LM98722CCMTSLASHNOPB datasheet(13/150 Pages) TI1

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AGND

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LM98722

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SNAS487B – SEPTEMBER 2009 – REVISED MARCH 2015

7 Detailed Description

7.1 Overview

The LM98722 is a 16-bit, three-input, complete Analog Front End (AFE) for digital color copier and Multi-Function

Peripheral (MFP) applications. The system block diagram of the LM98722, shown in LM98722 Overall Chip

Block Diagram highlights the main features of the device. Each input has its own Input Bias and Clamping

Network which are routed through a selectable Sample/Hold (S/H) or Correlated Double Sampler (CDS)

amplifier. A +/-9-Bit Offset DAC applies independent offset correction for each channel. A -3 to 17.9dB

Programmable Gain Amplifier (PGA) applies independent gain correction for each channel. The LM98722 also

provides independent Digital Black Level Correction Feedback Loops for each channel. The Black Level

Correction Loop can be configured to run in Manual Mode (where the user inputs their own values of DAC offset)

or in Automatic Mode where the LM98722 calculates each channel’s Offset DAC value during optical black pixels

and then adjusts the Offset register accordingly. The signals are routed to a single high performance 16-bit, 45-

MHz analog-to-digital converter.

The analog inputs are protected as shown in Figure 1. Input voltage magnitude up to 500 mV beyond the supply

rails will not damage this device. However, input errors will be generated if the input goes above VA and below

AGND.

Figure 1.

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LM98722CCMT/NOPB 데이터시트(PDF) 13 Page - Texas Instruments