Service manual

CHAPTER 2

2 - 13

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2002 CANON INC. CANOSCAN 8000F REV.0 OCT. 2002 PRINTED IN JAPAN (IMPRIME AU JAPON)

1) D/A Converter

D/A converter removes ununiform analog data generated by the CCD. It adjusts CCD output

to keep max. 5V of input signal to the A/D converter, to make the black level of the image

constant.

2) A/D Converter

The A/D converter converts the black-level-corrected image signal (analog signal) to a 16-bit

image data (digital signal) in the order of red, green and blue image signal.

5V is applied to the Vcc terminal and reference voltage is applied to the Vref terminal. A/D

converter outputs “0” when input signal is 5V, and outputs “255” when input signal is

reference voltage. This converts 1 pixel signal into the image data of 65536 gradations for red,

green and blue each.

Figure 2-14

2. A/D Conversion

Output signal from the CCD is an analog signal which cannot be used as image data. So

RGB output signal from the CCD is amplified by analog amplifier to generate analog data. The

generated data is converted into averaged analog signal by D/A converter, then got feedback to

the A/D converter to output constant digital data to the ASIC.

Figure 2-13

CCD

Analog

Amplifier

D/A Converter

A/D Converter

Digital data

To ASIC

Analog IC

A/D Converter

Output

Image Data

+5V

CCD_B

CCD_G

CCD_R

Blue Image Signal

Green Image Signal

Red Image Signal

Vcc

Vref

Reference Voltage