Thomas Wirschem and Paul McCormack, National Semiconductor
Automotive Designline Europe11/17/2011 8:37 PM EST
Camera-based driver assistance systems are a rapidly gaining popularity. But to enable highest quality and video display capabilities, seamless integration of all system components is mandatory.
This article describes a parking assistance system using four camera sensors, connected to an FPGA baseboard through the serializer/deserializer (SerDes) interface chip. Specifically, the FPD-Link product family is designed for serial interfaces of embedded displays and camera sensor systems, and also has industrial applications.
The video interfaces of the latest generation, FPD-Link III, simplify the architecture of driver assistance systems. In this context the innovative implementation of a full-duplex control channel is of noteworthy importance. In addition to the forward channel drivers and receivers, the I/Os contain specific back channels within the relevant counterparts. In forward direction the control data are embedded into the video data stream. The back channel exchanges its data simultaneously at the same time as the video data over the same set of differential pair transmission lines. This enables a continuous data exchange in real-time with the lowest latencies, independent of timing considerations like the length of blanking intervals.
Parking assistant systems with several distributed camera heads allow for a very precise synchronization excluding the creation of possible artifacts during the computation of the entire image. In order to enhance the EMC compliance, the receiver is equipped with specific reduction methods like spread-spectrum clocking. Doing so, the additional functionalities allow for an implementation with further decreased RF emissions. There is no need for an additional physical transmission channel, and this function makes additional control buses, such as CAN or LIN, obsolete for this purpose—thus allowing for a reduced number of connector and cable connections, decreasing in turn the system costs as well as the weight of the wiring harness, which will have a positive ecological effect.
This two-wire solution with additional AC-coupling allows for the use of ultrathin and long cable connections at exposed locations and facilitates the placement within the car chassis. The combination of high bandwidth, low EMI, noise immunity, autonomous synchronization, and support of cost-effective twisted pair cable media assure that the chipsets are a plug-and-play solution.
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