corresponding servo control signal and separately output focus, track, main axis, feed and other
servo control signals from pin 41, 40, 36 and 37 in MT1389. After passing integrating circuit composed
by resistance and capacitor, focus, track, main axis and feed signals are separately sent to servo driving
circuit to have driving amplify. After that, these signals separately drive focus winding, track winding,
main axis electric motor and feed electric motor. Focus and track servo are used to adjust lenses
position accurately; feed servo is used to drive laser head to perform radial large-scale motions , which
belongs to initial adjustment to pick-up position; main axis servo is used to control main axis electric
motor to read signal by way of constant wire speed and drive disc to rotate. The other part signals
switches into digital signals through internal A/D convertor after amplified by VGA voltage controlled
amplifier in MT1389 and compensated by balanced frequency . When loader reads CD/VCD signals,
these signals take EFM demodulation in MT1389, then CIRC error adjustment is also finished in it. After
that, those signals output to posterior pole to have audio video decode. When loader reads DVD signals,
which have ESM demodulation in MT1389 and finish RSPC error adjustment. Then they were sent to
posterior pole to have decode. Ordinary DVD has one tray open and close circuit to control tray eject
and retract motions to realize disc transmission goal.
3. Servo items explanation
1 Focus: As disc may produce errors or may moving upward or downward or shaking during
rotating, laser focus emitted by pick-up can not drop on the data pits of disc accurately. At this time,
focus point of lense should be adjusted to make focus align with data pits. The motion is to move lense
upward and downward.
2 Track: Digital information is stored on disc by form of track. When disc rotates, track may
deviate, then pick-up adjustment is needed. During this progress, lense moves forward and backward
with a small moving range.
3 Feed: It is similar with track motion, but moving range is larger than track moving. Feed may
firstly make a larger range moving, then track make smaller moving in this range. Feed makes
intermittent movement and track makes constant movement. Feed is coarse adjustment and track is fine
adjustment. It is quite obvious when power on and select tracks.
4 Main axis: Execution structure of main axis rotating speed depends disc rotating speed. Its
rotation is production of a single direct current electric motor. Speed of DVD rotation is almost two times
faster than CD rotation.
MT1389 defaults disc to DVD. Pin 54 of MT1389 outputs a low
voltage signal, Q5 and Q4 are cut off, Q3 is on, laser receiver tube inside loader selects DVD channel,
3.2.4 Disc identification circuit
1. Disc identification circuit is shown as the following figure 3.2.4.1:
2. Working principle: the function of disc identification circuit is to identify the disc inserted to loader
and judge whether the disc is VCD or DVD to perform the corresponding control acts. When disc is
inserted in, decode servo control IC
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