Laser Driver Module (Ldm) - AGFA Avantra 36/44 Service Manual

Section I: Imagesetter
Figure 2-5 Sensor grid.
–Row 0. –Row 1. –Column 0. –Column 1.
–Column 2. –Column 3. –Column 4. –Column 5.
2.8

Laser Driver Module (LDM)

The LDM controls the laser diode current so that the laser diode light output wave-
form corresponds to that of the clocked data from the image buffer. The light out-
put intensity on an image basis is programmable via the control panel by varying
the laser diode power and polarizer setting.
Laser diode output light intensity variations due to variations in laser cavity temper-
ature are reduced by the use of wideband active feedback. This feedback loop
compares the laser diode photodiode current with a reference current. In order to
keep the loop disturbance to a minimum when the laser diode is turned off, a cur-
rent steering type feedback loop is used. The laser diode is turned off by steering
the loop current into a dummy laser, which keeps the loop active.
A dip switch mounted on the LDM calibrates the effect of the laser diode photo-
diode sensitivity variations from unit to unit. The LDM PCB is not a field replace-
able unit. The Laser Diode Module Assembly, which includes the LDM PCB, is not
field replaceable due to the extremely tight mechanical tolerances.
Functional Analysis 2-13