New connector options benefit C4ISR designStory
February 07, 2013
Connectors today represent decades of lessons learned. The real magic is how these lessons are blended such that an optimal solution is realized, especially when it comes to modern C4ISR systems.
Advanced C4ISR systems are driving the evolution of interconnects used in embedded computing and, as the interconnects improve, the systems raise the bar again by demanding higher speeds in a rugged, compact form factor. People debate Moore’s Law or other doctrines describing this phenomenon, but systems evolution forges onward. Interconnects for rugged applications represent a fine balance of electrical performance and mechanical integrity. Adding third, fourth, and fifth dimensions to the situation are such things as standards, physical attributes like weight, and real-world issues like ease of installation and repair. During their trades, designers need to address each of these items along the way.
Upping the bar in VPX ruggedness
The standard connector for VITA 46 (VPX) has represented a huge step forward in the world of rugged computing and C4ISR-enabling technology. Such a modular connector system might feature a protected backplane connector and use a pinless wafer design in place of pin contacts, an approach well established in commercial applications (Figure 1). Wafers, available for differential, single-ended, and power needs, can be easily modified to support specific needs for characteristic impedance, propagation delay, and other electrical parameters. Even though the wafers can be “tuned” to specific electrical needs, standard wafers – such as 100 ohm wafers for differential signals – suffice in most cases. These connector systems also offer built-in ESD features enabling field serviceability, are extremely lightweight, and are fully qualified for VITA 47 environments.
Figure 1: The MULTIGIG RT 2 connector for VPX features rugged daughtercard wafers, offering ease of reconfiguration and eliminating the hazard of bent pins.
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There are design communities that have applications beyond VITA 47 environmental performance, who want to leverage all of the technical and economic benefits of the VITA 46 VPX. New testing levels have been explored to characterize the interconnects beyond the severest anticipated exposure levels of the application. One such public initiative has been the VITA 72 (Connector Comparison Testing) Study Group (SG). The VITA 72 SG devised the vibration “torture test,” exposing a 6U VPX test unit to random vibration levels of 0.2 g2/Hz for 12 hours. To meet the requirements of VITA 72, TE Connectivity engineers modified the contact system of the VITA 46 connector to provide quad-redundant contact rather than the two points of the existing system. Increasing the points of redundancy increases reliability in a high-vibration environment. The new version doubles the points of contact between the receptacle contact and the wafer.
Another important balance in contact design is insertion force (the force required to mate the two connector halves) versus normal force (the spring pressure that maintains the connection between the contacts). A high normal force is desirable to maintain reliable connections, especially in a high-vibration environment. A low insertion force prevents wear and tear on the contacts and allows high-contact-count connectors to be mated. The ruggedized VPX connector’s new contact design offers up to 10 percent lower insertion force while maintaining high normal force.
Designers of embedded computing systems are always looking for scalable solutions – a set of building blocks able to support multiple configurations to meet the widest range of needs. For VPX systems, designers can choose between rugged or ultra-rugged connector options. These new systems are backward compatible with the original so that they can be dropped into designs without changes to the board layout, thereby allowing the user community to leverage all of the equity of the existing VITA 46 (VPX) ecosystem. Because the exterior dimensions and footprint are identical, both connectors support optical and RF connectivity through VITA 66 (Optical Interconnect on VPX) and VITA 67 (Coaxial Interconnect on VPX). As a result, scalability for the VITA 46 (VPX) now comes with two types of flexibility:
Modularity – The modular nature of VITA 46 enables scalability across a board edge with single-ended and differential signals, optical, and RF for both 3U and 6U systems.
Ruggedness – Two tiers of robustness are represented by the original VPX connector and the newer, more rugged version.
Raising the bar in speed and compactness
While the VPX ecosystem is the leading-edge standard for high-performance embedded computing, designers are also looking at next-generation systems – and for connectors that are fast, smaller, and rugged. These connectors are designed for the rigors of aerospace and defense applications (Figure 2). One example is the Fortis Zd, based on the synthesis of a highly impedance matched, commercially derived leadframe and a mini-box military-style separable interface, offering advanced levels of electrical and mechanical performance. To meet next-generation speeds, the connector supports 12+ Gbps data rates in a modular design that can support up to 300 differential pairs in a 6U system. Modules include 10 and 20 columns with either 6 or 9 rows.
Figure 2: The Fortis Zd family of high-speed backplane connectors enables 12+ Gbps data rates, while offering a smaller, lighter architecture.
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Onward and upward in all dimensions
The two dimensions of signal integrity and mechanical robustness have been well explored. What about the third, fourth, and fifth dimensions?
Standards – VPX is a mature standard with well-established connector choices, and the Fortis Zd connector, for example, is under consideration for two standards presently.
Weight – VITA 46 connectors represent the lightest VPX backplane solutions on the market, a vitally important attribute for items such as UAVs and spacecraft where every gram counts. The next generation of high-speed connectors addresses additional weight savings by being offered in a lightweight, all-plastic variety, or they can be specified with a shield or machined shell. All varieties are intermatable.
Installation and repair – All the described connectors are modular and compliant pin technology. This allows the use of simple flat rock press tooling for installation and the ability to easily remove individual modules if a repair is needed.
Advanced C4ISR systems require advanced technologies
As C4ISR systems migrate to new platforms such as UAVs, they must support faster processing, reduced size and weight, and new levels of ruggedness. In recognition of the need to meet the mechanical and environmental realities of real-world applications, forthcoming standards place new demands on connector performance. The connector industry is meeting the new levels with new variations of existing connectors and new connector designs based on well-established technology.
Gregory Powers serves as Market Development Manager for the Electronic Systems and Space segments within the Global Aerospace, Defense & Marine business unit of TE Connectivity. He received a BSME from Syracuse University, has completed numerous graduate-level studies, and holds two patents relative to optical datacom devices. He can be contacted at [email protected].