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• Hysteresis operation
Because the servo feed is deteriorated at setup and
track jump, hysteresis is operated to perform a servo
feed to a stable servo loop. The hysteresis operation
holds a TE signal and improves the convergence of the
tracking servo when a beam spot arrives at an off track.
DIRECTION OF THE EXTERNAL SURFACE
TE
SIGNAL
RFRP
SIGNAL
AFTER
TE SIGNAL
HOLD
Fig.13:HYSTERESIS OPERATION
3) Carriage servo system
The carriage servo inputs the output of the low
frequency component (lens position information) of the
tracking equalizer to the carriage equalizer, and outputs
a drive signal from the LSI after a fixed gain has been
obtained. The signal further applies to the carriage
motor via the driver. Specifically, because the entire
pickup needs to move to the forward direction when
the lens offset during play reaches a certain level, the
gain of the equalizer is set so as to output a higher
voltage than the starting voltage of the carriage motor
at that time. Besides, as a practical operation, only
when a threshold level against the equalizer output is
exceeded inside the servo LSI, a drive voltage is output.
The threshold level is set slightly higher than the
starting voltage of the motor to reduce power
consumption and stabilize operation. This drive output
waveform has a pulse shape.
DIRECTION OF THE INTERNAL SURFACE
IC301 TC9495FP
from
TRACKING
DIGITAL
EQUALIZER
EQUALIZER
CONTROL
Fig.14:CARRIAGE SERVO CIRCUIT BLOCK
TRACKING DRIVE
(LOW FREQUENCY)
LENS POSITION
CRG DRIVE
(INSIDE TC9495FP)
CRG MOTOR VOLTAGE
CRG moved at these point
Fig.15:CARRIAGE SIGNAL WAVEFORM
4) Spindle Servo System
Fig. 16 shows a block diagram of the spindle servo.
IC301 TC9495FP
Master
Clock
SPEEDERROR
SYNCHRO-
DIGITAL
EFM
PWM
NOUS
Eq.
DETECTION
PHASEERROR
VCO
Fig.16:SPINDLE SERVO CIRCUIT BLOCK
The spindle servo has the following modes:
• CLV servo
This CLV servo mode is the servo until the brake is
applied to stop the disk after focus close. The spindle
servo operates in this mode before tracking close and
at normal reproduction.
In the EFM demodulation block inside the CD-LSI, the
spindle servo performs synchronous detection and
operates so as be kept in a specified speed of rotation.
The synchronous detection is also enabled before
tracking close by using the VCO speed control of the
inside of the LSI in the PLL circuit. After tracking close,
the VCO speed control is muted and switched to the
speed and phase control by a master clock (a ceramic
oscillator is used).
CX-961
IC401
BA5811FM
FMO
15
PMW
26
OUTPUT
53
CIRCUIT
25
16
SD
DRIVE ON/OFF THRESHOLD
FG
Mechanism Unit
MD
EC
Brushless
54
Motor Unit
23
22
IC401
BA5811FM
COP
CRG
M
MOTOR
COM
9
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