1-2. ALPC(Automatic Laser Power Control) Circuit Operation
ALPC (Automatic Laser Power Control) function in CD-R/RW analog front-end is for constant power level
control purpose. Based on the accurate power sensor(FMD) in PU, APC feedback loop maintains constant
power level against laser diode’s temperature variation.
There are three power control loops in CD-R/RW analog front-end, which are used with different
combination for different applicatioins. Generally, the first APC loop is used for read power control. The 2nd &
3rd APC loop is used for write (or erase) power control for CD-R/RW disc.
The first APC loop amplifies (up to 10x) the FMD signal (FPDO) to enhance the accuracy of read power
control. VRDCG is used to adjust the gain of FMD signal. The built -in 8-bit RDAC is used to set the read power
level.
The 2nd & 3rd APC loop is used for high power control. Both WDAC1 and WDAC2 are 10-bats DAC,
which are used to set the wanted power level. The 3rd APC loop can alos be used as a voltage divider, which
take input from 2nd APC loop (VWDC1B).
Besides, three 8-bit potentiometers (VRDCDA, VWDC1DA, and VWDC2DA) and amplifiers (VRDCDAG,
VWDC1DAG, VWDC2DAG) are used to speed up the transient response of VRDCO, VWDC1O, VWDC2O.
On the other hand, the input signal FPDO after amplification (x2 or x4) will send the MPXOUT2 for
monitoring.
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