JPH07121879A - Signal reproducing circuit for optical disk device - Google Patents

Abstract

PURPOSE:To obtain the signal reproducing circuit of an optical disk device suitable for a high density recording by realizing a more stable data reproducing at the time of reproducing data recorded by a mark edge system with a differential detection. CONSTITUTION:In a signal reproducing circuit 11, the maximum value of a reproducing signal differential signal equivalent to the preceding edge of a mark on a disk is detected by a differential detecting circuit 22 and the minimum value of a differential signal equivalent to the succeeding edge of the mark is detected by a differential detecting circuit 26. Then, obtained results with both differential detecting circuits are superposed in a superposing circuit 29 to be outputted to a demodulation circuit 12 as a binary result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal reproducing circuit of an optical disk device which realizes high density recording.

[0002]

2. Description of the Related Art A mark edge recording method has been studied as a method for increasing the storage capacity of an optical disk device. In the conventional mark position recording method, the position where the mark is formed is regarded as information "1", whereas the edge portions at both ends of the mark are regarded as information "1". In the edge recording method, both ends of one mark can be given meaning, and a large amount of information can be taken per mark, resulting in good recording efficiency. In mark position recording, only a mark is formed at the "1" portion of the information, but in mark edge recording, an elongated mark is formed between "1" and the next "1".

On the other hand, as a signal reproducing method suitable for high density,
There is something called difference detection. Difference detection does not directly binarize the value of the reproduced signal itself, but samples the reproduced signal and binarizes it based on the relative magnitude relationship of the sampling results. For example, in the case of DBF, which is one of the sample servo formats, the 1-byte data is always modulated such that the number of '1' becomes 4 (4/11 modulation), and the reproduction signal level was large. Binarization is performed by selecting 4 bits. The difference detection method is suitable for high-density recording / reproduction because it does not require an absolute value of a reproduction signal and thus is resistant to various signal deterioration and has a large allowance for a decrease in reproduction signal amplitude due to high-density recording. In order to perform the difference detection, it is necessary to be able to reproduce the channel clock used for sampling from other than the data like the sample servo (it is an external clock).

The applicant of the present invention has proposed in Japanese Patent Application No. 5-220240 a high density recording / reproducing method combining a difference detection method and a mark edge recording method. This is to differentiate the reproduced signal when reproducing the data recorded by the mark edge method, and perform difference detection for selecting a pit having a large absolute value of the signal level with respect to the differentiation result.

By the way, when the edge recording is performed by the light modulation method, there is a problem that the edge position of the mark formed by the recording condition moves and the mark length varies. In mark edge recording in which the position of the edge has a meaning, such a variation directly leads to a detection error. Therefore, it is necessary to perform correction at the time of recording and reproducing the mark. For such a correction method, for example, “Jitter characteristics in mark length recording of magneto-optical disk” (Journal of Applied Magnetics, Vol. 16,
No. 5, 1992) and JP-A-2-183471.

[0006] In these corrections, the edge variation depending on the pattern of the data to be written is corrected at the time of recording, and the variation of the entire length of the edge due to temperature variation is corrected at the time of reproduction. That is, when recording, the emission pattern of the laser is controlled in consideration of the data patterns before and after, and at the time of reproduction, only the interval between the front edge and the rear edge of the mark is changed, and the edge variation is small for each edge. Use it to handle the front and back edges independently. For example, in the method disclosed in Japanese Patent Laid-Open No. 2-183471, the leading edge and the trailing edge are separately input to the synchronizing circuit at the time of reproduction, each synchronizing circuit performs binarization independently, and then synthesizes. is there.

[0007]

However, even when the difference detection method and the mark edge recording are combined, it is unavoidable that the mark edge fluctuates especially in the case of the light modulation method. If the position of the mark edge fluctuates, the positional relationship between the channel clock for sampling and the edge position shifts, so that a detection error is likely to occur even if the difference detection method is used.

Since the correction at the time of recording can use the same method as the conventional method, it is easy to suppress the edge variation depending on the recording pattern. However, it is difficult to suppress even the variation of the entire mark length depending on the variation of the environmental temperature by the correction at the time of recording. Therefore, it can be said that some correction at the time of reproduction is necessary even when the difference detection method is used.

However, in the difference detection method, an external clock exists independently of the mark on the disc, and the reproduced signal is sampled according to the clock to compare the relative magnitude relationship of the sampling results.
It is not possible to separate the front edge and the rear edge in advance (the position of the front edge / the rear edge can be known only when the difference detection is completed after reaching the last bit). Therefore, it is not possible to directly use the method of compensating for the mark length variation by performing temporal correction after independently detecting the front and rear edges, which is used in the related art, and only the mark length variation is used. There is a problem that the margin is reduced and consequently high density recording cannot be performed.

The present invention has been made in view of the above circumstances, and realizes more stable data reproduction when reproducing data recorded by the mark edge method by difference detection, and is suitable for high density recording. An object is to provide a signal reproducing circuit for an optical disk device.

[0011]

The signal reproducing circuit of the optical disk device of the present invention reproduces the channel clock from the unique marks intermittently provided on the optical disk,
The recorded information is NRZI-converted, the mark is formed on the optical disc in synchronization with the channel clock so that the edge portion of the mark corresponds to '1' of the information, and the information is recorded. In a signal reproducing circuit of an optical disk device for synchronously reproducing information, a signal detecting means for detecting a signal associated with the mark based on the reflected light from the optical disk, and a phase detector having the same frequency as the channel clock. First and second reference clock generation means for generating different first and second reference clocks, sampling means for sampling the output of the signal detection means according to the first and second reference clocks, and the sampling means And a binarizing means for binarizing the recorded information based on the sampling result of According to the lock, the front edge of the mark is obtained by the difference detection, the rear edge is obtained according to the second reference clock, and the front edge and the rear edge are sampled at different timings by different clocks to detect the difference independently. By doing so, it is possible to perform accurate difference detection.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. Here, a case where magneto-optical recording is performed by using 4/11 modulation adopted in DBF as a modulation method will be described.

FIG. 2 is a block diagram of an optical disk device including the signal reproducing circuit of the present invention. In FIG. 2, reference numeral 1 denotes an optical disc, which is of the sample servo type. A motor 2 rotates the optical disk 1 at a predetermined rotation speed.
A pickup 3 irradiates the optical disc 1 with laser light and detects reflected light from the disc. A magnetic head 4 applies a predetermined magnetic field to the optical disc 1 when writing and erasing data. 5 is a light control circuit,
By controlling the laser diode in the magnetic head 4 and the pickup 3, a mark is formed on the optical disc 1 to write data. A modulation circuit 6 modulates the write data sent from the host controller by 4/11, and further, NRZ
I conversion is performed and a write signal is output to the write control circuit 5.
A head amplifier 7 photoelectrically converts and amplifies the reflected light detected by the pickup 3. A clock reproduction circuit 8 extracts a pattern corresponding to a clock pit on the disk from a reproduction signal (intensity signal) sent from the head amplifier and multiplies it by a PLL to reproduce a channel clock. A servo circuit 9 detects various error signals and controls focus / tracking and seek of the pickup 3. A differentiating circuit 10 differentiates the reproduction signal (magneto-optical signal) sent from the head amplifier 7 and outputs a signal which becomes maximum or minimum at the edge portion of the mark on the disk. A signal reproducing circuit 11 reproduces recorded data based on the signal from the differentiating circuit 10.
Reference numeral 12 denotes a demodulation circuit, which is 4/11 for the reproduced data.
It demodulates and sends read data to the host controller.

Since techniques such as optical disc rotation control, channel clock reproduction, data recording and erasing methods, error signal detection and pickup servo are well known, detailed description thereof will be omitted here.

FIG. 1 is a more detailed diagram of the signal reproducing circuit 11. 21 is A for A / D converting the differential signal of the reproduced signal
/ D converter, 22 is a difference detection circuit, 23 is a programmable delay line, and 24 is a control circuit for controlling the delay line 23. Here, the A / D converter 2
1 is a decimal number 0 by A / D converting the differential signal with 4 bits
It is assumed that it operates so as to obtain a value of ˜15 (a positive large value is converted to 15, a negative large value is converted to 0, and a zero level is converted to 8). 25-28 has the same structure as 21-24,
Reference numeral 29 is a combining circuit.

In the signal reproducing circuit 11, the difference detecting circuit 22 detects the maximum value of the reproduced signal differential signal corresponding to the front edge of the mark on the disc, and the difference detecting circuit 26.
Thus, the minimum value of the differential signal corresponding to the trailing edge of the mark is detected. Then, the results obtained by both the difference detection circuits are combined by the combining circuit 29 and output to the demodulation circuit 12 as a binarization result. In the following description, a subscript of "L" may be attached to one handling a front edge, and a "T" may be attached to one handling a rear edge. Further, since the specific method of difference detection and the circuit configuration are known, the description thereof will be omitted.

FIG. 3 is a diagram showing the operation of the signal reproducing circuit 11. Modulate circuit 6 writes certain write data to 4/1
If the result of 1 modulation is as shown in FIG. 3 (a),
When mark edge recording is performed, the write signal to the disc is as shown in FIG. The write control circuit 5 causes the magnetic head 4 to generate a bias magnetic field in the writing direction, and causes the laser in the pickup 3 to emit light in accordance with the signal in FIG. At this time, if the emission power of the laser is optimally controlled with respect to the sensitivity of the disc and the ambient temperature, the edge portion of the mark to be formed and the edge portion of the write signal match, but generally such control is performed accurately. It is difficult to perform, and recording is not always performed under optimum conditions. Here, consider the case where the laser emission power is slightly high and a mark slightly longer than the write signal is formed as shown in FIG.

At the time of reproduction, a laser beam is irradiated onto the optical disk with a power weaker than that at the time of writing, and the optical beam is optically generated.
The mark (c) is detected, and the detection result is photoelectrically converted to obtain a reproduction signal. Since the spot diameter of the laser used for reading is not infinitely small, the reproduced signal obtained changes gently at the edge portion of the mark as shown in FIG.

The reproduced signal is differentiated by the differentiating circuit 10 to obtain a differentiated signal as shown in FIG. In the conventional method, the differential signal is binarized by detecting the difference according to the channel clock CHCLK in FIG. 3 (f), but in the present invention, the frequency is the same as CHCLK and the phase is shifted (delayed). LCHCLK, which is the clock
(FIG. 3 (g)) and TCHCLK (FIG. 3 (i)) are used to detect the difference. Here, LCHCLK is a clock whose phase is aligned with the maximum of the differential signal of FIG. 3E corresponding to the front edge of the mark, while TCHCLK is phase with respect to the minimum of the differential signal corresponding to the rear edge of the mark. Are clocks that have been matched (the clock phase setting method will be described later).

Then, the differential signal is sampled by the A / D converter (L) 21 in accordance with LCHCLK. If the result is as shown in FIG. 3 (h), for example, the difference detection for obtaining the two maximum values is performed. The binarization result that the second bit and the eighth bit are "1" is performed by the difference detection circuit (L) 22. Similarly, A
In the / D converter (T) 25, the differential signal is sampled according to TCHCLK, and the difference detection circuit (T) 26 detects the difference between the two minimum values. Then, the binarization result obtained by both the difference detection circuits is the synthesis circuit 2
9 is combined, and is output to the demodulation circuit 12 as a final binarization result (FIG. 3 (k)).

Next, a method of adjusting the phases of LCHCLK and TCHCLK (a method of determining the delay amount) will be described.
FIG. 4 is a diagram showing a method of adjusting LCHCLK.

First, when data is recorded, a specific pattern (for example, 101010 ... Is displayed in a specific area on the optical disk, for example, a head portion of a sector which is a unit of recording and reproduction, as shown in FIG. (It is not necessary to follow the rule of 4/11 modulation). Since this specific pattern is recorded under the same recording conditions as the data to be written subsequently, the state of the edge shift of the subsequent data can be known depending on how this specific pattern is written.

At the time of reproduction, the phases of LCHCLK and TCHCLK are controlled so that the absolute value of the sampling result of the differential signal in this specific pattern portion becomes large.
For example, in the case of LCHCLK, the delay line (L)
The differential signal is sampled by the A / D converter (L) 21 according to LCHCLK while sequentially changing the delay time of 23, and the delay time at which the sampling result becomes maximum is the delay time of the delay line (L) 23 in the sector. Set as. Similarly, the delay amount in the delay line (T) 27 may be set so that the sampling result of the differential signal in the A / D converter (T) 25 is minimized.

Similar to FIG. 3, FIG. 4 also shows a case where the laser power is higher than the optimum value and a long mark is formed.
In this case, the front edge moves slightly before the original timing (the rising edge of CHCLK), and the delay amount of the delay line (L) 23 is set to the reference value (LCHCLK and CHCL).
A / D when the delay time is set to less than
The conversion result is the maximum (underlined part (4) in FIG. 4). The delay amount at this time is adopted as the delay amount of LCHCLK with respect to CHCLK when reading the subsequent data. Although not shown in the figure, the delay amount from CHCLK is determined by the same method for TCHCLK which is a clock for the rear edge,
Here, a value slightly larger than the reference value will be set as the delay amount.

Contrary to FIG. 4, when the laser power is lower than the optimum value, a shorter mark is formed and the front edge moves backward and the rear edge moves forward.
The delay amount of CLK is large and the delay amount of TCHCLK is small.

By such a procedure, the steady shift amounts of the front edge and the rear edge are obtained in the specific pattern area, and the A / D conversion is performed by the clock corrected for this shift amount, and the difference is independently applied to each edge. Detection is performed, and both difference detection results are combined to obtain a final binarization result.

Further, since it becomes possible to detect the variation of the mark length in the specific pattern portion, the mark length is checked when reproducing by the verify operation immediately after data recording,
If the mark length is longer than the normal length (the front edge moves to the front and the rear edge moves to the rear), the laser power is considered excessive and the power for the next recording is lowered. It is also possible to do

As described above, according to this embodiment, the difference is detected independently of the front and rear edges by the clock whose phase is matched with the peak of the differential signal of the reproduced signal at the front edge and the rear edge, so that the recording condition is Even when the mark length to be formed is not optimally controlled and fluctuates, the difference can be detected at the optimal timing, and more accurate data can be reproduced. That is, even if the mark length varies, if the variation in the front edge / the rear edge alone is small, the binarization can be performed by the difference detection without a detection error. As a result, the reliability of data reproduction is increased and the margin is increased, so that it is possible to record data at a higher density. Further, since the mark length variation can be corrected at the time of reproduction, it is not necessary to make a strict correction at the time of recording, and the recording system can be simplified.

In this embodiment, two A / D converters are used separately for the front edge and the rear edge, but the sampling of differential signals at both edges is made the same by using a faster A / D converter. The A / D converter may be used. In this case, the A / D result obtained at the timing of the leading edge and the A / D result obtained at the timing of the trailing edge may be stored in a register of a different system from the beginning, and the difference detection may be performed independently for each edge. Yes, and decide which of the leading edge and the trailing edge to take according to the A / D conversion result (A
If the / D result is a positive value, the A / D result at the front edge is adopted), or binarization may be performed by a single difference detection circuit. As for the difference detection method, in addition to the conventionally used method, the applicant of the present invention has filed Japanese Patent Application No. 5-22024.
The method with correction proposed in No. 0 can be used.

Further, in the present embodiment, the reproduction signal is differentiated by the electric circuit to obtain the signal having the extreme value at the edge of the mark and the signal is input to the A / D converter. However, the optical method is used before the photoelectric conversion. It is also possible to detect the edge of the mark and perform the same processing as the differentiation, and photoelectrically convert the result to perform A / D conversion. Such an optical mark edge detecting method is disclosed, for example, in Japanese Patent Laid-Open No. 63-313335. Since the optical edge detection method does not amplify noise unlike the differentiation by the electric circuit, it can be said that the optical edge detection is more suitable.

Further, instead of detecting the difference with respect to the signal after edge detection, the edge position is detected by performing difference detection for selecting a value close to the intermediate value or average value of the reproduced signal before differentiation. When doing (for example, JP-A-5-10139)
The method disclosed in No. 6) can be applied to the present invention. In this case, each clock is set to a phase where the A / D conversion result is closest to the intermediate value or the average value.

Further, the present invention can be directly applied to the case other than magneto-optical recording (phase change recording etc.), and even if the modulation method is other than 4/11 modulation, after modulation within a block which is a delimiter of modulation. If the number of '1's is constant, the modulation method can be applied. Also, even if the optical disk is a general continuous servo that is not a sample servo,
The present invention can be applied if there is a mark serving as a reference and the channel clock can be reproduced with the mark as a reference.

[0033]

As described above, according to the signal reproducing circuit of the optical disk device of the present invention, when reproducing the data recorded by the mark edge method by the difference detection, the first
The front edge of the mark is obtained by the difference detection according to the reference clock, the rear edge is obtained according to the second reference clock, and the front edge and the rear edge are sampled by different clocks at the respective optimum timings to detect the difference independently. By doing so, there is an effect that accurate difference detection can be performed, more stable data reproduction can be realized, and a signal reproduction circuit of an optical disk device suitable for high-density recording can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a signal reproducing circuit of an optical disc device of the present invention.

2 is a block diagram of an optical disc device including the signal reproduction circuit of FIG.

FIG. 3 is a timing diagram illustrating an operation of the signal reproduction circuit of FIG.

4 is a timing diagram illustrating a method of adjusting LCHCLK of the signal reproduction circuit of FIG.

[Explanation of symbols]

 1 ... Optical disk 3 ... Pickup 4 ... Magnetic head 5 ... Write control circuit 6 ... Modulation circuit 7 ... Head amplifier 8 ... Clock reproduction circuit 9 ... Servo circuit 10 ... Differentiation circuit 11 ... Signal reproduction circuit 12 ... Demodulation circuit 21 ... A / D Converter (L) 22 ... Difference detection circuit (L) 23 ... Programmable delay line (L) 24 ... Control circuit (L) 25 ... A / D converter (T) 26 ... Difference detection circuit (T) 27 ... Programmable delay line ( T) 28 ... Control circuit (T) 29 ... Synthesis circuit

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[Procedure amendment]

[Submission date] January 13, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

On the other hand, as a signal reproducing method suitable for high density,
There is something called difference detection. Difference detection does not directly binarize the value of the reproduced signal itself, but samples the reproduced signal and binarizes it based on the relative magnitude relationship of the sampling results. For example, in the case of DBF, which is one of the sample servo formats, the 1-byte data is always modulated such that the number of '1' becomes 4 (4/11 modulation), and the reproduction signal level was large. Binarization is performed by selecting 4 bits. The difference detection method is suitable for high-density recording and reproduction since the absolute values strongly to various signal degradation for not required, allowable amount for the amplitude reduction of the reproduced signal due to high density recording of the reproduced signal is large. In order to perform the difference detection, it is necessary to be able to reproduce the channel clock used for sampling from other than the data like the sample servo (it is an external clock).

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction content]

The applicant of the present invention has proposed in Japanese Patent Application No. 5-220240 a high density recording / reproducing method combining a difference detection method and a mark edge recording method. This is to differentiate the reproduced signal when reproducing the data recorded by the mark edge method, and perform a difference detection for selecting a bit having a large absolute value of the signal level with respect to the differentiation result.

Claims (5)

[Claims] 1. A channel clock is reproduced from a unique mark intermittently provided on an optical disc, and recorded information is NR.
ZI conversion is performed, and in synchronization with the channel clock, information is recorded by forming marks on the optical disc so that the edge portions of the marks correspond to information "1", and in synchronization with the channel clock. In a signal reproducing circuit of an optical disk device for reproducing information, a signal detecting means for detecting a signal associated with the mark based on the reflected light from the optical disk, and a first signal having the same frequency as the channel clock but a different phase. First and second reference clock generation means for generating a second reference clock, sampling means for sampling the output of the signal detection means according to the first and second reference clocks, and a sampling result by the sampling means And a binarizing means for binarizing recorded information based on Raw circuit. 2. On the optical disk, data modulated by a modulation method such that "1" in a block which is a unit of modulation becomes 2N bits, the "1" portion of the data is the edge portion of the mark. Written in a corresponding manner, the sampling means samples the output of the signal detecting means according to the first reference clock.
And sampling means for sampling the output of the signal detecting means in accordance with the second reference clock, the binarizing means of the first sampling means in the block. First difference detecting means for selecting N bits from the output sequence, second difference detecting means for selecting N bits from the output sequence of the second sampling means in the block, and the first and second 2. The signal reproducing circuit of the optical disk device according to claim 1, further comprising a synthesizing unit for synthesizing the output of the difference detecting unit. 3. The signal detecting means outputs a signal having an extreme value at the edge portion of the mark, and the first difference detecting means is included in the output sequence of the first sampling means in the block. From the output sequence of the second sampling means in the block, the second difference detecting means selects N bits having a smaller sampling result from the output sequence of the second sampling means. The signal reproducing circuit of the optical disk device according to claim 2, wherein the difference detection to be selected is performed. 4. The first reference clock generation means controls the delay amount of the first delay means based on the output of the first delay means for delaying the channel clock and the first sampling means. The second reference clock generating means, the second delay means for delaying the channel clock, and the second delay means based on the output of the second sampling means. 2. The signal reproducing circuit of the optical disk device according to claim 1, comprising a second control means for controlling the delay amount of the means. 5. The first control means controls the delay amount of the first delay means so that the output of the first sampling means at the front edge of the specific pattern on the optical disc is maximized, 5. The second control means controls the delay amount of the second delay means so that the output of the second sampling means at the rear edge of the specific pattern on the optical disc is minimized. A signal reproducing circuit of the optical disk device described in 1.