CXA1782CQ/CR
Focus OK Circuit
RF
VCC
RF_O
RF_I
20k
31
30
54k
C5
0.01µ
× 1
25 FOK
VG
92k
0.625V
15k
FOCUS OK
COMPARATOR
FOCUS OK AMP
The focus OK circuit creates the timing window okaying the focus servo from the focus search state.
The HPF output is obtained at Pin 30 from Pin 31 (RF signal), and the LPF output (opposite phase) of the
focus OK amplifier output is also obtained.
The focus OK output reverses when VRFI – VRFO ≈ –0.37V.
Note that, C5 determines the time constant of the HPF for the EFM comparator and mirror circuit and the LPF
of the focus OK amplifier. Ordinarily, with a C5 equal to 0.01µF selected, the fc is equal to 1kHz, and block
error rate degradation brought about by RF envelope defects caused by scratched discs can be prevented.
DEFECT Circuit
After the RFI signal is reverted, two time constants, long and short, are held at bottom. The short time constant
bottom hold responds to 0.1ms or greater disc mirror defects, and the long time constant bottom hold holds the
pre-defect mirror level. By differentiating and level-shifting these constants with capacitor coupling and
comparing both signals, the mirror defect detection signal is generated.
0.033µ
CC1
27
CC2
26
a
RF_O
b
31
c
e
× 2
SENS
24
DEFECT AMP
d
DEFECT SW
DEFECT COMPARATOR
DEFECT BOTTOM
HOLD
28
CB
0.01µ
RFO
a
b
DEFECT
AMP
BOTTOM
HOLD (1) ;
solid Line:
CC1
d
BOTTOM
c
HOLD (2) ;
dotted Line:
CC2
H
L
e
DEFECT
– 20 –
ETC [ ETC ]
