Panasonic UF-890 Service Manual page 232

6.2.3 Picture Signal Scanning Block
The image data read by the optical unit is input to the CCD mounted on the CCD PC Board, then
transferred to the FCB PC Board after the optical information is converted into an electrical signal by the
CCD. The following shows a block diagram of the picture signal scanning circuit. This picture signal
scanning circuit consists of (1) ABC circuit, (2) shading correction circuit, (3) offset control circuit, (4) picture
signal binary coding correction circuit and (5) reducing circuit.
uPD3734ACY
ABC Circuit
This circuit consists of IC180, IC160, C650, R673 and R674. Its function is to prevent deterioration of
picture quality due to dirt on the document or degrading of the luminous energy of the LED light source.
The picture signal from the CCD is amplified in IC180 and input to IC160, where it is converted from
analog to digital and the shading is corrected. When the signal exceeds +3.0V as the result of this
amplification and correction, capacitor C650 is charged through R673. This charging voltage lowers the
level of the picture signal input to IC180. When the picture signal voltage rises, this charge voltage
becomes higher. When the picture signal level lowers due to the background color, etc., of a transmitting
document, the voltage of the charged capacitor C650 is discharged through R674. Consequently, the
output of the ABC circuit is kept constant to maintain the picture quality, regardless of changes in the
CCD output level.
CCD
W
B
(1)
VIDEO
(odd)
ADIN1
2048 bit
Effective Scan Width
232
(2)(3)(4)(5)
ADIN1
IC160
MN86075
CCD
Drive
Circuit
IC140
DZZAC000168