CX-890
2.2 Servo (UPD63702AGF: IC201)
The servo consists of mainly two parts. The first part is
the servo processing unit to equalize error signals and
control track jump, carriage move, in focus, etc. The
second part is the signal processing unit to perform
data decoding, error correction, and interpolation.
The system converts FE and TE signals from analog to
digital in IC201, then outputs drive signals of the focus,
tracking, and carriage systems via the servo block. The
EFM signal input from the preamplifier is decoded by
the signal processing unit, and eventually output as
audio signal after conversion into analog from digital
signals via the DA converter (IC201 contains audio
DAC). Then, the system generates error signal for the
spindle servo in the decoding process, sends the signal
to the spindle servo to generate drive signal for spin-
dle.
After that, drive signals for focus, tracking, carriage,
and spindle are amplified in IC301 and BA5986FM, and
supplied to respective actuators and motors.
1) Focus servo system
The main equalizer of focus servo is located in the
IC 201 UPD63702AGF
UPD63702AGF. Fig. 9 shows block diagram of the focus
IC301
servo.FOCUS
BA5986FM
ERROR
For the focus servo system, the lens must be posi-DIGITALFOPLENS
76A/DFD
EQUALIZER
tioned within the focusing range in order to perform14
CONTROL DAC 642
focus closing. To achieve this, the system moves theFOCUS SEARCHR301
TRIANGULAR WAVE10kW13
D/A3
lens upward/downward by focus-search voltage of tri-GENERATORFINFOM
4
angular waveform to detect the focusing point. DuringR302
15kW
searching, the system kicks the SPDL motor to main-
DRIVER
tain rotation speed to set speed.
The servo LSI monitors FE and RFOK signals so that
Fig. 9 Focus servo block diagram
focus closing is performed automatically at an appro-
priate point.
Focus closing is performed when the following four
conditions are satisfied:
(1)When the lens moves nearer to the disc.
(2)RFOK = "H"
(3)FZD signal (in IC) is latched to "H"
(4)FE = 0 (REFOUT as reference)
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ACEC
