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3-5. FOCUS SERVO
IC101
FE
18
1.65V
Focus servo system is used to find focus ON point and to trace focus actuator into focus point using parallel
digital compensator.
Refer to below focus search diagram.
FE
IC201
109
FOD
IC201
119
AS
IC201
110
FOK
(Used only inside of IC201)
1. Light laser on through the IC101.
2. Move lens up or down and determine disk. Check amplitude of AS signal to make FOK.
3. Move lens up and down, find S-curve amplitude of FE.
4. Move lens down and up, monitor FE voltage. If [reference voltage (about 1.65V) - FE s-curve amplitude/8],
close servo loop and focus ON.
5. If AS signal is 2ms higher than threshold, FOK is "H" and focus servo is ok.
When AS is 2ms lower than threshold, FOK is "L".
FOK is using only in IC201, not in IC 201. (Impossible to FOK signal check with termina of IC201)
A/D
109
Amplitude
Detect
Focus search
Algorithm
Focus servo system
a
Focus search diagram
IC201
Parallel digital
compensator
DC Voltage
Generator
a
16
Focus on
2ms
FD
D/A
119
(Drive IC)
Threshold
2ms
IC301
25
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