TC221 Datasheet, PDF (4/14 Pages) Texas Instruments – SMALL-FORMAT CCD IMAGE SENSORS

TC221, TC225, TC227
SMALL-FORMAT CCD IMAGE SENSORS
SOCS037C – DECEMBER 1991 – REVISED AUGUST 1997
detailed description
The TC221, TC225, and TC227 consist of four basic functional blocks: (1) the image-sensing area, (2) the serial
registers, (3) the sensor node, and (4) the low-noise source-follower amplifier. The location of each of these
blocks is identified in the functional block diagrams.
image-sensing area
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, blooming protection is activated by applying a burst of pulses
to the antiblooming gate. This prevents blooming by the spilling of charge from overexposed elements into
neighboring elements. After integration and under dark conditions, the charge is transferred line by line into the
serial register(s). The required timing is shown in Figure 1 through Figure 3. During transfer, the antiblooming
gate is held at a low level. Each imager contains a specified number of dark pixels on the left side of the
image-sensing area. These elements provide the dark reference used in subsequent video-processing circuits
to restore the video black-level.
serial register(s)
Once an image line is transferred into the serial register, the serial-register gate can be clocked until all of the
charge packets are moved out onto the sense node. A drain is also included to provide the capability to clear
the image-sensing area of unwanted charge. Such charge can accumulate in the imager during the start-up of
operation or under special conditions when nonstandard TV operation is desired.
sense node(s) and source-follower amplifier(s)
After the charge packet is placed on the sense node, the potential of this node changes in proportion to the
amount of signal received. It is then buffered by a dual-stage source-follower amplifier. The sense node and
amplifier are located some distance from the serial register; a specified number of dummy elements is used to
span the distance. The location and number of the dummy elements are shown in the functional block diagrams.
Terminal Functions
TERMINAL
NAME
NUMBER
I/O
TC221
TC225
TC227
ABG
2
4
5
I
ADB
4
7
3
IAG
3
5
4
I
NC
N/A
6
N/A
OUT1
5
9
2
O
OUT2
N/A
8
N/A
O
SRG1
1
2
6
I
SRG2
N/A
3
N/A
I
SUB
6
10
1
TRG
N/A
1
N/A
I
N/A – not applicable
DESCRIPTION
Antiblooming gate
Amplifier-drain bias
Image-area gate
No internal connection
Output signal 1
Output signal 2
Serial-register gate 1
Serial-register gate 2
Substrate
Transfer gate
4
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