TC255P

336-

× 244-PIXEL CCD IMAGE SENSOR

SOCS057 – JUNE 1996

2-4

POST OFFICE BOX 655303

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.

ABG

IAG

10

µm

Clocked Barrier

Virtual Barrier

Antiblooming Gate

Virtual Well

Clocked Well

Light

Antiblooming

Clocking Levels

Accumulated Charge

10

µm

Figure 1. Charge-Accumulation Process

SAG

Channel Stops

Virtual Phase

Clocked Phase

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.