KA3011BD

10

5. ROTATIONAL DIRECTION DETECTION

• 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.

On the other hand, if the spindle rotates in forward rotation, the phase relationship is H3

→H2→H1 as shown in Fig.(b).

The output of the rotational direction detector is low, when the spindle rotates forward, and high in the reverse rotation.

20

+

−

+

−

DIR

D-F/F

D

Q

CK

H2+

H3+

H3

−

H2

−

Rotation

DIR

Forward

Low

Reverse

High

20

( a) Reverse rotation

H1

H2

H3

( b) Forward rotation

H1

H2

H3