The World of Sensor Technology

Practically all microprocessor and memory chips are sensitive to light and so are normally protected by light-tight covers. There are several varieties of CCD and CMOS devices used in digital cameras, and although they do not differ in the basic principle of how they work, they do vary in the way in which the information captured by the sensors is used.

In CCDs, the charges built up in each sensor must be read off serially - one-by-one. Thus, the image is effectively scanned over its whole area to retrieve the data. In addition, the reading must be taken before the sensor array is ready to make another exposure.

CMOS devices are wired differently: each sensor element can be read off individually - they are said to be X-Y addressable - and each one can be reached by giving its reference. As a result, CMOS sensors may be put to many uses - not just image capture but also exposure metering and even autofocusing.

What CCDs lack in versatility they compensate for by being far simpler and cheaper to make, while giving a clean signal that is easier to process than that from CMOS sensors. In digital cameras, however, CMOS has the advantage of working at a single, low voltage, compared with the high and varying voltages of CCD devices.

Triple-well sensors

In this type of CCD, each sensor measures all three colours of light using a sophisticated design that depends on how deeply each colour penetrates the sensor. In this Way, mere is no need for a separate colour filter array and, in theory, the sensors can obtain at least three times more information than the equivalent using a Bayer pattern of coloured filters through a much reduced need for colour interpolation. In addition, the integration of colour separation into individual sensors means that pixels can be simply grouped - this lowers resolution but can increase sensitivity as well as the speed of image capture.

Steve J. Wilson is living in the United States and is a freelance writer since 2006, in digital photography related topics. If you are interested in some useful Digital Photography Class, than you are in the right place.

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