Fully stacked: Hands-on with Sony's RX100 IV and RX10 II
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Fully stacked: Hands-on with Sony's RX100 IV and RX10 II

Sony has released updates to its popular RX-series compact cameras, leaving the externals pretty much unchanged, but with a major update to their sensors. 

Both cameras use a 'Stacked CMOS' design, which Sony calls Exmor RS. This is the next generation of CMOS technology, following on from the backside illuminated (BSI) design. Unlike BSI and the older front side illuminated technology, Stacked CMOS separates the photosensitive regions and the supporting circuitry into different layers, maximising the proportion of each pixel that can be light sensitive.

Originally developed for the tiny sensors in smartphones, this 1"-type sensor is by far the largest we've seen on this design. And, because the photosensitive region and the circuitry aren't competing for space, both can be maximised, allowing for potentially more light-gathering area, and more sophisticated logic to be performed on-chip. The sensor used by the RX100 IV and RX10 II, for instance, incorporates DRAM memory within the chip itself and it's this physically close buffer that's likely to enable the chip's impressive frame rates.