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1
1.2 SERVO SECTION (UPD63763AGJ,UPD63761AGJ: IC 201)
A
The servo section operates servo control such as
equalizing of error signal, in-focus, track jump, carriage
move, etc. DSP is section for signal processing and
operates data decoding, error correction, interpolation
processing, etc. FE, TE signal generated in preamp stage
is A/D converted and outputs drive signal of focus,
tracking, and carriage system via servo block. And EFM
signal is decoded in the signal processing section and
outputs audio signal after D/A convert via D/A converter
finally. In addition, in this decoding process, error signal of
a spindle servo is generated, and supplied to the spindle
B
servo section, and outputs drive signal for the spindle.
Each drive signal of focus, tracking, carriage and spindle
is amplified by the driver IC BD7962FM (IC302) after that
and supplied to each actuator and motor.
1) Focus servo system
The main equalizer of focus servo is made up of digital
equalizer section. The fig 10 shows a block diagram of
C
focus servo.
In the focus servo system, it is necessary to bring a lens
within in-focus range to focus-close. In order to do that,
triangle wave of focus search voltage moves a lens up
and down to find in-focus point. During that time, a
spindle motor is kicked to maintain rotation at the fixed
speed. The servo LSI monitors FE signal & RFOK signal,
and operates focus-close automatically in appropriate
point. The focus-close is performed when following 3
conditions are set;
1 A lens is moving from away to near toward a disc.
D
2 RFOK= "H"
3 Just at the moment when FZC signal is once over the
threshold of FZD register and latched to "H" again (the
edge of FDZ). As the result, FE converges "0" (=REFO).
IC201 UPD63763AGJ,UPD63761AGJ
A+C
125
FE
A/D
B+D
AMP
128
FOCUS SEARCH
E
TRIANGULAR
WAVE GENERATOR
Fig.5 Focus servo block diagram
F
6
1
2
DIG.
EQ
FD
R218
CONTROL
DAC
101
10K
2
3
BD7962FM
R311
8R2K
C219
1000pF
CX-3168
3
4
IC302
LENS
FO+
18
10
17
FO-
11
4
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