Encoder/decoder transmits HD video signals via low-cost connections

July 13, 2021 // By Christoph Hammerschmidt
Encoder/decoder transmits HD video signals via low-cost connections
Renesas has unveiled a technology that enables HD video to be transmitted via low-cost cables and connectors that are actually only designed for standard definition video. The Automotive HD Link (AHL) also allows other components to be coupled together. The measure will significantly reduce the cost of implementing numerous safety functions, Renesas advertises.

The new AHL encoder RAA279971 and the decoder RAA279972 from Renesas use a modulated analogue signal to transmit the video content. Through data compression, this allows a bit transmission rate that is ten times lower than that of conventional digital HD signals. This means that conventional twisted pair cables (UTP) and standard connectors can be used as well as existing analogue video cables and connections. Digital connections such as SerDes, on the other hand, require heavily shielded cables and high-end connectors that cost significantly more. In addition, these have to be replaced after 5 to 7 years due to ageing and are difficult to install due to restrictions on the bending radius.

AHL is robust against interference signals, Renesas promises. The technology also has a bidirectional control channel that works independently of the video data. This allows camera modules to be initialised, programmed and monitored. An important feature is the ability to control the camera via the common UTP cable connection in parallel with the video transmission, which saves costs.

Another safety advantage of AHL is its performance compared to a digital connection. In a rear camera application, digital transmissions can be compromised by faults in the wiring harness or connectors. Weak signals can lead to the display of macroblocks, which means that large parts of the display area are no longer shown correctly. If, on the other hand, an AHL cable connection is used under the same (fault) conditions, the AHL link will only cause a slight change in video colour or contrast. However, all pixels will still appear on the screen and the image will accurately identify an object or person behind the vehicle.

AHL supports resolutions from VGA up to 720 p/60 or 1080 p/30 for flexible display of non-standard vertical resolutions (not just standard TV resolutions of 16:9). It supports MIPI-CSI2, BT656 and DVP interfaces and requires only a 27 MHz crystal input frequency, as internal


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