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FL8370

1.5 Mirror Circuit

IRF signal is amplified by the mirror amp, and the peak and bottom component of amplified signal are
detected by peak and bottom hold circuit. The peak hold circuit covers traverse signal of up to 100KHz
component and bottom hold circuit capable of covering the envelope frequency of disc rotation. The time
constant for the mirror hold must be sufficiently larger than that of the traverse signal.

Figure 8. Mirror Circuit

1.6 EFM Comparator

The EFM comparator converts a RF signal into a binary signal.
Beacuse the asymmetry generated due to variations in disc manufacturing can not be eliminated by the
AC coupling alone, this circuit uses to control reference voltage of EFM comparator for eliminating
asymmetry.

Figure 9. EFM Comparator & asymmetry circuit

75

-

1

IRF

Peak and
Bottom
Hold

-

39

-

-

17K

38K

19K

2.5K

96K

17K

1.5K

MIRROR

MCP

77

1

RFI

39

-

ASY

EFM

-

-

40K

19K

100K

100K

20K

85K

13

FL8370

1.7 Defect Circuit

The RFO signal bottom, after being inverted, is held with two time constants of long and short.
The short time-constant bottom hold is done for a disc mirror defect more than 0.1msec, the long time-
constant bottom hold is done with the mirror level prior to the defect. By differentiating this with a
capacitor coupling and shifting the level, both signals are compared to generate the mirror defect
detection signal.

Figure 10. Defect Circuit

1.8 APC (Auto Power Control) Circuit 

The laser diode has large negative temperature characteristic in its optical output when driven with a
constant current on laser diode. Therefore, the output on processing monitor photo diode, must be a
controlled current for getting regular output power, thus the APC (Auto Power Control) circuit is
composed.

Figure 11. APC Circuit

75

RFO

41

-

SSTOP/DFCT

2

BOTTOM

HOLD

5

-

4

DCC1

DCC2

DCB

75K

37.5K

28K

75K

VC+0.6254V

43K

DFCT

BOTTOM

HOLD

69

PD

70

-

LD

-

43.5K

150K

5.5K

150K

150K

PN (From micom command)

300K

LDON

0.75K

(From micom command)

1.25V

14

FL8370

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

Ω

 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

Ω

, 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.

Figure 15. Focus servo block

58

-

60

28

27

Focus  Phase
Compensation

26

47

-

-

-

-

3

3.6K

60K

FZCI

FE2

470K

DFCTI

20K

48K

FS4B

130K

FGD

FS3

46K

580K

FS3

4

7

0

K

40K

FS2B

FLB

FRCH

50K

10K

3.6K

FS1

92K

40K

FE-

FEO

VC

FSCMPO

48

FDFCT

PS

4      3

X1

X2

X3

X4

0     0

0     1

1     0

1     1

 6

FSET

X1

X2

X3

X4

15

FL8370

2.2 Tracking Servo Block

During detection of defect, the tracking error signal is outputted through the tracking servo loop after
passing the low pass filter formed by connecting a capacitor(0.1uF) and a built-in 470K

Ω

 resistor to the

TDFCT pin(pin57) in case of tracking phase compensation. The value of tracking gain up/down can be
controlled by TGU and TG2 pin. The peak frequency of tracking loop phase compensation, the dynamic
range and offset of opamp can be adjusted by changing the value of resistor connected to FSET pin
same as focus loop. In case of unstable status of actuator after jumping, the ON/OFF of tracking loop is
controlled by TM7 switch of break circuit.
After 10-track jumping, servo circuit gets out of the liner range and actuator's tracking becomes
occasionally unstable. Hence unnecessary jumping with many tracking error should be prevented.

Figure 16. Tracking servo block

-

53

57

61

62

TRACKING
PHASE
COMPENSATION

49

50

TE2

470K

TDFCT

680K

TGU

TG2

470K

20K

10K

110K

82K

680K

66PF

10K

90K

FSET

TE-

TG1

TG1

TM1

TG2

TM7

TM3

TM4

DFCTI

 6

TEO

16