TLV990

3-V, 10-BIT, 28-MSPS AREA CCD AND VIDEO SIGNAL PROCESSOR

SLVS298 – MAY 2000

21

POST OFFICE BOX 655303

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

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.