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1-2. ALPC(Automatic Laser Power Control) Circuit Operation
This circuit consists of Feedback Loop to maintain light output of the Laser Diode(FPDO).
Feedback signal, output voltage from PD(Photo Detector) of P/U, is used monitor the light power of
Laser Diode.
1) Read Loop
RREF(Read Reference Voltage) of IC401(CXA2638R) Pin 96, which is from DAC(IC403) Pin 18, is the
reference level of the Read Loop part of this ALPC Circuit.
• When Playback
VRDC(Pin 97) signal of IC401(CXA2638R) is output to P/U through Gain Control S/W and drives
Laser Diode during play back.
This S/W Ciruit is designed to reduce transition time from CD-RW writing mode to playback mode.
• When writing mode
- CD-R
Three Laser Power Levels, Read, Write, and Overwrite, are used to write on CD-R disc, and Read
Level is used to monitor the output laser power.
For stabilizing read loop, the S/H signal(RFPDSH), which sample and hold the Read Level of laser
power in the CD-R writing mode, is input through Pin 32 of IC401(CXA2638R).
- CD-RW
Three Laser Power Levels, Read, Erase and Write, are used to write on CD-RW disc, and Erase
Level is used, during CD-RW writing, to monitor output laser power.
It is not VRDC but VWDC that is the output signal of the control loop performed by Erase level.
2) Write Loop
For stabilizing write Loop, the S/H signal(WFPDSH), which sample and hold the Erase Level of laser
power in the CD-RW writing mode, is input through Pin 31 of IC401(CXA2638R).
Output voltage of Write Loop, VWDC(Pin 93 of IC401(CXA2638R)), is protected by the high limit diode
applied to P/U.
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