CMOS stands for complementary metal oxide semiconductor and is an alternative to CCD (charge couple device) as an imaging receptor. The difference in technology was once explained to me in layman's terms as follows.
In a CCD the data is downloaded by applying a charge to one end of the row of pixels and cascading the electric charge from each cell to the other end of the row where they are collected/measured. There is no ability to control the output of individual cells.
On a CMOS chip, each cell is effectively mounted on a board with a "wire" going to each one, so the charge can be downloaded individually from each cell. Other components can be mounted on the same board coupled directly to individual cells. This means that the output from individual cells can be controlled and also less heat is generated.
Probably an over simplistic and crude explanation but it helped me understand.
CMOS chips are cheaper to manufacture, have the advantage that other components (such as a/d (analogue/digital) convertors, clock etc) can be mounted on the chip and can therefore be simpler. CMOS chips run at a lower voltage and consume less power.
On the downside - first, the stationary noise pattern is higher than found in a CCD; and second, in that each pixel contains not just a photo diode, but in addition, amplifiers and selection circuitry, the actual area of the pixel that gathers photons is smaller. This is reflected as a reduction in sensitivity in comparison to a similar sized CCD. This is often referred to by describing the "fill factor" of the pixel, or the percentage of the pixel that gathers photons.
Hope that helps.
best
Francis Newman Webshot Ltd
On Thursday, February 27, 2003, at 04:23 PM, John Thompson wrote:
Forgive my ignorance, I have only just joined this list. What is cmos?
The Nikon stand said they had no intention of going down the cmos road as it
wasn't good enough from an image quality point of view????!
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