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7.3 EXPLANATION
7.3.1 CIRCUIT DESCRIPTIONS
The LSI (UPD63711GC) used on this unit comprises six main blocks ; the pre-amp section, servo, signal processor,
DAC, CD text decoder (not used on this model) and LPF. It also equips with nine automatic adjustment functions.
1. PRE-AMP SECTION
This section processes the pickup output signals to cre-
ate the signals for the servo, demodulator and control.
The pickup output signals are I-V converted by the pre-
amp with the built-in photo-detector in the pickup, then
added by the RF amp to obtain RF, FE, TE, TE zero cross
and other signals.
This pre-amp section is built in the servo LSI
UPD63711GC (IC201). The following describes function
of each section.
Since this system has a single power supply (+5V), the
reference voltage for this LSI and pickup are set to
REFO (2.5V). The REFO is obtained by passing the
REFOUT from the LSI through the buffer amplifier. The
REFO is output from Pin 89 of this LSI. All measure-
ments are done using this REFO as reference.
Note : During the measurement, do not try to short the
REFO and GND.
1) APC Circuit (Automatic Power Control)
When the laser diode is driven with constant current,
the optical output has large negative temperature char-
acteristics. Thus, the current must be controlled from
the monitor diode so that the output may be constant.
APC circuit is for it. The LD current is obtained by mea-
suring the voltage between LD1 and V+5. The value of
this current is about 35mA.
EFM
71
ASY
72
RFI
74
AGCO
75
AGCI
76
Vref
RFO
77
EQ2
78
EQ1
79
Vref
RF-
80
Vref
A
82
C
83
Vref
B
84
D
85
Vref
F
86
Vref
E
87
PD
97
VREG
GND
APN
LDON
PN
99
Fig.1 : BLOCK DIAGRAM OF BUILT-IN RF AMPLIFIER
PD
97
·····Vref(+2.5V)
Vref
100k
16k
VREG
100k
150k
1k
GND
3p
AMP_PN
(H:Nch L:Pch)
LDON
(H:LD MOVE L:STOP)
99
PN
Fig.2 : APC CIRCUIT
Vref
PEAK DET.
BOTTOM DET.
S/H
LPF
73
C-3T
Vref
Vref
Vref
91
FEO
Vref
90
FE-
A/D
D/A
Vref
TEO
93
92
TE-
Vref
A/D
TE2
94
D/A
Vref
Vref
LD
98
·····Vref(+2.5V)
+5V
C103
R102
100µF/6.3V
10
R101
Q101
12
2SB1132
LD
1k
98
110k
14
3p
C102
0.1µF
YPM-2306ZF
EFM
MIRR
To the
following stage
DEFECT
of the LSI
A3T
FOK
PU UNIT
5
R103
C105
2.2k
0.33µF
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