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6-3.
operation of APC Circuit and Laser Power
LD-VDD
R506
4.7
LD-SNS
(2.7[V])
Q501
LD DRIVE
CN501
2
ILCC
5
LD
LDGND
8
KGND
7
PD
PD
6
Fig. 6-4. shows the APC (Automatic LASER Power operation) circuit and main waveform timings. The APC circuit
controls the driving current of the laser so that the voltage supplied from outside becomes the same as the monitor diode
voltage. With functions such as PLAY where the laser diode emits light, Pin $¡ [APC REF] of the system controller (IC801)
outputs a 88.1 kHz (2 fs:fs=44.1 kHz) PWM waveform at the waveform timing (1) shown in the figure. In the LPF, the DC
APC REF signal is input to Pin !™ [PD-I] of the RF amplifier (IC501), passed through the two differential amplifiers inside,
output from Pin !¢ [LD-DRV], passed through the LD drive (Q501) to drive the laser diode inside the optical block.
Inside the monitor diode (PD), the photoelectric current corresponding to the amount of radiated laser light is converted to
voltage by the resistor connected between the monitor diode anode and GND, input to Pin !¡ [PD-IN], and fed back to the first
stage amplifier to control the laser power. A constant current circuit is composed by feeding back the voltage decreased by the
R506 resistor (4.7 Ω) connected to the emitter of the LD drive, so that the driving current does not change even when the
power supply voltage changes.
The ON/OFF of the laser driving current is controlled by the system controller via the serial bus (SBUS).
During normal playback, an approximately 1.8 seconds ON and 2.8 seconds OFF are repeated as shown by the timing in the
figure to save power.
2.8[V](VC)
IC501
RF AMP
16
15
LD-DRV
14
PD-IN
11
3
SSB-I/F
21
22
18
Fig. 6-4. APC Circuit and Waveform Timing
PD-O
13
LPF
R504
C506
R883
1
PD-I
APCREF
12
(2fs)
C806
APPROX.4.6[s]
APPROX.1.8[s]
IC801 SYSTEM CONTROLER
1
41 pin APCREF
0
2
Q501 COLLECTOR
0
IC501 RF AMP
3
11 pin PD-IN
0
ON
OFF
— 30 —
IC801
SYSTEM CONTROLLER
41
35
34
2.7[V]
2[V]
750[mV]
ON
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