E-M5 has DR 13!

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

Detail Man wrote:

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 !

.

dotborg wrote:

An analog to digital converter can be designed to encode any input voltage range. The assumption that one bit equals one stop is not necessarily true.

The amplification of a signal also does not define the input voltage range of an ADC.

If you could speak in more than short unconnected declarative "snippets", it might be possible to better understand what it is that you actually mean to say - and to discover what of substance may or may not exist behind the one-liners. Could you be more comprehensive in your expressions?

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