LG GDR-8161B Service Manual page 8

3. Structure of the Photo Diode (DVD-ROM)
1) Focus Error Signal –> (a+c) - (b+d)
• In case of DVD Disc
This signal is generated in RF AMP IC (IC101) and controls the pick-up's up and down to
focus on DVD Disc.
2) Tracking Error Signal (DPD Method) –> Differential phase of A and B + Differential
phase of C and D
• In case of DVD Disc
This signal is generated in RF AMP IC (IC101) and controls the pick-up's left and right shift to find the track
on DVD Disc.
3) RF Signal –> (a+b+c+d)
• In case of DVD Disc
This signal is converted to DATA signal in DSP IC (IC201).
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a
d
b
c
Pick-Up module
Photo Diode
(As seen from light
receiving side)
Tracking
Red laser
Focusing