TC237B

680-

× 500-PIXEL CCD IMAGE SENSOR

SOCS063 – APRIL 2001

3

POST OFFICE BOX 655303

Terminal Functions

TERMINAL

I/O

DESCRIPTION

NAME

NO.

I/O

DESCRIPTION

ADB

4

I

Supply voltage for amplifier drain bias

IAG1

12

I

Image area gate 1

IAG2

2

I

Image area gate 2

ODB

1

I

Supply voltage for drain antiblooming bias

OUT1

5

O

Output signal 1

OUT2

6

O

Output signal 2

RST

7

I

Reset gate

SAG

10, 11

I

Storage area gate

SRG

8

I

Serial register gate

SUB

3, 9

Substrate

detailed description

The TC237B CCD image sensor consists of four basic functional blocks: the image-sensing area, the image

storage area, the serial register gates, and the low-noise signal processing amplifier block with charge detection

nodes and independent resets. The location of each of these blocks is identified in the functional block diagram.

image-sensing and image storage areas

Figure 1 and Figure 2 show cross sections with potential well diagrams and top views of the image-sensing and

storage area elements. As light enters the silicon in the image-sensing area, electrons are generated and

collected in the wells of the sensing elements. Blooming protection is provided by applying a dc bias to the

overflow drain bias pin. To clear the image before beginning a new integration time (for implementation of

electronic fixed shutter or electronic auto-iris), apply a pulse of at least 1

µs to the overflow drain bias. After

integration is complete, charge voltage is transferred into the storage area. The transfer timing depends on

whether the readout mode is interlace or progressive scan. If the progressive-scan readout mode is selected,

the readout may be performed by using one serial register or at high speed by using both serial registers (see

Figure 3 through Figure 5). A line-summing operation, which is useful in off-chip smear subtraction, can be

implemented before the parallel transfer (see Figure 6).

Twenty-two columns at the left edge of the image-sensing area are shielded from incident light; these elements

provide the dark reference used in subsequent video-processing circuits to restore the video black level. In

addition, four dark lines between the image-sensing and the image storage area prevent charge leakage from

the image-sensing area into the image storage area.

advanced lateral overflow drain

The advanced lateral overflow drain structure is shared by two neighboring pixels and provides several unique

features in the sensor. By varying the dc bias of the drain pin, you can control the blooming protection level and

trade it for the well capacity.

To clear charge voltages in the image area, apply a 10-V pulse for a minimum duration of 1

µs above the nominal

dc bias level. This feature permits a precise control of the integration time on a frame-by-frame basis. The

single-pulse clear capability also reduces smear by eliminating accumulated charge from the pixels before the

start of the integration (single-sided smear).

Application of a negative 1-V pulse to the ODB signal during the parallel transfer is recommended to prevent

slight column-to-column pixel well capacity variations in some artifacts.