Sony A7s sensor design

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Horshack
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Sony A7s sensor design
3 months ago

The A7s will be released in about two weeks. As far as I'm aware this is Sony's first modern large-pixel sensor design. What's interesting to see is how Sony was able to achieve 15.3EV of base ISO dynamic range (as stated by Sony's Mark Weir in this video), while also achieving what appears to be a new benchmark for High ISO DR as well (based on the very low shadow noise in these A7s converted raw images - to my eyes the A7s demonstrates 1EV lower High ISO shadow noise vs the D3s/1DX/Df).

Based on what I've learned here (and please correct me if I'm wrong), there is a dichotomy between DR at base ISO and High ISO due to the differences in conversion gain required between a large pixel, high full-well-capacity (FWC) sensor like the D3x/1DX/Df vs higher density sensors like the Sony 24MP/36MP Exmors. In a large pixel sensor, the FWC is much higher, resulting in a higher amount of referred read noise, which translates to lower base ISO DR, but this disadvantage turns into an advantage at Higher ISOs due to both the higher conversion gain of the sensor and also the lower total read noise aggregate from fewer sensels that must be read. The opposite appears to be the case in smaller pixel sensors, as they have shallower FWC but also benefit from Sony's Exmor Column-Parallel A/D conversion technology.

The D4 appeared to change matters from what is presumed to be the incorporation of Aptina's dual-conversion gain technology (PDF Whitepaper), where the sensor uses a low conversion gain at base ISO and then switches to a higher conversion gain at higher ISOs. This improved the base DR over the D3s by 1EV (13EV vs 12EV) without significantly reducing High ISO DR vs the D3s.

So the question is, what techniques did Sony use to achieve a 15.3EV base ISO DR (vs the D4's 13EV) while also maintaining and seemingly significantly improving on High ISO DR vs the D4. Is it a dual-gain technology like Aptina's? And/or in combination with Sony's low read-out noise due to the Exmor column-parallel A/D design?

Nikon D3S Nikon D3X Nikon D4 Sony Alpha 7S
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