Canon ImageRunner iR8500 Series, Service Manual, Page: 313 / 1122

Chapter 6
6-3
6.2.3 Driving the CCD
0008-9642
/ iR8070
The machine's CCD sensor is a single-line linear image sensor, and is composed of 7450 pixel photo cells.
The signals subjected to phtoconversion in the light-receiving segment are sent out in two types of analog signals: even-number (EVEN) pixels and odd-
number (ODD) pixels.
F-6-5
6.2.4 Gain Correction and Offset Correction of the CCD Output
0008-9643
/ iR8070
To correct discrepancies in the efficiency of photoconversion among pixels, the analog video signals from the CCD are corrected: in gain correction, the
rates of amplification are standardized; in offset correction, on the other hand, the output voltage in the absence of incoming light is set to a specific level.
6.2.5 A/D Conversion of the CCD Output
0008-9644
/ iR8070
The analog video signals of odd-number and even-number pixels after correction are converted into 8-bit digital signals that correspond to specific pixel
voltage levels by the A/D converter.
Service Mode:
- COPIER/ADJUST>ADJ-XY>ADJ-Y (CCD read start position adjustment)
It is used to adjust the parameter used determining the read start position in main scanning direction.
Range: 100 to 400
(A change by '1' results in a shift of 0.1 mm.)
F-6-6
6.2.6 4-Channel High-Speed Reading CCD
0006-9671
iR105i/iR105+ / iR9070
To support high-speed reading at 80 ipm, the machine uses a 4-channel high-speed reading CCD. It consists of two CCDs connected to form a single entity
(each, half length of a common CCD); the entire CCD is divided in the middle into first half and last half.
Reading starts simultaneously at both left and right sides, thereby cutting the data transfer time required for reading by half and ultimately enabling high-
speed reading.
The image data is divided into 4 channels: first-half even-numbered pixels, first-half odd-numbered pixels, last-half even-numbered pixels, and last-half
odd-numbered pixels. The following diagram shows how CCD data is transferred:
Shift register
Light receiving
segment
(photodiode)
Shift register
Output buffer
Output buffer
Gate
Gate
1 2 3 4 5 6
Odd-number pixel data
Even-number pixel data
Decrease
Increase
Original
Vertical size plate
Read start position