XRD98L62 Datasheet, PDF(30/37 Page) Exar Corporation – CCD Image Digitizers with CDS, PGA and 12-Bit A/D

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XRD98L62 Datasheet, PDF (30/37 Pages) Exar Corporation – CCD Image Digitizers with CDS, PGA and 12-Bit A/D

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XRD98L62

Preliminary

Line Rate Clocks

CLAMP & CAL are the two line rate clock signals.

There are two modes of operation for these clocks.

CAL & CLAMP Mode

In this mode the CLAMP signal is used to activate the

DC restore Clamp at the CDS input, and the CAL signal

is used to define the Optical Black pixels to be used for

the Black Level calibration function. Typically the

CLAMP pulse comes during the dummy or optical

black pixels at the beginning of each scan line, and the

CAL pulse comes during the longer string of optical

black pixels at the end of each scan line. CLAMP &

CAL must not be active at the same time.

In this mode there is an option to disconnect the CDS

from the input pins during the Vertical Shift time. To

enable this option write a â1â to the VSreject bit in the

Clock register. To properly define the Vertical Shift time

you must set the ClampCal bit properly.

In the typical case, the CCD has a few OB pixels at the

beginning of a line (CLAMP time) and a larger number

of OB pixels at the end of a scan line (CAL time). In this

case set the ClampCal bit = 0, this will define the

Vertical shift time as the time from the end of the CAL

pulse to the beginning of the CLAMP pulse.

If a CCD has more OB pixels at the beginning of a line,

then CAL should be active during these pixels and

CLAMP should be active at the end of the line. In this

case, set the ClampCal bit = 1, this will define the

Vertical shift time as the time from the end of the

CLAMP pulse to the beginning of the CAL pulse.

The ClampCal bit is also used by the Calibration logic.

If ClampCal is set as defined above, it should be correct

for the Calibration logic as well.

Active Video

Pixels

CCD

Signal

CAL

(Black Level)

CLAMP

(DC restore)

Vert. Shift Reject

(internal)

End of Line N

OB pixels

tCAL

Vertical Shift

Start of Line N+1

Dummy &

OB pixels

Active Video pixels

Disconnect CDS from

input pins

tCLAMP

Figure 20. Line Rate Timing with OneShot=0, VSreject=1 & ClampCal=0

Rev. P2.00

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