Canon CP660 Service Manual page 72

CHAPTER 3 LASER EXPOSURE SYSTEM
The signals are further converted into laser drive signals on the laser driver PCB
(internal signals of the laser/scanner assembly) used to turn on and off the laser diode,
thereby generating a laser beam.
The modulated laser beam is turned into a parallel beam by means of a collimating
lens and a cylindrical lens, and is directed to a 6-facet mirror rotating at a specific speed.
When reflected by the 6-facet mirror, the laser beam moves through an imaging lens
and a reflecting mirror arranged in front of the 6-facet mirror to focus on the photosensi-
tive drum.
The 6-faced mirror rotates at a specific speed, enabling the laser beam to scan the
surface of the photosensitive drum at a specific speed.
An image takes shape on the surface of the photosensitive drum as the drum rotates
at a specific speed and, while at the same time, as the laser beam scans its surface at a
specific speed.
Note:
Low Voltage Differential Signal
The machine's PWM modulation circuit is on the DC controller PCB, requiring PWM-
modulated laser drive signals to move through a cable for turning on and off the laser.
If PWM-modulated laser drive signals were sent over a cable as they are, the noise
radiating from the cable would affect the PCBs on the way. To prevent such a problem,
the signals are processed to suppress amplitude. The printer unit generates two sets
of signals (differential signals) to avoid a decrease in the noise margin, otherwise
caused by low amplitude.
3-2
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CANON 660/2100 REV.0 FEB. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)