Sharp DV-500D Technical Manual page 22

DVD-Series
2. How to Make FES (Focus Error Signal)1· · · Hologram Foucault Method
Note: The following PD form is slightly different from the actual one. (image only)
(At the time of just focus)
C
B
From the deviation of focus, the light shown above (black part) comes back on PD. By
receiving the output through a differential amplifier, DC voltage, which responded to
defocusing, is output.
3. How to Make Thread Error Signal
Take out the low frequency component for tracking error signals.
Tracking Error Signal _ LPF _ Thread Error Signal
With this, move the thread to make OL stay around the free neutral point.
D
A
No
+
– error
Actual form has I/V amplifiers here
When thread does not move.....
(Close to the disc)
+
–
OL
Bump
PU
22
(Far from the disc)
+
+
–
–