Coax Cabling for 1394 Vehicle Networks Offer Highest Data Speeds, Lowest Cost

Contributed by:
Peter Helfet
Eqcologic Corporation

The 1394 Trade Association recently approved the 1394 Copper Automotive Standard, the blueprint for next generation networking in vehicles.  Systems based on the new Standard will offer net data rates of up to 800mbits/s (1394 “S800” speed), from the start.  This compares extremely favorably with 25mbit/s offered by MOST optical networks today and even the “future” 150mbit/s MOST specification. The 1394 Copper Automotive Standard allows for networks built on a number of cable/connector systems, including “Shielded Twisted Quad” (STQ), “Shielded Twisted Pair” (STP) and single COAX operating in full duplex mode. 

The COAX Option

To work with COAX cabling, small, low cost transceivers are required at both ends of the cable.  EqcoLogic provides such a transceiver – the EQCO 800SC. The COAX transceiver connects to standard 1394 PHYs.  Each transceiver has a cable driver to launch transmit signals onto the cable and a receiver with an adaptive equalizer to receive and enhance signals.  The COAX transceiver also supports node “wake-up” requirements to allow the complete system node to shut down when not needed.  The COAX transceiver “sleeps” in a very low power state and wakes itself and the PHY when signals are received from another device on the network.

Figure 1 - COAX system with Transceivers connecting COAX cable to PHYs

Performance and Economics
Using low cost automotive COAX cables, like RG174, with FAKRA COAX connectors, the transceiver allows a cable range at S800 speeds of up to 20m with the network operating at S800 even with a number of in-line connectors.  This is effectively double the range achieved with current STQ or STP cable systems.  In addition, COAX cabling and connectors are very low cost so that, even taking into account the addition of the transceiver circuits, total link cost can be as low as 50% of the cost of more complex cabling.  The COAX cables and connectors are low cost because they are in very high volume production, being used in many different applications and environments; in addition, their construction is simple, allowing fully automated termination and inspection.

Active Connectors
Figures 2 and 3 show two approaches to active connectors; these are systems developed by Radiall of France and the US company, Autosplice, respectively. 

In both cases, the electronics are integrated in a well shielded metal housing that is easily mounted on PCB’s.  Radiall bonds the transceiver silicon directly to the miniature circuit board, making for a very compact package.  Autosplice uses its automotive approved compliant pin technology to create a solder free final assembly for Tier 1 suppliers along with design features to couple the intergrated connector to the chassis for enhanced EMI/RFI protection. With these active connectors, customers will have a number of ways of implementing an optimized 1394 COAX network.
The EqcoLogic EQCO 800SC transceiver is sampling now and is being evaluated by a number of automotive suppliers and OEMs.  It will be available in volume in 2009.