The issue they are working on is the short back focus distance in a mirrorless camera that has lots of high tech fixes to help with the severe light falloff at the edges of the sensor. Those fixes interfere with autofocus. So, special "Ranging Pixels" near the edges of the sensor are designed to generate accurate autofocus data.
The effort to make mirrorless cameras small introduces lots of complex work-arounds due to the short back focus distance, and those generate fixes on fixes, and so on.
From the Patent:
"Description of the Related Art
Nowadays, in order to reduce the size of digital cameras, there is a demand for solid-state image
sensors that are compatible with camera lenses having a short back focus. In addition, in order to
broaden the dynamic range of digital cameras, large-size solid-state image sensors are being used
even in small-size digital cameras. In digital cameras that meet the aforementioned demands, light
beams are incident on pixels in peripheral regions of the solid-state image sensors at large
angles, and thus the light beams are incident on the pixels at positions that are shifted from
photoelectric conversion units disposed in the pixels. Consequently, the utilization efficiency of
the light beams are reduced, and the sensitivity of the pixels in the peripheral regions
decreases."
More:
"The present invention provides a solid-state image sensor that includes one or more ranging pixels,
and the one or more ranging pixels each include a microlens, a plurality of photoelectric
conversion units, and a plurality of wave- guides disposed between the microlens and the plurality
of photoelectric conversion units so as to correspond to the plurality of photoelectric conversion
units. The plurality of waveguides each include a core and a clad. In at least one of the ranging
pixels that is located in a peripheral region of the solid-state image sensor, the microlens is so
disposed that a ...."
