LYNX Manual RA02
1.3
LYNX TECHNICAL SPECIFICATIONS
A CCD camera is an electronic device for converting light into an electrical
signal. The camera contains a light sensitive element CCD (Charge Coupled
Device) where an electronic representation of the image is formed. The CCD
consists of a two dimensional array of sensitive elements – silicon photodiodes,
also known as pixels. The photons falling on the CCD surface create
photoelectrons within the pixels, where the number of photoelectrons is linearly
proportional to the light level. Although the number of electrons collected in each
pixel is linearly proportional to the light level and exposure time, the amount of
electrons varies with the wavelength of the incident light. When the desired
exposure is reached, the charges from each pixel are shifted onto a vertical
register, VCCD, and then one row downwards in a vertical direction towards a
horizontal register, HCCD. After that the electrons contained in the HCCD are
shifted in a horizontal direction, one pixel at a time, onto a floating diffusion
output node where the transformation from charge to voltage takes place. The
resultant voltage signal is buffered by a video amplifier and sent to the
corresponding video output. There are two floating diffusions and two video
amplifiers at each end of the HCCD, and the charges can be transferred towards
any of the outputs (depending on the mode of operation). The time interval
required for all the pixels, from the entire imager, to be clocked out of the HCCD
is called a frame. To generate a color image a set of color filters (Red, Green,
Blue) arranged in a “Bayer” pattern, are placed over the pixels. The starting color
is Green. Figure 1.1 shows the CCD pixel structure. Table 1.1 shows the
individual pixel structure for different LYNX cameras. Figures 1.2, 1.3 and 1.4
show the camera’s spectral response.
Figure 1.0 - CCD Pixel Structure
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