PIX 2015

Dynamic Range -- what it is, what it's good for, and how much you 'need'

Started Oct 17, 2011 | Discussions thread
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Nemianiu Skqergl
Regular MemberPosts: 156
Re: Hilarious!
In reply to Great Bustard, Oct 23, 2011

Great Bustard wrote:

FrankyM wrote:

Great Bustard wrote:

FrankyM wrote:

You are assuming that read noise scales with pixel area.

I am not "assuming" -- I am defining "equally efficient sensors" as two sensors with the same QE, same read noise / area, and same saturation limit / area.

Yes, you are defining a situation designed to give you the answer you want.

What is the "answer that I want", and what's my agenda for wanting that answer? That smaller pixels, for equally efficient sensors, always result in greater IQ?

But if you really want to make a comparison between large and small pixels you should start with a level playing field. Read noise, for a given manufacturing process, simply does not scale with pixel area. Therefore, your definition is comparing apple with oranges.

Sensors are made of silicon, not playing fields. The point of comparison is to yield useful information, not as a sport (except maybe here). Sensor designers reduce pixel size because they can , due to process geometry improvements. What you are asking is 'what if they eschewed these improvements', in which case one needs to ask 'can they achieve the lower read noise of small transistors with bigger pixels?' The answer is, only up to a point, because the lower read noise is due to the high charge voltage 'gain' of a small transistor. That means that a large pixel would produce a larger voltage swing than the small transistor can deal with. Given some process geometry, there is only a small range of optimised pixel sizes that work within that.

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