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1. ALPC (Automatic Laser Power Control) Circuit
1-1. Block Diagram
CN 201
VRDC
25
Optical
Pick-up
KRS-340B
FVREF
22
FPDO
19
VWDC1
26
LD
Drive
VWDC2
27
1-2. ALPC(Automatic Laser Power Control) Circuit Operation
ALPC 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¡fl s temperature variation.
There are two power control loops in MT1516, which are used with different combination for different
applications. Generally, the first APC loop is used for read-power control. The 2nd APC loop is used for
write(erase) power control for CD-R(CD-RW) disc.
Owing to the small signal level in read-power control mode, the first APC loop amplifies (x5/x10/x15/20x) the
FMD signal(FPDO) to enhance the accuracy of read power control. The built-in 8-bit DAC(RDAC) is used to set
the read power level. Moreover, the 2nd APC loop is used for high power control. The built-in 10-bit
DAC(WDAC1) is used to set the wanted power level. And the register VWDC1G is employed to adjust the gain
of FMD signal.
The following potentiometers(VRDCDAC, VWDC1DAC, and WDAC2) and amplifiers(VRDCDAG, VWDC1DAG
and WDAC2G) are used to set the wanted levels of the output pins VRDCO, VWDC1O, and VWDC2O.
Moreover, the input signal FPDO after low-pass filtering & amplification(x1 or x2) will send the MPXOUT2 for
monitoring.
DESCRIPTION OF CIRCUIT
IC 401 ( MT1516 )
VRDCO
VRDC
63
DAC
& Gain
52
54
65
FPDOLP
VWDC1O
VWDC1
62
DAC
& Gain
VWDC2O
WDAC2
61
&
Amplifier
S/H &
VRDCG &
Level Shift
RDAC
WDAC1
& x1/x2
S/H &
VWDC1G &
Level Shift
RLDON
128
57
RFPDSH
IC 101
112
71
MT1518
Write
Strategy
Write
S/H Signal
Micro
Processor
WFPDSH
111
72
WLDON
127
58
27
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