JP2000311347A - Driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a selection in a real reproduction of the next sector to maintain a setting state or to return to an initial value by changing a parameter setting state at every retrial during retrials due to reproduction NG and by estimating a cause of reproduction NG from the setting state when retrial becomes OK at a certain parameter setting state. SOLUTION: When reproduction NG occurs during reproducing a certain sector, a retrial process moves in, a change of a parameter setting corresponding to the number of the retrial times is executed, and the setting state reaches if it is the first retrial. Here by changing a gain of VGA 8 and accessing to the top of the present sector that fails the real reproduction, the reproduction as the first retrial is executed. When reproduction NG occurs again, the reproduction as the second retrial is made and a timing setting of RGATE signal is changed. Hereafter retrial is repeated by changing the setting state as long as reproduction NG occurs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive device capable of reproducing data from a recording medium.

[0002]

2. Description of the Related Art In a drive device that performs a reproducing operation on a recording medium such as an optical disk or a magneto-optical disk, when a data reproducing operation is performed on a certain sector (a sector is a unit area of data on the recording medium). NG, that is, data read may not be properly performed. Causes include that the reproduction RF signal is disturbed due to the presence of a defect or birefringence in the sector, or that the laser power at the time of recording in the sector is inappropriate. These causes can be broadly classified into error causes having continuity in the preceding and succeeding sectors (sectors which are not necessarily physically continuous but preceding and succeeding in data content) and error causes peculiar to the sector.

[0003] The cause of a continuous error is a cause of a high possibility that, when a reproduction NG occurs in one sector, a reproduction NG due to the same cause occurs in the next sector. For example, an error cause that the laser power at the time of recording is inappropriate corresponds to this. For example, one reproduction operation normally reproduces a plurality of sectors recorded in one recording operation. In a series of recording operations for a plurality of sectors, it is highly possible that each sector is recorded with the same recording laser power. This means that if the recording laser power is appropriate in the first sector, the following sectors are also appropriate, while if the recording laser power is inappropriate in the first sector, the following sectors may be inappropriate. Means higher.

On the other hand, the causes of errors specific to the sector include defects and birefringence. That is, the occurrence of defects (scratch, dirt, etc.) and birefringence in the sector affects the reproduction RF signal of the current sector, and does not naturally affect the reproduction of the next sector.

[0005]

By the way, the reproduction system of the disk drive device has various parameters that can be changed in various processing steps related to the reproduction processing. For example, an amplifier gain for a reproduced RF signal, a cutoff frequency and a boost band in a filtering process, a boost level, an offset feedback gain, an offset mode, a PLL loop gain for obtaining a reproduced clock, and an amplitude reference value when Viterbi decoding is employed. Yes, specific examples of these will be described later, but by changing these parameters, the characteristics of the read capability can be changed. If the reproduction of a certain sector is NG for some reason as described above,
The reproduction process (retry) for the sector is performed again. At the time of the retry, all or some of the parameters are changed. That is, by changing various parameters to settings that enable reading in response to possible causes of errors, it is possible to increase the possibility of leading to successful reading at the time of retry.

Of course, the cause of the error cannot always be specified at the time of the reproduction NG, so that it is not possible to uniquely determine which parameter should be changed and how it is optimal at that time. Therefore, if the parameter setting state is changed every retry (the retry operation is set to the upper limit number of times, but is repeated until the reproduction is OK until the upper limit number is reached), the reproduction is performed at a certain retry point. The possibility of being OK can be increased. That is, it is possible to significantly increase the possibility of leading to the reproduction OK, rather than simply repeating the retry (without changing the parameter).

[0007] For the sake of explanation, the initial reproduction for a certain sector (that is, reproduction that is not a retry performed in a normal reproduction operation) is referred to as "main reproduction" to distinguish it from reproduction by retry. Is referred to as “retry reproduction.” The term “reproduction” simply includes main reproduction and retry reproduction.

Usually, at the time of main reproduction for a certain sector, each parameter is set to an initial value. Here, the initial value is a value that is set in advance for each parameter as a value (a value that is optimal as read capability) at which the most appropriate reproduction process can be performed in a normal state. And
If the playback is NG, one of all parameters
Alternatively, a plurality of parameters are changed from the initial values to other values.

Here, when the retry reproduction in the parameter setting state becomes reproduction OK and the reproduction of the next sector proceeds, there is a problem in how to set the parameters. For example, since the parameter initial value is an optimal value in a normal state, it is conceivable to return the parameter to the initial value when starting the main reproduction of the next sector. However,
If you have the above persistent error cause,
Returning the parameter to the initial value in the next sector increases the possibility of a reproduction NG. On the other hand, if the cause of the reproduction NG that occurred in the previous sector is specific to the sector, it is preferable to return the parameters to the initial values having the best read capability at the time of the main reproduction in the next sector. is there. For these reasons, there is a situation in which an optimal parameter cannot be determined as the initial parameter setting for the next sector. Of course, when the main reproduction is performed with parameters that are not optimal for the next sector, the possibility of executing the retry reproduction as the reproduction NG increases. In this case, while changing the parameter setting state, 1
Alternatively, there is a high possibility that the reproduction can be successfully performed by performing the retry a plurality of times. However, ideally, no retry should be performed in the first place.
Since leading to K is preferable from the viewpoint of shortening the reproduction time, improving the response as a device, and reducing power consumption, it is difficult to always set the optimal parameters for each sector during the main reproduction. This is disadvantageous in that the performance of the drive device is improved.

[0010]

SUMMARY OF THE INVENTION In view of the above problems, the present invention makes it possible to set appropriate parameters in a drive device at the time of main reproduction of each sector, thereby improving the performance of the drive device. The purpose is to:

For this purpose, the drive device according to the present invention comprises a head means capable of reading a data signal recorded on a recording medium by irradiating a laser beam, and a data signal read by the head means. A reproduction circuit means for performing reproduction signal processing based on various set parameters to obtain reproduction data; and performing a reproduction operation by a head means and a reproduction circuit means for each unit area on a recording medium, and reproducing the unit area. When the reproducing circuit means does not obtain appropriate reproduction data for the data signal read by the head means at the time, the reproduction control means executes a retry of the reproducing operation for the unit area, and the reproduction control means executes the retry. For each controlled retry, the setting state of various parameters in the reproducing circuit means is changed,
If appropriate playback data is obtained by a retry operation in a certain setting state, according to the type of the setting state,
When reproducing the unit area to be subsequently executed, a parameter setting means for maintaining the set state or returning the set state to the initial value is provided.

That is, at the time of retry by reproduction NG, the parameter setting state is changed every retry. If the retry succeeds in a certain parameter setting state, the cause of the reproduction NG up to that time can be estimated from the setting state at that time. According to the type of the setting state, it is possible to select whether to maintain the setting state or return to the initial value.

In particular, when the type of the setting state when proper reproduction data is obtained by the retry operation is a setting state capable of coping with a continuous error cause in the next unit area, Then, when the unit area is reproduced, the set state is maintained. If the type of the setting state when proper reproduction data is obtained by the retry operation is a setting state that can cope with an error cause specific to the unit area, the setting state is set when the unit area is subsequently reproduced. Return the state to the initial value.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described, but in order to facilitate understanding of the embodiments,
In the following order, first, the configuration of a disk drive device having a reproduction system that performs the Viterbi decoding method, the Viterbi decoding method, and the like will be described, and then, the configuration and operation of the disk drive device as an embodiment will be described. 1. 1. Description of disk drive device having playback system for performing Viterbi decoding method 1-1 Overview of device configuration 1-2 Viterbi decoding method 1-3 Viterbi decoder 2. Disk drive device of embodiment 2-1 Configuration of disk drive device 2-2 Relationship between recording laser power and asymmetry 2-3 Offset error detection method 2-4 Parameter setting example 2-5 Processing example at reproduction

1. 1. Description of Disk Drive Device Having Reproduction System Performing Viterbi Decoding Method 1-1 Overview of Device Configuration First, an example of a typical disk drive device (recording / reproduction device) having a reproduction system performing a Viterbi decoding method will be described. FIG. 1 is a block diagram showing a configuration of an example of a disk drive device having a reproducing system for performing a Viterbi decoding method on a magneto-optical disk or an optical disk. However, in this figure, the servo system and the like are omitted.

At the time of recording, the controller 2 receives user data to be recorded according to a command from the host computer 1, performs encoding based on the user data as information words, and performs RLL (1, 7) encoding as code words. Generate This code word is supplied as recording data to a laser power control unit (hereinafter, referred to as LPC) 4. In addition to such processing, the controller 2 performs operations such as decoding processing described later, control of each mode such as recording, reproduction, and erasing, and communication with the host computer 1.

The LPC 4 generates a laser drive signal (drive pulse) so as to execute laser output from the optical pickup 7 at each of reproduction, recording, and erasing. This drive pulse is APC (Auto Power C
and a drive section (hereinafter, APC) 10 to apply a current corresponding to a drive pulse to the laser diode by the APC 10, thereby performing laser output from the laser diode in the optical pickup 7. Further, the APC 10 performs feedback control so as to keep the laser level at a predetermined value.

As described above, the LPC 4 and APC 10 control the laser power of the optical pickup 7 in accordance with the supplied recording data to form a pit row on the disk 6 rotated by the spindle motor 9. Thus, recording is performed. For example, in the case of a drive device corresponding to a rewritable magneto-optical disk (MO disk),
A pit row having a magnetic polarity is formed on the disk 6. In this case, the magnetic head 5 applies a bias magnetic field to the disk 6. In addition, a write-once disc (WORM)
Disk) and a drive device that supports so-called abrasive type (perforated) disks,
An emboss pit row is formed by the laser beam. In the case of a write-once disk (WORM disk), which is a drive device corresponding to a so-called alloy type disk, a pit row is formed by causing a change in the reflectance of the disk recording surface by laser light. Further, in the case of a drive device corresponding to a phase change type disk, a phase change pit row is formed by a laser beam.

In the pit train, mark edge recording described later is performed in accordance with a precode output generated as described later based on the recording data. A method for associating each pit to be formed with each pit in a precode output generated as described later based on the recording data will be described with reference to FIG. A pit is formed for, for example, “1” during precode output,
A recording method in which no pit is formed for 0 'is called a mark position recording method. On the other hand, a recording method in which the polarity inversion at the boundary of each pit in the precode output expressed by the edge of each pit corresponds to, for example, “1” is referred to as a mark edge recording method. At the time of reproduction, the boundary of each pit in the reproduction signal is recognized according to a read clock DCK generated as described later.

The configuration and operation of the reproduction system shown in FIG. 1 are as follows. The optical pickup 7 irradiates the disk 6 rotated by the spindle motor 9 with laser light, receives reflected light generated by the laser light, and generates reflected light information. Although not described in detail, the reflected light information includes a focus error signal and a tracking error signal in addition to the reproduced RF signal corresponding to the reproduced data. As a reproduction RF signal, for example, a magneto-optical disk
In a sector format on a disk, if there is a portion where an embossed pit is formed and a portion where a pit row is recorded magneto-optically, there are two types of so-called sum signal and difference signal. Switching processing is performed accordingly.

The RF signal is supplied to the filter section 11 after gain adjustment and the like are performed by the amplifier 8. The filter unit 11 includes a low-pass filter that performs noise cut and a waveform equalizer that performs waveform equalization. As will be described later, the waveform equalization characteristics used in the waveform equalization process at this time are adapted to the Viterbi decoding method performed by the Viterbi decoder 13. The A / D converter 12 to which the output of the filter unit 11 is supplied samples the reproduction signal value z [k] in accordance with a read clock DCK supplied as described later.

The Viterbi decoder 13 outputs a reproduced signal value z [k]
, And generates decoded data by the Viterbi decoding method. Such decoded data is a maximum likelihood decoded sequence for the recorded data recorded as described above. Therefore,
If there is no decoding error, the decoded data matches the recorded data. The Viterbi decoder 13 includes a branch metric block (BMC) 132, an add compare select block (ACS) 133, a status memory unit (SMU) 134, and a merge block 135. These will be described later. The Viterbi decoder 13 also includes a shift register 131 and an amplitude reference value adaptation unit (RAA) 136. And A / D converter 1
The output of 2 is also supplied to the shift register 15, and after being given a predetermined delay time by the shift register 131, is supplied to the amplitude reference value adaptation unit (RAA) 136. These operations will also be described later.

The decoded data obtained by the Viterbi decoder 13 is supplied to the controller 2. As described above, the recording data is a codeword generated from user data by encoding such as channel encoding. Therefore,
If the decoding error rate is sufficiently low, the decoded data can be regarded as recording data as a codeword. The controller 2 reproduces user data and the like by performing a decoding process corresponding to the above-described encoding such as the channel encoding on the decoded data.

The output of the filter unit 11 is also supplied to a PLL unit 14. The PLL unit 14 generates a read clock DCK based on the supplied signal. This P
The LL unit 14 is configured to detect a phase error by using a signal of a constant frequency recorded in the magneto-optical disk 6, for example. The read clock DCK is supplied to the controller 2, the A / D converter 12, the Viterbi decoder 13, and the like. The operations of the controller 2, the A / D converter 12, and the Viterbi decoder 13 are performed at timing according to the read clock DCK.

1-2 Viterbi decoding method A Viterbi decoding method performed by the Viterbi decoder 13 will be described below. As described above, the user data is converted into a codeword as recording data by various encoding methods. An appropriate encoding method is adopted according to the characteristics of the recording medium and the recording / reproducing method. In the disk drive device shown in FIG. 1, in block encoding, an RLL (Run Length Limited) encoding method for limiting the number of "0" between "1" and "1" is used. A Viterbi decoding method can be used to decode a reproduction signal reproduced from data recorded by a combination of such an RLL encoding method and the above-described mark edge recording method.

Such an RLL encoding method can meet the conditions required for the encoding method from two viewpoints of improving the recording density and ensuring the stability of the reproducing operation. First, as described above, the mark edge recording method associates "1" in a precode output generated as described later based on recording data with the inversion of the polarity represented by the edge of each pit. "
As the number of "0" s between "1" and "1" is increased, the number of pits recorded per l pits can be increased, and the recording density can be increased.

On the other hand, the reproduction clock DCK necessary for adjusting the operation timing of the reproduction system is, as described above,
It is generated by the PLL section 14 based on the reproduction signal.
For this reason, in the recording data, "1" and "1"
When the number of 0 "s is increased, the operation of the PLL unit 14 becomes unstable during the reproducing operation, so that the entire reproducing operation becomes unstable.

Considering these two conditions, "1"
The number of “0” s between “1” and “1” needs to be set within an appropriate range that is neither too large nor too small. Regarding the setting of the number of “0” in the recording data, R
The LL encoding method becomes effective.

By the way, as shown in FIG.
In the combination of the LL (1,7) encoding method and the mark edge recording method, at least one "1" is inserted between "1" and "1" in the precode output generated based on the recording data.
Since 0 ”is included, the minimum inversion width (RLmin) is 2. When such an encoding method with the minimum inversion width of 2 is used, it is affected by intersymbol interference and noise. As a method for decoding recorded data from a reproduced signal, a 4-level 4-state (6-level 4-state) Viterbi decoding method can be applied as described later.

As described above, the reproduced signal is subjected to the waveform equalization processing by the filter unit 11. Such a waveform equalization process performed as a preceding stage of the Viterbi decoding method includes:
A partial response method that actively uses intersymbol interference is used. The waveform equalization characteristics used at this time are:
From the partial response characteristics generally represented by (1 + D) ⁿ , the linear recording density and MTF (M
odulation transfer function).
For data recorded by a combination of the RLL (1,7) encoding method and the mark edge recording method described above,
The waveform equalization processing using PR (1,2,1) is a preceding stage of the 4-value 4-state Viterbi decoding method.

As shown in FIG. 3, in the mark edge recording method, prior to actual recording on a magneto-optical disk or the like, precoding based on the recording data encoded by the above-described RLL encoding or the like is performed. Assuming that the recording data sequence at each time point k is a [k] and the precode based on this is b [k], the precoding is performed as follows. b [k] = mod2 {a [k] + b [k-1]} (1) Such a precode output b [k] is actually recorded on the disk 6.

When such recorded data is reproduced, a waveform equalization characteristic P made by the waveform equalizer in the filter unit 11 is obtained.
The waveform equalization processing at R (1, 2, 1) will be described. However, in the following description, the waveform equalization characteristic is PR (B, 2A, B) without normalizing the signal amplitude. The value of the reproduced signal when noise is not taken into account is denoted by c [k]. Further, an actual reproduced signal including noise (that is, a reproduced signal reproduced from the disk 6) is denoted by z [k].

PR (B, 2A, B) indicates that the contribution of the amplitude at the time point k to the value of the reproduced signal at a certain time point k is 2A times the amplitude value. The contribution of the amplitude is B times the amplitude of the signal at each point in time. Therefore, the maximum value of the value of the reproduction signal is a case where a pulse is detected at any of the time points k−1, k, and k + 1. In such a case,
The maximum value of the reproduction signal is as follows.

B + 2A + B = 2A + 2B The minimum value of the reproduced signal is 0. However, in the actual handling, A + B of the DC component is used as c [k].
The following is used by subtracting c [k] = B * b (k-2) + 2A * b (k-1) + B * b [k] -AB (2)

Therefore, the reproduction signal c [k] when noise is not taken into account takes any one of A + B, A, -A, and -AB. In general, as one of the methods for indicating the properties of a reproduced signal, a pattern obtained by superimposing a large number of reproduced signals in units of, for example, five points is called an eye pattern. FIG. 4 shows an example of an eye pattern of an actual reproduced signal z [k] which has been subjected to waveform equalization under PR (B, 2A, B) in a recording / reproducing apparatus to which the present invention can be applied. From FIG. 4, the reproduced signal z [k] at each time point
Has a variation due to noise, but is approximately A +
It can be confirmed that any one of B, A, -A, and -AB is obtained. As described later, A + B, A, -A, -AB
Is used as an identification point.

The outline of the Viterbi decoding method for decoding the reproduced signal subjected to the above-described waveform equalization processing is as shown in steps 1 to 3. Step: Specify all possible states based on the encoding method and the recording method for the recording medium. Step: Starting from each state at a certain time point, all possible state transitions at the next time point, and the recording data a [k] and the value c [k] of the reproduction signal at the time of each state transition are specified. . Note that all states and state transitions specified as a result of the step and the state, and {recorded data value a [k] / reproduction signal value c [k]} when each state transition occurs are schematically shown. This will be a state transition diagram as shown in FIG. 6, which will be described later. The Viterbi decoder 13 is configured to perform a decoding operation based on this state transition diagram.

On the premise of the state transition shown in step..., The maximum likelihood state transition based on the reproduction signal z [k] reproduced from the recording medium at each time point k is selected. However, as described above, the reproduction signal z [k] has been waveform-equalized in a stage before being supplied to the Viterbi decoder 13. Each time such a maximum likelihood state transition is selected, the value of the recording data a [k] is set as a decoded value in accordance with the selected state transition, so that a maximum likelihood decoded value sequence for the recording data is obtained. Can be obtained as decoded data a ′ [k]. Alternatively, a state data value representing the selected state transition itself can be obtained. In the example of FIG. 1, the state data value sm [k +
[n].

Hereinafter, the above steps 1 to 5 will be described. First, the steps will be described in detail. As the state used here, the state at a certain time point k is defined as follows using the precode output before the time point k. That is, n = b [k], m = b [k−1],
The state when l = b [k-2] is defined as Snml. With such a definition, it is considered that there are 2 ³ = 8 states, but as described above, the states that can actually occur are limited based on the encoding method and the like. In the recording data sequence a [k] encoded as the RLL (1, 7) code, "
Since at least one “0” is included between “1” and “1”,
Two or more “1” s do not continue. Based on such conditions imposed on the recording data string a [k], certain conditions are imposed on the precode output b [k], and the resulting states are restricted.

The above-mentioned restriction is specifically as follows. As described above, in the recording data sequence generated by the RLL (1, 7) encoding, there is no pattern in which two or more “1” s are continuous, that is, the following pattern. a [k] = 1, a [k−1] = 1, a [k−2] = 1 (3) a [k] = 1, a [k−1] = 1, a [k− 2] = 0 (4) a [k] = 0, a [k−1] = 1, a [k−2] = 1 (5) Such a kind imposed on the recording data sequence Considering the conditions imposed on b [k] in accordance with the above equation (1) based on the conditions, it is found that S0 in the definition of Snml.
It can be seen that the two states of 10 and S101 cannot occur. Therefore, there are 2 ³ −2 = 6 possible states.

Next, the steps will be described. To obtain a state that can occur at the next time point j + 1 starting from the state at a certain time point j, the value a [j + 1] of the recording data at the time point j + 1 becomes 1 or 0
It is necessary to investigate separately when it becomes.

Here, the state S000 will be described as an example. According to the above equation (1), S000, that is, n =
b [j] = 0, m = b [j-1] = 0, l = b [j-2] = 0
The following two are conceivable as recording data pre-coded as follows. a [j] = 0, a [j-1] = 0, a [j-2] = 1 ... (6) a [j] = 0, a [j-1] = 0, a [j- 2] = 0 (7)

When a [j + 1] = 1 At this time, b [j + 1] is calculated as follows according to the equation (1). Therefore, the value of the reproduced signal c [j] is calculated as follows according to the above equation (2).

C [j + 1] = {B × b [j + 1] + 2A × b [j] + B × b [j−1] −AB = {B × 1 + 2A × 0 + B × 0} −AB = −A ... (9)

The state Snml at the next time point [j + 1]
For n = b [j + 1], m = b [j], 1 = b [j
-1]. Then, as described above, b [j + 1] =
Since 1, b [j] = 0 and b [j-1] = 0, the state at the next time point, j + 1, is S100. Therefore, when a [j + 1] = 1, it can be specified that a transition of S000 → S100 occurs.

When a [j + 1] = 0 At this time, b [j + 1] is calculated as follows according to the equation (1). Therefore, the value of the reproduced signal c [j + 1] is calculated as follows according to the above equation (2).

C [j + 1] = {B × b [j + 1] + 2A × bj] + B × b [j−1]} − AB = {B × 0 + 2A × 0 + B × 0} −AB = −A− B ... (11)

The state Snm at the next time point j + 1
For l, n = b [j + 1], m = b [j], l = b
[j-1]. Then, as described above, b [j + 1] =
Since 0, b [j] = 0 and b [j-1] = 0, the state at the next point in time is S000. Therefore, a [j
In the case of +1] = 0, it can be specified that a transition of S000 → S000 occurs.

Thus, S000 at time j
, The state transitions that can occur at the next time point j + 1 starting from them and the correspondence between the recording data value a [j + 1] and the reproduction signal value c [j + 1] when such state transitions occur Can be requested.

As described above, for each state, the correspondence between the state transition that can occur starting from the state and the value of the recording data and the value of the reproduction signal when each state transition occurs is shown as a schematic diagram. FIG. Time points j and j + 1 described above are not special time points. Therefore, the correspondence between the possible state transitions obtained as described above and the accompanying values of the recording data and the values of the reproduction signals can be applied at any time. For this reason, in FIG. 5, the value of the recording data accompanying the state transition occurring at an arbitrary time point k is denoted as a [k], and the value of the reproduced signal is denoted as c [k].

In FIG. 5, state transitions are represented by arrows. Further, the sign given to each arrow is Δrecorded data value a
[k] / reproduced signal value c [k]}. State S00
There are two types of state transitions starting from 0, S001, S111, and S110, whereas only one transition can occur starting from states S011 and S100. Further, in FIG. 5, S000 and S001 both take a value of c [k] = − A for a [k] = 1, and have transited to S100. On the other hand, for a [k] = 0, a value of c [k] =-AB is taken and the process transits to S000. Similarly, S111 and S110 have the same a
The value of [k + 1] has the same value of c [k + 1], and the state transits to the same state. Therefore, S000 and S001 are collectively expressed as S00, and S111 and S11
0 can be collectively expressed as S11. further,
FIG. 6 shows an arrangement in which S011 is expressed as S10 and S100 is expressed as S01.

FIG. 6 is a state transition diagram used in the 4-level 4-state Viterbi decoding method. For example, when there are four states such as a four-level four-state Viterbi decoding method or the like, these four states can be expressed by two bits, and such two-bit data can be used as a state data value. . Therefore, in FIG. 6, each state is represented by S0 using the 2-bit state data values 00, 01, 11, and 10, respectively.
0, S01, S11, and S10.

In addition, a trellis diagram as shown in FIG. 7 is used as a format for expressing the state transition along time corresponding to FIG. FIG. 7 shows a transition between two time points, but a transition between a larger number of time points may be shown. As the time elapses, a state in which the image sequentially transits to the right time point is expressed. Therefore, a horizontal arrow indicates, for example, S0
A transition to the same state such as 0 → S00 is shown, and an oblique arrow represents a transition to a different state such as S01 → S11.

Assuming the steps of the above-described Viterbi decoding method, that is, the state transition diagram shown in FIG. 6, a method of selecting the most likely state transition from the actual reproduced signal z [k] including noise is as follows. Become.

In order to select the maximum likelihood state transition, first, for the state at a certain time point k, the sum of the likelihoods of the state transitions between a plurality of time points passed in the process of reaching the state is calculated. It is necessary to select the maximum likelihood decoded sequence by comparing the calculated sums of likelihoods. Such a sum of likelihoods is called a path metric.

In order to calculate a path metric, it is first necessary to calculate the likelihood of a state transition between adjacent time points. Such calculation of likelihood is performed as follows based on the value of the reproduced signal z [k] with reference to the above-described state transition diagram. First, as a general explanation, the time k-
Consider the case where the state is Sa in state No. 1. At this time, when the reproduction signal z [k] is input to the Viterbi decoder 13, the likelihood that a state transition to the state Sb occurs is calculated according to the following equation. However, the state Sa and the state Sb are any of the four states described in the state transition diagram of FIG.

(Z [k] −c (Sa, Sb)) ² ... (12) In the above equation, c (Sa, Sb) is a state transition from the state Sa to the state Sb in the state of FIG. This is the value of the reproduced signal described in the transition diagram. That is, in FIG. 7 described above, for example, for the state transition S0 → S1, the value is calculated as −A. Therefore, equation (12) is the Euclidean distance between the value of the actual reproduced signal z [k] including noise and the value of the reproduced signal c (Sa, Sb) calculated without considering noise. The path metric at a certain point in time is defined as the sum of likelihoods of state transition between such adjacent points up to that point.

1-3 Viterbi Decoder In the Viterbi decoder 13, BMC 132, ACS 133,
The SMU 134 detects state data corresponding to the state transition as described above, and the merge block 135 decodes the state data, whereby the controller 2
Can be supplied with the decoded data. The configuration and operation of the Viterbi decoder 13 will be described.

In the following description, P (P, B, 2A, B) is used as the waveform equalization characteristic instead of PR (B, 2A, B).
It is assumed that R (α, β, γ). This premise takes into account that it is difficult to obtain an ideal partial response characteristic in an actual disk drive device, and the waveform equalization characteristic is often asymmetric. The reasons why it is difficult to obtain the ideal partial response characteristics include the limitation of the operation accuracy of the waveform equalizer, the asymmetry (asymmetry of the waveform) due to the laser power during recording being too large or too small, and the reproduction signal. There is a phase error of the read clock used when sampling is performed by the A / D converter 12.

In the case of the four-value four-state Viterbi decoding method, RLL (1, 7) coding or the like is performed at the time of recording such that RLmin = 2, and the partial response characteristic at the time of reproduction is PR (α, β). , Γ), it can be seen that there are six values and four states. That is, for each of 2 ³ −2 = 6 {b [j−1], b [j], b [j + 1]} sets other than the two states excluded by the condition of RLmin = 2, , Ie, the reproduced signal value c [j + 1] after waveform equalization in an ideal case with no noise takes a different value. (Ideally four values, but in reality c011 and c110, and c100 and c001 described below
Do not match, and therefore have six values. )

The values of the six discrimination points are denoted as cpqr. Here, p, q, and r are b [j−
1], b [j] and b [j + 1]. In FIG. 6, the values cpqr of the identification points relating to the transitions of the respective states S00, S01, S11, and S10 are added. That is, c00
0, c001, c011, c111, c110, c10
0. Since RLmin = 2, c010
And c101 do not exist. The following description is made on the premise that the 6 values and 4 states follow the state transition diagram of FIG.

The branch metrics calculated corresponding to the six state transitions in FIG. 6 are described as follows. First, two-bit state data values indicating the state before the transition and the state after the transition are written and arranged to form a sequence of four numbers. Next, a branch metric that can occur during one read clock is expressed as a sequence of three numbers by using the two numbers (ie, the second and third numbers) near the center as one number. . For example, state transition S11 →
The branch metric associated with S10 is denoted by bm110. In this way, the branch metrics corresponding to the six types of state transition in FIG. 6 can be represented as shown in FIG.

Further, the branch metric defined as the Euclidean distance between the actual reproduced signal value z [k] sampled by the A / D converter 12 operating according to the read clock and the value of each discrimination point is as follows. Is calculated.

Bm000 = (z [k] −c000) ² ... (13) bm001 = (z [k] −c001) ² ... (14) bm011 = (z [k] −c011) ^2. (15) bm111 = (z [k] -c111) ² ... (16) bm110 = (z [k] -c110) ² ... (17) bm100 = (z [k] -c100) ^2. (18) When the branch metric is calculated in this way, the value of each discrimination point is directly used as the amplitude reference value. When a standardized path metric is used for the purpose of avoiding the square calculation or the like, the branch metric corresponding to the standardized path metric is different from those according to the equations (13) to (18). In such a case, the value of each identification point cannot be used as it is as the amplitude reference value, but the present invention can be applied.

Using the value of such a branch metric, the path metric mij of the state Sij at the time point k
[K] is calculated as follows. m10 [k] = m11 [k-1] + bm110 (19) m11 [k] = min {m11 [k-1] + bm111, m01 [k-1] + bm011} (20) m01 [k ] = M00 [k-1] + bm001 (21) m00 [k] = min {m00 [k-1] + bm000, m10 [k-1] + bm100} (22)

As shown in FIG. 1, the output of the A / D converter 12 is supplied to the BMC 132 and the shift register 131 in the Viterbi decoder 13. The Viterbi decoder 13
Based on the reproduction signal value z [k] supplied from the A / D converter 12, the BMC 132, ACS 133, SMU 134
The state transition sm [k + n] expressing the selected state transition itself is generated by selecting the maximum likelihood state transition by the above operation. Then, based on the state data, the merge block 135
To generate the decoded data and supply it to the controller 2. The controller 2 performs a decoding process based on the supplied decoded data and reproduces user data, address data, and the like, similarly to the above-described example of the magneto-optical disk device.

The status data from the SMU 134 is also supplied to an amplitude reference value adaptation unit (RAA) 136. Further, the shift register 131 delays the reproduction signal value z [k] supplied from the A / D converter 12 by a predetermined time to RA
A136. This delay is performed to adjust the timing so that the state data generated by the Viterbi decoder 13 has a delay of n read clocks with respect to the reproduced signal value z [k]. Therefore,
The state data value generated by the SMU 134 in the Viterbi decoder 13 is represented by sm [k + n] because of this delay time.

The RAA 136 stores the state data value sm [k + n] supplied at each time point and the shift register 13.
Based on the reproduction signal value z [k] delayed by n clocks at 1, the amplitude reference value is updated for each read clock.
Then, the updated amplitude reference value is stored in B in the Viterbi decoder 13.
Supply to MC132.

Here, each block in the Viterbi decoder 13 will be described. Each block in the Viterbi decoder 13, ie, BMC 132, ACS 133, SMU 134,
Merge block 135, shift register 131, RAA
136 is supplied with a read clock DCK (hereinafter, also simply referred to as a clock) from the PLL unit 14 and the operation timing is adjusted.

The BMC 132 calculates the branch metrics bm000 to bm111 according to the above equations (13) to (18) based on the amplitude reference value supplied from the RAA 16 based on the reproduced signal value z [k]. The calculated branch metric is supplied to the ACS 133.

The ACS 133 calculates the value of the path metric according to the equations (19) to (22) based on the supplied branch metric value, and selects the most likely state transition by comparing the calculated values. . And the selection signal S
EL00 and SEL11 are supplied to the SMU 134.

The SMU 134 will be described with reference to FIG. The SMU 134 performs processing in units of 2-bit state data values, and the processing generates state data as a series of state data values sm [k + n].

As shown in FIG. 8, the SMU 134 has two A-type status memories 150 and 151 and two B-type status memories 152 and 153. Further, select signals SEL00, SEL11, clock,
In addition, a signal line for transferring state data to and from another status memory is connected. The A-type status memories 150 and 151 store the states S00 and S, respectively.
Corresponds to 11. The B-type status memories 152 and 153 correspond to states S01 and S10, respectively. The connection between these four status memories is in accordance with the state transition diagram of FIG.

FIG. 9 shows the configuration of the A-type status memory 150 corresponding to the state S00. The A-type status memory 150 has n processing stages. That is, n selectors 201-0 to 201- (n-1) and n registers 202-0 to 202- (n-1) are alternately connected. The select signal SEL00 is supplied to each of the selectors 201-0 to 201- (n-1). Further, as described above, the status data inherited from the B-type status memory 153 corresponding to S10 is supplied to each selector as PM3 having n bits. As described above, the status data inherited by the B-type status memory 152 corresponding to S01 is output to each register as PM0 including n-1 status data values. Further, a clock is supplied to each of the registers 202-0 to 202- (n-1).

The operation of each selector will be described. FIG.
As shown in (1), the state one clock before which can make a transition in S00 is either S00 or S10. When the state one clock before is S00, a transition that inherits itself is performed. Therefore, the first-stage selector 201
As “-0”, “00” is input as the latest state data value in the state data generated by the serial shift. Selector 201-0 has a parallel load B
The latest state data value PM3 [1] in the state data supplied from the mold status memory 153 is supplied. The selector 201-0 operates according to the above-described selection signal SEL00.
One of these two status data values is supplied to the register 202-0 at the subsequent stage.

The selectors 201-1 to 201-
201- (n-1) is a B-type status memory 153 corresponding to S10 as two pieces of data, that is, a parallel load.
, And one status data value supplied from a register in the preceding stage as a serial shift. Then, from these two state data, the state data value determined to be the maximum likelihood is supplied to the subsequent register according to the selection signal SEL00. All the selectors 201-0 to 201- (n-1) have the same selection signal SEL.
Therefore, the state data as the sequence of the maximum likelihood state data values selected by the ACS 133 is inherited.

Further, each of the registers 202-0 to 202- (n-
1) updates the held state data value by capturing the supplied state data value according to the clock as described above. Further, as described above, the output of each register is supplied to the status memory corresponding to a state to which a transition can be made after one clock. That is, since the transition can be made to S00 itself, it is supplied to the subsequent selector as a serial shift. The data is supplied to the B-type status memory 152 corresponding to S01 as a parallel load. The state data value VM00 is output from the register 202- (n-1) at the last stage. By outputting state data value VM00 according to the clock, state data is generated as a whole.

The A-type status memory 151 corresponding to the state S11 has the same configuration as the A-type status memory 150. However, the state data PM1 is supplied from the B-type status memory 152 corresponding to S01 as a parallel load corresponding to the state transition S01 → S11 in FIG. Also, the state data PM2 is supplied to the B-type status memory 153 corresponding to S10 as a parallel load corresponding to the state transition S11 → S10 in FIG.

Next, the B-type status memory 152 corresponding to the state S01 will be described with reference to FIG. B
The type status memory does not inherit itself in FIG.
In addition, this corresponds to a state where only one state can transition after one clock. Therefore, no serial shift is performed, and no selector is provided. Therefore, n registers 212-0, 212-1, ... 212
-(n-1) is provided, a clock is supplied to each register, and the operation timing is adjusted.

Each register 212-0, 212-1,... 2
12- (n-1) is supplied with the status data inherited from the A-type status memory 150 corresponding to S00 as PM0 consisting of n-1 status data values. However, '00' is always input to the register 2120 as the first processing stage in synchronization with the clock. This operation corresponds to the fact that the latest state transition that can transit to S01 is always S00, as shown in FIG. Each register 212-0
.About.212- (n-1) updates the held state data value by taking in the supplied state data value according to the clock. In addition, the output of each register performed according to the clock is a state S11 that can transition after one clock as state data PM1 including n-1 state data values.
Is supplied to the A-type status memory 151 corresponding to.
From the final register 212- (n-1), the state data value VM
01 is output. By outputting the state data value VM01 in accordance with the clock, the state data is generated as a whole.

The B-type status memory 153 corresponding to the state S10 has the same configuration as the B-type status memory 152. However, the state data PM2 is supplied from the A-type status memory 151 corresponding to S11 as a parallel load corresponding to the state transition S11 → S10 in FIG. Further, the state data PM3 is supplied to the A-type status memory 150 corresponding to S00 as a parallel load corresponding to the state transition S10 → S00 in FIG. Also,
'11' is always input to the register serving as the first processing stage in synchronization with the clock. This operation corresponds to the state one clock before, which can transit to S10, is S11 as shown in FIG.

By the way, in the Viterbi decoding method, the state data values VM00, V
M11, VM01 and VM10 match each other if the memory length n of the status memory is made sufficiently large. In such a case, any of the state data values generated by the four status memories may be output to the subsequent stage as sm [k + n]. The memory length n is determined in consideration of the C / N of the reproduced signal, frequency characteristics, and the like.

The state data sm [k + n] obtained by the SMU 134 is supplied to the merge block 135. The merge block 135 is implemented by means such as a ROM in FIG.
Is stored. Then, by referring to the decoding matrix, decoded data based on the state data is generated and supplied to the controller 2.
It can be seen from the state transition diagram of FIG. 6 that the decoded data value corresponds to two consecutive state data values. That is, the state data value sm [k + n] generated corresponding to the reproduction signal value z [k] and the state data value generated corresponding to the reproduction signal value z [k−1] one clock before that. sm
Based on [k + n-1], the decoded data value at time point k + n can be determined.

For example, if sm [k + n] is “01” and sm
When [k + n-1] is "00", it is understood from FIG. 6 that "1" corresponds to the decoded data value. Such a correspondence is summarized in the table of the decoding matrix in FIG.

Next, updating of the amplitude reference value by the RAA 136 will be described. As described above, the six amplitude reference values c
The value of 000 to c111 varies depending on various factors. Moreover, since the degree of the fluctuation is not constant, the amplitude reference value cannot be shifted in advance. Therefore, by adaptively controlling the amplitude reference value, the amplitude reference value can follow the distortion and fluctuation of the RF signal, the clock phase error, and the like, thereby improving the accuracy of the calculated value of the branch metric. Can be.

As described above, based on the state data generated by SMU 134 and the reproduced signal value z [k] delayed by shift register 131, RA
A136 performs a calculation for updating the amplitude reference value for each clock. This calculation is performed as follows.

FIG. 6 shows the state data value sm [k + n] generated corresponding to the reproduced signal value z [k] and the state data value sm [k + n-1] generated one clock before the same.
Accordingly, the state transition occurring between these two state data values and the amplitude reference value corresponding to the state transition can be specified. With respect to the amplitude reference value specified in this way, a new amplitude reference value is calculated from the existing value and the reproduction signal value z [k]. In the case of a disk in which an embossed pit area and a magneto-optical area are mixed like a magneto-optical disk, the calculation of the amplitude reference value is performed separately for each area. Therefore, in this case, for the 6-value 4-state Viterbi decoding method, 6 · 2 = 12 amplitude reference values are adapted.

For calculation of the amplitude reference value, sm [k +
n] = '01' and sm [k + n-1] = '11'
This will be described in detail by taking the case of as an example. This is the case where the state transition S01 → S11 in FIG. 6 occurs. FIG. 6 shows that the amplitude reference value corresponding to the state transition is c011. Therefore, RAA136
Performs the calculation for updating the amplitude reference value as follows. c011 (new) = δ · z [k] + (1−δ) · c011 (old) ·· (23)

Generally, when sm [k + n] = pq and sm [k + n−1] = qr, a new value of the amplitude reference value is calculated as follows. cpqr (new) = δ · z [k] + (1−δ) · cpqr (old) ·· (24)

In these equations, δ is a correction coefficient. When setting the value of δ, the relatively continuous characteristics of the recording system and the reproducing system such as the amplitude of the reproduced signal and its fluctuation, distortion such as asymmetry, error in the operation of the waveform equalizer, and the like on the recording medium It is necessary to consider irregular characteristics due to defects and the like. That is, as the value of δ is larger, the amplitude reference value more strongly reflects the amplitude fluctuation of the reproduced signal, the error in the asymmetry and the operation of the waveform equalizer, etc., by the update performed according to the equation (23) or (24). Becomes On the other hand, the amplitude reference value is easily affected by an irregular signal such as a defect caused by a defect or the like on the recording medium. On the other hand, when the value of δ is reduced, the amplitude reference value is less likely to be affected by irregular signals such as defects, but on the other hand, the amplitude reference value follows the reproduced signal more slowly.
The effect of the adaptation of the amplitude reference value by the update made according to 3) or (24) is reduced.

According to the above equations (23) and (24), RA
At A16, a new amplitude reference value is calculated and supplied to the BMC 132. As understood from the above description, for example, in the case of Viterbi decoding of 6 values and 4 states, the amplitude reference values to be adapted are c000, c001, c011, and c1.
00, c110, and c111. The amplitude reference value is adaptively changed according to various factors such as a recording situation and defocus, so that the influence of various factors can be absorbed.

FIG. 12 shows states sm [k + n-1] and sm
A list summarizing which amplitude reference value is updated for [k + n] is shown. For example, state data sm [k + n-
1] is '00' and the state data sm [k + n] is '00'
, That is, when the state transits from state S00 to S00,
The amplitude reference value c000 is updated. Further, when the state transits from the state S00 to S01, the amplitude reference value c001 is updated. In addition, as shown in FIG. 12, the specific amplitude reference value is updated according to the state transition.

[0092] 2. 2. Disk Drive Apparatus of Embodiment 2-1 Configuration of Disk Drive Apparatus As an example employing the Viterbi decoding method described above,
A disk drive device according to an embodiment of the present invention will be described. This example will be described as a disk drive device corresponding to an MO disk.

FIG. 13 shows the structure of the disk drive of this embodiment. The same functional portions as those described in FIG. 1 are denoted by the same reference numerals, and redundant detailed description thereof will be omitted. Further, this block diagram mainly shows a processing system for a recording / reproducing signal, and there are some other parts omitted from the servo system.

The disk 6 (MO disk) serving as a recording medium is recorded / reproduced / erased by the operation of the optical pickup 7 and the magnetic head 5 in a state where the disk 6 (MO disk) is rotationally driven by the spindle motor 9 in the drive device. . Position control of the optical pickup 7 and the magnetic head 5 during recording / reproducing / erasing (seek, tracking servo,
The thread servo), the focus servo of the laser beam from the optical pickup 7, and the rotation servo of the spindle motor 9 are performed by a servo system (not shown).

A drive controller (hereinafter, referred to as a controller) 2 serves as a master controller of the drive device and controls various operations and communicates with the host computer 1. That is, the controller 2 controls the operation of recording the supplied data on the disk 6 in response to the recording instruction from the host computer 1, and also reads the requested data from the disk 6 in response to the instruction from the host computer 1. Control of the transfer to the host computer 1.
The controller 2 also has a function of encoding and decoding data.

The CPU 3 is a part that controls each part for a recording / reproducing operation based on an instruction from the controller 2. For example, it performs various controls on the RF block 20 of the reproduction system, and gives instructions to the DSP 17 functioning as a servo processor.

At the time of recording, the controller 2 receives user data to be recorded in accordance with a command from the host computer 1 and encodes the data based on the user data as information words, for example, RLL (1,
7) Generate a code. This code word is recorded data WDAT
A is supplied to the LPC 4. Further, the controller 2 instructs the LPC 4 as a WGATE signal on the light emission operation in the recording mode and its timing. Further, a recording clock WCLK serving as a reference for the recording processing operation is generated, and LP
Supply to C4.

The LPC 4 and the APC 10 cause the laser output from the optical pickup 7 to be executed in accordance with the recording data WDATA and WGATE signals as described with reference to FIG. During playback,
The laser output level at each time of recording, ie, LP
The drive pulse value of the laser output from C4 is DSP1
7 (CPU 3). Therefore, the controller 2 can change the recording laser power and the reproduction laser power by instructing the CPU 3.

At the time of reproduction (at the time of normal reproduction and at the time of data reading for write-verify operation for reading data immediately after recording and confirming (verify) proper recording), the controller 2 and the CPU 3 are used.
The following operation is performed by the control of.

The controller 2 receives the RGATE signal, PGA
The TE signal is supplied to the LPC 4 and the RF block 20,
The playback operation is controlled. That is, the controller 2 is RGATE
A signal instructs the LPC 4 to continuously emit light with the laser power as the reproduction level,
0 is instructed to perform a reproduction process. Further, a switching process corresponding to an area on the disk 6 (an embossed pit area and a magneto-optical area in a sector) is executed by the PGATE signal.

At the time of reproduction, first, LPC4 sets RGAT
A laser drive pulse is generated according to the E signal, and a laser output for a reproducing operation is executed from the optical pickup 7. The optical pickup 7 irradiates the magneto-optical disk 6 with laser light, and receives reflected light generated thereby. Further, various signals are generated by arithmetic processing of signals according to the amount of reflected light. That is, it includes a reproduced RF signal, a focus error signal (not shown), a tracking error signal, and the like.

The reproduced RF signal is supplied to the filter unit 11 after the gain is adjusted by the variable gain amplifier 8 in the RF block 20. The gain setting in the variable gain amplifier 8 is performed by a control signal from the CPU 3. For example, the gain setting is changed according to the RF signal level that varies depending on the type and characteristics of the disk so that an RF signal optimal for reproduction signal processing is obtained. (In the figure, an arrow C indicates a transmission / reception system of a control signal with the CPU 3. This relates to parameter setting by the CPU 3, which will be described later.)

Note that there are two types of reproduction RF signals supplied from the optical pickup 7 to the variable gain amplifier 8, namely, a so-called sum signal and a difference signal, and the switching processing is performed according to the area in the sector according to the PGATE signal. . That is, the reproduced data of the portion where the embossed pit is formed is processed for the sum signal, and the reproduced data of the portion where the pit row is magneto-optically recorded is processed for the difference signal. The reflected light information includes a focus error signal, a tracking error signal, and the like in addition to the reproduction RF signal corresponding to the reproduction data. The focus error signal and the tracking error signal are supplied to the DSP 17 (not shown).
Used for controlling the servo system by P17.

The filter section 11 is composed of a boost circuit for the RF effective band, a low-pass filter for noise reduction, a waveform equalizer for waveform equalization, and the like. The input signal is equalized so that a partial response characteristic suitable for the Viterbi decoding method performed by the Viterbi decoder 13 is obtained. The output of the filter unit 11 is supplied to the A / D converter 12 after the offset component is canceled by the offset cancel unit 19. The offset cancel operation will be described later.

The output of the filter unit 11 is also supplied to the PLL unit 14. The PLL unit 14 generates a read clock DCK based on the supplied signal. This P
The LL unit 14 is configured to detect a phase error by using a signal of a constant frequency recorded in the magneto-optical disk 6, for example. The read clock DCK includes a controller 2, an A / D converter 12, a Viterbi decoder 13, and a circuit unit (MTG 15, described later) for offset cancellation.
The signals are supplied to the OCU 16 and the D / A converter 18). The operations of the controller 2, the A / D converter 12, the Viterbi decoder 13, and the offset cancel system are performed by the read clock DCK.
It is made at the timing according to.

The A / D converter 12 controls the offset cancel unit 1 according to the reproduction clock DCK from the PLL unit 14.
9 is subjected to A / D conversion to obtain a reproduced signal value z.
[K] is output.

The Viterbi decoder 13 outputs the reproduction clock DCK
, The decoded data DD is generated by the Viterbi decoding method based on the reproduced signal value z [k]. Viterbi decoder 1
3, the BMC 132, the ACS 13
3, the Viterbi decoding operation by the SMU 134, the merge block 135, the shift register 131, and the RAA 136 is the same as described above, and a description thereof will be omitted.

However, for the RAA 136, the amplitude reference values c000 to c111 calculated for updating are
, And can be used for calculation of asymmetry as described later.

The decoded data DD decoded by the Viterbi decoder 13 is supplied to the controller 2. The controller 2 reproduces user data and the like by performing decoding processing corresponding to encoding such as channel encoding on the decoded data DD. For example, (1-7) RLL decoding processing, ECC decoding processing (error correction processing), and the like are performed. The decoded data (such as user data) is transferred to the host computer 1 as reproduction data. As will be described later in detail, at the time of reproduction, when reproduction data is not obtained as a decoding NG for a certain sector, the controller 2 controls to execute a reproduction retry to the sector.

In the reproducing system for performing Viterbi decoding in this example, the A / D conversion is performed after the partial response characteristic is set by the filter unit 11, and the reproduced signal value z [k] is supplied to the Viterbi decoder 13. However, after performing A / D conversion on the reproduced RF signal, a partial response characteristic may be obtained by a transversal filter or the like. Even in such a configuration, the operation of the present example described later can be similarly applied.

In this drive device, in order to cancel the offset of the reproduction RF signal, the MTG (MSB)
Timing Generator) 15, OCU (Offset Calculatio)
n Unit) 16, a D / A converter 18, and an offset cancel unit 19. Further, the output of the shift register 13 of the Viterbi decoder 13 and the status data from the SMU 134 are configured to be used for offset error detection in the OCU 16.

The output z of the A / D converter 12 is provided to the MTG 15.
[K] is supplied, and the MTG 15 generates timings tA to tD for an MSB determination mode to be described later based on this. The OCU 16 is a block that calculates an offset error signal OE according to the offset amount on the reproduced RF signal. In the OCU 16, the shift register 131 is used.
Calculation of the data (A / D conversion value) supplied from
An offset error signal OE is calculated. In addition, as a timing for taking in a value used for the calculation, MS
It is possible to switch between the B determination mode and the Viterbi determination mode. In the case of the MSB determination mode, calculation is performed according to timings tA to tD from the MTG 15. On the other hand, in the case of the Viterbi determination mode, calculation is performed according to timings tA to tD generated according to the state data from the SMU 134. Whether to execute the Viterbi determination mode or the MSB determination mode is specified by the mode select signal MS from the controller 2. Note that, since it is necessary to change the delay amount of the data z [k] in the shift register 131 depending on the mode, the mode select signal MS is also supplied to the shift register 131, and the shift register 131 sends the data to the OCU 16 in response to this. The amount of delay of supplied data is changed.

The offset error signal OE calculated by the OCU 16 is converted into an analog signal by the D / A converter 18 and then supplied to the offset cancel unit 19. The offset canceling unit 19 is a subtraction circuit, and outputs a reproduced RF signal without an offset by subtracting an offset error signal (that is, a DC value for an offset) from the reproduced RF signal from the filter unit 11. Thus, a feedback loop for offset cancellation is configured.

The CPU 3 can variably set various parameters relating to the reproduction processing for each required part in the RF block 20. For example, the gain of the variable gain amplifier 8, the cutoff frequency in the filter unit 11, the boost band, the boost level, the loop gain or band in the PLL unit 14, and B by the RAA 136
An amplitude reference value set in the MC 132, an adaptation gain of the amplitude reference value, a loop gain of offset feedback by the OCU 16, and the like. Further, parameters affecting the reproduction process in the RF block 20 include the rising timing of the RGATE signal by the controller 2 and the offset mode selected by the mode select signal MS. The details of the parameters affecting the read capability and the change processing in the RF block 20 will be described later.

2-2 Relationship between Recording Laser Power and Asymmetry Here, the recording laser power, which is one of the causes of reproduction NG, and the recording laser power, which is one of the causes of reproduction NG, are related to the amplitude reference value, which is one of the parameters relating to read performance. The relationship between laser power and asymmetry will be described.

In a normal optical disk system, the recording laser power is set to an optimum power according to the medium and the state and temperature of the drive at that time. Calibration is performed at the time of recording in order to find the optimum recording laser power. However, in practice, recording is not always performed with the optimum recording laser power. For example, as a calibration, test writing is performed in a certain area on the medium and reproduced, and the optimum recording laser power is searched for depending on whether or not the recording was properly performed, but the calibration was performed. When the recording sensitivity characteristic differs between the region and the region where data is actually recorded thereafter, the recording laser power obtained by the calibration does not become an appropriate power. Of course, there may be a case where the calibration has not been correctly performed for some reason or a case where the setting of the recording laser power obtained by the calibration has not been correctly performed.

At the time of recording, the operation of reproducing the sector immediately after recording and checking whether or not the data has been correctly recorded, that is, an operation called so-called write and verify may be performed. In this case, if it is detected at the time of the verification that the recording laser power is inappropriate and the recording has not been properly performed, the recording operation can be performed again with an appropriate recording laser power as a write retry process. However, the write-and-verify operation is not always performed for all data sectors, and there are many usages in which write-and-verify is not performed.

From these facts, at the time of reproduction, it cannot be considered that the data to be reproduced is all recorded with an appropriate recording laser power. When data is recorded on the disk 6 by an optical modulation method such as a magneto-optical disk or a WORM disk, the size of a mark (pit) recorded on the disk largely depends on the value of the recording laser power. It also greatly affects the waveform of the reproduced RF signal. Therefore, at the time of reproduction, a reproduction error may occur due to inappropriate recording laser power.

How the magnitude of the recording laser power affects the reproduced RF signal will be described by taking an impulse response as an example. FIG. 14 shows the relationship between the magnitude of the recording laser power and the impulse response of the reproduced RF signal. Note that this is an example of a PR (1, 2, 1) partial response response. When the recording laser power is at the optimum value, the impulse response becomes as shown by a curve (b) in FIG. At this time, the amplitude ratio at three time points k−1, k, and k + 1 as the sampling time points of the A / D conversion is 1:
2: 1.

However, when the recording laser power is increased,
Since the recording mark on the disk becomes large, the impulse response becomes as shown by the curve (a), that is, the pulse width becomes large. Therefore, the amplitudes at the sampling times k−1 and k + 1 are larger than half the peak value. On the other hand, when the recording laser power decreases, the recording mark on the disk becomes smaller, so that the impulse response becomes as shown by the curve (c), that is, the pulse width becomes narrower. Therefore, the amplitudes at the sampling times k−1 and k + 1 are smaller than half the peak value.

An eye pattern for an actual reproduced RF signal can be represented by superposition of impulse responses at an arbitrary time point k. FIG. 15 shows the degree of eye opening of the eye pattern due to the difference in recording laser power. FIG.
(B) shows an eye pattern in a state where the recording laser power is optimal, and the eyes are vertically symmetric. On the other hand, when the recording laser power is large and small, the eye is shifted upward or downward as shown in FIGS. 15A and 15C, respectively. This FIG.
The state in which the eye is opened asymmetrically due to the non-optimal recording laser power as in (a) and (b) is called asymmetry. That is, the asymmetry is an asymmetric distortion generated in the reproduction RF signal waveform due to an excess or deficiency of the recording laser power.

In order to quantitatively express the asymmetry, the asymmetry value is defined as γasy and is defined as follows. γasy = (center voltage of 2T envelope−center voltage of 8T envelope) / (peak-to-peak voltage of 8T envelope) (25)

FIGS. 16A and 16B show a 2T pattern signal waveform and an 8T pattern signal waveform. When the waveform equalization process is performed on the reproduced RF signal corresponding to the 2T pattern, FIG.
As shown in FIG. 6A, the amplitude reference values c001, c01
The waveform has a waveform in which 1, c110, and c100 are periodically repeated. When the waveform equalization process is performed on the reproduced RF signal corresponding to the 8T pattern, as shown in the figure, the amplitude reference value c00
0, c000, c000, c000, c000, c00
0, c001, c011, c111, c111, c11
1, c111, c111, c111, c110, c10
0 and c001 are periodically repeated.

FIG. 17 shows the waveforms of the 2T pattern and the 8T pattern together. FIG. 17 visually shows the asymmetry value γasy. Based on FIG. 17 and the above equation 25, the asymmetry value γ is obtained for each eye pattern shown in FIG.
It can be seen that asy is as follows. When the recording laser power is too large: γasy> 0 When the recording laser power is optimal: γasy = 0 When the recording laser power is too small: γasy <0

As described above, it is possible to estimate the value of the recording laser power from the asymmetry value γasy. Therefore, if the recording laser power is set so that the asymmetry value γasy falls within a certain range,
That will be the proper recording laser power.

According to the above equation (25), the reproduction R
To calculate the asymmetry value γasy of the F signal, “2
It is necessary to detect the center voltage of the T envelope, the center voltage of the 8T envelope, and the peak-to-peak voltage of the 8T envelope, respectively. Here, FIG.
6. As can be seen from FIG. 17, these values can be calculated from the amplitude reference values in the Viterbi decoder 13. That is,
The “center voltage of the 2T envelope” is the amplitude reference value c00
It can be obtained as an average value of 1, c011, c110, and c100. Also, "center voltage of 8T envelope"
Can be obtained as an average value of the amplitude reference values c000 and c111. Further, “peak-to-peak voltage of the 8T envelope” can be obtained as a difference between the amplitude reference values c000 and c111. Therefore, when the amplitude reference value is applied to the above equation (25), γasy = ((c001 + c011 + c110 + c100) / 4− (c000 + c111) / 2) / (c111−c000) (26) ).

As described above, the amplitude reference values c000 to c1
11 are adapted in the RAA 136 in the Viterbi decoder 13 and updated in the BMC 132. Assuming that the amplitude reference value is adapted in this way, if the reproduced RF signal has asymmetry, each amplitude reference value follows that. Therefore, FIG.
The CPU 3 (or the controller 2) of the above can use the amplitude reference value calculated by the RAA 136 to calculate the above equation (26) to know the value of the recording laser power for the reproduced RF signal at that time. it can.

Next, it is considered what range the asymmetry value γasy falls within and the recording laser power is appropriate. FIG. 18A shows the recording laser power (Write Po
wer) shows the characteristics of the byte error rate (BER). Here, the characteristic when the Viterbi decoding method is employed as the reproduction signal processing system, and the characteristic when the bit-by-bit method is employed.

As can be seen from this figure, in the A region where the recording laser power is low (LP1 or less), the error rate becomes high in both the Viterbi decoding method and the bit-by-bit method. That is, when the recording laser power is equal to or lower than LP1, it can be said that the power is too low. Even in the D region where the recording laser power is high (LP3 or higher), the error rate is high in both the Viterbi decoding method and the bit-by-bit method. That is, when the recording laser power is equal to or higher than LP3, it can be said that the power is excessive. In the C region where the recording laser power is in the range of LP2 to LP3, the error rate is low in any decoding method. That is, LP2 to LP3
Can be said to be a suitable recording laser power. In the region B where the recording laser power is in the range of LP1 to LP2, the error rate is low in the case of the Viterbi decoding method. That is, the range of LP1 to LP3 can be said to be a suitable recording laser power for the drive device of the Viterbi decoding method. However, in the B region, the bit-by-bit method has a high error rate. That is, for a bit-by-bit decoding drive device, the range of LP1 to LP2 cannot be said to be an appropriate recording laser power. From the above, it is OK in any of the Viterbi decoding system and the bit-by-bit decoding system if the recording laser power is in the range of LP2 to LP3.

FIG. 18 (b) shows the asymmetry value of the reproduced RF signal corresponding to FIG. 18 (a). Thus, the asymmetry value is proportional to the recording laser power. And the optimum recording laser power range is LP
If it is 2 to LP3, it suffices that the asymmetry value γasy satisfies γasy2 <γasy <γasy3 (27). That is, for example, at the time of reproduction, if the asymmetry value γasy calculated by the above equation (26) is within the range of the above equation (27), the recording laser power at the time of recording is appropriate for the data to be reproduced. You may judge that it was a value.

In the case of the drive device of the present embodiment as shown in FIG. 13, the Viterbi decoding method is adopted,
Since the amplitude reference value is subjected to adaptive control, the reproduction capability is extremely high. Therefore, even if the asymmetry value γasy is not within the range of γasy2 <γasy <γasy3, it is often the case that the reproduction is actually OK.
In such a case, there is no problem. However, if the recording laser power greatly deviates from an appropriate range, the read N
May be G. In this case, the reproduction retry of the sector is started. At this time, the amplitude reference value is updated according to the state of the recording laser power estimated from the asymmetry value (that is, according to the RF signal for the data). By doing so, it may be possible to make it reproducible.

In other words, for example, in the case where a reproduction NG is performed for a certain sector and a retry is performed, changing the amplitude reference value is one of the effective methods for leading to the successful reproduction of the sector. Therefore, as described later, in this example, a change in the amplitude reference value is included as one of the changes in the parameter setting state at the time of retry.

2-2 Offset Error Detection Method Next, a parameter (offset mode or feedback loop gain) concerning the offset feedback loop, which is one of the parameters that can be changed, will be described.

As described above, in this example, the offset error signal OE is calculated by the OCU 16, and the offset error signal OE is fed back to perform the offset cancellation.
First, the calculation method and two types of modes (Viterbi determination mode and MSB determination mode) employed in this example will be described.

One of the causes of a reproduction NG when a data reproduction operation for a certain sector is performed is an offset of a reproduction RF signal read from a disk. The reproduction circuit of the optical disc has a DC component due to optical characteristics (MTF). If there is such a DC component,
The reproduced RF signal has an offset corresponding to the average. In addition, since the DC offset value fluctuates depending on the data pattern of the reproduced RF signal, a data pattern having a short mark (pit) portion and a long space portion and a pattern having a long mark portion and a short space portion are repeated as recording data. In some cases, the DC offset value will fluctuate greatly. Further, optical birefringence may occur due to the occurrence of mechanical distortion during the manufacture of the disk substrate, and the DC level of the reproduced RF signal may fluctuate.

As a result, the offset value in the reproduced RF signal may fluctuate, thereby deteriorating the error rate of the decoded data. When binarizing (decoding) the reproduced RF signal using the Viterbi decoder 13 as in this example, the waveform is controlled to a partial response characteristic by the filter unit 11 (analog filter) as shown in FIG. Thereafter, A / D conversion is performed and digital Viterbi decoding processing is performed. Alternatively, as described above, the Viterbi decoding process may be performed after the partial response characteristics are obtained by using a digital filter such as a transversal filter after the A / D conversion. In any case, when there is a change in the DC offset, it is necessary that the reproduced signal including the change in the DC offset falls within the dynamic range of the A / D converter 12 as a whole. If the DC offset fluctuation is large, the peak-to-peak of the actual reproduced RF signal becomes smaller with respect to the dynamic range of the A / D converter 12, so that the resolution of the A / D converter 12 with respect to the reproduced waveform becomes smaller. This lowers the decoding accuracy of the Viterbi decoder 13.

Therefore, the reproduction R using the Viterbi decoder 13 is performed.
When binarizing the F signal, it is necessary to cancel the DC offset fluctuation by the feedback loop as described above.

Now, the value obtained by A / D conversion (the above z [k];
Hereinafter, also referred to as an AD value) is represented by a two's complement expression, and if the offset is zero and the AD value when there is no signal is zero, the reproduction R
The offset value of the F signal is represented by the total average of the sampling values. However, the offset value can be obtained as an average of the sample values at the timing obtained from the rising and falling timings without representing the total average of the sampling values. That is, A: AD value at the rising clock B: AD value at the clock following the rising C: AD value at the falling clock D: AD value at the clock following the falling , And the sum of these four sampling values. Note that, as shown in FIG. 6, the falling of the waveform is the timing of the transition from the state S11 to the state S10. The rising edge of the waveform is a transition timing from the state S00 to the state S01.

In the case of PR (1, 2, 1, 1), the above four AD values (A, B, C, D) are four values excluding peak-to-peak among six values in six values and four states. The offset value can be found by looking at the average of these four values. That is, (Sampling value of A + Sampling value of B + Sampling value of C +
The offset value (that is, the value of the offset error signal OE) is obtained by calculating the sampling value of D (the offset value is strictly speaking, one fourth of the calculated value).

FIG. 20 shows the timing t of the offset calculation.
A, tB, tC, and tD detection are shown. The timings tA, tB, tC, and tD correspond to the above-mentioned ADs, respectively.
This is the timing for obtaining the values (A, B, C, D).

As described above, the SMU 13 of the Viterbi decoder
4, the rising timing (S00 → S01) and the falling timing (S11 → S10) can be obtained. Therefore, the offset signal detection timings tA, tB,
tC and tD are obtained. FIG. 20A shows a reproduced RF signal waveform and its sampling point (AD value).
0 (b) shows a state transition (state data) at each AD value. 20 (d) to (g) show timing signals tA, tB, which can be generated based on the state data.
tC and tD are shown. That is, by generating the timing signals tA, tB, tC, and tD based on the state data, the timing signals for calculating the offset error signal OE can be obtained.
Two AD values A, B, C, and D (shown in FIG. 20A) can be captured.

The AD values A, B, C, and D are supplied from the shift register 131, and the OCU 16
Is to latch the output of the shift register 131 based on the timing signals tA, tB, tC, and tD,
Each of the AD values A, B, C, and D will be captured (OCU
16 is shown in FIG. 19; However, if the timing signals tA, tB, tC, and tD are obtained by the transition from the state of the (n-1) th stage to the state of the nth stage in the SMU 134, the offset signal is detected after the data is actually read out. Is delayed by the number of stages of the SMU 134 in addition to the delay in the circuit unit until before. Normally, since the SMU 134 of the Viterbi decoder 13 has a sufficiently long number of stages for merging, if this is used as it is as an offset signal, the delay is large with respect to the reproduced RF signal and offset cancellation cannot be performed well. Therefore,
From the middle stage of the SMU 134, the maximum likelihood state at that stage is detected, and a timing signal is obtained from the transition of the state.
In the Viterbi decoder 13, as the number of metric stages increases, the accuracy of the maximum likelihood path increases. Therefore, when selecting the transition from the (k−1) th state to the kth state, if the state corresponding to the smallest metric is selected, the correct state can be selected even if the metrics are not merged. Sex is very high. Therefore, there is no problem in obtaining the timing signals tA, tB, tC, and tD based on the state data.
In order to match the values, the necessary delay amount is given by the shift register 131.

As described above, the method of obtaining the offset error signal OE using the state transition of the Viterbi decoding is called a Viterbi determination mode.

On the other hand, an offset error signal can be obtained by a method called MSB determination mode.
This is the MSB (sign bit) of the AD value of the reproduced RF signal.
Is detected, timing signals tA, tB, tC, and tD are obtained as timings before and after the timing, and an offset error signal OE is obtained using the AD value (A, B, C, D) at that timing. Mode. FIG.
(C) shows how the MSB is inverted. From this inversion timing, the timing signals tA, tB, tC, and tD shown in FIGS. 20 (d) to (g) are generated. That is, the MTG 15 monitors the MSB inversion timing of the output of the A / D converter 12 and, based on the MSB inversion timing, converts the timing signals tA, tB, tC, and tD shown in FIGS. Generated and supplied to OCU16. It should be noted that the shift register 131 converts the AD value with the delay amount corresponding to the delay of the processing in the MTG 15 so that the timing of the timing signals tA, tB, tC, and tD matches the timing of the AD value.
Will be supplied to

As described above, the Viterbi determination mode and the MSB
FIG. 19 shows a configuration example of the OCU 16 that calculates the offset error signal OE in the determination mode. As shown, the OCU 16 includes a mode switching unit 161 and a latch circuit 16.
2 to 165, an adder 166, and an amplifier 167 are provided. The output (AD value) of the shift register 131 is supplied to each of the latch circuits 162 to 165. Also MT
The timing signals tA, tB, tC, tD from G15,
And the status data from the SMU 134
1 is supplied. The mode switching unit 161 is also supplied with a mode select signal MS from the controller 2.

First, the mode select signal MS causes M
When the SB determination mode is instructed, the mode switching unit 161 outputs the timing signals tA and t from the MTG 15.
B, tC, and tD are used as is in each of the latch circuits 162 to 165.
Is output as the latch timing for. Therefore, the latch circuit 162 latches and outputs the AD value at a timing according to the timing signal tA as shown in FIG. That is, the AD value “A” is latched and output. Similarly, the latch circuits 163, 164, and 165 latch and output the AD values according to the timing signals tB, tC, and tD, respectively, so that
165 output AD values “B”, “C”, and “D”, respectively. These latch outputs “A”, “B”, “C”, “D”
Are added in the adder 166, and the added output is the offset error signal O corresponding to the offset value.
E. This offset error signal is supplied to the amplifier 167
After the loop gain is given by the D / A converter 18 shown in FIG.
9. The amplifier 167 may be provided after the D / A converter 18 as an analog amplifier.

On the other hand, when the Viterbi determination mode is instructed by the mode select signal MS, the mode switching section 161 determines the mode based on the state data from the SMU 134.
The timing signals tA, tB, tC, and tD are generated. In other words, the rising of the waveform based on the state transition,
The fall timing is obtained, and the timing signals tA, t
B, tC and tD are generated, and are generated by the respective latch circuits 162 to 162.
This signal is output as the latch timing for 165. The latch circuits 162 to 165 latch and output the AD values “A”, “B”, “C”, and “D” based on the timing signals tA, tB, tC, and tD, as in the case of the MSB determination mode. An offset error signal OE is obtained in the adder 166. This offset error signal is supplied with a loop gain by the amplifier 167, and then the D / A of FIG.
The signal is converted into an analog signal by the converter 18 and supplied to the offset cancel unit 19.

As described above, in this example, the Viterbi determination mode, M
Select the SB determination mode and set the offset error signal OE
Can be generated. The Viterbi determination mode and the MSB determination mode have the following features, respectively. As a disadvantage of the MSB determination mode, if the DC offset becomes too large, the offset error signal OE may not be generated properly. For example, FIG. 21 shows a state in which the offset of the reproduced RF signal increases, and the period T during which the amplitude of the reproduced RF signal crosses the zero level in the two's complement representation of the AD value is shown.
A can generate the offset error signal OE because the inversion of the MSB is observed. However, in the period TB in which the offset is considerably large and the amplitude of the reproduced RF signal always exceeds the zero level, the inversion of the MSB is not observed, so that the offset error signal OE cannot be detected. However, in the case of the MSB determination mode, usually, there is an advantage that the offset amount can be easily and accurately detected, and even if the offset error signal cannot be generated as described with reference to FIG. Since the feedback loop is not stable at that point,
It converges in the direction where the offset is zero.

On the other hand, the case of the Viterbi determination mode is as follows. In the case of the Viterbi determination mode, the detection timing of the offset error signal OE is obtained from the Viterbi decoding result. Therefore, even when the DC offset of the reproduced RF signal becomes large as shown in FIG. ) Is obtained correctly. That is, even in such a case, the offset error signal OE can be obtained, and in that respect, it can be said that the performance is higher than that of the MSB determination mode. However, if the Viterbi decoder 13 makes a misjudgment in decoding processing (misjudgment of state transition) or the like, the offset loop may be set to OE = 0 and the feedback loop may be stabilized despite the presence of an offset. . In other words, in that case, despite the presence of the offset, it is stable without offset cancellation,
It will not converge to the state where the offset = 0. Naturally, in this case, accurate Viterbi decoding is hindered. This will be described.

If there is a large defect or birefringence on the disk, the DC offset value changes rapidly. Therefore, in both the Viterbi determination mode and the MSB determination mode, the offset feedback should follow this. Can not. However, in the case of a defect, the offset value is disturbed only in a certain section, so that the offset feedback recovers the tracking of the reproduced RF signal soon. However, if there is birefringence, the reproduced RF signal changes as shown in FIG. FIG. 22 shows the envelope of the reproduced RF signal. In this case, only the offset value changes instantaneously.

Even if there is such an instantaneous change in the DC offset, the DC offset value usually converges to zero after a time determined by the time constant of the offset feedback loop. However, during execution in the Viterbi determination mode, in some cases, the Viterbi decoder 13 determines that certain data is different from the original data, and erroneous detection of data occurs. Since the offset error signal OE becomes zero, the offset feedback loop becomes stable.

Such a phenomenon will be described by taking a 3T pattern as an example. As shown in FIG. 23, the reproduced RF signal of the 3T pattern is a pattern in which the six amplitude reference values transition one after another without staying at the same place. That is, c00
0 → c001 → c011 → c111 → c110 → c10
The pattern changes from 0 to c000.

Here, it is assumed that the reproduced RF signal is shifted as shown by a broken line in FIG. 24 due to a sudden change in offset due to birefringence. Then, in the A / D converter 12, data that should be sampled at the positions of T, U, V, W, X, Y, and Z in the figure are respectively T ',
It will be sampled at the positions of U ', V', W ', X', Y ', Z'. Then, since the Euclidean distance of U ′ is closer to c000 than to c001, the Viterbi decoder determines that U ′ is c000. That is, the state should have actually transitioned from S00 to S01,
To S00. As a result, 6
According to the rules for the state transition of the 4-state Viterbi decoder (see FIG. 6), V 'can only take c000 or c001. Therefore, from the metric calculation, V ′ is originally c01
Although it is 1, it is determined that it is c001. Similarly,
W ′ is originally c111, but is determined to be c011.

As described above, the metric calculation of the Viterbi decoder goes out of order, and therefore, as shown in FIG.
c001 → c011 → c111 → c110 → c100 →
The data that transitions to c000 is c000 → c000
→ c001 → c011 → c110 → c100 → c000
It will end up transitioning. This is the playback RF
The state of the signal indicates that the Viterbi decoder 13 determines that the 3T pattern is a 2T / 4T pattern.

In other words, in the case shown in FIG. 24, the Viterbi decoder 13 assumes a 3T pattern as a 2T / 4T pattern and is stable, so that the offset feedback is stabilized assuming that the offset is zero. Therefore, a decoding error will occur.

As described above, each of the MSB determination mode and the Viterbi determination mode has an advantage and a disadvantage. In the case of this example, the MSB determination mode and the Viterbi determination mode can be selectively used, and accordingly, depending on the situation. If a suitable mode is selected, it is possible to appropriately execute offset cancellation, thereby preventing a decoding error. For example, in this example, the offset feedback loop is normally operated in the Viterbi determination mode. However, when a retry is performed due to a decoding error occurring during the reproduction operation, mode switching is performed as one of the variable parameters at the time of the retry, and in that case, the retry is performed in the MSB determination mode.

In addition, for example, the amplifier 166 (or D /
A loop gain by an amplifier (disposed at a stage subsequent to the A converter 18) can also be one of the parameters. That is, the followability as the offset cancel operation can be adjusted by increasing or decreasing the loop gain. Therefore, by changing the gain setting, it is possible to perform a canceling operation adapted to the offset situation. For example, when the offset amount fluctuates, the loop gain is increased to increase the offset cancellation with good tracking performance and the reproduction capability. It can encourage improvement. Therefore, the offset loop gain is also one of the parameters to be considered for change at the time of retry, for example.

2-4 Example of Parameter Setting As described above, the controller 2 and the CPU 3 can variably set various parameters relating to the reproduction process for the required units in the RF block 20. That is, in the case of this example, the gain of the variable gain amplifier 8, the cutoff frequency in the filter unit 11, the boost band, the boost level, the loop gain or the band in the PLL unit 14, the amplitude reference value set in the BMC 132 by the RAA 136, and the amplitude reference value. Adaptive gain of OCU16
The variable parameters include the offset mode, the loop gain of the offset feedback, and the rising timing of the RGATE signal. These parameters can cope with the error cause when the reproduction becomes NG. For example, as described above, changing the setting of the amplitude reference value can deal with an error caused by the recording laser power. Switching to the offset mode or the gain can cope with offset fluctuations due to the influence of birefringence or the like. Further, changing the other parameters can realize a reproducing operation corresponding to, for example, the influence of a defect and other various error causes. For example, playback RF for some reason
When the signal level is too low or too high, changing the gain of the variable gain amplifier 8 is effective. If a synchronization error occurs for some reason and the playback becomes NG, RG
The change of the ATE signal timing becomes effective.

Therefore, when the reproduction becomes NG in the sector, it is preferable to change the required parameters according to the cause of the error and perform the retry. However, it is difficult to identify the cause of the error at the time of the reproduction NG. Therefore, in this example, the parameter setting is changed every retry. For the sake of explanation, if it is set that retry in the case of reproduction NG is performed up to eight times, for example, as shown in FIG. 25, parameter setting is performed at each of eight retry times.

At the time of main reproduction for a certain sector (the first reproduction which is not a retry), each parameter is set to an initial value (default value). This initial value is a value selected as a value with the highest read capability for each parameter when a normal state is assumed.

However, when the first retry is performed as the reproduction NG during the main reproduction, for example, the gain of the variable gain amplifier (VGA) is changed from the initial value. Further, when the second retry is performed after the first retry, the reproduction NG is performed, and only the timing of the RGATE signal is changed from the initial value. Hereinafter, until the reproduction is OK, the retry is performed up to the maximum of eight times. At each retry, the parameter setting is changed as shown in the figure. Of course, the example of FIG. 25 is merely an example set for the sake of explanation, and various parameter setting changes are actually determined. In addition, the order in which setting state is set for which number of retries is only an example, and the order of setting states that can respond to the order is actually determined in an order that is likely to occur as an error cause. And so on.

The controller 2 sets each parameter setting state (setting numbers PD, P1 to P1) as shown in FIG.
8) is set in advance, and at the time of normal main reproduction, the RF block 20 performs a reproduction operation in the set state PD,
At the time of retry, the reproduction operation in the set states P1 to P8 is executed depending on the number of retries.
Hereinafter, the processing at the time of reproduction of the present example including such parameter settings will be described.

2-5 Example of Processing at Reproduction FIG. 27 shows the processing of the controller 2 at the time of reproduction. When receiving a data reproduction instruction from the host computer 1, the controller 2 starts operation control for reproducing the instructed one or a plurality of sector data from the disk 6. That is, as described above, the RGATE signal, PGATE
Signals are instructed to each section to execute the servo control by the DSP 17, the laser emission operation, the reproduction processing in the RF block 20, the decoding processing for the decoded data supplied from the Viterbi decoder 13, and the host computer 1. Transfer processing to the server. The reproduction operation is performed in units of sectors. In many cases, a plurality of sectors are reproduced by a single reproduction instruction from the host computer 1.

When the controller 2 starts the reproducing process, first, in step F101, each parameter in the RF block 20 is set as an initial value. That is, in addition to setting the offset mode to the Viterbi determination mode by the mode select signal MS, for example, the above-described parameters (the gain of the variable gain amplifier 8, the cutoff frequency of the filter unit 11, the boost band, the boost amount, the PLL The loop gain of the section 14, the amplitude reference value in the BMC 132, the offset loop gain, etc.) are set to the initial values. This is Figure 2
5 corresponds to the setting state PD.

Then, as step F102, the DSP 1
7 is instructed to make the optical pickup 7 access the first sector to be reproduced. When the access is completed, a read operation (main reproduction) of the sector data is executed in step F103. As a result, the decoded data DD is supplied from the RF block 20, and the controller 2 performs a decoding process (1-7 decoding / error correction, etc.) on the decoded data DD. The decoded data is transferred to the host computer 1. During this reproducing operation, RA
By the operation of A136, the amplitude reference value is sequentially adapted.

In step F104, it is determined whether or not the data reading has been properly completed, that is, whether or not the synchronization processing and the ECC processing have no error and the decoding of the sector data has been properly completed. If it is determined that the sector reproduction operation has been properly completed, the process proceeds from step F104 to F105 to determine whether or not the reproduction of the previous sector requested by the host computer 1 has been completed. Move on to the regeneration of the sector to be done. In this case, the process of step F108 is executed in accordance with the determination of step F107. If the current parameter setting state is not P (x) in FIG. 25 in step F107, the parameter setting is initialized to the initial value (setting) in step F108. State P
D). Although the meaning will be described later, in the case of this example, P (x) =
In P4, that is, in step F107, it is determined whether or not the current state is the setting state P4. If the reproduction of the sector is OK in the main reproduction, the reproduction proceeds to the next sector without entering the retry process. Therefore, after the parameter is returned to the initial value in step F108, the retry counter R indicating the number of retries is set.
C is cleared, the next sector is accessed in step F110, and the process returns to step F103 to start the reproduction process of the next sector. When the reproduction is OK only in the main reproduction in which the parameters are set to the initial values, the process in step F108 may not be necessary because the parameter setting state PD (initial value) remains. However, since only the amplitude reference value may have been updated by the adaptation processing, the amplitude reference value is returned to the initial value in step F108. However, the amplitude reference value updated from the initial value by the adaptation processing of the RAA 136 may be left as it is without returning to the initial value in step F108, assuming that the amplitude reference value is an optimum value at that time.

In particular, when the reproduction is OK without retrying each sector, step F
At 105, it is determined that the reproduction of all the sectors is completed.
Proceeding to 106, the parameters are set to the initial value state, the retry counter RC is cleared, and a series of reproduction processing ends normally.

[0168] However, if the reproduction becomes NG for some reason during reproduction of a certain sector, the process proceeds from step F104 to F111. If the number of retries has not reached the upper limit, the process proceeds to the retry process from step F112. First, in step F112, the retry counter RC
Then, in step F113, the setting of the parameter is changed according to the number of retries (the value of the retry counter RC). That is, in the case of the first retry, the setting state is set to P1 in FIG. That is, in the case of this example, the gain of the variable gain amplifier 8 is changed (other parameters are initial values). Then, in step F114, the head of the current sector where the main reproduction has failed is accessed, and the flow returns to step F103 to execute reproduction as the first retry.

If the reproduction NG is obtained again after the first retry, step F112 is executed again.
After the processing of F113 and F114 and subsequent steps, step F103
And the reproduction as the second retry is performed. In this case, in step F113, the parameter is set to the setting state P2. That is, the timing setting of the RGATE signal is changed (others are set to initial values).

[0170] Further, when the reproduction becomes NG, 3
The second retry is performed, in which case the parameters are as shown in FIG.
5 is set to P3. Thereafter, as long as the reproduction is NG, the retry is performed while the setting state is changed as shown in FIG. 25. However, if the upper limit number of retries is set to 8, y = 8 in step F111 is set. That is, if the reproduction is unsuccessful even after the eighth retry, the error ends from step F111. In this case, the controller 2 reports to the host computer 1 that the reproduction operation is terminated with an error.

By the way, the cause of the reproduction NG can be considered in various ways, but by performing the retry while switching the parameter setting state as described above, a certain retry point (that is, a parameter that can cope with the error cause at that time) is obtained. At the time of the retry reproduction at the time of the setting state), the possibility of the reproduction OK is high. In that case, the reproduction is OK in step F104, and if there is a next sector, the process proceeds from step F105 to F107, and the process for reproducing the next sector is performed as described above. Then, the parameter setting state at that time is determined, and execution of the process of step F108 is determined according to the type as the setting state (that is, whether or not the setting state is P4 in this example).

Therefore, for example, if the reproduction of a certain sector succeeds in the second retry, it is in the set state P2.
The real reproduction of the next sector will be started. Also in the case where the first retry, the third retry, and the fifth to eighth retries succeed, each of the retries is returned to the setting state PD in step F108, and the main reproduction of the next sector is started.

However, in the example of FIG. 25, when the retry is performed for the fourth time, that is, when the setting of the amplitude reference value is changed as the setting state P4, the retry succeeds, and the process of step F108 is not performed. The main reproduction of the next sector is started as it is.

The reason is as follows. The setting of the amplitude reference value as the setting state P4 is a setting state that can cope with a case where the laser power at the time of recording is inappropriate. On the other hand, the setting states P1 to P3 and P5 to P8 are for setting defects such as defects and birefringence. This is because the setting state is set to be able to cope with the influence. Therefore, when the retry is successful in the setting state P4, it can be estimated that there is a problem in the recording laser power. On the other hand, when the retry is successful in another setting state,
It can be estimated that there was a cause such as a defect.

Here, defects, birefringence, and the like are errors that are inherent to the sector. Therefore,
Normally, it does not affect the reproduction of the next sector. For this reason,
Even if the current sector is reproduced OK in a parameter setting state capable of dealing with a defect or the like, the setting state cannot be said to be optimal in the next sector. That is, normally, the initial value (setting state PD) should be optimal. Therefore, returning to the initial value, considering that the next sector has no defect, makes the reproduction capability higher for that sector, and the reproduction succeeds. The possibility can be increased.

However, in the case where the reproduction NG is caused due to an inappropriate laser power at the time of recording, it is considered that there is a high possibility that the next sector will be the reproduction NG for the same reason. That is, one reproduction operation normally reproduces a plurality of sectors recorded in one recording operation, and in a series of recording operations involving a plurality of sectors, each sector has the same recording laser power. It is likely that it was recorded in. Therefore, if the recording laser power is inappropriate in a certain sector, there is a high possibility that the succeeding sectors are also inappropriate.

Therefore, in this processing example, if the recording laser power is estimated to be inappropriate due to the successful retry at the time of retry in the setting state P4, the setting state will be set at the time of the main reproduction of the next sector. Setting status P without returning to PD
Leaving it at 4 increases the possibility of successful reproduction at the time of main reproduction of the next sector.

Note that the sectors to be sequentially reproduced in a series of reproduction operations are not limited to sectors that are physically continuous on the disk. That is, in a disk medium, at the time of recording, one continuous data can be recorded in a physically distant sector. For example, the next sector is a sector physically distant from the current sector. There may be.

As described above, in this example, if it is estimated that a sector-specific error cause has occurred in a certain sector, the parameters are set to the initial values (setting state PD) at the start of the main reproduction of the next sector. Will be back. on the other hand,
If you suspect a persistent error source,
At the start of the main reproduction of the next sector, a parameter setting state (setting state P4 in FIG. 25) that can cope with the continual error is set. By performing the parameter setting processing in this manner, it is possible to increase the possibility that each sector is led to the reproduction OK only by the main reproduction (that is, without performing the retry), thereby speeding up the reproduction operation of the drive device. , Higher efficiency and higher performance can be realized.

If the retry succeeds in the setting state P4 in the above example and remains in the setting state P4 at the time of the main reproduction of the next sector, the setting state at the time of retrying the sector is, for example, as shown in FIG. Become. That is, at the time of the main reproduction, the setting state is set to P4.
If it becomes G, at the time of the first retry, the setting state P
D (that is, the initial value). Further, at the time of the second, third, and fourth retries, the setting states P1,
P2 and P3. After the fifth retry, the process is the same as that in FIG. That is, the setting state normally used at the time of the fourth retry is used at the time of the main reproduction, so that the setting state used at the time of the third retry is usually shifted from the time of the main reproduction.

The following is a general description. For example, k
The setting state Pk used in the second retry is step F
Suppose that this corresponds to P (x) in 107, and that the set state Pk is set at the time of the main reproduction of a certain sector.
In the case of the n-th retry (k ≧ n), the setting state P (n−
1), and in the case of the n-th retry (k <n), the state is set to P (n).

In this example, only the recording laser power is taken as an example of a continuous error cause, and an example in which the amplitude reference value is changed as a parameter setting corresponding thereto has been described. Certain error causes exist. For example, in the case where the reproduction becomes NG due to a malfunction of the reproduction system in the RF block 20 or the like, even if the reproduction is OK at a certain retry time, the reproduction may be NG due to the same cause when reproducing the next sector. Is high. It is difficult to determine whether there is such a continual error cause only by the occurrence of one reproduction NG, but in such a case, the retry succeeds at the same retry count over a plurality of sectors. Often.

For example, in the case where the retry succeeds successively at the fifth retry in the setting state P5 (that is, when the PLL gain is changed) in a plurality of sectors, some trouble occurs in the PLL unit 14. It can be estimated that there was. And it is a continual error source that also affects the playback of the next sector. Therefore, it can be considered that it is preferable to perform the main reproduction in the next sector in the setting state P5.

That is, if the reproduction is OK in the same setting state for a predetermined number of times or more, it is preferable not to return to the initial value from the next sector. For this purpose, in step F107, it is also determined whether or not the reproduction is OK in the same setting state other than the initial value when the number of sectors is equal to or more than the predetermined number of sectors. So that the process does not proceed to step F108. This makes it possible to proceed with the reproducing operation without retrying as much as possible in order to appropriately cope with a continuous error cause other than the recording laser power.

In addition to such a defect in the reproducing system and the laser power at the time of recording, there are continuous causes of errors. For example, the laser pulse waveform at the time of recording is not appropriate, or the recording sensitivity of the disk 6 is not appropriate. Therefore, if the reproduction is OK when the parameter settings corresponding to those are used, the setting state is used as it is at the time of the main reproduction of the next sector.

In the above description, a specific setting change method (for example, up / down and level of gain, up / down and range of cutoff frequency, etc.) is set as a parameter setting state.
However, it is needless to say that these settings are appropriately changed in order to cope with each of the assumed error causes. In particular, with respect to the setting change of the amplitude reference value, it is possible to calculate a value to be changed based on the estimated recording laser power. For example, as described above, since the asymmetry value and the recording laser power are in a proportional relationship, it is possible to determine from the asymmetry value whether the recording laser power is appropriate or not and whether the recording laser power is too small or too large. Further, by being in a proportional relationship, it is possible to accurately estimate how much the laser power deviates from an appropriate value. So, for example, γ
asy> γasy3, that is, if the recording laser power is excessive, how much (ie, γasy)
−value of −γasy3), the amplitude reference value may be set. That is, a large number of amplitude reference values for high recording power are prepared according to the level. The same applies to the case where the recording laser power is too low.

As a method of calculating the asymmetry value γasy, the amplitude reference value may be used as described above, but the asymmetry value may be obtained by sampling the envelope of the RF signal and using the sampling value.
That is, the asymmetry value γasy can be calculated by collecting the sampling values necessary for the calculation of the above equation (25), and such a calculation method may be adopted.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above examples, and various modifications are possible. Of course, the example of the parameter setting change and the number of retries as shown in FIGS. 25 and 26 are merely examples used for the description, and actually, various parameter setting change examples can be considered. Similarly, the processing example shown in FIG. 27 is only an example.

In addition, the present invention provides, for example, a three-valued four-state, a seven-valued six
The present invention can also be applied to a drive device employing various Viterbi decoding methods such as a state, and a drive device employing a bit-by-bit decoding method. Further, the present invention can be applied to various types of playback devices that play back data recorded on a recording medium. That is, a magneto-optical disk (MO)
In addition, for example, a phase change disk such as a DVD, a CD-
Rewritable disc such as RW (CD-Rewritable), C
Write-once discs such as DR (CD-WO) and WORM,
The present invention can be applied to a disk reproducing apparatus corresponding to a read-only disk such as a DVD-ROM and a CD-ROM.

[0190]

As can be understood from the above description, the drive device of the present invention changes the parameter setting state for each retry at the time of retry by reproduction NG. If this happens, when we move on to the next sector,
Depending on the type of the setting state at the time of the successful retry, it is possible to select whether to maintain the parameter setting state or to return to the initial value. That is, by performing the retry while changing the parameter setting state, when the retry succeeds, the reproduction state is changed from the setting state at that time to the playback N
Since the cause of G can be estimated, the main sector of the next sector can be successfully reproduced by determining the parameter setting state at the time of reproducing the next sector (unit area) according to the estimated cause. Can be enhanced. As a result, it is more likely that a playback operation with an optimum read capability and a playback operation that does not shift to retry can be executed, and thus a quick and efficient playback process can be realized, so that the performance as a drive device can be improved. This has the effect.

If the type of the setting state when proper reproduction data is obtained by the retry operation is a setting state capable of coping with a continuous error cause in the next unit area, the unit area to be executed subsequently During playback, the setting state at the time of retry success is maintained, while the setting state type when proper playback data is obtained by the retry operation can cope with the error cause specific to the unit area. In the case of the state, the parameter setting state is returned to the initial value at the time of subsequent reproduction of the unit area, whereby the most accurate parameter setting is realized.

Further, the setting state that can cope with the error cause with continuity is a setting state that can cope with an inappropriate laser power at the time of recording, while it can cope with an error cause specific to a unit area. The setting state is a setting state capable of coping with defects and birefringence existing in the unit area, and by making a determination on the parameter setting of the next sector as described above, appropriate parameter setting becomes possible, and the The performance of the device can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a general disk drive device using Viterbi decoding to which the present invention can be applied.

FIG. 2 is an explanatory diagram of an outline of a mark position recording method and a mark edge recording method.

FIG. 3 is an explanatory diagram of a minimum magnetization reversal width in an RLL (1, 7) encoding method.

FIG. 4 shows a reproduction signal of data recorded by an RLL (1, 7) code and a mark edge recording method in PR (1, 2, 2,
FIG. 4 is an explanatory diagram of an eye pattern when the waveform is equalized in 1).

FIG. 5 is an explanatory diagram of a state transition process of a Viterbi decoding method.

FIG. 6 is an explanatory diagram of a state transition of the Viterbi decoding method.

FIG. 7 is an explanatory diagram of a trellis diagram of state transition of the Viterbi decoding method.

FIG. 8 is a block diagram of the SMU of the Viterbi decoder.

FIG. 9 is a block diagram of an A-type status memory of the SMU of the Viterbi decoder.

FIG. 10 is a block diagram of a B-type status memory of the SMU of the Viterbi decoder.

FIG. 11 is an explanatory diagram of an operation of selecting a state data value in a merge block of the Viterbi decoder.

FIG. 12 is an explanatory diagram of an amplitude reference value adapted by a Viterbi decoder.

FIG. 13 is a block diagram of the drive device according to the embodiment.

FIG. 14 is an explanatory diagram of a relationship between a recording laser power and an impulse response.

FIG. 15 is an explanatory diagram of a relationship between a recording laser power and an eye pattern.

FIG. 16 is an explanatory diagram of envelopes of 2T and 8T patterns.

FIG. 17 is an explanatory diagram of asymmetry values observed in envelopes of 2T and 8T patterns.

FIG. 18 is an explanatory diagram of an appropriate asymmetry value range in the embodiment.

FIG. 19 is a block diagram of an OCU according to the embodiment.

FIG. 20 is an explanatory diagram of offset error detection timing according to the embodiment.

FIG. 21 is an explanatory diagram of a state in which an offset becomes large.

FIG. 22 is an explanatory diagram in a case where an offset changes rapidly due to birefringence or the like.

FIG. 23 is an explanatory diagram of a reproduced RF signal in a 3T pattern.

FIG. 24 is an explanatory diagram of a case where a reproduced RF signal in a 3T pattern is erroneously detected due to an offset.

FIG. 25 is an explanatory diagram of a parameter setting change example of the embodiment.

FIG. 26 is an explanatory diagram of a parameter setting change example of the embodiment.

FIG. 27 is a flowchart of a process at the time of reproduction according to the embodiment.

[Explanation of symbols]

1 host computer, 2 drive controller,
3 CPU, 4 LPC, 5 magnetic head, 6 disk, 7 optical pickup, 8 amplifier, 9 spindle motor, 10 APC, 11 filter section, 12 A /
D converter, 13 Viterbi decoder, 14 PLL unit, 15
MTG, 16 OCU, 17 D / A converter, 19 offset cancel unit, 131 shift register, 13
2 BMC, 133 ACS, 134 SMU, 135
Merge block, 136 RAA, 161 mode switching unit, 162, 163, 164, 165 latch circuit,
166 adder, 167 amplifier

Claims (5)

[Claims] 1. A head unit capable of reading a data signal recorded on a recording medium by irradiating a laser beam, and a data signal read out by the head unit in accordance with various set parameters. A reproducing circuit means for performing reproduction signal processing based on the reproduction signal means to obtain reproduction data; and performing a reproducing operation by the head means and the reproducing circuit means for each unit area on a recording medium, and reproducing the unit area. A reproduction control unit for performing a retry of a reproduction operation for the unit area when proper reproduction data is not obtained by the reproduction circuit unit with respect to the data signal read by the unit; For each retry to be executed and controlled, the setting state of various parameters in the reproduction circuit means is changed, and If the appropriate playback data is obtained by the retry operation in the following, depending on the type of the setting state, the setting state is maintained or the setting state is returned to the initial value when the unit area to be subsequently executed is reproduced. A drive device comprising: parameter setting means capable of performing the following. 2. The method according to claim 1, wherein when the type of the setting state when proper reproduction data is obtained by the retry operation is a setting state capable of coping with a continuous error cause in the next unit area. 2. The drive device according to claim 1, wherein the set state is maintained when the unit area is subsequently reproduced. 3. The parameter setting means, if the type of the setting state when proper reproduction data is obtained by the retry operation is a setting state capable of coping with an error cause unique to the unit area, subsequently. 2. The setting state is returned to an initial value when a unit area to be executed is reproduced.
The drive device according to item 1. 4. The drive according to claim 2, wherein the setting state that can cope with a continuous error cause is a setting state that can cope with an inappropriate laser power at the time of recording. apparatus. 5. The drive device according to claim 3, wherein the setting state capable of coping with an error cause specific to a unit area is a setting state capable of coping with a defect or birefringence existing in the unit area. .