LM98725CCMTSLASHNOPB datasheet(35/145 Pages) TI1

35 / 145 page

-4

-3

-2

-1

128

160

192

224

PGA Register Value

Overall Gain (dB)

Overall Gain (V/V)

Gain (dB) =

20LOG10(180/(277-PGA Code))

Gain (V/V) =

(180/(277-PGA Code))

LM98725

www.ti.com

SNAS474H – APRIL 2009 – REVISED MARCH 2015

Figure 18. PGA Gain vs. PGA Gain Code

•

Dual Gain Mode - Page 1, Register 0x00h, Bit 1, and Registers 0x16h, 0x17h, 0x18h

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In many scanning systems, the system illumination and optics characteristics will result in a much higher

optical efficiency in the pixels near the middle of the sensor, compared with the pixels at the beginning

and end of the sensor. If a single gain setting is used for all pixels, the middle pixels will be near clipping,

while the ones at the edges can be at 1/2 scale or lower. This results in lower signal to noise for the edge

pixels. To combat this problem, the LM98725 incorporates an optional Dual Gain system. When enabled,

the system provides a second set of PGA gain registers to set the “high” gain for each input channel. The

“normal” gain settings will be applied during the “active/white” pixels, while the “high” gain settings will be

applied for all pixels before and after the “active/white” pixels (see LM98725 Typical Line Timing and Pixel

Gain Regions ).

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The Dual Gain enable bit is found at Page 1, Register 0x00h, Bit 1. The High Gain PGA settings are found

at Page 1, Registers 0x16h to 0x18h.

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LM98725CCMT/NOPB Datasheet(PDF) 35 Page - Texas Instruments