SerDes eyed for fatter bandwidth pipes inside smart cars


When it comes to advanced driver assistance systems (ADAS), much of the design limelight goes to cameras and sensors that generate video, audio, and control information to enable features like autonomous braking, pedestrian detection, parking assistance, and collision avoidance. But what about the underlying data transport technology that moves around the high-resolution content in vehicles? A surround view system, for instance, streams 1280 x 800 pixel video at a rate of 30 frames per second.

Whether it's ADAS or infotainment or connected car technologies like V2V and V2X, they all mandate greater bandwidth, complex interconnect, and robust data integrity in order to facilitate real-time driver assist and safety features. Market research firm Strategy Analytics forecasts that bandwidth requirements in vehicles will grow 25 times by the year 2020 from where they are in 2017. The meteoric rise in the amount of aggregated sensor data will inevitably overwhelm the automotive bandwidth now mostly served by buses or networks such as CAN, LIN, MOST, FlexRay, LVDS, and Ethernet. In fact, the advent of megapixel resolution imaging in vehicles seems to preclude these automotive links, except LVDS and Ethernet.

[Figure 1 | How a high-speed serial link such as GMSL works]

But while in-vehicle Ethernet backbone can transport data 100x faster than a CAN bus link, it still requires compression of video feeds and doesn't seem to scale to frame rates for high-resolution video streams from multiple cameras. And that's where high-speed serial links come into the picture.

High-speed serial links

Take, for example, Maxim Integrated's gigabit multimedia serial link (GMSL) technology, which provides a compression-free alternative to Ethernet for transfer of 4K videos and high-definition audio in the cars of future.

The serializer and deserializer (SerDes) chipsets in GMSL connectivity solutions ensure that shielded twisted pair (STP) or coax cables of up to 15 meters meet the most stringent electromagnetic compatibility (EMC) requirements of the automotive industry. The spread spectrum technology built into the SerDes chips eliminates the need for an external spread spectrum clock while boosting the protection against electromagnetic interference (EMI).

The serializer IC boasts error detection of video and control data via a crosspoint switch for multiple cameras. And it drives longer cables with programmable pre/de-emphasis features. On the other hand, deserializer IC, which tracks data from a spread-spectrum serial input, also facilitates adaptive equalization to improve error rates.

[Figure 2 | MAX96708: the 14-bit GMSL deserializer for megapixel cameras features a crosspoint switch that maps data to multiple outputs.]

The GMSL technology has recently been adopted as a miniature automotive chassis in the ADAS Surround View kit offered by Renesas. Earlier, Maxim's GMSL interface has been used to transport high-speed data in Nvidia's DRIVE CX (cockpit) and PX (piloted driving) platforms.

Here, GMSL transported data between the Nvidia SoC and multiple camera inputs. And the deserializer chipset synchronized video streams from four cameras while simultaneously powering each camera over the same coax cable.

Maxim's SerDes technology is striving to fill the bandwidth gaps in the rapidly changing automotive design landscape. And for that goal, having automotive powerhouses like Renesas and Nvidia on its side seems to be a good start.

Majeed Ahmad is the former Editor-in-Chief of EE Times Asia. He is a journalist with an engineering background and two decades of experience in writing and editing technical content. He is also the author of six books on electronics: Smartphone, Nokia’s Smartphone Problem, The Next Web of 50 Billion Devices, Mobile Commerce 2.0, Age of Mobile Data, and Essential 4G Guide.

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