KA3016D

CD-ROM PRODUCTS

10

MIC-99D001

January 1999

5. ROTATIONAL DIRETION DETECTION

•

The forward and the reverse rotations of the CD are simply detected by using the D-F/F and the truth table is

shown in the above table.

•

The rotational direction of the CD can be explained by the output waveforms of the hall sensors. Let 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). Thus the

phases orderd in H1

→H2→H3 with a 120°C phase difference.

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

→H2→H1 as shown in

fig.(b).

Therefore, the output of the rotational direction detector is low, when the spindle rotates forward, while high as in

the case of 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 rotaion

H1

H2

H3