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參數(shù)資料
| 型號： | LM9801CCVF |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 模擬信號調理 |
| 英文描述： | Greyscale/24-Bit Color Linear CCD Sensor Processor |
| 中文描述： | SPECIALTY ANALOG CIRCUIT, PQFP52 |
| 封裝： | TQFP-52 |
| 文件頁數(shù)： | 25/34頁 |
| 文件大?。?/td> | 520K |
| 代理商： | LM9801CCVF |
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Applications Information
(Continued)
5.2 Coarse Gain Calibration
The LM9801’s PGA corrects for up to 9 dB of varIation in
the CCD output signal’s white level intensity. That 9 dB
range has to be centered inside the 9 dB window of correc-
tion as shown inFigure 7. The window’s upper limit is deter-
mined by the Target code, and the lower limit by the Target
code divided by 2.8 (this corresponds to the minimum gain
range of the PGA). To allow proper calibration, the ampli-
tude of all the pixels in the CCD should be inside this range
when those pixels are scanning an image corresponding to
the Target code. The placement of the pixels inside the 9
dB window can be controlled by any of three ways: chang-
ing the gain of the VGA, changing the integration time of the
CCD, or changing the intensity of the light source.
In most designs, the output waveform of the CCD can be
brought into the 9 dB correction range of the PGA by adjust-
ing the gain of the VGA. This is the next step in system
calibration.
TL/H/12814–34
FIGURE 7. CCD Input Signal In Range
Figure 8 is a flowchart of one technique to find the optimum
VGA gain setting during calibration. Calibration begins with
a VGA gain setting of 1V/V and increments the VGA gain
until one of the four possible results occur. Result 1 is the
desired outcome, where the signal falls into the range
shown in Figure 7 and the VGA calibration has been suc-
cessful.
TL/H/12814–35
FIGURE 8. VGA Calibration Flowchart
http://www.national.com
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