Canon iR8500 Servise Manual page 62

CHAPTER 2 NEW FUNCTIONS
2.2.3 4-Channels High-speed CCD
To accommodate the reading speed of 80 ipm, a 4-channel high-speed CCD is used. The
CCD consists of two CCDs (half the length of the existing CCD) combined together. The
resulting CCD is divided into the first half and the second half in the middle, and reading is
started at both ends (left/right), thereby reducing the data transfer time needed for reading
by half and ultimately enabling high-speed reading.
The image data comes in four channels: even-number pixels from first half, odd-number
pixels from first half, even-number pixels from last half, and odd-number pixel from last
half. The CCD data is transferred as shown in F02-202-02:
Direction of charge transfer
Clock pulse C
Output
unit C
Light-
receiving
7500 7499 7498 7497
unit
Output
unit D
Clock pulse D
Direction of charge transfer
2-18
Transfer unit C Transfer unit A
3754 3753 3752 3751 3750 3749 3748 3747
Transfer unit D Transfer unit B
F02-202-02
COPYRIGHT© 2001 CANON INC.
Direction of charge transfer
Clock pulse A
4 3
Clock pulse B
Direction of charge transfer
2000 2000 2000 2000 CANON iR8500 REV.0 MAR. 2001
Output
unit A
CCD
shift
2 1
pulse
Output
unit B