The present invention relates to a disk recording and/or reproducing apparatus, such as a video disk player, compact disk player, optical disk apparatus, or the like. More particularly, the invention relates to such an apparatus in which a spindle motor for rotating a disk is accelerated or decelerated so as to keep the number of rotations (rotational speed) of the disk within a predetermined range.
FIG. 1 is a block diagram showing circuitry in a conventional video disk player in which a disk may be rotated at a constant angular velocity (CAV) or a constant linear velocity (CLV). When a CAV disk is being used, a high level signal is applied to a terminal 2 and an NPN transistor 17 is turned on accordingly. A non-inverting input terminal A of an amplifier circuit 21 is clamped to a potential determined by a voltage V and resistance values of resistors 12 and 13, and a predetermined constant voltage is outputted from the amplifier circuit 21, which includes an operational amplifier. A frequency generator (not shown) is attached to a spindle motor not shown) which rotates the video disk, and an FG (frequency generator) pulse outputted from the frequency generator is applied to a terminal 5. A monostable multivibrator (MMV) 20 is triggered by the FG pulses and outputs pulses having a duration adjusted and determined by a variable resistor 14. The output of the multivibrator 20 is inverted by an inverter 19 and the resultant pulses are applied to an FET 18. The FET 18 is turned off while the output pulses from the inverter 19 are supplied. As a result, a potential at the junction point between resistors 8 and g is held at a high level while the MMV 20 supplies the pulses, and at a low level during the remaining period of time.
Assuming the potential at point B changes as shown in FIG. 2A when the rotational speed of the CAV disk coincides with a reference value, the potential at the point B changes, as shown in FIG. 2B, so that the duration of the low level value is extended when the rotational speed is lower than a reference value. On the other hand, when the rotational speed thereof is higher than the reference value, the potential at the point B changes, as shown in FIG. 2C. so that the duration of the low level value is shortened.
The signal at point B is integrated by an integration circuit comprised of resistors 9. 10 and 11, capacitors 15 and 16, and an operational amplifier 22. Accordingly, the potential at a point C becomes low when the rotational speed of the CAV disk is relatively low, and becomes high when the rotational speed thereof is relatively high.
The potential at the output terminal of the integration circuit is compared with reference voltages in comparison circuits 23 and 24. The comparison circuit 23 outputs a first output signal at a terminal 3 when the potential at the point C is lower than a first reference voltage, while the comparison circuit 24 outputs a second output signal at terminal 4 when the potential at the point C is higher than a second reference voltage where the second reference voltage is higher than the first reference voltage. The spindle motor is accelerated in response to the first output signal outputted from the comparison circuit 23, and decelerated in response to the second output signal outputted from the comparison 24. In this manner, the spindle motor is either accelerated or decelerated in response to the outputs from the comparison circuits 23 and 24 so that the rotational speed of the disk is maintained within a predetermined range. When the rotational speed of the spindle or the disk falls within the predetermined range, a spindle servo loop is turned ON.
When a CLV disk is being used, the transistor 17 is rendered OFF. so that the potential at the point A is set to a value obtained by dividing the potential of an input signal supplied to a terminal 1 by a ratio of the resistance values of resistors 6 and 7. A signal whose level changes in accordance with the radial position of a pickup (not shown) is applied to the terminal 1. The level of the signal at the terminal 1 may be changed, for example, in accordance with an output supplied from a potentiometer (not shown). When the pickup is positioned in an inner circumferential portion, the potential at the point B is lowered as shown in FIGS. 3A through 3C. whereas when the pickup is positioned in an outer circumferential portion the potential at point B is- made higher as shown in FIGS. 4A through 4C. Wherever the pickup may be positioned, the duration of the low level is extended when the disk is rotating at a slower speed (see FIGS. 3B and 4B) than the reference speed (see FIGS. 3A and 4A). On the other hand, when the disk is rotating at a higher speed (see FIGS. 3C and 4C). the duration of the low level is shortened. Therefore, the CLV disk also can be rotated at a linear velocity within a predetermined range, as is done for the CAV disks.
Because a conventional disk reproducing apparatus controls spindle motor rotation by means of FG pulses generated from a frequency generator attached to the spindle motor, the structure of the apparatus has been complicated and the cost of the apparatus has been expensive.