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FL8370
2.Servo Block 2.1 Focus Servo Block When defect is "H"(the defect signal is detected), the focus servo loop is muting in case of focus phase compensation. At this time, the focus error signal is outputted through the low pass filter formed by connecting a capacitor(0.1uF) and a built-in 470K� resistor to the FDFCT pin(pin 60). Accordingly, the focus error output is held at the error value just before defect error during defect occurring. The peak frequency of focus loop phase compensation is at about 1.2KHz when the resistor connected to FSET pin(pin 6) is 510K�, and it is inversely proportional to the resistor connected to the FSET pin. While the focus search is operating, the FS4 switch is on and then the focus error signal is isolated, accordingly the focus search signal is outputted by FEO pin(pin 48). When the FS2 switch is on(focus on), the focus servo loop is on and the focus error signal from FE2 pin(pin 58) is outputted through the focus servo loop.
3.6K 60K
VC
+
FSCMPO
+
FZCI
48K
+
20K
48
FEO
FE2
58
470K
Focus Phase Compensation
92K
X4
X3
X2
X1
FDFCT
60
FS4B
40K 130K FS2B
-
+ 47
FE-
DFCTI FGD 470K
10K 40K 50K
28 27
46K 580K FS3
3.6K FS1
4 X1 X2 X3 X4 0 0 1 1
PS
3 0 1 0 1
FS3
+
26
FLB
6
FSET
3
FRCH
Figure 15. Focus servo block
27
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