How can dynamic-range be larger than sensor bit-depth?

Question

Found something that confused me and so I thought the crowd here can probably answer this one since its camera-related and technical at the same time.

How can dynamic-range be larger than sensor bit-depth?

Someone sent me the DXOMark results for the Pentax K-5 which shows 14.1 EV of dynamic-range at its lowest ISO. However, given that the sensor is 14-bits, this does not fit with my intuition... It seems strange that a linear device like a CMOS-sensor can capture more DR than it has bits. Would it have a sparse dynamic-range, skipping EVs in the middle?

Answer

Cambridge in Colour has a very good article on this. If the sensor has a linear A/D converter, the bit depth would cap dynamic range at at 14 EVs as a theoretical limit. However, if it is non-linear, then the bit depth doesn't necessarily correlate. From that, I think we can determine that the sensor in the K-5 doesn't have a linear A/D converter.

I can say, from personal experience, that this sensor definitely has enormous dynamic range. I managed to recover an image that was close to 8 stops underexposed on the K-5.

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