By Terry Jones and Dana Bergey, FCI
It wasn't too long ago that after all of the critical system design elements were complete, the design engineering group would call in a connector supplier and ask how to put all of this together, so that the system would fit into the applicable space requirements (and of course complete it by tomorrow since this element of the design wasn't in the system timeline). The requirements from a connector standpoint were usually purely mechanical in nature. The electrical requirements were usually determined by the crosstalk and power requirements. The number of signals required, power requirements and routing requirements would be evaluated and translated into a connector design that would satisfy the design requirements.
However, with the increase in high-speed signal requirements all of that has changed. The intricate balance of components required to enable a high-speed system to function requires that the system engineers understand both the contribution and advantages that connectors deliver to system performance. As a result the connector companies are playing a major role in enabling the design of newer, faster, high-speed systems. The system designer who understands the advantages of utilizing early involvement with the connector designer can gain a significant competitive advantage in the marketplace.
Playing an integral role in these developments is the connector company's Signal Integrity Engineering Group. At FCI, the Signal Integrity group is brought into a project as soon as the initial design concept is formulated. Connector electrical performance criteria, and the ability to be able to adequately model the connector performance are instrumental in designing a connector system that best fits the customer requirements.
This process can happen in many ways. In some cases the customer requirement may be satisfied by an existing connector product, and the only actions necessary are to perform an electrical simulation or test the product in the system. At the next higher level, modifications to an existing design may be required and the modeling/testing process is of increased importance to aid in modifying the existing design.
The most challenging instances occur when the customer and connector company has identified a need that now requires a totally new design or completely different way of thinking.
In these cases, the coordination between the mechanical design groups and signal integrity design groups is critical. To build a product that is both reliable and which meets all of the customer's electrical and mechanical design requirements, the design process could require numerous cycles represented by the diagram in Figure 1.
The process begins with the initial connector design concept. This concept will also be modeled as a purely electrical model. By working together the Connector Designer and Signal Integrity Engineer create a basic design that meets the requirements, however this design must be evaluated for "Manufacturability" and "Cost to product" considerations. These changes usually require connector design changes and each time the design changes it results in electrical changes in the system that must be evaluated and adjusted.
After each iteration of the design cycle the design for manufacturability must be evaluated and optimized and so on and so on until the final solution is agreed upon. The ability to adequately model the connector system and predict the electrical performance of the connector in a stand alone mode and in a system can drastically shorten the time required to bring an idea from the drawing board to the production floor.
For instance, initial connector concepts can be evaluated using simple electrical models to assess their feasibility. These early simulations help the design team quickly make critical decisions regarding the trade-offs between electrical performance goals and mechanical goals such as density, material choice, and contact design. After feasibility is determined, the mechanical designer and the signal integrity engineer work together to develop a design that electrical simulations predict will meet the performance goals. With a prototype in hand, the signal integrity engineer can evaluate the new product in the laboratory. Using signal integrity test tools such as Vector Network Analyzers and Time Domain Reflectometers, he can isolate the effects of individual parts of the connector's transmission path, and determine what mechanical changes (if any) are required to optimize the impedance, insertion loss, and crosstalk performance of the design.
By utilizing these types of tools and innovative thinking we have been able to stretch the capabilities of copper based systems to speeds that were un-thought of just a few years ago and who knows where the current boundaries lie.