Thursday, October 14, 2021

Prophesee CEO on Future Event-Driven Sensor Improvements

IEEE Spectrum publishes an interview with Prophesee CEO Luca Verre. There is an interesting part about the company's next generation event-driven sensor:

"For the next generation, we are working along three axes. One axis is around the reduction of the pixel pitch. Together with Sony, we made great progress by shrinking the pixel pitch from the 15 micrometers of Generation 3 down to 4.86 micrometers with generation 4. But, of course, there is still some large room for improvement by using a more advanced technology node or by using the now-maturing stacking technology of double and triple stacks. [The sensor is a photodiode chip stacked onto a CMOS chip.] You have the photodiode process, which is 90 nanometers, and then the intelligent part, the CMOS part, was developed on 40 nanometers, which is not necessarily a very aggressive node. Going for more aggressive nodes like 28 or 22 nm, the pixel pitch will shrink very much.

The benefits are clear: It's a benefit in terms of cost; it's a benefit in terms of reducing the optical format for the camera module, which means also reduction of cost at the system level; plus it allows integration in devices that require tighter space constraints. And then of course, the other related benefit is the fact that with the equivalent silicon surface, you can put more pixels in, so the resolution increases.The event-based technology is not following necessarily the same race that we are still seeing in the conventional [color camera chips]; we are not shooting for tens of millions of pixels. It's not necessary for machine vision, unless you consider some very niche exotic applications.

The second axis is around the further integration of processing capability. There is an opportunity to embed more processing capabilities inside the sensor to make the sensor even smarter than it is today. Today it's a smart sensor in the sense that it's processing the changes [in a scene]. It's also formatting these changes to make them more compatible with the conventional [system-on-chip] platform. But you can even push this reasoning further and think of doing some of the local processing inside the sensor [that's now done in the SoC processor].

The third one is related to power consumption. The sensor, by design, is actually low-power, but if we want to reach an extreme level of low power, there's still a way of optimizing it. If you look at the IMX636 gen 4, power is not necessarily optimized. In fact, what is being optimized more is the throughput. It's the capability to actually react to many changes in the scene and be able to correctly timestamp them at extremely high time precision. So in extreme situations where the scenes change a lot, the sensor has a power consumption that is equivalent to conventional image sensor, although the time precision is much higher. You can argue that in those situations you are running at the equivalent of 1000 frames per second or even beyond. So it's normal that you consume as much as a 10 or 100 frame-per-second sensor.[A lower power] sensor could be very appealing, especially for consumer devices or wearable devices where we know that there are functionalities related to eye tracking, attention monitoring, eye lock, that are becoming very relevant."

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