XRD98L63 Datasheet, PDF(21/41 Page) Exar Corporation – CCD Image Digitizers with CDS, PGA and 12-Bit A/D

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XRD98L63 Datasheet, PDF (21/41 Pages) Exar Corporation – CCD Image Digitizers with CDS, PGA and 12-Bit A/D

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XRD98L63

Hold Mode

The purpose of this mode is to prevent any changes in

the Fine or Coarse accumulators. This mode is in-

tended to optimize digital still camera applications

(DSC). The idea is to first run the calibration normally

so the Fine and Coarse accumulators converge on the

correct values to achieve the programmed Offset

Code. Then, just before acquiring the final image data,

activate the Hold mode. This will ensure the black level

offset of the CDS/PGA does not change while the final

image is being transferred out of the CCD. Once the

image has been acquired from the CCD, turn off the

Hold mode so the chip can continue to compensate for

any changes in offset due to temperature drift or other

effects.

To activate the Hold mode, write a â1â to the CAL Hold

bit in the Calibration register. By default, the Hold

mode is not active.

Manual Mode

The purpose of the Manual Mode is to disable the

automatic calibration feature and allow a system to

write directly to the Coarse and Fine Offset Adjust

DACs. When Manual mode is enabled, the Coarse

Offset DAC (CDAC) is programmed by writing to the

CDAC Even register, CDE[8:0]; the Fine Offset DAC is

programmed by writing to the FDAC Even register,

FDE[9:0].

If the Multiple Gain Mode is enabled, then the CDAC

Odd register and the FDAC Odd register are also used

to program the Offset Adjust DACs.

To activate the Manual mode, write a â1â to the ManCal

bit in the Calibration register. By default, the Manual

mode is not active.

Ignoring Fringe Pixels

Fringe pixels are the first few OB pixels at the edge of

the metal shield. Usually, these pixels receive some

reflected and/or scattered light, so they do not repre-

sent true âOptical Blackâ. If the CAL signal is active

while the CCD outputs Fringe pixels, the Calibration

logic will not converge properly. The OBdel[1:0] param-

eter can be used to tell the Calibration logic to ignore (or

delete) the first 0-3 OB pixels every time the CAL signal

is activated.

OBdel[1:0]

Number of

Fringe Pixels

to Ignore

Table 6. Ignoring Fringe Pixels

Light

Metal Shield

CCD V V V V Fr Fr Fr OB OB OB OB OB OB OB OB OB OB OB

Active Video pixels Fringe pixels Good Optical Black pixels

CAL

Ignore these 3 pixels by

setting OBdel[1:0]=11

Figure 13. Example of Ignoring Fringe Pixels Using OBdel[2:0]

Rev.1.01

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