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5
1.1 PREAMP SECTION
The preamp section is processing pick-up output signal and generating signal to servo section, demodulator section and
control section of the next stage. The signal from pick-up is I-V converted by photodetector-built-in preamp in the pick-up,
then added by RF amp and created RF, FE, TE, TE empty cross signal. This preamp section is embedded in CD LSI
UPD63763AGJ,UPD63761AGJ (IC201), and each section of it is explained below. Since the spec of this LSI is single
power supply (+3.3V), reference voltage of this LSI and pick-up should be all REFO (1.65V). REFO is the output from
REFOUT in the LSI through buffer amp, and its output comes from the number 133 pin of the LSI. All measurement is
based on the REFO.
NOTE: Never short-circuit REFO and GND.
1.1.1 APC circuit (Automatic Power Control)
Since light output has large minus temperature characteristics when laser diode is operated under constant current, it is
necessary to control current by monitor diode so that constant output is maintained. This is APC circuit. LD current is
generated by measuring current between LD1 and V3 R3 and dividing the value by 7.5 , and its current value should be
about 30mA.
PU unit
MD
11
VR
13
LD-
10
LD+
9
Fig.2 APC
5
6
CD core unit
11
13
10
+
9
CX-3168
6
7
PD
143
REG 1.25V
+
-
6R5K
LD
142
1K
LDS
UPD63763AGJ,
UPD63761AGJ
7
8
+
-
6R5K
VREF
APN
+
-
100K
110K
100K
3P
8
A
B
C
D
E
F
3
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