Last year, Canon demonstrated their 250MP APS-H sensor at the Canon Expo Show in New York City. Recently, at the ISSCC 2016 Conference on image sensors, Canon presented a detailed paper on their ground breaking invention.
Harvest Imaging reported on the Canon presentation :
"Hirofumi Totsuka of Canon presented a 250 Mpixel APS-H size imager : 1.5 um pixel pitch (4 sharing) made in 0.13 um technology node. The device is consuming 1.97 W at full resolution 5fps. An interesting build-in feature of this sensor is the following : ALL pixel signals are converted by column SS-ADCs with a single ramp, but in front of the ADC, each column has its own PGA that can be switched to 4x or 1x gain, depending on the signal level.
So when the pixels are sampled, a first check is done to look whether the signal is above or below a particular reference level, and then the right gain of the PGA is set to 1x or 4x. Simple method, but I think that the issues pop up in the reconstruction of the signal at the cross-over point between the two settings of the PGA."
The megapixel capability of this sensor will be best utilized in a full frame camera, if and when Canon decides to bring it to market.