If you recall back in November, I talked about a sensor that Canon was going to show off at IEDM (International Electron Devices Meeting) in December, we haven't heard much about that until now. When I talked about this twisted sensor back in November, my thoughts on it were that it was a quad-pixel arrangement to support better AF in horizontal and vertical directions.
You may tell me, Richard, the title is clickbait. Well, perhaps. New information has recently surfaced about Canon's presentation and reading the sensor descriptions in the two articles, this is very much an “I don't know what it is.”. Canon specifically mentions that autofocus in various orientations and edge alignment improves with this new sensor and that they “twisted” the photodiodes to accomplish it. They mention that the pixels are rotated 90 degrees from each other, which traditionally indicates a quad-pixel arrangement (and they call this in the articles as being twisted). Canon describes this sensor as a “cross dual-pixel twisted-photodiode” sensor. So even Canon calls it a dual-pixel sensor, and not a quad sensor. So that's why you got that title and here we are.
Canon showed off this diagram at IEDM which illustrates how much better the new autofocus can see lines at various angles versus the more traditional DPAF sensor.
The far left column is the item being imaged, the middle is with the new twisted sensor, and the far right column shows the autofocus output from a traditional DPAF sensor. You can see that with a regular dual-pixel AF sensor, it simply can't recognize some of the lines at all, but that's not the case with the new sensor. The more the AF can recognize, the more it can do pattern recognition and autofocus, and the quicker it can do the calculations.
Canon also claims that this sensor is much quicker at autofocus than the current DPAF sensors, even with increased data reading. Canon suggests that it should be almost twice as fast as current sensors.
We are lacking any more information on this, to which I'm very sad. I would have loved to see if they are actually twisting the photodiodes for improvements or just used that terminology as a catchy phrase. I was telling Craig that I tried for a week to get my dirty little hands on that whitepaper.
We talked more about twisted photodiodes in the prior article, but just a refresher, the difference between a twisted photodiode and a regular one, is the small layer on top of the photodiode, in the above picture called TBG. In this example, it's a twisted bilayer graphene photodiode. We don't know if this is what Canon is doing. But it should be something similar.
This is research – we don't know when Canon would implement (if ever) this sensor, but it stands the reason that if Canon is talking about it publically like this, they have a high degree of confidence in the solution. No one wants to look like an idiot in front of their peers when Canon presented it at IEDM last December.
Source: Image Sensors World