LG GSA-4167B - Manual (Page 48)

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3-2-1. Tracking Servo
The aim of tracking servo is to make laser beam trace the data track on disc.
Tracking Error(TE) Signal is generated from tracking error detected block in R2S35002 using DPP(Differential
Push-Pull) Method and DPD (Differential Phase Detection) Method.
DPP Method uses not only main beam(A, B, C, D) but also side beam(EF1~EF4) for correcting DC offset
generated in Push-Pull Method.
The remaining procedure of TE signal processing in R8J32007 is similar to Focus Servo.
The role of DSP IC(R8J32007) is Tracking Digital Controller.
TE Signal is input to DSP IC(R8J32007 173pin), and after A/D Conversion, Digital Equalizer Block and D/A
Conversion in R8J32007, the output signal TRD(R8J32007 181pin) is input to Drive IC(39pin).
The drive output signal TACT+/TACT- generated according TOIN(R2S30202FP 39pin), and drives tracking
actuator in the P/U unit.
3-2-2. Sled Servo
The working distance of tracking actuator is too short to cover whole disc radius.
Sled Servo make P/U move by little and little so that the laser beam keep tracing the data track on disc
continuously when tracking actuator reaches the working limit.
TE Signal is input to DSP IC(R8J32007 173pin), and after A/D Conversion, Digital Tracking Equalizer Block,
Digital Sled Compensator Block and D/A Conversion in R8J32007, the output signal SL1, SL2(R8J32007 182,
183pin) is input to Drive IC (R2S30202FP SL1:3 pin, SL2:2pin) after Low-Pass filtering.