Dvd Servo Circulation - Sharp DV-500D Technical Manual

DVD-Series

4. DVD Servo Circulation

4-1 Outline of Disc Servo
Spindle Motor
Focus Drive Signal
Tracking Drive Signal
1. Focus Servo
Move OL up and down to focus on the disc pit.
Disc (DVD) face shake ± 300µm
Accuracy of Turn Table 150µm p-p
2. Tracking Servo
Move the Object Lens between the internal and external circumference (at a right-angle to
the track) to place the beam on the track.
Disc (DVD) core 100µm p-p
Core at TT, fastened 50µm p-p
3. Thread Servo
Because the object lens' movement is small (about ± 0.35m/m in the tracking direction), the
entire pick-up is moved near the target track with the thread motor.
In normal reproduction, it is necessary to make a fine movement, in which the object lens
stays around a free neutral point. In this case, it is necessary to make a high-speed move in
order to suppress object lens vibration.
OL (Object Lens)
PU (Pick up)
RF Signal
(A, B, C & D)
FES
(Focus Error Signal)
Servo IC
Driver
(Gain Revision, Phase Compensation)
Thread Motor
Thread Drive Signal
AGC
RF Amplifier
EQ
and
Error Formation
TES
(Tracking Error Signal)
Suppression under ± 0.23µm
_
Suppression under ± 0.022µm
_
20
Slice .
Asymmetrical PLL
Revision
CLV Error Signal