TC255P Datasheet, PDF (4/18 Pages) Texas Instruments – 336- × 244-pixel ccd image sensor

TC255P
336- × 244-PIXEL CCD IMAGE SENSOR
SOCS057 – JUNE 1996
detailed description
The TC255P consists of five basic functional blocks: 1) the image-sensing area, 2) the image-clear line, 3) the
image-storage area, 4) the serial register, and 5) the charge-detection node and output amplifier.
image-sensing area
Cross sections with potential-well diagrams and top views of image-sensing and storage-area elements are
shown in Figure 1 and Figure 2. As light enters the silicon in the image-sensing area, free electrons are
generated and collected in the potential wells of the sensing elements. During this time, the antiblooming gate
is activated by the application of a burst of pulses every horizontal-blanking interval. This prevents blooming
caused by the spilling of charge from overexposed elements into neighboring elements. To generate the dark
reference that is necessary in subsequent video-processing circuits for restoration of the video-black level, there
are 12 columns of elements on the left edge of the image-sensing area shielded from light. There is also one
column of elements on the right side of the image-sensing area and one line between the image-sensing area
and the image-clear line.
10 µm
Clocked Barrier
Light
IAG
ABG
10 µm
Virtual Barrier
Antiblooming Gate
Antiblooming
Clocking Levels
Virtual Well
Clocked Well
Accumulated Charge
Figure 1. Charge-Accumulation Process
Clocked Phase
SAG
Virtual Phase
Channel Stops
Figure 2. Charge-Transfer Process
image-clear line
During start-up or electronic-shutter operations, it is necessary to clear the image area of charge without
transferring it to the storage area. In such situations, the two image-area gates are clocked 244 times without
clocking the storage-area gate. The charge in the image area is then cleared through the image-clear line.
2-4
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