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3D EM Simulation in the Design Flow of High-Speed Multi-Pin Connectors

Application and Simulation courtesy of  Thomas Gneiting, AdMOS GmbH, Frickenhausen, Germany.
This article describes the design flow for a high speed connector using different simulation tools. The goal is to enable a first pass design without time-intensive and costly iteration steps. In addition to other simulation tools, CST MICROWAVE STUDIO® (CST MWS) is used during different stages of the design process to find fundamental design parameters and to predict the behaviour of a complete telecommunication system.
The requirement of a new high speed multi pin connector is to enable a data transmission rate of at least 10Gbit/s in a communication system, (Figure 1), where two daughtercards are connected via a backplane. The connections should be point-to-point connections applying differential signal trace layout. Other technical requirements include:

• 100 Ohm differential impedance.
• SMT interface to printed circuit board.
• Extreme shielding to achieve a minimum of crosstalk between differential signal pairs.
• Minimum signal skew between the two contacts of a differential signal pair.
• Economical and easy trace routing.

Figure 1: Backplane and daughtercard system


EM simulation can be used in the early stages of the design process to help determine the main dimensions of the connector and how it will behave in the aforementioned system. The protyping process is shown in Figure 2.




Figure 2: Design and prototype process flow


Once the requirements have been defined, a study is performed to establish the conductor dimensions. The main parameters are the trace width and the distance between the differential signal pair of the connector in addition to the the distance between the 2 signal pairs inside the wafers. In the design process it is necessary to obtain a realistic prediction of the overall communication system performance. The S-parameters of the parametric connector model were exported in touchstone format and used in a circuit simulator (Agilent ADS) for further analysis.  An accurate analysis must contain the behaviour of not just the connector but also the connector to PCB board interface, the backplane, daughtercards and signal path vias. This approach allows the performance of the complete communication system and not just the connector to be established. The CST MWS model is shown in Figure 3. It consists of 3 wafers with 4 signal pairs per wafer. It was used to verify the impedance matching,  reflection, crosstalk & multiline crosstalk, to generate a SPICE model  and to determine the overall system behaviour based on the obtained S-parameters.




Figure 3: CST MWS 3D model of the prototype connector


An accurate 3D simulation using CST MWS is vital for the highly critical and expensive manufacturing process of the cutting tools and plastic housing components. In addition to the investment costs, a major issue is the time at which the first sample is obtained since time consuming changes to the production tools may be necessary if the sample does not meet the required specifications. The overall time to market is an important factor that is heavily influenced by the design, prototype and test phases. The Stamping and molding tools are designed and manufactured to allow a high volume production of the connector system. The the investment costs for those tools are in the range of 1 Million