Stepping into next generation ADAS multi-camera architectures: Page 5 of 6

December 14, 2016 //By Thorsten Lorenzen, Texas Instruments
Stepping into next generation ADAS multi-camera architectures
Highly integrated approach to achieve extended synchronization and advanced HDR image quality to enable Automotive Surround View & Mirror Replacement Applications.

Line based Synchronization

Commonly, deserializer hubs support several line synchronization modes. In Non-Synchronized Forwarding Mode, the deserializer hub embeds the lines from all video streams in a first come, first send order. The same video lines from all cameras do not arrive in the ISP at the same time. Hence, lines captured at the same time are not stored in the buffer queues of the vision processor sequentially. In Synchronized Forwarding Mode however, the deserializer hub waits for the video lines from all camera modules to arrive prior to encoding the lines and embedding them into the CSI-2 output stream. As a result, the same lines from all cameras are interleaved. Deserializer’s job is to pack the incoming streams into one or two MIPI CSI-2 output streams. To do so, the use of virtual channels (VC-ID) are used to differentiate video streams on the MIPI CSI-2 output bus. Hence, the ISP and further the vision processor are able to distinguish the streams. If the vision processor is programmed to provide four independent buffer queues in memory, frames from each of the video streams can be stored in their own queue. This method leads to a scheme in which each frame captured at same time will be stored in the queues side by side. For instance, the frame from all the four streams captured at time slot x can be found in buffer queues at the same location x. Therefore, no timestamp support is required.


Figure 5. Virtual channels transfer multiple video streams across single interface

Power-over-Coax (PoC)

Applying power over the data coax cable, or power-over-coax (PoC), provides a convenient way to power the camera without extra cabling. In order to save additional wires, the camera modules can be supplied over the coax line and the shield from the processor ECU side. On the deserializer side power can be injected to supply all camera modules. In order to separate the DC power supply from the data signals, PoC filters need to be incorporated. The data signal frequency band begins at 1MHz for the back channel (depending on serializer backchannel speed). In contrast, the forward channel band can go higher than 700MHz. Hence, a 100nF capacitor needs to block any DC to pass. On the other side one 100uH inductor passes the DC but helps minimize AC noise interfering with the data signals.

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