CX-938
1.2 SERVO SECTION (UPD63710GC :
IC201)
The servo section controls the operations such as error
signal equalizing, in focus, track jump and carriage
move. The DSP is the signal processing section used
for data decoding, error correction and interpolation
processing, among others.
This circuit implements analog to digital conversion of
the FE and TE signals generated on the pre-amplifier,
then outputs them through the servo block as the drive
signal used on the focus, tracking and carriage system.
The EFM signal is decoded on the signal processing
section and finally output via the D/A converter as the
audio signal. The decoding process also generates the
spindle servo error signals which is fed to the spindle
servo block to generate the spindle drive signal.
The focus, tracking, carriage and spindle drive signals
are then amplified on the driver IC BA5986FM (IC301)
and fed to respective actuators and motors.
1) Focus Servo System
The focus servo main equalizer is consisted of the
digital equalizer. Fig.10 shows the focus servo block
diagram.
When implementing the focus close on the focus servo
system, the lens must be brought within the in-focus
range. Therefore, the lens is moved up and down
according to the triangular focus search voltage to find
the focus point. During this time, the spindle motor is
kicked and kept rotating as a set speed.
The servo LSI monitors the FE and RFOK signals and
automatically carries out the focus close at an
appropriate point.
The focus closing is carried out when the following
three conditions are met :
1 The lens approaches the disc from its currentIC301
IC201 UPD63710GCBA5986FM
position.
A+C
2 RFOK = "H"82FEDIG.
A/DLENS
B+DAMPEQR301FOP
3 The FZC signal is latched at high after it has once85FD10k14
CONTROL DAC 623
FOCUS SEARCH
crossed the threshold set on the FZD register (Edge
TRIANGULAR R30213
15kFOM
of the FZD).WAVE GENERATOR
4
As the result, the FE ( = REFO) is forced to low.
Fig.10 : FOCUS SERVO BLOCK DIAGRAM
7 |
ACEC
PIONEER
