Datasheet
SLAS326A − JANUARY 2001 − REVISED MARCH 2004
20
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
PRINCIPLES OF OPERATION
automatic optical black and offset correction (continued)
Due to different exposure times, there might be a sudden optical black level shift at the start of each frame. Thus,
a quick optical black level correction is desirable. The user can set an internal control bit (the SOF bit in control
register2) to automatically disable the hot/cold pixel limits and to set the digital filtering weighting factor to 1
(equivalent to one-line averaging). In this way the optical black correction could be performed very quickly for
the first line of each frame.
The number of black pixels in each line is programmable. The number of black pixels per line that can be
averaged is 2
N
, where N can be any integer from 0 to 6.
The autocalibration feature can be bypassed if the user prefers to directly program the offset DAC registers.
Switching the autocalibration mode to the direct-programming mode requires two register writes. First, the
control bits for the offset DACs in the control register must be changed, then the desired offset value for the
register is loaded to the offset DAC registers for proper error correction. If the total offset, including optical black
level is less than ±255 ADC LSBs, only the FDAC needs to be programmed. When switching from direct-
programming mode to autocalibration mode, the previous DAC register values, rather than default DAC register
values, are used as starting offsets.