Elektroonika Alused
Consider a segment of the CD player containing several tracks.
If the optical head is on track, then the primary beam will be centered on a track (with pits and bumps) and the
two secondary beams will be centered on land. The three spots are deliberately offset approximately 20 micro
with respect to each other.
Two additional detectors are placed alongside the main quadrant detector in order to pick up these subsidiary
beams. If the three beams are on track, then the two subsidiary photodetectors have equal amounts of light and
will be quite bright because they are only tracking on land. The central beam will be reduced in brightness
because it is tracking on both land and pits.
However, if the optical head is off track, then the center spot gets more light (because there are fewer pits off
track) and the side detectors will be misbalanced.
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