Drive apparatus
View Patent ↗Optical disc drives designed for reduced power consumption switch the supply voltage in three stages between first, second, and third power supplies. The reduction in power consumption that is possible in the focusing and tracking drive circuits with three stage switching control is limited. This drive apparatus enables further reductions in power consumption. A drive output tracking signal is generated according to the drive conditions of the focusing or tracking drive circuit. The drive output tracking signal is applied to the drive circuit power supply, and the power supply is controlled according to the drive output tracking signal. A power supply change detector detects sudden changes in the drive output tracking signal, and inputs the detection signal to the DSP controlling the entire system. The DSP determines whether to improve the power supply response by comparison with predetermined conditions, and returns the result to the power supply.
1. A drive apparatus operable to supply drive output to an actuator operable to operate a movable head, comprising:
a fixed output generator operable to produce a predetermined fixed output;
a drive output tracking signal generator operable to detect the drive output required to drive the actuator, and to generate a drive output tracking signal that follows the drive output;
a control output generator operable to generate control output slightly greater than the drive output based on the fixed output and the drive output tracking signal; and
a drive output generator operable to produce the drive output using the control output.
2. The drive apparatus according to claim 1 , further comprising:
a sudden-change-in-drive-output detector operable to detect a sudden change period in which the drive output tracking signal changes suddenly;
wherein the control output generator improves response by outputting a constant output containing no actual change in the fixed output during the sudden change period.
3. The drive apparatus according to claim 2 , further comprising:
a response improvement not-needed period detector operable to detect response improvement not-needed period in which improved response is not needed;
wherein the constant output is not output in the response improvement not-needed period even if a sudden change period is detected.
4. The drive apparatus according to claim 1 , wherein:
the actuator comprises first and second input terminals;
the drive output generator comprises
a servo circuit operable to generate a drive waveform signal, and
a drive circuit;
wherein the drive circuit comprises a drive output generating element group operable to generate a pair of drive outputs with an opposite phase relationship using the control output based on the drive waveform signal; and
the pair of drive outputs is supplied to the first and second input terminals.
5. The drive apparatus according to claim 4 , wherein the drive output tracking signal is based on the absolute value of the difference between the drive waveform signal and a predetermined first reference voltage.
6. The drive apparatus according to claim 1 , wherein the drive output tracking signal is the greatest of a plurality of drive outputs.
7. The drive apparatus according to claim 4 , wherein the pair of drive outputs are supplied to the first and second input terminals of the actuator from the emitter or source terminals of the pair of drive output generating elements; and
the drive output tracking signal is the maximum base voltage or gate voltage of the pair of drive output generating elements.
8. The drive apparatus according to claim 4 , wherein the drive output generating elements are npn transistors or n-channel MOS transistors.
9. The drive apparatus according to claim 1 , wherein the movable head is an optical pickup.
10. The drive apparatus according to claim 2 , wherein the sudden-change-in-drive-output detector comprises:
a differentiating circuit operable to differentiate the drive output tracking signal; and
a wave shaping circuit operable to detect a period in which the absolute value of the output of the differentiating circuit exceeds a predetermined level as the sudden change period, and to generate a sudden-change-in-drive-output signal representing the sudden change period.
11. The drive apparatus according to claim 3 , wherein the response improvement not-needed period detector comprises a mask period setting arrangement operable to set a predetermined mask period operable to avoid initial operating instability, and
the response improvement not-needed period is in the mask period.
12. The drive apparatus according to claim 1 , wherein the actuator is a focus actuator operable to move the objective lens of the movable head in the focusing direction; and
the drive output generator is a focusing drive output generator operable to supply drive output to the focus actuator.
13. The drive apparatus according to claim 1 , wherein the actuator is a tracking actuator operable to move the objective lens of the movable head in the tracking direction; and
the drive output generator is a tracking drive output generator operable to supply drive output to the tracking actuator.
14. The drive apparatus according to claim 1 , wherein there are n actuators and n drive output generator; and
the drive output tracking signal generator comprises
n secondary drive output tracking signal generator operable to detect at least the n drive outputs required to drive each of the n actuators, and to generate n secondary drive output tracking signals following the n drive outputs, and
a wrapping arrangement operable to bundle the n secondary drive output tracking signals and to generate a single drive output tracking signal.
15. The drive apparatus according to claim 2 , wherein the control output generator comprises a step-down DC-DC converter operable to generate a supply voltage corresponding to a second reference voltage that is equal to the drive output tracking signal plus a predetermined tracking signal offset voltage; and
the step-down DC-DC converter generates the control output based on the fixed output and the second reference voltage.
16. The drive apparatus according to claim 15 , wherein:
the step-down DC-DC converter comprises
a voltage comparator operable to compare the second reference voltage and the output voltage of the step-down DC-DC converter, and to output the voltage difference;
a PWM comparator operable to convert the voltage difference to a PWM signal;
a switching circuit operable to switch the fixed output based on the PWM signal; and
a step-down voltage generator operable to convert the switched fixed output to the control output;
the step-down voltage generator comprises a coil and a capacitor; and
the control output is output from a control output terminal to which the coil and capacitor are connected.
17. The drive apparatus according to claim 16 , wherein:
the switching circuit comprises a pnp transistor having the base connected to a control terminal operable to control the switching circuit, the emitter connected to the fixed output generator, and the collector connected to the output terminal of the switching circuit; and
a diode of which the anode is to ground and the cathode is connected to the collector of the transistor and the output terminal of the switching circuit.
18. The drive apparatus according to claim 16 , wherein the switching circuit comprises two MOS power transistors in a synchronous rectifier circuit.
19. The drive apparatus according to claim 3 , wherein the control output generator generates a sudden operation signal denoting the sudden change period outside the response improvement not-needed period.
20. The drive apparatus according to claim 2 , wherein;
the control output generator comprises an unconditional drive circuit;
the sudden operation signal is input to the control terminal operable to control the unconditional drive circuit; and
the unconditional drive circuit is connected between the control output terminal and the fixed output terminal, goes ON in the sudden change period to cause the control output generator to output the constant output, and is otherwise OFF so that the control output generator outputs the control output.
21. The drive apparatus according to claim 20 , wherein:
the unconditional drive circuit comprises one pnp transistor; and
the emitter of the pnp transistor is connected to fixed output terminal, the collector is connected to the control output terminal, and the base is connected to the control terminal of the unconditional drive circuit.
22. The drive apparatus according to claim 20 , wherein:
the unconditional drive circuit comprises one p-channel MOS transistor; and
the source of the p-channel MOS transistor is connected to fixed output terminal, the drain is connected to the control output terminal, and the gate is connected to the control terminal of the unconditional drive circuit.
23. The drive apparatus according to claim 2 , wherein the sudden operation signal is input to the control terminal of the switching circuit; and
in the sudden change period the switching circuit goes ON and the control output generator outputs the constant output, and the switching circuit is otherwise OFF and the control output generator outputs the control output.
24. The drive apparatus according to claim 2 , wherein the PWM comparator has an ENABLE terminal;
the sudden operation signal is input to the enable terminal; and
in the sudden change period the switching circuit goes ON and the control output generator outputs the constant output, and the switching circuit is otherwise OFF and the control output generator outputs the control output.
25. The drive apparatus according to claim 1 , wherein:
the control output generator comprises a step-down DC-DC converter operable to generate a supply voltage corresponding to a second reference voltage that is equal to the drive output tracking signal plus a predetermined tracking signal offset voltage; and
the step-down DC-DC converter generates the control output based on the fixed output and the second reference voltage.
26. The drive apparatus according to claim 25 , wherein:
the step-down DC-DC converter comprises
a voltage comparator operable to compare the second reference voltage and the output voltage of the step-down DC-DC converter, and to output the voltage difference;
a PWM comparator operable to convert the voltage difference to a PWM signal;
a switching circuit operable to switch the fixed output based on the PWM signal; and
a step-down voltage generator operable to convert the switched fixed output to the control output;
the step-down voltage generator comprises a coil and a capacitor; and
the control output is output from a control output terminal to which the coil and capacitor are connected.
27. The drive apparatus according to claim 26 , wherein:
the switching circuit comprises a pnp transistor having the base connected to a control terminal operable to control the switching circuit, the emitter connected to the fixed output terminal of the fixed output generator, and the collector connected to the output terminal of the switching circuit; and
a diode of which the anode is to ground and the cathode is connected to the collector of the transistor and the output terminal of the switching circuit.
28. The drive apparatus according to claim 26 , wherein the switching circuit comprises two MOS power transistors in a synchronous rectifier circuit.
29. A method operable to supply drive output to an actuator operable to operate a movable head, comprising:
a step of producing a predetermined fixed output;
a step of detecting the drive output required to drive the actuator, and generating a drive output tracking signal that follows the drive output;
a step of generating control output slightly greater than the drive output based on the fixed output and the drive output tracking signal; and
a step of producing the drive output using the control output.