Originally posted by johnmflores Cool! Follow up question...the Sony A9 can shoot 20fps. Is that the stacked sensor at work? And does that suggest that the same technology applied to the Oympus OM-D EM1 II or any other M43 camera could result in 40fps (assuming same number of pixels)?
Thanks for sharing your knowledge.
The general trend in sensor design has been to increase the number of read-outs where the analog pixel signal goes into an analog-to-digital convertor (ADC) which was on a different chip on the main board. The first CCD sensors had only one read-out: the CCD shift registers moved all the pixel contents to one edge where a second linear CCD register moved the pixel contents to one corner for read-out by a second CCD line. In time, the design evolved to split the frame in halves, quadrants, sub-rectangles to read more pixels in parallel. Increasing the number of ADCs lets one either add more pixels, increase the frame rate, or slow the reading of each pixel (which gives more time for the analog signal to be carefully measured). But the number of ADCs is limited by how many wires can be run from the sensor to the main board.
Sony has moved the ADC on to the sensor chip and seems to have put one ADC for each column or two which enables each pixel to be more slowly and carefully measured. Thus, the A9 chip has something like 3000 or 6000 ADCs. But putting so many ADCs on the sensor creates a second problem of getting all that digital data off the sensor. A stacked design attaches a buffer RAM chip directly to the sensor chip which enables faster handling of the raw sensor data. (Note: there's some added design issues with minimizing rolling-shutter effects that also push the design toward the stacked chip design for the fastest-possible read-out.)
All of this development is actually being pushed by the smartphone market. There's huge pressure on Apple and Samsung to deliver better cameras with high IQ, 4K video, super-slow-motion, etc. Apple buys on the order of $4 billion in camera modules a year which provides a significant financial incentive for Sony to push the envelope. For example, Sony now has a 3-chip stack for smart phones that include the sensor, RAM, and GPU/CPU for doing extremely sophisticated image processing of high frame rate data.(
Image Sensors World: Sony Presents 3-Layer Stacked Sensor for Smartphones). Big sensor photography is actually lagging application.