Serial buses: Faster than cars

-February 05, 2014

In some of my previous articles, I talked about integration of more wireless connectivity to vehicles, and the evolution of RF connectors used in vehicles. This time, let's look at  data connectivity within the vehicle other than RF.

TE Connectivity has developed a 4-wire connectivity system that can support two twisted pairs of conductors and gigabit-per-second data speeds. Figure 1 shows examples of the HSD connector.

Figure 1  TE Connectivity High Speed Data (HSD) connector. On the left are images of straight and right-angle cable versions. On the right is a USB to HSD adapter. The interface and cable can be used for USB as well as Ethernet, Gigabit Video (GVIF), and Low Voltage Differential Signaling (LVDS).

The TE HSD Catalog lists straight and right-angled cable versions, as well as board mounted in various orientations. (Note: This particular catalog has a very nice introduction to signal integrity for high speed data; it is worth looking at just for that.) TE indicates these connectors are compatible with the USCAR specifications I mentioned in the previous article. In addition, similar to the RF Fakra connectors I discussed before, the HSD connectors are available keyed and color-coded. Figure 2 shows the scheme TE uses for these connectors.

Figure 2  Keying and color coding for TE HSD connectors is similar in concept to the Fakra RF connectors used in automotive RF.

A different path
Molex has taken another path supporting high-speed data for automotive by repackaging a consumer grade, 5-pin shielded connector into what they call HSAutoLink. This data bus is also called USCAR USB, and meets automotive requirements for USB 2.0.

Figure 3  Molex HSAutoLink connectors. Source: Molex According to a datasheet and application note, Molex has certified the HSAutoLink parts to 5000 mating cycles and other USCAR-30 requirements. In addition to USB, Molex provides connectivity in this family for LVDS, IEEE 1394 for automotive, FlexRay (ISO 10681-1:2010), Ethernet, and MOST. FlexRay, now ISO 10681, was developed by a consortium of automotive companies to provide a higher-speed bus than the traditional CAN bus used in automotive.

MOST connectivity
In an article by Masahiko Otake of Mitsubishi in Laser Focus World last year, he gave the history of the MOST Cooperation (not Corporation). Formed in 1998 by Partners Audi, BMW, Daimler, Harman, and Microchip Technology, MOST was a response to Mercedes Benz's successful use of POF (plastic optical fiber) in cars in their D2B network. The Cooperation wanted to standardize a high-speed data architecture as well as take advantage of an EMI-impervious and lightweight solution.

A MOST network is used to interconnect various electronics modules in vehicles, for driver information, safety systems, and entertainment. On their website, the MOST Cooperation lists, in addition to the five partners, 16 Integrators (which includes many additional OEMs) and over 60 suppliers certified in the program. MOST150 is the latest standard; it specifies up to 150Mb/s data rate transport, using PMMA (polymethyl methacrylate) plastic optical fiber. Mitsubishi Rayon Corporation is a supplier of PMMA fibers to this market through their ESKA brand. Figure 4 shows some examples of how MOST is used.

Figure 4  Top—a hybrid connector from TE Connectivity; the MOST optical fibers are seen in the 4 positions at the lower left of the top left connector. Middle left—A representation by TE Connectivity of a MOST network in a vehicle. Middle right—graphic of a possible cable assembly for a vehicle. Bottom—breakdown of typical product categories.

LVDS is a twisted pair technology where information is transmitted as the difference in voltage between two lines (a differential pair), at a constant current. On Future Electronics’ website, they provide a brief summary of LVDS, and explain that it has been used since the mid-1990s in computing for high-speed buses. However, because it is designed with high immunity to EMI and has low power consumption, it has found application more broadly, including in automotive.

LVDS implementations can support up to 3Gb/s data rates, and as already noted, can be implemented in various connector interfaces. Figure 5 shows the basic idea of an LVDS signal pair.

Figure 5  Basic LVDS concepts. Source: Maxim Integrated tutorial.

As more electronic systems are integrated into cars, including broadband internet and in-car video, solutions are already in place to provide over 1Gb/s performance, and optical fiber if needed. It is interesting that there are so many co-existing standards, as well as unique OEM offerings in automotive connectivity. Although it may be surprising to some, connectivity within cars is a constantly-developing technology area, and is now beginning to catch up with consumer electronics.

Does your car have a high-speed serial bus? Does it work?

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