Connecting with demand

Historically, system design engineers looking for a boost in system performance when using designs based on 2mm hard metric connectors have been unable to maximise performance and signal integrity because of the severe crosstalk that occurs at speeds greater than 1Gbit/s. Increased signal density, functionality and use of high speed serial protocols have pushed existing 2mm connector systems to their limits. However, that situation has changed with the advent of fully shielded Ultra Hard Metric (UHM) socket connectors, which can deliver in excess of 7Gbit/s backplane performance for systems based on 2mm hard metric connectors. Not only has this been achieved without a corresponding increase in crosstalk, neither does the approach require costly backplane redesign or 'fork lift' upgrades. UHM connectors can be mated with existing 2mm hard metric (IEC 61076-4-101) headers and are compatible with 2mm hard metric pcb footprints, so they can fit into legacy backplane designs. As a result, standard CompactPCI and VME 64x systems can support high density multigigabit, high speed serial I/O protocols, such as SAS, SATA, Rapid I/O, PCI Express and Gigabit Ethernet. This makes UHM connectors well suited to backplane designs that require higher signal speeds combined with higher signal densities, such as test and measurement equipment, process control, military, enterprise computing, telecommunications and factory automation applications. Low cross talk, high performance So, technically, how does this new generation of connectors achieve this without increasing crosstalk? The 'virtual coaxial box' provides a matched impedance signal path and gives the designer the freedom to drive 100ohm differential signal pairs in both columns and rows. This provides maximum signal density and performance, but also maintains compatibility to common column differential pair configurations found in legacy hard metric (HM) systems and cable applications. Unlike standard 2mm hard metric and CompactPCI connectors, UHM sockets contain row and column shielding between the signal contacts to improve connector signal integrity characteristics. The row and column shielding build a coaxial structure that enables combining two signal pins to a 100ohm differential pair in both rows and columns. Row differential pairs provide maximum signal density – especially for five row systems – and low skew, while column differential pairs maintain compatibility to older configurations, like many hard metric cabling options. When used in CompactPCI systems, the socket uses the outer ground wipers to contact the outer rows of ground pins on the header. This connection provides a return ground path through the coaxial style shielding to the daughter card. Tested and compatible In tests, the crosstalk was evaluated for a HM-HM mated pair and HM-UHM mated pair with two neighbouring aggressor pairs. Even at 7Gbit/s, the UHM socket connector maintained its shielding properties and reduced crosstalk significantly. In addition, the new CompactPCI plusIO concept, PICMG v2.30 – which is an extension to the existing CompactPCI standard – describes how the UHM connector is used to incorporate SATA, PCIExpress, USB and gigabit Ethernet into legacy 3U or 6U CompactPCI or new hybrid systems. Test results demonstrated that the UHM right angle socket, when mated to legacy CompactPCI 2mm hard metric headers, could sustain data rates of up to 5Gbit/s. The CompactPCI plusIO concept defines a new J2 connector and pin out to support high speed differential signal up to 5Gbit/s to include PCIExpress (4x), SATA (4x), 10G-Ethernet (2x) and USB 2.0 (4x), while remaining 100% downward compatible to CompactPCI 2.0. This downward compatibility guarantees access to all existing peripheral cards using the PCI bus but, at the same time, provides new high speed serial interfaces. The Ultra Hard Metric (UHM) connector enables this concept by providing low crosstalk, impedance controlled signal paths while maintaining footprint compatibility to hard metric sockets and intermateability to 5+2 hard metric headers designed to IEC 61076-4-101. Therefore, the UHM connector can replace a hard metric socket in legacy or other systems without restriction. Other options The modular design of the UHM Socket Connector also gives system design engineers the flexibility to design the right level of signal integrity while satisfying required mechanical constraints. Five row (A, B, CL, CR, AB) and eight row (D, E, DE, FL, FR) form factors are available for high signal density. In addition, UHM connectors support new high speed serial protocols, like SATA, SAS and PCIexpress. In some cases, the existing backplanes and possible HM cabling systems on the rear side of the backplane – as well as the standard PCI bus with its associated peripheral cards – can continue to be used. Due to the UHM connector's internal shielding, high speed signals can be placed next to each other without the need for adding ground, increasing the potential signal throughput significantly, especially for 3U systems. Looking ahead Moving forward, UHM has a clearly defined new product roadmap which will deliver increased functionality and performance. On the horizon are UHM headers which, when mated to a UHM socket, will target in excess of 10Gbit/s controlled impedance performance. The headers will be designed to be completely forward and backward compatible with standard 2mm hard metric sockets. Also in the pipeline are UHM backplane cable assemblies, again targeting in excess of 10Gbit/s performance when mated with a standard 2mm hard metric or ultra hard metric header. As the needs of the market change UHM will deliver a product family capable of meeting the challenges of modern system design and upgrade. The intention is to minimise expensive manufacturing and maximise performance and return. Obviously, there are times when a complete 'fork lift' redesign makes more sense, but UHM connectors give the large number of system designers currently working with CompactPCI backplance architectures a new range of possibilities. Gone are the days when organisations can justify complete system redesigns in order to meet a functional change in an application. Designers are being challenged to deliver more from their common platforms and legacy systems in order to maintain profitability and reduce costs. Technologies such as UHM might just provide the key.