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SCANNER
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6.5 Contact Image Sensor Unit Control Circuit
6.5.1 Exposure LED control circuit
The cell guide mounted on the contact image sensor (CIS) unit is the main light source of the red/green/
blue LEDs and is used to expose originals. Also mounted is the LED array which is the subsidiary light
source of the yellow-green LEDs.
Turning each light source ON/OFF is controlled by the control signal (SCNLEDR/G/B/ASTOFF-1)
output from the ASIC on the MAIN board. According to the amount of each light source, white standard
generation is performed (reading the reflected light amount of the white shading correction plate). Black
standard generation is also performed (reading the light amount when the light source is turned off),
and according to the result, adjustment by the light amount adjustment signal (SCNLEDVR1/2/3-1)
output through the D/A converter from the SoC is made. However, the light amount of the green light
source is not changed because it is the standard value of the adjustment. The other light amount is
changed based on the green light source; in this way the total light amount is adjusted.
Fig. 6-4
+24V
SoC
D/A
converter
ASIC
Red Green Blue Yellow-Green
+
-
+
-
+
-
+
-
+4V
+5V
Serial data
SCNLEDVR3-1
SCNLEDVR1-1
SCNLEDVR2-1
SCNLEDROFF-1
SCNLEDGOFF-1
SCNLEDBOFF-1
SCNLEDASTOFF-1
Contact image sensor unit MAIN board