I've not read this, haven't got time. It's from the
Konica Minolta Photo World site. I remember seeing it when I first joined.
Light sensors in digital cameras – light becomes an electrical current
As is common knowledge, a light sensor takes the role of traditional film material in digital cameras. It converts the incident light into electrical signals, thus generating an image signal.
With development of high-resolution sensors, a new era of image recording technology has been heralded, and the traditional film-based image recording procedures are starting to pale by comparison
In this article, we want to focus on the basic mode of operation of the light sensor and introduce two different types of sensors.
CCD and CMOS – What's the difference?
Same physics – different composition
In both technologies, the photo-diodes are the key element of the light-sensor. They are responsible for converting incident light into an electrical signal.
Here CCD and CMOS principally work exactly the same way and both are based on the so-called photoelectric effect. To make the functionality clear, we have to briefly branch off into semiconductor technology, because the basic material of all sensors is the semiconductor silcon.
Semiconductors
Semiconductors are materials whose conductivity is located between highly conductive elements and isolators.
To selectively affect the conductivity of semiconductors, impurities are added – they are endowed. When endowing, foreign atoms are inserted into a rigid crystal-structure. So-called n-(negative) and p-(positive) semiconductors are the result.
If a p- and a n-semiconductor are adjoined, a thin border-layer with an ideal crystal-structure is created; the distinct halves are now respectively charged positively and negatively. If light lands on the n-layer, it can penetrate it, until an electron is knocked out of the border-layer.
If the p- and n-layer are now combined, a current of electrons arises: light has become electricity!
Differences CCD/CMOS
While CCD and CMOS-sensors are based on the same effect, they differ fundamentally in the way the image data is read out from the chip.
The word CMOS (Complementary Metal Oxide Semiconductor – transistors, that are arranced in pairs complementary to each other) refers to the way the sensors are produced.
By contrast to the CCD (Charged Coupled Device), where the current that is generated by each photo-diode is read out, transported (bucket brigade principle) and finally amplified and digitized on a line by line basis, the amplification and digitalization in a CMOS is done for every pixel directly by individually dedicated control-elements on the same chip that contains the light-sensitive photo-diodes.
What counts in practice?
The majority of up-to-date digital cameras work with CCD-sensors; it's only recently that CMOS sensors have also been used.
Since CMOS-sensors consist of the same material as common computer components and the control- and processing-elements are, unlike the CCD-sensor, integrated into the sensor in a single production process, CMOS-technology is more cost-effective.
This advantage is, however, relatively small for digital cameras.
While numerous low-cost devices like webcams work using CMOS-sensors, the costs for production rise proportionally to the demands on image quality, due to the necessarily complex image-signal enhancing, so that in the end both technologies are roughly equally expensive for high-quality applications.
Without elaborate image-signal enhancing, the CMOS-technique suffers from heavy image-quality problems, especially from image noise, and the multitude of integrated control-circuits results in a lower light-sensitivity (owing to the small size of a photo-diode).
CMOS – advantages at the moment mainly in beginner applications
For the time being, CMOS-technology can trade off its advantages mainly in those fields where a small size (for example mobile-phones with camera) and a cost-efficient mass-production are mandatory. The energy-consumption can, due to the sensor-composition, also be held to a very low level in such devices.
The possibility of individually addressing each pixel in a CMOS-sensor plays no decisive role in current camera-technology and is of greater interest in special appable technology and can list advantages with respect to the most important image-quality criteria like light-sensitivity, signal-to-noise ratio and dynamic range in the most applicatilications like mechanical image analysis.
If the image quality is the top-priority, CMOS technology loses, for the time being, its advantages over the CCD, and CMOS high-end cameras are neither cheaper, nor consume significantly less energy than comparable cameras with CCDs.
CCD – standard for high-developed image recording technology
If the image quality is the top-priority, CMOS technology loses, for the time being, its advantages over the CCD, and CMOS high-end cameras are neither cheaper, nor consume significantly less energy than comparable cameras with CCDs.
CCD – standard for high-developed image recording technology
CCD-technology is a highly-developed and relion classes.
The future: CCD or CMOS?
Both systems have their specific strengths and weaknesses, but it is unlikely that one technology will 'prevail' over the other. It is far more likely, that future sensor-systems will try to combine the advantages of both systems; which is spoken of as hybrid sensor technology.
Weeeeee..
