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CCD sensor types

CCD sensors are complex electronic components that consist of multiple arrays of light sensitive semiconductor elements. Each element represents a photo detector, a pixel that converts incoming photons into electrons.

During the integration phase (exposure time) all electrons released by the incoming light at the semiconductor-oxide interface are accumulated in a potential well. The accumulated capacity is proportional to the amount of the incident light and the exposure time. The capacity per pixel is then read out following several sensor read out techniques that are described in the following:

In addition to light sensitive pixels, interline transfer (ILT) sensors include vertical shift registers. Instead of shifting the charge through the light sensitive pixels, it is moved into a shielded shift register situated next to each line of pixels. The charge is moved to the vertical shift registers in one step before reaching the horizontal readout register and being clocked into the output amplifier, pixel by pixel. The reduction in fill factor imposed by the presence of the shift registers can be compensated for by microlenses to improve sensitivity. Although the full well capacity is reduced compared with other CCD architectures, well sizes of 30-50 KeV are commonly available on Sony and ON Semiconductor CCDs, which is adequate for 8-10 bits of digitisation. ILT CCDs are the most common type of sensor for modern vision cameras as the single step shift to the readout register allows for short exposure times and suitability for fast moving images. Over the next few years it is expected that the majority of applications that would have used interline CCDs will be using CMOS sensors.