| 摘要 |
The track counting circuit has a pickup passing a track detected through a differential amplifier receiving signals from photo diodes, an amplifier, a tracking processor, a positive zero crossing detector, and a negative zero crossing detector. The signals sensed by photo diodes are applied to one of the input terminals of each of a pair on NAND gates through a differential amplifier, level comparators and a flip-flop. The other input terminals of the NAND gates receive the signals which are obtained by the signals sensed by the photo diodes being processed through an adder and a level comparator to distinguish whether the pickup is placed on the track or land of the disk. The output signals of the NAND gates control the output signals of a flip flop which control an up/down counter to make an up/down count depending on the moving direction of the pickup on the track.
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