JPH04263169A - Spindle servo system for optical disk apparatus - Google Patents

Abstract

PURPOSE:To construct a spindle servo circuit which is used to output a stable clock signal even when the lock range of a PLL circuit which forms a clock signal by using a signal replayed from an optical disk apparatus is narrow. CONSTITUTION:A circuit in which the control signal of a VCXO 24 constituting a PLL circuit 20 is fed back to a first comparator 23 via a low-pass filter 26, a second comparator 27 and a phase compensator 28 is provided. As a result, the oscillation frequency of the VCXO 24 becomes nearly equal to a reference voltage Ereff supplied to the second comparator 27, and a spindle servo circuit is operated in this state. When the reference voltage Ereff is set to a voltage by which the VCXO 24 composed of a quartz oscillator is oscillated at its central frequency, a spindle motor M is controlled in such a way that the PLL circuit 20 is operated near the center of a lock range, and a stable clock signal can be output without requiring any adjustment even at a low-cost PLL circuit.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] This invention relates to a servo system for controlling the rotation of a spindle motor that rotates an optical disk, and in particular, in a device that records and reproduces data on an optical disk, a system clock is formed by a PLL circuit. The present invention relates to a spindle servo system suitable for such optical disc devices.

0002

[Background Art] Optical discs that can record and reproduce information in response to light have two methods: one in which data is sequentially recorded on continuous recording tracks, and the other in which data is recorded in advance on predetermined positions on the tracks of the optical disc. A method of recording data based on servo pits is known. In FIG. 3, a plurality of sample servo pits P are formed in advance in each sector obtained by dividing the recording surface of an optical disk in the circumferential direction, and various servo signals are generated by detecting the sample servo pits P. , which shows the surface of an optical disk in which a focus servo signal and a tracking servo signal are formed on the optical disk, and each sample servo pit P is arranged radially in the radial direction.

Furthermore, as shown in the enlarged view of FIG. 4, each sample pit P includes wobbling pits P1 and P2 for detecting tracking errors and a clock pit P3 for detecting a clock signal. The clock signal can be detected from the reproduced RF data by sampling the clock pit P3 while rotating the optical disc at a constant rotation angle. FIG. 5 shows a conventional example of a spindle servo circuit for rotationally driving an optical disk as described above, in which an optical disk D is chucked onto the rotating shaft of a spindle motor M, and is rotationally driven together with an FG transmitter F that detects the number of rotations. be done.

The rotation pulse output from the FG oscillator F is input to a phase comparator 1, and a crystal oscillator 2 serves as a reference signal.
The signal is compared with a signal obtained by dividing the signal by the frequency divider 3. A phase difference error signal is then formed via the low-pass filter 4. On the other hand, the output pulse of the FG oscillator F is input to the frequency-voltage converter 5, and a signal corresponding to the rotational frequency of the spindle motor is detected via the comparator 6. It is then supplied to an adder 7 together with the phase difference error signal, and the output of this adder 7 is supplied to the spindle motor M via a phase compensator 8 and a drive circuit 9.

[0005]

According to this spindle servo circuit, since the spindle motor M rotates in synchronization with a constant cycle signal output from the crystal oscillator 2, the frequency division ratio of the frequency divider 3 must be set at a predetermined value. If set to a value of It is possible to form a system clock that performs playback processing.

However, when the optical disc D is eccentric as shown by the dotted line due to chucking misalignment, or when the track of the optical disc itself is not a perfect circle, the rotation speed of the spindle motor M is controlled to be constant. Also, jitter will occur in the reproduced clock signal. The amplitude of this jitter is 2 (Δr1 + Δr2) /j ω, where r1 is the eccentricity due to the disk and r2 is the eccentricity due to chucking misalignment. /j becomes π. This frequency deviation is around 0.1% for a normal disk, and is a value that cannot be ignored as a jitter component.

[0007] Therefore, a clock reproducing circuit for an optical disk is equipped with a PLL circuit that can sufficiently follow and synchronize with fluctuations in the reproduced clock signal, and is configured to absorb this jitter component. However, as the jitter of the reproduced RF signal increases, the oscillation frequency f of the VCO in the PLL circuit, that is, the control signal e0 of the VCO, becomes positive with respect to the control voltage E0 with respect to the center frequency f0 of the VCO, as shown in FIG. Changes significantly in the negative direction. Therefore, for example, an inexpensive PL with a narrow lock challenge using a crystal oscillation method that stabilizes the center frequency of the PLL circuit.
When using the L circuit, if there is a discrepancy between the center frequency of the VCO and the clock frequency included in the reproduced RF signal,
When the control voltage e deviates in the positive or negative direction as shown in e1 or e2 in FIG. 6, it goes out of the lock range and it becomes difficult for the PLL circuit to follow the jitter and maintain the locked state. Not only is it impossible to obtain a stable clock signal, but the system may go down.

[0008]

[Means for Solving the Problems] The present invention has been made to solve such problems, and is configured to be synchronized by a clock signal detected from, for example, a sample servo pit of an optical disk. Comprising means for comparing a signal corresponding to the output frequency of the PLL circuit and a signal corresponding to the rotational frequency of a spindle motor that rotates the optical disk, and controlling the rotational speed of the spindle motor that rotationally drives the disk by the output of the comparison means. At the same time, a control signal is injected into the spindle servo circuit so that the PLL circuit operates at approximately the center voltage of its lock range.

[0009]

[Operation] When the optical disc is rotated to a predetermined rotational speed and a clock signal is extracted from the PLL circuit in synchronization with the optical disc's reproduction RF signal, this clock signal causes the spindle motor that drives the optical disc to rotate. In addition to controlling the frequency, the PLL circuit is controlled to operate at approximately the center voltage of the lock range by the reference voltage supplied to this servo circuit from the outside. P
It is possible to prevent an accident in which the LL circuit loses synchronization due to eccentricity of the optical disk or uneven rotation of the spindle motor.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of a spindle servo system for an optical disk according to the present invention. An FG transmitter F that detects the rotation speed of the spindle motor M is provided. The output pulse of the FG oscillator F is supplied to a phase comparator 11, and is compared with the output of a frequency divider 12 that divides the frequency of a clock signal CLK output from a PLL circuit 20, which will be described later. The phase difference signal is then supplied to the spindle motor M via the phase compensation circuit 13 and the drive circuit 14 to control the rotational speed of the optical disc D.

[0011] As a rough adjustment servo circuit for the rotational speed, F
It is also possible to add a frequency servo loop that converts the output of the G transmitter F into a voltage by the F/V converter 11A, compares this voltage with a reference voltage Er, and drives the drive circuit 14 with the difference output. On the other hand, the recorded data on the optical disc D is read by the optical head 15 and outputted via the reproduction RF signal amplifier 16. The signal whose waveform is formed by the reproduction RF signal amplifier 16 is binarized by the data detection circuit 17 supplied with clock pulses for data detection, and is reproduced via the buffer circuit 18 that adjusts the time axis. The signal is supplied to the data signal processing circuit 19.

A clock component in the reproduced data outputted from the reproduced RF signal amplifier 16 is supplied to a phase comparator 21 forming a PLL circuit 20. The output is then supplied to a voltage controlled oscillator (hereinafter referred to as VCXO) 24 via a loop filter 22 and a first comparator 23, and the oscillation output of this VCXO 24 is divided by a frequency divider 25, and then the phase comparator 21 is the other input signal. The output of the VCXO 24, which uses a crystal resonator as a resonant element, forms a clock signal for data signal processing in this optical disk device, and is also supplied to the frequency divider 12, which divides the frequency by 1/M. The phase comparator 11 is configured to output a control signal corresponding to the rotation period of the spindle motor M.

In order to form a control signal for the PLL circuit 20, the embodiment of the present invention uses a control reference voltage Ereff.
is supplied to the other input of the first comparator 23 via a second comparator 27 and a phase compensator 28. Further, the output of the first comparator 23 is fed back to the second comparator 27 via a low-pass filter 26. Next, the operation of the spindle servo system of the present invention will be explained.

When the spindle motor M is started up by the frequency servo loop and reaches a predetermined rotation speed, the above-mentioned clock pit P3 reproduced from the optical disk D is activated.
This brings the PLL circuit 20 into a synchronous state and outputs the clock signal CLK. And this clock signal CLK
is phase-compared with the output pulse of the FG transmitter F via the frequency divider 12 in the phase comparator 11, and the spindle motor M
phase control is performed by this clock signal CLK. Therefore, if the optical disc D has eccentricity, the spindle motor M is controlled so that the output jitter is reduced accordingly.

By the way, in the spindle servo system of the present invention, the control voltage e that controls the oscillation frequency of the VCXO 24 is controlled by a DC servo loop consisting of a low-pass filter 26, a second comparator 27, a phase compensator 28, and a first comparator 23. controlled. Therefore, the center voltage (average value) of the control voltage e of the VCXO 24 is always controlled to a value approximately equal to the reference voltage Ereff supplied to the other input terminal of the second comparator 27. Since the value of the reference voltage Ereff is set so that the center frequency f of the VCXO is equal to the center frequency of the lock range of the PLL circuit 20, the rotational frequency fo of the spindle motor M is also regulated by this reference voltage Ereff. , the jitter component is controlled to be reduced around this rotational frequency fo.

Therefore, V constituting the PLL circuit 20
Since the CXO24 is equipped with a crystal oscillation element, even if its lock range is narrow, the control voltage e of the VCXO24 always changes based on the center frequency, and P
It is possible to prevent the LL circuit 20 from easily becoming out of synchronization. Note that when controlling the rotation of the spindle motor M in this manner, the spindle motor M is rotated at a period corresponding to the center frequency of the lock range of the PLL circuit 20 for each model.
As a result, the period of the clock signal will vary slightly depending on the model, but this variation can be corrected by correcting the time axis in the buffer 18 in the digital signal processing circuit, so that it does not affect operation. It can be done.

FIG. 2 is a circuit diagram of a servo system for a spindle motor showing another embodiment of the present invention, in which the same functional parts as in FIG. 1 are given the same reference numerals. In this example,
A comparator 30 is provided in order to control the control voltage e of the VCXO 24 to be the center value of the lock range of the PLL circuit 20, and the comparator 30 is configured to be supplied with a reference voltage Ereff. Further, the comparison output of the comparator 30 is supplied to an adder circuit 31, and is combined with a difference signal component obtained by comparing the frequencies of the crystal oscillator 32 and the FG oscillator F. Then, rotation control of the spindle motor M is performed based on the combined output.

According to this circuit, when the center voltage of the control voltage e of the VCXO 24 differs from the reference voltage Ereff, drive power corresponding to the difference signal is supplied to the spindle motor M, and the center voltage of the control voltage e of the VCXO 24 becomes the reference voltage. It becomes equal to the voltage Eref. In other words, by setting the reference voltage Ereff so as to obtain the clock signal CLK that is the center of the lock range of the PLL circuit 20,
The LL circuit is always in a synchronized state near the center of the lock range, and the rotation of the spindle motor M is controlled so as to suppress jitter caused by the eccentricity of the optical disk D and other factors.

[0019]

As explained above, the spindle servo of the optical disk device of the present invention has a center frequency that allows the lock range of the PLL circuit that extracts the clock signal from reproduced RF data to be wider in both the positive and negative directions. Since the rotation of the spindle motor M is controlled so that
For example, even when using a non-adjustable, inexpensive circuit that uses a crystal resonator with a stable center frequency, the synchronization relationship is reliably maintained and a stable clock signal can be obtained. be.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a spindle motor servo system of an optical disc device of the present invention.

FIG. 2(a) is a block diagram showing another embodiment of the present invention.

FIG. 3 is a diagram for explaining clock pits of an optical disc.

FIG. 4 is a diagram showing an example of a clock pit.

FIG. 5 is a block diagram of a conventional optical disc spindle motor servo circuit.

[Explanation of symbols] D Optical disc M spindle motor 20 PLL circuit 21 Phase comparator 23 First comparator 24 Voltage controlled oscillator (VCXO)

Claims (2)

[Claims] 1. A PLL circuit that forms a system clock signal based on data reproduced from an optical disc;
Comparing means for comparing a signal corresponding to the output frequency of the PLL circuit and a signal corresponding to the rotational frequency of a spindle motor that drives the optical disk, and a servo circuit for controlling the rotation of the spindle motor based on the output of the comparing means. and a control voltage is injected into the servo circuit to control the oscillation frequency of the voltage variable oscillator constituting the PLL circuit to be approximately the center frequency of the lock range of the PLL circuit. Spindle servo method. 2. The spindle servo system for an optical disk device according to claim 1, wherein a signal source for setting the rotational speed of the spindle motor is provided in the servo loop. .