Monday, October 22, 2018
Sony Enhances MIPI D-PHY with Multiple Devices Connection Capability
Sony IMX418 global shutter CMOS sensor comes with an interface capable of multiple sensor connection on a single MIPI D-PHY input port, said to be the world-first sensor based on Sony's original data transmission technology. The company expects this product to be used in head mounted displays (HMD), drones, autonomous robots and other products that perform SLAM and obstacle detection based on information obtained with image sensors.
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Not being an expert on Mipi, I would guess that the maximal framerate of 120fps would be lower the more cameras you add to the Mipi, or is Mipi generally not the bottle neck?
ReplyDeleteIn theory, D-PHY 1.2 can go as fast as 2.5Gbps per lane. Sony uses 2 lanes, so it's 5 Gbps aggregated. 1MP 120fps 10b sensor generates 1.2 Gbps of data, so that they could connect 4 sensors without slowdown.
DeleteHowever, D-PHY is point-to-point interface that needs termination on both sides. If they just connect multiple sensors with no termination, the speed would be much slower than 2.5 Gbps.
Possibly, they use each sensor as a re-translator in the chain where each sensor has both Rx and Tx D-PHYs. The Rx receives image data from its neighbor in a point to point manner. Then the sensor adds its own data and sends everything together through Tx to the next sensor in the chain.
"1MP 120fps 10b sensor generates 1.2 Gbps of data". I do not think the DPHY sends only useful pixel data. You need some sort of coding of the data stream. The question is: what is the percentage of pixel data in the 2.5Gbps data stream? 70%? 80%?
DeleteThere is a number of coding options in MIPI, some of them have very little overhead. Remember, there is no CDR in D-PHY, so coding is more flexible.
DeleteI think the sensor at far end and at controller are terminated, others are not.
Deletethe sensors are tagged using virtual channels. the state machine inside the sensor knows when its bus slot is available. It only works with global shutter.
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