JP2000163752A - Method and device for playing optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize a device, to reduce power consumption and costs, to execute the waveform equalization of a reproducing RF signal deteriorated by skewing within a short time, and to perform the waveform equalization even of a reproducing RF signal deteriorated by tangential skewing. SOLUTION: This device is provided with an equalizer 4 having a transversal filter for reproducing waveform equalization to equalize the waveform of a reproducing RF signal, a waveform memory 5, an 8T detecting circuit 6 and a ROM 12 for measuring the polarity and size of sagging generated when tangential skewing exists with respect to the 8T pattern of the reproducing RF signal, a ROM 15 for storing the preset coefficient group of each tap of the reproducing wave equalizing transversal filter of the equalizer 4, and an adder 14 for selecting the preset coefficient group of each tap from the ROM 15 with a measured value set as an evaluation function.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing method and apparatus for decoding a reproduced RF signal read from an optical disk on which information is recorded using, for example, a run-length limited (RLL) code and outputting channel bit data. More particularly, the present invention relates to an optical disk reproducing method and apparatus for performing waveform equalization of a reproduced RF signal deteriorated by tangential skew.

[0002]

2. Description of the Related Art An optical disk apparatus using an optical pickup for recording and reproducing information on an optical recording medium such as an optical disk is known.

In such an optical disk device, when coma aberration occurs due to, for example, the tilt of the optical disk, so-called disk skew, the original reading performance cannot be exhibited, and a reading error may occur.

For example, when tangential skew, which is the inclination of the spot scanning direction of the optical disk with respect to the objective lens of the optical pickup, occurs, the asymmetry of the spot causes an increase in intersymbol interference in the reproduced digital signal, and the signal is sufficiently transmitted. It becomes difficult to extract. Also,
In an analog signal, C / N (carrier-to-noise ratio) decreases due to an increase in tangential skew, and a group delay occurs. In particular, a so-called video disc or the like appears on a screen as color unevenness.

[0005] From the above, conventionally, as a first method for reducing the influence of skew, for example, a skew of an optical disk is measured by using a skew sensor (a disk comprising an LED of a different system from the optical pickup and two photodiodes). (Tilt detection sensor), and corrects the waveform aberration by moving the pupil phase correction plate placed on the collimator lens side of the objective lens to the left or right, or
There is a method of driving with a shaft actuator and tilting so as to correct skew.

As a second technique for reducing the influence of skew, for example, an RF waveform equalization-dedicated area is provided on the innermost circumference of an optical disc, for example, and a reference waveform for automatic equalization is recorded in advance or trial-written. After that, there is a method of adjusting the coefficient of each tap of a transversal filter for an equalizer (EQ) so that the reproduced waveform is equal to a preset waveform.

[0007]

However, in the case of the first method, a skew sensor and an actuator for skew correction are required, which hinders downsizing, low power consumption, and low price. Further, it is necessary to adjust the angle of the skew sensor.

Further, in the case of the above second method, it takes a long time to converge the waveform equalization because many tap coefficients are sequentially adjusted. Furthermore, it is difficult to equalize the tangential skew of the rotation period of the optical disk because the dedicated area for waveform equalization is required.

Therefore, the present invention has been made in view of such a situation, and it is possible to reduce the size of the configuration, reduce power consumption, and reduce the price, and to equalize the waveform of a reproduced RF signal deteriorated by skew. It is an object of the present invention to provide an optical disc reproducing method and apparatus which can be realized in a short time and can equalize the waveform of a reproduced RF signal deteriorated by tangential skew.

[0010]

SUMMARY OF THE INVENTION An optical disk reproducing method and apparatus according to the present invention is an optical disk reproducing method and apparatus for performing waveform equalization on a reproduced waveform reproduced from an optical disk, and includes a longest inversion interval pattern of the reproduced waveform or the longest inversion. Measure the polarity and magnitude of the sag that occurs when tangential skew exists for a pattern with a length close to the interval,
The above-described problem is obtained by selecting a preset coefficient group of each tap of the transversal filter for reproduction waveform equalization using the measured value as an evaluation function and performing waveform equalization of the reproduction waveform by the transversal filter for reproduction waveform equalization. Solve.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a configuration of a main part of an optical disk apparatus according to an embodiment to which an optical disk reproducing method and apparatus of the present invention is applied. Prior to a detailed description of FIG. RF by skew in the form of
The principle of waveform equalization for signal waveform degradation will be described.

FIG. 2 shows an LSF (Line Spread Function: line image distribution) of a reading light spot on an optical disk as an example. FIG. 2 shows the LSF when the tangential skew is 0 degree, and the disk thickness t =
The case of 0.6 mm, light wavelength λ = 0.65 μm, numerical aperture NA of the objective lens = 0.60, bit length 0.3 μm / bit, and (1.7) RLL is taken as an example.

The convolution of the LSF and the signal sequence (for example, when the land is 1 and the pit is 0) in the example of FIG. 2 is the reproduction RF from the optical disk.
FIG. 3 shows a reproduced RF signal waveform after amplitude equalization. The signal sequence is (1.7) RLL modulation,
The minimum inversion interval Tmin = 2T and the maximum inversion interval Tmax = 8T. Here, T indicates a channel bit clock interval.

At this time, a transversal filter with a tap interval of T is used as an equalizer (EQ) for equalizing the reproduced RF signal waveform, and the coefficient is, for example, -0.19 (T).
If you select 1.38 (T) and -0.19 (T) respectively,
The reproduced RF signal waveform of FIG. 3 is obtained, and the signal can be read well.

However, the optical disk is inclined in the direction in which the pits are traced (ie, tangential skew).
, The LSF and the reproduced RF signal waveform are as shown in FIGS. FIG. 4 shows the LSF when tangential skew is present, and FIG. 5 shows the reproduced RF signal waveform of FIG. 4 after waveform equalization (the number of taps is the same as in FIG. 3). The angles in FIGS. 4 and 5 indicate tangential skew angles.

As can be seen by comparing FIG. 3 and FIG.
A so-called sag occurs at the rising edge of the reproduced RF signal waveform having the maximum inversion interval Tmax or a length close to the maximum inversion interval Tmax.

As shown in FIG. 4, side lobes (wave swells and bumps) occur at positions delayed by 1.64.lambda./2NA with respect to the main lobe (wave peaks) of the LSF. It is because of.

According to the simulation, the amount of sag of the reproduced RF signal waveform and the height of the side lobe of the LSF are 0 to 0.
The first degree of tangential skew is substantially proportional to the skew angle.

When the optical disk is tilted in the opposite direction, a side lobe appears on the opposite side of the main lobe of the LSF, as shown in FIG. This occurs at the fall of the waveform having a length close to the inversion interval Tmax.

Here, as is apparent from the fact that the reproduced RF signal waveform is a convolution of the LSF and the signal sequence, the tangential skew causes intersymbol interference in the read waveform and increases the so-called jitter. If the skew angle exceeds 0.6 to 0.8 degrees, the jitter exceeding the channel bit clock interval T increases, and error correction becomes impossible.

From the above, it is necessary to determine the maximum inversion interval Tmax of the reproduced RF signal waveform or the amount of sag having a length close to the maximum inversion interval Tmax and whether the generated location is a rising edge or a falling edge. By estimating the amount of tangential skew, and canceling the side lobes of the LSF by, for example, a transversal filter, it becomes possible to reduce intersymbol interference and reduce jitter. As a result, even in the reading system of the optical disk device, even if the tangential skew occurs close to ± 1 °, it is possible to configure a system with a large margin so that error correction cannot be performed.

The configuration of the embodiment of the present invention shown in FIG.
This achieves the above, and the configuration of FIG. 1 will be described below.

In FIG. 1, a reproduction RF signal read by an optical pickup from an optical disk (not shown) is supplied to a terminal 1. The reproduced RF signal is sent to an A / D (analog / digital) converter 3 after the RF envelope amplitude is controlled to be constant by an AGC (automatic gain control) circuit 2.

The A / D converter 3 has a channel bit clock from an oscillator (OSC) 19 via a selection switch 20 immediately after the start of reproduction of the optical disk, and has a phase locked by a PLL (phase locked loop) circuit 22. After that, the PLL circuit 2 via the selection switch 20
2 based on the channel bit clock from
The reproduced RF signal from the GC circuit 2 is converted into, for example, an 8-bit digital signal.

The digital signal from the A / D converter 3 is sent to an equalizer (EQ) 4 composed of a transversal filter, which will be described later, and is subjected to RF waveform equalization. This equalizer 4 also has a selection switch 2
Waveform equalization is performed based on the channel bit clock via 0. The output signal from the equalizer 4 is output to the interpolation circuit 2
1 is sent to the 8T detection circuit 6 and the waveform memory 5 described later.

The interpolation circuit 21 performs an interpolation process on the output signal of the equalizer 4 on the basis of the channel bit clock via the selection switch 20, and outputs the interpolation result signal to the Viterbi decoding circuit 23 and a PLL (phase locked loop). ) Send to circuit 22.

The PLL circuit 22 extracts a channel bit clock from the output signal from the interpolation circuit 21 and converts the channel bit clock into an interpolation circuit 21, a Viterbi decoding circuit 23, a (1.7) RLL demodulation circuit 24, and an error correction decoding circuit. 25, and is sent to the selection switch 20 and output from the clock output terminal 27.

The Viterbi decoding circuit 23 performs a Viterbi decoding process on the output signal from the interpolation circuit 21. (1.7) RL
In the L demodulation circuit 24, the signal after the Viterbi decoding (1.
7) RLL demodulation processing is performed, and a switching timing signal for switching the selection switch 20 to the channel bit clock side from the PLL circuit 22 when normal demodulation becomes possible is output. Further, the error correction decoding circuit 2
In step 5, an error correction decoding process is performed on the signal after the above (1.7) RLL demodulation process. This error correction decoding circuit 25
Is output from the output terminal 26 as reproduction data reproduced from the optical disk.

On the other hand, the waveform memory 5 has eight memory elements 51 to 5 for storing and outputting the supplied digital signal for the time (T) of the channel bit clock.
The digital signal for 8T is sequentially sampled and stored for each channel bit clock time (T), and the stored digital signals are output to the 8T detection circuit 6.

The 8T detection circuit 6 detects a maximum inversion interval Tmax (8T) pattern from the digital signal from the equalizer 4 and the digital signal for each time T from the waveform memory 5, and every time the 8T pattern is detected. The detection timing signal is sent to the latch circuits 7 and 8 and the averaging circuits 9 and 10 for n times.

Here, an output digital signal of the memory element 53 separated from the output of the memory element 58 at the last stage of the waveform memory 5 by 5T is input to the latch circuit 7, and the latch circuit 8 receives the digital signal of the waveform memory 5. An output digital signal of the memory element 55 separated from the output of the memory element 58 at the last stage by 3T is input. According to the latch circuits 7 and 8, as shown in FIG. 6, the instantaneous values I ₃ and I ₅ of the 3T portion and the 5T portion in the 8T pattern detected by the 8T detection circuit 6 are latched. . The portion closer to the leading edge than 3T is closer to the trailing edge than 5T because of the impulse response of the optical system of the optical disk device in FIG.

Next, the instantaneous values I ₃ and I ₅ obtained by the latches in the latch circuits 7 and 8 are sent to the corresponding n-times averaging circuits 9 and 10, respectively. These n-times averaging circuit 9,
10, every time the 8T pattern is detected by the 8T detection circuit 6, the instantaneous value I from the latch circuits 7 and 8 is output.
₃ and I ₅ e.g. n = 16 times averaging and outputs.

The instantaneous values I ₃ and I ₅ added and averaged 16 times by the n-times averaging circuits 9 and 10 are sent to a subtractor 11.
In the subtractor 11 subtracts the instantaneous value I ₃ from the instantaneous value I ₅ which is averaged above 16 times. The output of the subtractor 11 is a signed sag amount.

The signed sag amount output from the subtracter 11 is sent as an address to the ROM 12. The ROM 12 stores a signed angle indicating the tangential skew amount. When the signed sag amount from the subtracter 11 is supplied as an address, the tangential skew amount corresponding to the signed sag amount is stored. Is output. Note that instead of the ROM 12,
It is also possible to generate a signed angle indicating the tangential skew amount by simply adjusting the gain of the signed sag amount from the subtractor 11.

The signed angle indicating the tangential skew amount obtained as described above is sent to the adder 14 via the selection switch 13. The adder 14 cumulatively adds the above-mentioned angle with a sign.

However, according to the configuration of the present embodiment, when the cumulative addition value output reaches, for example, +1 degree or -1 degree, the adder 14 receives an input in which the signed angle is directed to the 0 degree direction. , The cumulative addition is stopped. In order to realize this, in the configuration of FIG. 1, a positive / negative determination circuit 18 for determining whether the direction of the signed angle is directed to the 0 degree direction, and a cumulative addition value output of the adder 14 And an upper / lower limit determining circuit 16 for determining whether or not has reached the upper limit +1 degree or the lower limit -1 degree, and switching of the selection switch 13 according to each determination result of the positive / negative determining circuit 18 and the upper / lower limit determining circuit 16 And a switching control circuit 17 for performing control. That is, in the configuration shown in FIG.
When it is determined that the cumulative addition value output has reached +1 degree or -1 degree, the selector switch 13 is switched to select the value 0, and the sign judgment circuit 18 performs the sign control. This state is maintained until the direction of the angle is directed to the direction of 0 degrees, and then, when the direction of the signed angle is directed to the direction of 0 degrees by the positive / negative judgment circuit 18, the signed angle is Is controlled to switch the selection switch 13 so that is sent to the adder 14. Since this circuit is an integrator, it can be prevented from entering a nonlinear region.

The output of the cumulative addition value from the adder 14 is
It is sent to the ROM 15 as an address. The RO
M15 stores the optimum preset coefficient of each tap of the transversal filter with respect to the signed angle from -1 degree to +1 degree in increments of 0.1 degrees, which is experimentally obtained in advance. Therefore, the ROM 15 is supplied with the cumulative addition value output from the adder 14 as an address, thereby extracting the optimal preset coefficient of each tap of the transversal filter corresponding to the cumulative addition value output. That is, the tap coefficient output from the ROM 15 is the optimum preset coefficient (EQ coefficient) of the transversal filter constituting the equalizer 4.
Used as

As described above, in the present embodiment, the waveform equalization characteristic of the equalizer 4 is adjusted based on the signed sag amount (signed angle).

Here, the equalizer 4 of the optical disk device according to the present embodiment is constituted by a transversal filter as shown in FIG. Although the example of FIG. 7 shows a transversal filter having five taps for simplicity of illustration, the number of taps is actually larger than that.

In FIG. 7, a digital signal from the A / D converter 3 in FIG. A terminal 72 is supplied with a channel bit clock, and a terminal 73 is supplied with an optimal preset coefficient (EQ coefficient) from the ROM 15 of FIG.

The digital signal input to the terminal 61 is
The signals are sequentially sent to delay elements 62 to 65, each of which is delayed by one channel bit clock. The digital signal input to the terminal 61 and the outputs of the delay elements 62 to 65 are sent to corresponding coefficient multipliers 66 to 70, respectively, where the optimum preset coefficient (EQ coefficient) supplied from the terminal 73 is supplied. C ₀ -C ₄ is multiplied. The outputs of the coefficient multipliers 66 to 70 are added by an adder 71 and output from a terminal 74. The output from this terminal 74 is shown in FIG.
Is the waveform equalized output of the equalizer 4.

Here, the transversal filter needs to have coefficient taps in a range of ± 1.64 · λ / (2NA · v) or more. Here, v is a linear velocity. This allows the transversal filter to perform waveform equalization on tangential skew.

In this embodiment, each circuit configuration can be operated based only on the fixed oscillation frequency (output of oscillator 19) equal to the nominal value of the channel clock bit frequency. When the PLL circuit 22 is locked (1.7) and the RLL demodulation becomes possible as shown in FIG.
By switching to the channel bit clock extracted from the F signal, higher accuracy can be achieved.

As described above, according to the present embodiment, a sensor for detecting the skew amount as in the conventional example is not required, and the skew can be detected from the reproduced RF signal waveform itself. Accurate and highly accurate skew detection is possible.

Further, according to the present embodiment, the convergence time of the automatic equalization of the reproduced RF signal waveform can be shortened, so that it is possible to follow the rotation cycle component of the tangential skew of the optical disk, and the system tangential The skew margin can be greatly expanded. Further, according to the present embodiment, for example, waveform equalization can be performed even for a tangential skew that does not open a so-called eye pattern. If the numerical aperture NA of the objective lens is increased for the purpose of increasing the recording / reproducing capacity of the optical disc, for example, the tangential skew margin is inversely proportional to NA ³ (decreases).
If the present invention is adopted, the tangential skew margin can be maintained, so that the numerical aperture NA of the objective lens can be increased, that is, the recording / reproducing capacity of the optical disk can be increased.

In this embodiment, an optical disk apparatus for reproducing an optical disk has been described as an example. However, the present invention is of course applicable to an optical disk apparatus capable of recording and reproducing on an optical disk.

[0048]

As is apparent from the above description, in the optical disk reproducing method and apparatus of the present invention, the tangential skew is set to the longest inversion interval pattern of the reproduction waveform or the pattern having a length close to the longest inversion interval. Measure the polarity and magnitude of the sag generated when it is present, select the preset coefficient group for each tap of the transversal filter for reproduction waveform equalization using the measured value as an evaluation function, and use this transversal for reproduction waveform equalization. By performing the waveform equalization of the reproduced waveform by the filter, the configuration can be reduced in size, the power consumption can be reduced, and the price can be reduced. It is also possible to equalize the waveform of a reproduced RF signal that has deteriorated due to tangential skew.

That is, in the present invention, it is possible to detect the skew amount more accurately and precisely, and it is possible to follow the rotational cycle component of the tangential skew of the optical disk, and to obtain the tangential skew margin of the system. Can be greatly expanded. Further, according to the present invention, since the tangential skew margin can be increased, the numerical aperture NA of the objective lens can be increased, and as a result, the recording / reproducing capacity of the optical disk can be increased.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a configuration of a main part of an optical disk device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an LSF of a reading light spot on an optical disc when a tangential skew is 0 degree.

FIG. 3 is a waveform diagram showing a reproduced RF signal waveform of FIG. 1 after amplitude equalization.

FIG. 4 shows a case where tangential skew exists.
FIG. 3 is a diagram illustrating an LSF of a reading light spot on an optical disc.

FIG. 5 is a waveform diagram showing a reproduced RF signal waveform of FIG. 3 after amplitude equalization.

FIG. 6 is a diagram illustrating instantaneous values I ₃ and I ₅ of a 3T portion and a 5T portion in an 8T pattern for describing a latch operation.

FIG. 7 is a circuit diagram showing a schematic configuration of a transversal filter constituting the equalizer.

[Explanation of symbols]

2 AGC circuit, 3 A / D converter, 4 Equalizer, 5 Waveform memory, 6 8T detection circuit,
7,8 latch circuit, 9,10 n-time averaging circuit, 1
1 subtracter, 12,15 ROM, 13,20 selection switch, 14 adder, 16 upper / lower limit judgment circuit, 17 switching control circuit, 18 positive / negative judgment circuit,
19 Oscillator, 21 Interpolator, 22 PLL
Circuit, 23 Viterbi decoding circuit, 24 (1.7) R
LL circuit, 25 error correction decoding circuit

Claims (8)

[Claims] 1. An optical disk reproducing method for performing waveform equalization on a reproduced waveform reproduced from an optical disk, wherein a tangential skew exists for a longest inversion interval pattern of the reproduction waveform or a pattern having a length close to the longest inversion interval. The polarity and magnitude of the sag generated at the time are measured, and the measured values are used as an evaluation function to select a preset coefficient group of each tap of the transversal filter for reproducing waveform equalization. An optical disk reproducing method, comprising equalizing a reproduced waveform. 2. A correspondence relationship between a signed skew angle corresponding to the polarity and magnitude of the sag and an optimal preset coefficient group of each tap is set and stored in advance, and measured from the reproduced waveform. 2. The optical disk reproducing method according to claim 1, wherein an optimum preset coefficient group for each of the stored taps is selected based on a signed skew angle obtained from the polarity and magnitude of the sag. 3. The measurement of the polarity and magnitude of the sag is performed in the initial state by sampling the reproduced waveform with a clock having a fixed oscillation frequency equal to the nominal value of the channel bit clock frequency. 2. The optical disk reproducing method according to claim 1, wherein the reproducing is performed by sampling the reproduced waveform with a clock synchronized with the reproduced waveform by the phase locked loop. 4. When the linear velocity of the disk is v, the wavelength of the optical pickup is λ, and the numerical aperture of the objective lens is NA, a plurality of taps are set within a range of ± 1.64 · λ / (2NA · v) or more. 2. The method according to claim 1, wherein a transversal filter is used. 5. An optical disk reproducing apparatus for performing waveform equalization on a reproduced waveform reproduced from an optical disk, comprising: a waveform equalizing means having a transversal filter for reproducing waveform equalization for performing waveform equalization of the reproduced waveform; Measuring means for measuring the polarity and magnitude of sag generated when tangential skew exists for the longest inversion interval pattern or a pattern having a length close to the longest inversion interval, and the reproduction using the measured value as an evaluation function An optical disc reproducing apparatus comprising: a coefficient selecting means for selecting a preset coefficient group of each tap of a transversal filter for waveform equalization. 6. A storage means for setting and storing in advance a correspondence relationship between a signed skew angle according to the polarity and magnitude of the sag and an optimum preset coefficient group of each tap, and said coefficient selection means. Selecting an optimal preset coefficient group for each tap stored in the storage unit based on a signed skew angle obtained from the polarity and magnitude of the sag measured from the reproduced waveform. 6. The optical disk reproducing device according to 5. 7. A fixed oscillation frequency clock generating means for generating a clock having a fixed oscillation frequency equal to the nominal value of the channel bit clock frequency, and a phase lock loop means for extracting a clock synchronized with the reproduced waveform from the reproduced waveform. The measuring means measures the polarity and magnitude of the sag by sampling the reproduced waveform using a clock from the fixed oscillation frequency clock generating means in an initial state, and the phase lock loop means 6. The optical disk reproducing apparatus according to claim 5, wherein after performing the step, the reproduction waveform is sampled by using a clock synchronized with the reproduction waveform by the phase lock loop means. 8. When the linear velocity of the disk is v, the wavelength of the optical pickup is λ, and the numerical aperture of the objective lens is NA, a plurality of taps are set within a range of ± 1.64λ / (2NA · v) or more. 6. The optical disk reproducing apparatus according to claim 5, wherein a transversal filter is used.