LG GSA-4167B - Manual (Page 45)

49
2. Focus Circuit
2-1. Block Diagram
Disc
Motor unit Optical
Pick-up
HOP-7632TS
A,B,C,D
A,B,C,D
(EF1~EF4)
(A+C)-(B+D)
(A+C)-(B+D)+K[(EF1+EF3)-(EF2+EF4)]
HAVC
LS
to
V14
FE
FE
FE
R102
C405
R103
C406
GND
GND ADC
Focusing
Compensator
DAC
FOD
FOD
R329
R2S30202FP
IC601
FACT+
FACT-
FACT+ FACT-
IC101
R2S35002
IC301
R8J32007
EN1
EN2
CTL1
CTL2
C335
REF
1.65V
FOIN
A+B+C+D
LPF G
HAVC
LS
to
0.8V
PE
PE
3
LPF G 2
169
170
180
40
42
20
21
34
35
2-2. Focus Servo
The aim of Focus Servo is to maintain the distance between object lens of P/U and disc surface, so that the
detected RF signal(A, B, C, D, EF1, EF2, EF3, EF4) can be maximized.
Focus Error Signal(FE) generates from focus error detection block in RF IC(R2S35002) using Conventional
Astigmatism Detection method, Differential Astigmatism Detection method.
Focus Gain and path can be changed at the RF IC(R2S35002) according to the disc, and the resulting output
FE(R2S35002 2pin) is input to DSP IC(R2S35002 169pin).
The Focus Search operation is using FE, PE Signal, therefore check FE, PE signals when Focusing is failed.
The role of DSP IC(R8J32007) is Focus Digital Controller. The operation path is as follows;
FE Signal is input to DSP IC(R8J32007 169pin), and after A/D Conversion, Digital Equalizer Block and D/A
Conversion in R8J32006FP, the output signal FOD(R8J32007 180pin) is input to Drive IC(R2S30202FP 40pin).
The drive output signal FACT+/FACT- generated according FOIN(R2S30202FP 40pin), and drives focus
actuator in the P/U unit.