AD9974BBCZ datasheet(28/52 Pages) AD

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AD9974

Rev. A | Page 28 of 52

HORIZONTAL TIMING SEQUENCE EXAMPLE

Figure 36 shows an example of a CCD layout. The horizontal

clocked from the CCD. In the vertical direction, there are

10 optical black (OB) lines at the front of the readout and two

at the back of the readout. The horizontal direction has four

OB pixels in the front and 48 in the back.

Figure 37 shows the basic sequence layout to use during the

effective pixel readout. The 48 OB pixels at the end of each line

are used for the CLPOB signals. PBLK is optional and is often

used to blank the digital outputs during the HBLK time. HBLK

is used during the vertical shift interval.

Because PBLK is used to isolate the CDS input (see the Analog

Front End Description and Operation section), do not use the

PBLK signal during CLPOB operation. The change in the offset

behavior that occurs during PBLK impacts the accuracy of the

CLPOB circuitry.

The HBLK, CLPOB, and PBLK parameters are programmed

in the V-sequence registers. More elaborate clamping schemes,

such as adding a separate sequence to clamp all the shielded

OB lines, can be used. This requires configuring a separate

V-sequence for clocking out the OB lines.

The CLPOBMASK registers are also useful for disabling the

CLPOB on a few lines without affecting the setup of the

clamping sequences. It is important to use CLPOB only during

valid OB pixels. During other portions on the frame timing,

such as vertical blanking or SG line timing, the CCD does not

output valid OB pixels. Any CLPOB pulse that occurs during

this time causes errors in clamping operation and, therefore,

changes in the black level of the image.

HORIZONTAL CCD REGISTER

EFFECTIVE IMAGE AREA

28 DUMMY PIXELS

48 OB PIXELS

4 OB PIXELS

10 VERTICAL

OB LINES

2 VERTICAL

OB LINES

Figure 36. Example CCD Configuration

VERTICAL SHIFT

VERT. SHIFT

CCD OUTPUT

SHP

SHD

H1/H3

H2/H4

HBLK

PBLK

CLPOB

OPTICAL BLACK

DUMMY

EFFECTIVE PIXELS

OPTICAL BLACK

NOTES

1. PBLK ACTIVE (LOW) SHOULD NOT BE USED DURING CLPOB ACTIVE (LOW).

Figure 37. Horizontal Sequence Example

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