DV-720/DV-720W
DV-720X/DV-770X
7. OPERATION OF PICKUP
7-1. CIRCUIT CONFIGURATION OF PICKUP
The pickup unit reads signals from the disk, and the flexible cable is connected to the board. The following signals flow through the
cable.
7-2. EQUIVALENT CIRCUIT OF PICKUP7-3. POLARITIES OF SIGNAL
FO+
1TR�FocusWhen electric current is flowed
TR�
2FO+FO+, FO-from FO+ to FO-, the lens comes
TR+
3TR+to near the disk.
FO�
ACTUATORPower adjust4FO�TrackingWhen electric current is flowed
HIGH-FREQUENCY CONVOLUTION5VRTR+, TR-from TR+ to TR-, the lens goes
VOS
6PDtoward the outer circumference.OSC
7VCCGain switching DVD one LayerHigh gain
8(NC)LDGND
SgaDVD two LayerSga : +5V
PD9LD
CD
�VA10GND
+VB11VOS
�
+
�VC12NC
+
�VD13NC
+
SgaVref(VCC/2)
14
VrafVA
15
Vcc16VC
GND17Sga
HOLOGRAM LASER UNIT
18GND
19VB
20VD
1
7-4. SIGNALS OF PICKUP
7-4-1. Tracking drive signal (TR+, TR-)
The signal drives the tracking servo mechanism which projects the beam on the track by moving the objective lens (OL) to the outer
or inner circumference (at a right angle against the track) of the disk.
7-4-2. Focus drive signal (FO+, FO-)
The signal drives the focus servo mechanism which aligns the focus on the pit of the disk
by elevating OL (vertically against the disk surface.)
2-focus objective lens
The VR terminal is connected to GND.
Actuator assembly
7-4-3. Monitor Diode (PD)
Since the laser diode largely varies output of the laser light even if the flowing current is slightly varied, the projection light is detected
with the monitor diode to control the laser light to be equally output.
Since the current varies on the monitor diode according to the intensity of the received light of the laser diode, the drive current of
the laser diode is reduced if the current of the monitor diode increases. On the contrary, the drive current of the laser diode is increased
if the current of the monitor diode decreases.
As the projection light of the laser diode becomes stronger, the current of the monitor diode increases to increase the current which
flows into the monitor diode output (PD). This is input to the pin 44 of IC303 and is compared with the reference voltage to control
the drive current of the laser diode.
The circuit is called ALPC (Automatic Laser Power Control).
Monitor DiodeLaser Diode
7-4-4. Laser diode drive current control (LD)
Power supply to drive the laser diode
Basic Structure of Laser Diode
7-4-5. High-frequency convolution module power supply (VOSC)
The high-frequency convolution imposes the high-frequency signal on the DC current to impose the high frequency on the drive
current of the laser. Thus, the interference of outgoing light and reflected light is prevented.
LD
PD
7-4-6. HF Signal (VA, VB, VC, VD)When the quantity of laser light increases, the current shown in
Signals recorded in the diskfigure increases and the PD terminal voltage rises.
IC303 is used to control. The LD terminal voltage lowers, and
the quantity of light reduces. (IC303 is actuated by voltage
input.)
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ACEC
