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YPM-2306ZF

3) Carriage Servo System

The carriage servo supplies the tracking equalizer's

low-frequency component (lens position data) output to

the carriage equalizer, then, after providing a fixed

amount of gain to it, outputs the drive signal from the

LSI. This signal is then applied to the carriage motor via

the driver IC.

When the lens offset reaches a certain level during play,

the entire pickup must be moved into the forward direc-

tion. Therefore, the equalizer gain is set to the level that

allows to generate a voltage higher than the carriage

motor starting voltage. In actual operations, a certain

threshold level is set for the equalizer output by the

servo LSI so that the drive voltage may be output from

the servo LSI only when the equalizer output exceeds

the threshold level. This arrangement helps reducing

power consumption. Also, due to disc eccentricity or

other factors, the equalizer output may cross the

threshold level a number of times. In this case, the

drive voltage output from the LSI will have pulse-like

waveform.

IC201 UPD63711GC

FROM

DIG.

TRACK. EQ

CONTROL

KICK, BRAKE

REGISTERS

Fig.16 : CARRIAGE SERVO BLOCK DIAGRAM

TRACKING DRIVE

(LOW FREQUENCY)

LENS POSITION

CRG DRIVE

(INSIDE UPD63711GC)

CRG MOTOR VOLTAGE

Fig.17 : CARRIAGE SIGNAL WAVEFORM

IC301

BA5985FM

COP

CARRIAGE

DAC

MOTOR

COM

DRIVE ON/OFF THRESHOLD

CARRIAGE MOVED AT THESE POINTS