5. ROTATIONAL DIRECTION DETECTION
KA3011BD
VCC
H2+
+
H2−
−
H3+
+
H3−
−
DIR
20
D
Q
CK
D-F/F
Rotation
Forward
Reverse
20 DIR
Low
High
• The forward and the reverse rotations of the CD are detected by the D-F/F and the truth table is shown above.
• The rotational direction of the CD can be explained by the output waveform of the hall sensors. The three outputs of hall
sensors be H1, H2 and H3 respectively.
When the spindle rotates in reverse direction, the hall sensor output waveforms are shown in Fig.(a). The phases order are
in H1→H2→H3 with a 120°C phase difference.
H1
H2
H3
( a) Reverse rotation
On the other hand, if the spindle rotates in forward rotation, the phase relationship is H3→H2→H1 as shown in Fig.(b).
H1
H2
H3
( b) Forward rotation
The output of the rotational direction detector is low, when the spindle rotates forward, and high in the reverse rotation.
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