7
CX-961
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.
Fig.9:FOCUS SEARCH TIMING
→
OFFSET
FOCUS SERVO ON
FEI INPUT WAVEFORM : FE
HIGH PASS FILTER OUTPUT : FEHPF
HIGH PASS FILTER
STANDBY
LEVEL
F1
F1
FOCUS SERVO ON
REF LEVEL
STANDBY LEVEL : F1
15.(3)
FOCUS SERVO ON
REF LEVEL
FEHPF
SBAD
FOK
FOON
FOK LEVEL
88.1kHz
×
127 SAMPLE
SBOFF LEVEL
DEFECT(SCRATCHES)
=TOK
IC401
BA5811FM
CARRIAGE
MOTOR
COM
TOP
"
IC301 TC9495FP
DAC
A/D
TRACKING
EQ
+
A
T TH
E TIM
E O
F LEN
S K
IC
K
TE
TEI
TRO
M
TD
TOM
COP
CARRIAGE
EQ
+
PWM
FMO
AT THE TIME OF FEED KICK
JUMP
CONTROL
TEZI
RFRP
SD
46
47
49
53
6
16
15
12
11
25
26
42
Fig.10:TRACKING SERVO CIRCUIT BLOCK
