LM98714 datasheet(38/115 Pages) TI1

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LM98714

SNAS254A – OCTOBER 2006 – REVISED JANUARY 2014

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The loop is intended to be used prior to scanning the page or during the first several lines at the beginning of a

scan. The loop calibrates the channel offset such that the ADC outputs the desired code for Optical Black Pixels.

In automatic mode, the pixels used to calibrate the offset should be Optical Black pixels represented by the

internal “BLKCLP” pulse in Figure 31.

BLACK LEVEL OFFSET DAC

The offset level registers store the DAC value required to meet the respective channel’s black level output. While

using the Auto Black Level Correction Loop, the DAC registers are re-written as required every line the loop is

enabled.

BLACK LEVEL CLAMP (BLKCLP)

The BLKCLP pulse can be synchronized by either the falling edge of the SH pulse or the CLPIN pulse (both

shown in Figure 31). The automatic BLKCLP pulse will begin “n” number of pixel periods after the falling edge of

the reference pulse where “n” is the Auto Black Level Clamp Position register. The reference point is

programmed by the BLKCLP Mode Select Bits[1:0] within the Black Level Clamp Control register. The BLKCLP

pulse should not be programmed coincident to the CLPIN pulse (if the CLPIN pulse is being used).

Figure 31. Black Level Correction Timing

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LM98714 Datasheet(PDF) 38 Page - Texas Instruments