Image Processing Reference
In-Depth Information
on the available potential range by blooming suppression. This limitation is fast approach-
ing as pixel size becomes progressively smaller.
5.1.3 Progress of CCD Sensor
In this section, variation and progress of CCDs are described.
5.1.3.1 Frame Transfer CCD
FT-CCDs were proposed as the first CCD-type image sensor 4 rather than IT-CCDs. As
shown in Figure 5.27, an FT-CCD with 3(V) × 3(H) pixels is composed of four blocks: image
area, storage area (which does not exist in IT-CCDs), horizontal shift register (HCCD), and
output amplifier. In the imaging area, pixels are arrayed in a matrix in a plane. All parts
except for image area are usually covered with a light shield film so that they are not
affected by incident light. A four-phase CCD and isolation are built into the image area
and storage area. In the case of IT-CCDs, the sensor part and vertical shift register (VCCD)
are arranged independently. In contrast, there is no structural distinction in FT-CCDs; the
two functions work by time-sharing. During the exposure period, the CCD in the image
area integrates signal charges as sensor part. In the frameshift period, which is just after
the exposure period, it transfers signal charges integrated in it to the CCD in the stor-
age area with high frequency as vertical shift register (VCCD). Cross-sectional views and
potential distributions of pixels along vertical and horizontal directions are shown in the
Isolation
Pixel
φA1
φA2
φA3
φA4
Cross-section along vertical direction
VL
VH
VH
VL
n -
buried channel
p
Image
area
Potential distribution
0
Cross-section along horizontal direction
φB1
φB2
φB3
φB4
p +
p +
p +
n -
n -
p
Storage
area
Isolation
Potential distribution
0
HCCD
Photo electric
conversion
& charge
integration
Output amplifier
(FDA)
Light-shielding film
φC1
φC2
Photogate-type sensor part
(light transmissive material gate)
Light
Gate electrode
FIGURE 5.27
Configuration and structure of FT-CCD.
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