BOBCAT Hardware User’s Manual
Imperx, Inc.
Rev. 1.0
6421 Congress Ave.
5/4/2010
Boca Raton, FL 33487
+1 (561) 989-0006
19 of 212
1.3
BOBCAT SPECIFICATIONS
1.3.1 General Information
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, and Blue) arranged in a “Bayer” pattern, are placed over the pixels.
The starting color is typically Green for Kodak CCDs and Red for SONY CCDs,
but it varies from CCD to CCD. Figure 1.0 shows the CCD pixel structure. Table
1.1 shows the individual pixel structure for different BOBCAT cameras. Effective
pixels image consists of Active and Buffer pixels. Figures 1.1a, b, c and 1.2a,b
show the camera’s spectral response. Figure 1.3 shows the Bayer patter
arrangement.
