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CX-961
6) APC circuit section
A laser diode's driving current must be controlled so that
optical output could remain constant by using a monitoring
diode, because optical output has high negative
characteristics that causes a heat hang-up if the laser diode
were driven at constant current. This is exactly where APC
circuit works. LD current can be obtained by measuring
voltage between LD1 and GND, which value is about 35 mA
at room temperature.
1.2 Servo DSP (TC9495FP; IC301)
1) Focus servo system
The main equalizer of the focus servo is comprised with a
digital equalizer unit. Fig. 8 shows a block diagram of the
focus servo.
IC301 TC9495FP
FE
FEI
C
FOCUS
43
A/D
EQUALIZER
O
N
T
FOCUS SEARCH
R
WAVEFORM
O
GENERATION CIRCUIT
L
Fig.8:FOCUS SERVO CIRCUIT BLOCK
6
Fig.7:APC CIRCUIT
IC401 BA5811FM
FD
FOO
DAC
48
5
FOP
13
14
FOM
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