided in EBD format. The primary difference between the .HYP file and an EBD model is that the .HYP file contains physical details about trace routing, stackup, etc. EBD models are completely electrical with the interconnects represented as transmission lines and pre-calculated inductance, capacitance, impedance and delays. An .HYP file can be viewed since it is based on a physical routing; however, an EBD file has no physical information to display. Either file type may be used to include the effects of plug-in modules and boards for a multi-board simulation.


2.2.2 Models


Detailed device models may be created during the design analysis process. The I/O Buffer Information Specification (IBIS) standard is used by most IC manufacturers to provide models for their devices. IBIS models are widely available and can usually be downloaded from vendor web sites. HyperLynx supplies more than 6,900 IC models with BoardSim and LineSim. HyperLynx provides a special spreadsheet and component database for searching and sorting models based on manufacturer, part name, creation date, function, etc. Models may also be created for specialty or custom ICs that are not included in vendor or HyperLynx libraries.


Utilities are available to create the IBIS models from SPICE net lists. SPICE is useful for designing mixed-signal systems since HyperLynx does not have analog models. In some cases, a vendor may supply SPICE models because the IBIS models are not yet available. SPICE Writer is available as an option in LineSim and in BoardSim to automatically generate a SPICE netlist output file containing a complete description of a schematic (LineSim) or selected net (BoardSim) using SPICE transmission line elements. This output file also contains the passive components for the selected net as well as comment lines listing the drivers and receivers for which the user can provide SPICE models.


A detailed analysis may be performed on the critical nets and signals once the models that contain all of the required information are established. If the analysis indicates any potential emission problems, corrective action should be taken to modify the layout. After the placement of all critical devices has been determined, the routing patterns for critical signals can be specified. Trace routing constraints may be captured as a topology rule for reducing emission levels.


The radiation produced by a net's component packages can be as significant as that generated by the net's trace segments. BoardSim has the capability to analyze a device package's footprint to determine the package style (DIP, SOIC, etc.) and automatically generate a radiation model for the package.

3.0 Documentation


When all of the design constraints have been achieved and a detailed analysis of the critical nets does not indicate any potential problems, the design may proceed to the fabrication phase. The report and documentation capability of HyperSuite consists of schematic printing (LineSim), for documentation of interconnect circuits; board and net statistic summaries; and an archiving feature that can combine all of the design files (.HYP, IC models, session edits, etc.) into a single directory or zip file.



4.0 Recommendations


Any proposed PCB design changes should be carefully considered for possible impacts to other design objectives, such as overall circuit functionality, size requirements, manufacturing constraints, and thermal effects. Design changes made to reduce electromagnetic emissions may impact other circuit requirements. Some design alternatives may result in a higher level of PCB design complexity in order to optimize EMC performance. This may increase the cost of the circuitry and system of boards. A typical case is a design that requires an increase in the number of board layers to reduce electromagnetic emissions to acceptable levels, thus increasing board manufacturing costs. Some situations may require a more detailed analysis which takes into account the enclosure shielding, board image planes and EMI filters in order to compromise on such design changes.


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