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The operation of detecting an adjusted focus point and
turning on the focus servo is called focus search. In a
focus servo system, a lens needs to move to the
adjusted focus point to enable focus close.
Accordingly, the adjusted focus point is detected by
moving the lens up and down according to the focus
search voltage of a triangular wave. Further, in the
meantime, a spindle motor enters the simplified FG
mode and maintains a constant speed of rotation. The
focus servo turns on under the following three
conditions:
1. FOK = H
2. A focus error signal exceeds a focus standby level
threshold.
3. A focus error signal reaches a zero cross.
At this time, while the lens is fully separated from the
adjusted focus point, cancel the SBAD offset and set
this level to SBOFF. If the SBAD level exceeds the FOK
threshold from the SBOFF standard, FOK = "H" is set.
When the lens moves up and down, a focus error signal
changes at the adjusted focus point. However, CD-LSI
removes an offset component by passing through a
bypass filter after it has A/D-converted this error signal.
When this FEHPE signal (LSI signal) level exceeds a
focus standby high level, the servo standby state
occurs because the adjusted focus point approaches.
Subsequently, the FEHPF signal reaches the adjusted
focus point and turns on the focus servo.
The microcomputer monitors an FOON signal (Active at
servo ON; L for a probe) at focus search, and starts
monitoring a FOK signal in 40 ms after it has been set
to Active). If it is judged that FOK is not active, the
microcomputer performs protection operation.
Besides, when the Focus Close button is pressed with
the focus mode select set to Display 01 in the test
mode, a focus error, search voltage and the action of a
practical lens can be checked.
2) Tracking servo system
The main equalizer of the tracking servo is comprised
with a digital equalizer unit. Fig. 10 shows a block
diagram of the tracking servo.
FOCUS SERVO ON
OFFSET
→
HIGH PASS FILTER
FEI INPUT WAVEFORM : FE
STANDBY LEVEL : F1
15.(3)
FOCUS SERVO ON
REF LEVEL
FEHPF
FOK LEVEL
SBOFF LEVEL
SBAD
88.1kHz×
=TOK
127 SAMPLE
FOK
FOON
Fig.9:FOCUS SEARCH TIMING
IC301 TC9495FP
TE
TEI
+
TRACKING
A/D
46
DAC
EQ
+
CARRIAGE
PWM
EQ
AT THE TIME OF FEED KICK
TEZI
47
JUMP
RFRP
CONTROL
42
Fig.10:TRACKING SERVO CIRCUIT BLOCK
CX-961
STANDBY
FOCUS SERVO ON
F1
LEVEL
F1
HIGH PASS FILTER OUTPUT : FEHPF
DEFECT(SCRATCHES)
IC401
"
BA5811FM
TD
TRO
TOP
49
6
11
12
FMO
53
26
15
SD
25
16
REF LEVEL
TOM
COP
M
CARRIAGE
MOTOR
COM
7
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