TC254P Datasheet, PDF (4/16 Pages) Texas Instruments – 336- × 244-pixel ccd image sensor

TC254P
336- × 244-PIXEL CCD IMAGE SENSOR
SOCS060B – JUNE 1997 – REVISED JULY 1998
detailed description
The TC254P consists of five basic functional blocks: (1) the image-sensing area, (2) the image-clear line,
(3) the 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. Twelve columns of
shielded-from-light elements on the left edge of the image-sensing area generate the dark reference necessary
in subsequent video processing circuits for restoration of the video-black level. 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-clearing 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.
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