Table of Contents
Advertisement
DV-550U
8-4-2. Focus drive signal (FO+, FO-)
The signal drives the focus servo mechanism which aligns the focus on the bit of the disk by elevating OL (vertically against
the disk surface.)
Since an error of 67 µmP-P is produced by the turn table due to the surface run-out of ± 300 µm of the DVD disk, the error
is reduced to ± 0.23 µm or less with the focus servo.
8-4-3. Monitor diode bias voltage (VR)
The bias voltage of the monitor diode in the pickup is set. The reference voltage VCC is supplied from 1X1462.
8-4-4. 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 backward 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 backward current of the monitor diode increases. On the contrary,
the drive current of the laser diode is increased if the backward current of the monitor diode decreases.
As the projection light of the laser diode becomes stronger, the backward current of the monitor diode increases to
increase the current which flows into the monitor diode output (PD). Then, the emitter current of Q309 decreases to drop
the voltage of the collector of Q310. This is input to the pin 50 of IC304 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).
8-4-5. Laser diode drive current control (LD)
Power supply to drive the laser diode
8-4-6. 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 noise included in the light reflected on the disk surface can be reduced.
8-4-7. HF Signal (VA, VB, VC, VD)
Signals recorded in the disk
2-focus objective lens
Monitor Diode
Basic Structure of Laser Diode
8-2
Actuator assembly
Laser Diode
Advertisement
Table of Contents
