New ICs, topologies beat the automotive data-net bottleneck
Today’s automotive designers have an opportunity wrapped in a major challenge: customers want more connectivity and graphics—and are apparently willing to pay for it. Drivers and passengers want basic operating information, of course, but they also want real-time maps, entertainment, and information. If they have learned to live with and, in fact, love those multiple screens in their home and office environment, why should they also not want the same in their mobile automotive world? The reality is that this sort of connectivity and display has gone from being "nice to have" to "must have" with today’s younger buyers. It doesn’t matter if you call it infotainment, smart driver interface, networked vehicle, vehicle connectivity via the cloud, or anything else: it’s becoming a standard accessory on all but the low-end vehicles.
But there’s a technical problem. Issues which are manageable in the fixed home/office situation are very different in the automotive world. Supporting multiple screens is not just matter of computing "horsepower". It also brings complex cabling, connectors, power dissipation, and signal integrity concerns—all of which are at a premium and severely constrained in the automotive world.
Technically, there are three areas that must be addressed: the graphics processing core(s); the multiple displays; and the high-performance interconnecting network between the graphics engine and the displays. Consider that a vehicle will have an instrument cluster, a front passenger-side display, a central console, possibly a heads-up display [HUD], a rear backup camera, and even a rear-seat monitor camera. The overriding challenge is this: how do you effectively support four, five, or more displays and cameras from a single, centrally located graphics-rendering and image-processing core?
The obvious solution of using large, standard PC cables and interfaces such as HDMI will not work, for several reasons. First, there’s the sheer bulk of routing these cables. Signal integrity in the noisy auto environment is a problem, especially over the distances. Plus, there’s the cost and weight of the copper cabling, and the connectors themselves are too large and awkward. Reliability and performance in the harsh auto environment is also inadequate.
Fortunately, there is a solution which leverages the existing mass-consumer market technology, by adapting it in a cost- and performance-effective way for the automotive application and environment. It begins with the ability of today’s video subsystems to support 3D streaming video, with separate images for right eye and left eye.
But by leveraging the stereo video format and HDMI interface using a proprietary technique, Inova Semiconductors (Munich), in conjunction with leading IC vendors such as Analog Devices, Inc. (Norwood, MA) and others, solves both the bandwidth issue and the physical connectivity problem. Instead of 19 wires of the HDMI cable, this interface backbone requires just one four-wire cable, with differential signaling via two pairs, arranged as a "star quad" with 100Ω nominal impedance. The 1-Gbps APIXAIPX link was introduced in 2007, Figure 1, and has been proven effective and reliable.
Fig. 1: APIX Gigabit data link as introduced in 2007. For full resolution click here.
Of course, it appears that users can never have enough speed, so the second-generation AIPX2APIX2 reaches 3 Gbps (Figure 2); it is backward compatible with the original APIX1AIPX and has been in production since last year.
Fig. 2: The second APIX generation offers a bandwidth of 3 Gbps.
AIPX2 APIX2 is not just a speculative concept it is being used in automobiles on the road today. It was demonstrated at Electronica in November 2012 by Inova at Analog Devices’ booth, where it transmitted two uncompressed high-definition video streams, multi-channel audio, and 100Mbits/s Ethernet data over a single 4-wire, shielded, twisted-pair cable. The demonstration featured video conferencing and touch surfaces in remote displays via standard Ethernet protocols and the integration of real-time user interfaces and applications using HDMI connectivity to smart phones.
How it works
APIX2 continuously transmits data in frames—micro data packages—and supports video, audio, and bus protocol formats in what are called data containers. (Figure 3) The necessary high-speed clock is synthesized by the transmitting device, not derived from the pixel clock of the graphics processor or camera; this makes the link highly immune to pixel-clock jitter, and leads to stable and reliable transmission over relatively long cables.
Figure 3: The APIX2 frame accomodates two independent video streams plus audio and Ethernet data.
The architecture allows easy and inexpensive "daisy-chaining" of displays, with splitters to interface with individual displays. Using interface ICs such as the ADV7680 from Analog Devices, the system can provide the connection between the bus and a HDMI enabled GPU or CPU.
The net data rate for APIX2 is 2.8 Gbps (downlink) and 187.5 Mbps (uplink); this allows two independent video streams, multichannel digital audio, and control data; further, using a standard-compliant media independent interface (MII), even Ethernet data can be transmitted. The approach supports a cable distance up to 12 meters (more than sufficient for automotive) because its internal algorithm continuously adjusts the digital filters to maximum throughout and minimize bit error rate.
The other issue which automotive applications can’t ignore is the stringent EMC (electromagnetic compatibility) emission limits. The constant serial stream of the APIX2 approach provides an even spread of the energy spectrum, with overall emission levels well below permitted maximums.
The car of the future: different than what was envisioned
There have been countless predictions about the automobile of the future: silent, flying, and even self-driving (autonomous). And while there is good progress in that last category—Google, for example, is doing some interesting work—most of these futurists did not envision a vehicle that would be so intensely networked, connected to the "cloud", and loaded with both driver displays and passenger infotainment. The auto is becoming a combination of a sophisticated, data- and display-heavy aircraft cockpit, plus an infotainment center for the passenger (and perhaps even the driver).
Nonetheless, that’s where the market is going, due to the expectations of today’s buyers, especially the newer ones for whom digital access and connectivity have always been their reality. For auto vendors and especially the IC vendors who supply them, it’s both a challenge and an opportunity: the challenge of meeting expectations of features, functions, and performance at acceptable prices, but with the opportunity to add valuable content to the vehicle with resultant profit and return on investment in a growth market.
About the author: Peter Hall is Automotive Connectivity Marketing Manager for Analog Devices, Inc.
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