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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 MT1516 using DPP(Differential
Push-Pull) Method.
DPP Method uses not only main beam(A, B, C, D) but also side beam(E, F, G, H) for correcting DC offset
generated in Push-Pull Method.
The remaining procedure of TE signal processing in MT1518 is similar to Focus Servo.
The role of DSP IC(MT1518) is Tracking Digital Controller.
TE Signal is input to DSP IC(MT1518 40pin), and after A/D Conversion, Digital Equalizer Block and D/A
Conversion in MT1518, the output signal TRO(MT1518 22pin) is input to Drive IC(BD7907 23pin).
The drive output signal TRK+/TRK- generated according TKIN(BD7907 52pin), 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(MT1518 40pin), and after A/D Conversion, Digital Tracking Equalizer Block,
Digital Sled Compensator Block and PWM Conversion in MT1518, the output signal FMO, FMO2(MT1518
26,27pin) is input to Drive IC(BD7907 28,29pin) after Low-Pass filtering.
The PWM output signal A+, A-, B+, B- generated according to SLIN1, SLIN2(BD7907 28,29pin), and
drives the sled motor.
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