Table of Contents
Advertisement
5
1.2 SERVO BLOCK (UPD63760GJ: IC201)
The servo block controls the servo systems for error signal equalizing, in-focus, track jump and carriage move and so
on. The DSP block is a signal-processing block, where data decoding, error correction, and compensation are per-
formed.
After A/D-converted, the FE and TE signals (generated in the preamplifier block) are applied to the servo block and
used to generate the drive signals for the focus, tracking, and carriage servos.
The EFM signal is decoded in the DSP block, and finally sent out as the audio signal after D/A-converted. In this
decoding process, the spindle servo error signal is generated, supplied to the spindle servo block, and used to gener-
ate the spindle drive signal.
The drive signals for focus, tracking, carriage, and spindle servos (FD, TD, SD, and MD) are provided as PWM3 data,
and then converted to the analog data by the low-pass filter which uses the operational amplifier embedded in the
driver IC BA5996FM (IC301). These analog drive signals can be monitored by the FIN, TIN, CIN, and SIN signals
respectively. Afterwards, the signals are amplified and applied to each servo's actuator and motor.
1.2.1 Focus servo system
In the focus servo system, the digital equalizer block works as its main equalizer. The figure 1.2.1 shows the block dia-
gram of the focus servo system.
To close the focus loop circuit, the lens should be moved to within the in-focus range. While moving the lens up and
down by using the focus search triangular signal, the system tries to find the in-focus point. In the meantime, the spin-
dle motor rotation is kept at the prescribed one by using the kick mode.
The servo LSI monitors the FE and RFOK signals and automatically performs the focus close operations at an appropri-
ate timing. The focus loop will close when the following three conditions are satisfied at the same time:
1) The lens moves toward the disc surface.
2) The RFOK signal is shifted to "H".
3) The FE signal is zero-crossed. At last, the FE signal comes to the zero level (or REFO).
When the focus loop is closed, the FSS bit is shifted from "H" to "L". The microcomputer starts monitoring the RFOK
signal obtained through the low-pass filter 10msec after that.
If the RFOK signal is detected as "L", the microcomputer will take several actions including protection.
The timing chart for focus close operations is shown in fig. 1.2.2.
In the test mode, the S-shaped curve, search voltage, and actual lens movement can be confirmed by pressing the
focus close button when the focus mode selector displays 01.
UPD63760GJ
124
A+C
FE
127
B+D
AMP
Fig. 1.2.1 Block diagram of the focus servo system
5
6
DIG.
A/D
EQ
FOCUS SEARCH
TRIANGULAR
WAVE GENERATOR
6
7
BA5996FM
105
FD
PWM
CONTROL
CX-3057
7
8
12 FOP
LENS
6
FOM
11
8
A
B
C
D
E
F
7
Advertisement
Table of Contents
