CX-680
1.2 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 per-
form data decoding, error correction, and interpola-
tion.
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 eventual-
ly output as audio signal after conversion into analog
from digital signals via the DA converter (IC201 con-
tains 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 spindle.
After that, drive signals for focus, tracking, carriage,
and spindle are amplified in IC301 and BA6797FM,
and supplied to respective actuators and motors.
1) Focus servo system
The main equalizer of focus servo is located in theIC 201 UPD63702AGF
UPD63702AGF. Fig. 9 shows block diagram of the fo-IC301
FOCUS
BA6797FM
cus servo.ERROR
DIGITAL
76A/DFDFO+LENS
For the focus servo system, the lens must be posi-EQUALIZER16
tioned within the focusing range in order to performCONTROL DAC 6420FOCUS SEARCHR302
TRIANGULAR WAVE20kW17
focus closing. To achieve this, the system moves theD/A19
GENERATORFINFO
lens upward/downward by focus-search voltage of18
R301
triangular waveform to detect the focusing point. 30kW
DRIVER
During searching, the system kicks the SPDL motor
to maintain rotation speed to set speed.
Fig. 9 Focus servo block diagram
The servo LSI monitors FE and RFOK signals so that
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 = OH�
(3) FZD signal (in IC) is latched to OH.�
(4) FE = 0 (REFO as reference)
6 |
ACEC
PIONEER
