cxa1372bs Sony Electronics, cxa1372bs Datasheet - Page 15

• Manufacturer Part Number: cxa1372bs
• Description: Rf Signal Processing Servo Amplifier For Cd Player
• Manufacturer: Sony Electronics

Focus OK circuit
The focus OK circuit creates the timing window okaying the focus servo from the focus search state.
The HPF output is obtained at Pin 39 from Pin 40 (RF signal), and the LPF output (opposite phase) of the
focus OK amplifier output is also obtained.
The focus OK output reverses when V
Note that, C5 determines the time constants 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.
EFM comparator
EFM comparator changes RF signal to a binary value. The asymmetry generated due to variations in disc
manufacturing cannot be eliminated by the AC coupling alone. Therefore, the reference voltage of EFM
comparator is controlled through 1 and 0 that are in approximately equal numbers in the binary EFM signals.
As this comparator is a current SW type, each of the High and Low levels is not equal to the power supply
voltage. A feedback has to be applied through the CMOS buffer.
R8, R9, C8, and C9 form a LPF to obtain (V
EFM low-frequency components leak badly, and the block error rate worsens.
RF signal
RFI
AUTO ASYMMETRY
CONTROL AMP
39
0.01µ
Vcc
C5
EFM COMPARATOR
100k
RFO
6
40k
RFI
VC
40
39
40k
RFI
20k
– V
FOCUS OK AMP
RFO
CC
AUTO ASYMMETRY
+ DGND)/2V. When fc (cut-off frequency) exceeds 500Hz, the
15k
–0.37V.
BUFFER
– 15 –
1
VG
31
32
54k
ASY
0.625V
EFM
DGND = 0V
92k
C8
R8
FOCUS OK
COMPARATOR
C9
R9
20k
BUFFER
CMOS
V
CXD2500
CC
33
CXA1372BQ/BS
FOK