E-M5 has DR 13!

Started Apr 13, 2012 | Discussions thread
Detail Man
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Output Dynamic Range Specifications are limited by ADC Bit Depth
In reply to dotborg, Apr 14, 2012

dotborg wrote:

Detail Man wrote:

Note: Just remember that 12-bit analog/digital converters have less than 12 EV Dynamic Range ...

The bit depth has nothing to do with how much light the sensor can capture; it only defines the tonality.

The number of bits of an ADC process defines a quantization noise-floor (which is less than the number of bits of the ADC conversion process). With or without pre-ADC amplification, that quantization noise-floor limits the potential output Dynamic Range regardless of the input signals.

Without any dithering, due to an uncertainty of plus-or-minus 1 least-significant-bit, a 12-bit ADC has a maximum output Dynamic Range of 11 bits multiplied by 6 dB equalling 66 dB (10.96 EV)

Pre-ADC analog active MOSFET amplifiers have a Dynamic Range on the order of around 80 dB at unity-gain (no amplification). Let's (for demonstration) assume ideal photo-sites that (themselves) generates absolutely no noise whatsoever, and a system that exhibits no read-noise whatsoever ...

To simulate a perfect transducer and read-system, connect the amplifier inputs to electrical ground

At a unity gain setting of the Pre-ADC analog active MOSFET amplifiers, random, uncorrelated noise sources in the amplifiers and the ADC input noise sources will vector-sum to -65.83 dB (10.93 EV).

At a 2x gain setting of the Pre-ADC analog active MOSFET amplifiers, random, uncorrelated noise sources in the amplifiers and the ADC input noise sources will vector-sum to -65.36 dB (10.85 EV).

At a 4x gain setting of the Pre-ADC analog active MOSFET amplifiers, random, uncorrelated noise sources in the amplifiers and the ADC input noise sources will vector-sum to -63.88 dB (10.61 EV).

At a 8x gain setting of the Pre-ADC analog active MOSFET amplifiers, random, uncorrelated noise sources in the amplifiers and the ADC input noise sources will vector-sum to -60.54 dB (10.05 EV).

Do you see an ADC output Dynamic Range greater than 11 bits (or 11 EV) appearing above ? ..

Add a real image-sensor/read-system. At full illumination, it's output Dynamic Range is around 40 dB. Vector-summation of all of these noise-sources limits the ADC's output Dynamic Range more ...

At a unity gain setting of the Pre-ADC analog active MOSFET amplifiers, random, uncorrelated noise sources in the amplifiers and the ADC input noise sources will vector-sum to -39.99 dB (6.64 EV).

So it is indeed all about fully illuminating the image-sensor, at which point the weakest-link where it comes to output Dynamic Range is by far photon-shot-noise arising in the photo-sites themselves.

But when specifying a camera's Dynamic Range (by measuring the noise-floor with very little or no illumination whatsoever), the bit-depth of the ADC process is demonstrably a limiting factor !

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