JP2006164487A - Waveform equalizer and equalization method, waveform equalization program, and computer readable recording medium which records waveform equalization program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a waveform equalizer capable of more properly executing waveform equalization by suppressing impairment of convergence of equalization characteristics or divergence of the equalization characteristics. <P>SOLUTION: In an optical disk player 20, a path metric difference obtained from an input signal before the waveform equalization is computed by a SAM value before equalization computation circuit 10, whether or not this value is within a tolerance level is judged by a SAM value before equalization judgment circuit 11 and only when the value is within the tolerance level, a tap coefficient is updated in a tap coefficient update circuit 9. Thus, since an update operation of the tap coefficient is stopped and a tap coefficient obtained from a normal input signal immediately before the signal shows the abnormal value is held as it is when the input signal temporarily shows an abnormal value, divergence of the tap coefficient is prevented. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a waveform equalizer for adaptively equalizing a reproduced signal in a signal reproduction system, a waveform equalization program, a computer-readable recording medium recording the waveform equalization program, and a waveform equalization method. It is.

  In recent years, a PRML (Partial Response Maximum Likelihood) method has been adopted as a data detection method for realizing a higher recording density of an information recording medium. In PRML, it is necessary to perform waveform equalization in order to bring the reproduced signal waveform reproduced from the recording medium closer to the ideal frequency characteristic assumed in the PR class. Since there are reproduction characteristic fluctuations due to reproduction system characteristic fluctuations, such as servo offset and servo offset, an adaptive equalization technique for adaptively updating the waveform equalization characteristics in response to reproduction characteristic fluctuations is used.

  Previously, the applicant has applied for an adaptive equalization technique that can minimize the error rate in PRML (see Patent Document 1). In this method, the equalization coefficient is adapted so that the mean square error of the path metric difference in the Viterbi decoding process with respect to a predetermined target value is minimized.

  This conventional example will be briefly described with reference to FIGS. FIG. 7 is a block diagram showing a configuration of an optical disc reproducing apparatus 50 using a conventional waveform equalization technique. The optical disk playback device 50 is a device for playing back the optical disk 1, and includes an optical pickup 2, an A / D (Analog to Digital) converter 3, an FIR (Finite Impulse Response) filter 4, a Viterbi decoding circuit 5, a delay adjustment circuit 6. 7, a specific pattern detection circuit 8 and a tap coefficient update circuit 9 are provided.

  The optical disc 1 has a run length limited code with d = 1 such as a (1, 7) RLL (Run Length Limited) code, that is, the shortest mark length is 2T (T represents one channel bit length of a reproduction signal. The recording mark train of the modulation system is recorded.

  The optical pickup 2 reproduces an analog reproduction waveform having a reproduction signal string from the optical disc 1. The optical pickup 2 includes a semiconductor laser (not shown), various optical components, a photodiode, and the like. The optical pickup 2 condenses the laser beam emitted from the semiconductor laser onto the optical disc 1, reflects it with a recording mark recorded on the optical disc 1, and converts the reflected light into an electrical signal with a photodiode to perform analog reproduction. A waveform (hereinafter simply referred to as “reproduced waveform”) is output.

  The A / D converter 3 performs A / D conversion of the reproduction waveform output from the optical pickup 2 at the timing of the channel frequency clock. The A / D converter 3 then outputs a digital reproduction signal after A / D conversion (hereinafter referred to as “reproduction signal string”).

  The FIR filter 4 generates a signal sequence after equalization by performing waveform equalization on the reproduction signal sequence. The FIR filter 4 has two delay elements of time T, three gain variable amplifiers (gains are c (0, n), c (1, n), c (2, n), respectively), and an adder. It is a 3-tap digital filter with one. Here, the gains c (0, n), c (1, n), and c (2, n) are called tap coefficients, and the equalization characteristics of the FIR filter 4 can be changed by changing these values. it can. Note that the number of taps is set to 3 for simplification of explanation, and in fact, a higher performance filter can be obtained by using a larger number of taps. The FIR filter 4 includes tap coefficients c (0, n), c (1, n), c (2, n) and a reproduced signal sequence u (i, n), u (i-1, n), u (i The equalized signal sequence y (i-1, n) is output by performing a convolution operation while sequentially associating -2, n). The meaning of “n” will be described later.

  The Viterbi decoding circuit 5 performs Viterbi decoding of the equalized signal sequence y (i−1, n) output from the FIR filter 4 based on the PR (1, 2, 1) characteristic having a waveform interference width of 3T, The decoding bit string b (i) of the recording mark recorded on the optical disc 1 is output, and at the same time, the path metric difference s (n) between the two paths joined in the Viterbi decoding process is calculated and output. This path metric difference is a known technique called SAM (Sequenced Amplitude Margin) (see Non-Patent Document 1).

  The delay adjustment circuits 6 and 7 generate a reproduction signal string u (i, n) and a path metric difference s (n), and a decoded bit string b (i) generated by a delay corresponding to the time of the path memory length in the Viterbi decoding circuit 5. This is for correcting the time difference of each of these to achieve synchronization.

  The specific pattern detection circuit 8 uses the decoded bit string b (i-4), b (i-3),..., B (i) decoded by the Viterbi decoding circuit 5 as a specific decoding pattern (specific pattern) “ It is determined whether or not it matches any of “00111”, “00011”, “11000”, and “11100”.

Whenever the specific pattern detection circuit 8 detects the specific pattern, the tap coefficient update circuit 9
c (k, n + 1) = c (k, n) ± [mu] {s (n) -ds} {u (-2-k, n) + 2u (-1-k, n) + u (-k, n )}… (1)
Thus, a new tap coefficient c (k, n + 1) is obtained, and the tap coefficient of the FIR filter 4 is updated.

  Note that n is a value corresponding to the number of detections of the specific pattern, and means that the tap coefficient is updated for each detected nth specific pattern. μ is a minute value for controlling the response of the tap coefficient update and is called a step gain. The sign (±) to be applied to the coefficient correction term (the second term on the right side of equation (1)) is determined by the specific pattern detected by the specific pattern detection circuit 8, and is negative in the case of “00111” or “11100”. In the case of “11000” or “00011”, it is positive.

  A reproducing operation by the conventional optical disk reproducing apparatus 50 having the above configuration will be described. First, the optical pickup 2 emits a light beam onto the optical disc 1, whereby a reproduction waveform of a recording mark recorded on the optical disc 1 is output from the optical pickup 2. This reproduced waveform is converted into a reproduced signal sequence u (i, n) by the A / D converter 3. When the reproduction signal sequence u (i, n) is input to the FIR filter 4, waveform equalization processing is performed and an equalized signal sequence y (i-1, n) is output. The equalized signal y (i−1, n) is an equalized signal corresponding to the reproduction signal u (i−1, n) (the signal before and after equalization by matching the subscript “i−1”). Represents the corresponding relationship).

  When the equalized signal sequence y (i−1, n) is input, the Viterbi decoding circuit 5 obtains and outputs a path metric difference s (n), and a decoded bit sequence obtained as a result of Viterbi decoding. b (i) is output. That is, the Viterbi decoding circuit 5 generates a decoded bit string b (i) that is a decoding result of the reproduction signal string u (i, n). In addition, the Viterbi decoding circuit 5 performs path metrics between a correct path determined as a surviving path and an error path that confronts the correct path in the Viterbi decoding process based on the equalized signal sequence y (i−1, n). The difference s (n) is detected.

  The specific pattern detection circuit 8 includes “00111”, “00011”, “11000”, “11100” in which the decoded bit strings b (i-4), b (i-3),..., B (i) are specific patterns. It is determined whether or not they match, and if they match, a match signal is transmitted to the tap coefficient update circuit 9. The specific pattern is a bit string pattern in which, when an ideal waveform signal string that is an ideal waveform without noise for Viterbi decoding is assumed, the path metric difference obtained from the ideal waveform signal string becomes a minimum value. The specific pattern detection circuit 8 is a circuit that detects such a specific pattern from the decoded bit string b (i).

  When the coincidence signal is transmitted from the specific pattern detection circuit 8, the tap coefficient updating circuit 9 and the error {s (n) −ds} of the path metric difference s (n) with respect to the target value ds and the reproduction signal sequence u (ik, The product of the first order polynomial {u (-2-k, n) + 2u (-1-k, n) + u (-k, n)} obtained by applying a predetermined weight to n) is the tap coefficient c (k, n ) Is corrected. Specifically, the tap coefficient updating circuit 9 calculates the above equation (1).

  As the target value ds, when it is assumed that a signal corresponding to a specific pattern and corresponding to a signal waveform ideal for Viterbi decoding is input to the Viterbi decoding circuit 5, the Viterbi decoding circuit 5 The output path metric difference value (ideal value) or a value obtained by appropriately correcting the ideal value may be set.

  Here, the correspondence between the path metric difference s (n) and the reproduction signal sequence u (i−k, n) will be described with reference to FIG. When “00111” is detected as the nth decoded bit string that matches the specific pattern, it is assumed that the reproduced waveform reproduced from the recording mark corresponding to this decoded bit string is as shown in FIG. Let u (-4, n), u (-3, n), u (-2, n), u (-1, n), u (0, n).

  In the above equation (1), μ is a minute value for controlling the responsiveness, and is called a step gain. If μ is set to an appropriate value, the tap coefficient c (k, i) converges to the optimum value while the above update operation is repeated. The sign (±) applied to the coefficient correction term (the second term on the right side of the above equation (1)) is determined by the specific pattern detected by the specific pattern detection circuit 8, and is negative in the case of "00111" or "11100". , “11000” or “00011” is positive.

In the equalized signal equalized by the FIR filter 4 by the tap coefficient finally converged by repeating the tap coefficient updating operation according to the above equation (1), the mean square of the path metric difference s (n) with respect to the target value ds The error E [{s (n) −ds} ² ] (E [] is the expected value operator) is minimized, and it is theoretically explained that the error rate of the bit string decoded by Viterbi decoding is the best. (The reason for this is known from the prior art and will not be described in detail).

As described above, in the conventional waveform equalizer, the tap coefficient of the FIR filter 4 is updated so that the mean square error of the path metric difference is minimized, so that the error rate is adaptively minimized. Is possible.
JP 2004-63036 A (publication date February 26, 2004) T.Perkins, "A Window Margin Like Procedure for Evaluating PRML Channel Performance"; IEEE Transactions on Magnetics, Vol.31, No2, 1995, p1109-1114

  In the prior art, the tap coefficient is updated by the above equation (1). That is, the update amount of the tap coefficient is determined by the product of the error of the path metric difference s (n) with respect to the target value ds and a first-order polynomial obtained by applying a predetermined weight to the reproduction signal sequence, so that the reproduction waveform becomes abnormal. Directly affected.

  Optical discs also contain medium defects (defects, pinholes, etc.), and the reproduced waveform from such locations has a very small amplitude, a very large direct current component, and a very poor S / N ratio. . In addition to medium defects, there are many causes of abnormalities in the reproduced waveform, such as disturbances such as impact on the optical disk reproducing device 50 and noise propagated to the circuit.

  If such an abnormal reproduction waveform is temporarily input, the update value of the tap coefficient obtained by the above equation (1) also becomes an abnormal value, and the tap coefficient may diverge without going toward the convergence value. There is.

  The present invention has been made in view of the above-described problems, and its purpose is to suppress the convergence of the equalization characteristic or to prevent the equalization characteristic from diverging, and to provide a more appropriate waveform. The object is to realize a waveform equalization apparatus and a waveform equalization method capable of performing equalization.

  A waveform equalization apparatus according to the present invention is a waveform equalization apparatus that applies equalization characteristics to an input signal while equalizing the waveform of the input signal. Equalization means for generating an equalized signal by performing equalization; and post-equalization path metric difference detection means for detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the equalized signal; Equalization adaptation means for performing the adaptation based on an error with respect to a target value of a path metric difference of the detected equalized signal, and a signal quality evaluation means for evaluating the signal quality of the input signal or the equalized signal The equalization adapting means controls the adaptation processing based on the evaluation result by the signal quality evaluating means.

  A waveform equalization method according to the present invention is a waveform equalization method that applies waveform equalization to an input signal while adapting the equalization characteristics thereof. An equalization step of generating an equalized signal by performing waveform equalization, and an equalized path metric difference detection step of detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the equalized signal And an equalization adaptation step for performing the adaptation based on an error with respect to a target value of a detected path metric difference of the post-equalization signal, and an input signal evaluation step for evaluating the signal quality of the input signal. In the equalization adaptation step, the adaptation process is controlled based on the evaluation result in the input signal evaluation step.

  In the above configuration and method, the path metric difference between the correct path and the error path in the Viterbi decoding process for the equalized signal is detected. Although an ideal value is assumed for the path metric difference, the actually detected path metric difference has variations with respect to the ideal value. In order to reduce the error rate in Viterbi decoding, an ideal value or a value obtained by appropriately correcting the ideal value is set as a target value, and the path metric difference actually detected with respect to the target value is set. The equalization characteristics should be adapted so as to reduce the error.

  Here, if the signal quality of the input signal is good, the equalization characteristic tends to converge as the adaptation is repeated based on the input signal, but the signal quality of the input signal may be temporary. In the case of deterioration, the adaptation based on the input signal with deteriorated quality is performed, so that the convergence property of the equalization characteristic is lost, and in the worst case, the convergence occurs.

  Therefore, in the above configuration and method, the signal quality of the input signal or the equalized signal is evaluated, and the adaptation process is controlled based on the evaluation result. As a result, when the signal quality of the input signal or the equalized signal is deteriorated from a predetermined reference, the adaptation process can be controlled so that the convergence of the equalization characteristic is not adversely affected. become.

  As a result, the convergence of the equalization characteristic is impaired or the equalization characteristic is prevented from diverging, and the waveform equalization can be performed more appropriately.

  The waveform equalization apparatus according to the present invention further includes a pre-equalization path metric difference detecting means for detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the input signal in the above configuration, and the signal quality The evaluation unit may evaluate the signal quality based on the value of the path metric difference of the input signal detected by the pre-equalization path metric difference detection unit.

  The waveform equalization method according to the present invention further includes a pre-equalization path metric difference detection step for detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the input signal in the above method, In the input signal evaluation step, the signal quality may be evaluated based on the path metric difference value of the input signal detected in the pre-equalization path metric difference detection step.

  In the waveform equalizer according to the present invention, in the above configuration, the signal quality evaluation unit determines whether a value of a path metric difference of the input signal is within an allowable range, and the equalization adaptation unit includes When the signal quality evaluation means determines that the value of the path metric difference of the input signal is outside the allowable range, the adaptation process may be temporarily stopped. Also, for this purpose, the adaptation for temporarily stopping the adaptation process in the equalization adaptation unit when the signal quality evaluation unit determines that the value of the path metric difference of the input signal is outside the allowable range. You may provide the temporary stop means.

  In the above configuration, when the path metric difference obtained from the input signal before waveform equalization is outside the allowable range, the adaptation process is temporarily stopped. As a result, when the convergence of the equalization characteristic is likely to be impaired, the adaptation process is temporarily stopped and the previous normal equalization characteristic is maintained as it is. It is possible to prevent the performance from being lost or the equalization characteristic from diverging.

  In the waveform equalizer according to the present invention, in the configuration described above, the pre-equalization path metric difference detecting unit is configured to detect a path metric difference set in advance corresponding to a specific partial response characteristic and a specific decoding pattern of an input signal. An arithmetic expression may be executed.

  In the above-described configuration, the pre-equalization path metric difference detecting means executes an arithmetic expression of a path metric difference set in advance corresponding to a specific partial response characteristic and a specific decoding pattern of the input signal. Compared with the case where Viterbi decoding is executed, the present invention can be realized by a configuration capable of executing simpler calculations. Therefore, the pre-equalization path metric difference detecting means can be realized with a simple configuration.

  Alternatively, in the waveform equalizer according to the present invention, in the above configuration, the signal quality evaluation unit is based on a path metric difference value of the post-equalization signal detected by the post-equalization path metric difference detection unit. It may be configured to evaluate signal quality.

  The waveform equalization method according to the present invention is based on the path metric difference value of the post-equalization signal detected by the post-equalization path metric difference detection step in the input signal evaluation step. The signal quality may be evaluated.

  In this case, unlike the configuration described above, it is not necessary to separately provide a pre-equalization path metric difference detection unit, and thus the configuration can be simplified.

  In the waveform equalizer according to the present invention, in the configuration described above, the signal quality evaluation unit determines whether a value of a path metric difference of the equalized signal is within an allowable range, and the equalization adaptation is performed. The means may be configured to temporarily stop the adaptation process when the signal quality evaluation means determines that the value of the path metric difference of the equalized signal is out of an allowable range. For this purpose, when the signal quality evaluation means determines that the value of the path metric difference of the equalized signal is outside the allowable range, the adaptation processing in the equalization adaptation means is temporarily stopped. An adaptation pause means may be provided.

  In the above configuration, when the path metric difference obtained from the equalized signal obtained by equalizing the waveform of the input signal is outside the allowable range, the adaptation process is temporarily stopped. As a result, when the convergence of the equalization characteristic is likely to be impaired, the adaptation process is temporarily stopped and the previous normal equalization characteristic is maintained as it is. It is possible to prevent the performance from being lost or the equalization characteristic from diverging.

  A waveform equalization apparatus according to the present invention is a waveform equalization apparatus that applies equalization characteristics to an input signal while equalizing the waveform of the input signal, and performs equalization by performing waveform equalization on the input signal. Equalization means for generating a signal, post-equalization path metric difference detection means for detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the post-equalization signal, and the detected post-equalization signal An equalization adapting means for performing the adaptation by updating the equalization characteristic based on an error of the path metric difference with respect to a target value, and an equalization update amount evaluation means for evaluating the update amount of the equalization characteristic The equalization adaptation unit controls the adaptation process based on an evaluation result by the equalization update amount evaluation unit.

  The waveform equalization method according to the present invention is a waveform equalization method that adapts the equalization characteristics while equalizing an input signal, and performing waveform equalization on the input signal, etc. An equalization step for generating a post-equalization signal, a post-equalization path metric difference detection step for detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the post-equalization signal, and the detected equalization An equalization adaptation step for performing the adaptation by updating the equalization characteristic based on an error of a path metric difference of the post signal with respect to a target value, and an equalization update amount evaluation for evaluating an update amount of the equalization characteristic And the step of equalization adaptation is characterized in that the adaptation process is controlled based on the evaluation result in the equalization update amount evaluation step.

  In the above configuration and method, instead of evaluating the signal quality of the input signal or the equalized signal, the update amount of the equalization characteristic reflecting the signal quality of the input signal or the equalized signal is evaluated, and this Adaptation processing is controlled based on the evaluation result. As a result, when the update amount of the equalization characteristic becomes worse than a predetermined reference, the adaptation process can be controlled so that the convergence of the equalization characteristic is hardly adversely affected.

  As a result, the convergence of the equalization characteristic is impaired or the equalization characteristic is prevented from diverging, and the waveform equalization can be performed more appropriately.

  In the waveform equalization apparatus according to the present invention, in the above configuration, the equalization update amount evaluating means determines whether or not an update value of the equalization characteristic is within an allowable range, and the equalization adaptation is performed. The means includes an adaptation pause means for temporarily stopping the adaptation process when the equalization update quantity evaluation means determines that the update value of the equalization characteristic is out of an allowable range. It may be configured.

  In the above configuration, when the value of the equalization characteristic update amount obtained from the input signal is outside the allowable range, the adaptation processing is temporarily stopped. As a result, when the convergence of the equalization characteristic is likely to be impaired, the adaptation process is temporarily stopped and the previous normal equalization characteristic is maintained as it is. It is possible to prevent the performance from being lost or the equalization characteristic from diverging.

  The waveform equalization apparatus according to the present invention may be configured such that in any one of the configurations including the adaptation pause unit, the adaptation pause unit stops the adaptation process a plurality of times. .

  In the above configuration, by stopping the adaptation process a plurality of times, even if the path metric difference of the input signal or the equalized signal or the update amount of the equalization characteristic is intermittently outside the allowable range, an abnormality occurs. Since the stop of the adaptation process is continued during the input period, it is possible to more reliably prevent the convergence of the equalization characteristic from being lost or the equalization characteristic from diverging.

  In the waveform equalizing apparatus according to the present invention, in the above configuration, the equalizing means sequentially associates a plurality of equalization coefficients with a digital input signal sequence obtained by A / D converting the input signal. A digital filter that generates a post-equalization signal sequence by performing a convolution operation between the equalization coefficient and each digital input signal sequence associated with each equalization coefficient, and the equalization adaptation unit includes: The adaptation is performed by updating each equalization coefficient with a minute width so that a function representing the mean square value of the error created using each equalization coefficient as a variable approaches a minimum value. Can do.

  The waveform equalization program of the present invention is a waveform equalization program for operating any one of the above waveform equalization apparatuses, and is a program for causing a computer to function as each of the above means.

  With the above configuration, the waveform equalization apparatus can be realized by realizing each means of the waveform equalization apparatus with a computer. Therefore, as described above, a waveform equalization apparatus that can appropriately perform waveform equalization can be realized on a computer. .

  In addition, a computer-readable recording medium on which the waveform equalization program of the present invention is recorded records a program for causing a computer to function as each means.

  With the above configuration, the waveform equalization apparatus can be realized on the computer by the waveform equalization program read from the recording medium.

  As described above, the waveform equalization apparatus according to the present invention includes equalization means for generating an equalized signal by performing waveform equalization on an input signal, and a correct path in a Viterbi decoding process for the equalized signal. Post-equalization path metric difference detection means for detecting a path metric difference between a path and an error path, and equalization adaptation means for performing adaptation based on an error with respect to a target value of a path metric difference of the detected post-equalization signal; The signal quality evaluation means for evaluating the signal quality of the input signal or the equalized signal, and the equalization adaptation means is configured to control the adaptation process based on the evaluation result by the signal quality evaluation means. .

  The waveform equalization method according to the present invention includes an equalization step for generating an equalized signal by performing waveform equalization on an input signal, and a correct path and an error path in a Viterbi decoding process for the equalized signal. A post-equalization path metric difference detection step for detecting a path metric difference between the input signal, an equalization adaptation step for performing adaptation based on an error with respect to a target value of a path metric difference of the detected post-equalization signal, and an input signal In the input signal evaluation step for evaluating the signal quality and the equalization adaptation step, the adaptation processing is controlled based on the evaluation result by the input signal evaluation means.

  Alternatively, the waveform equalization apparatus according to the present invention includes an equalization unit that generates an equalized signal by performing waveform equalization on an input signal, and a correct path and an error path in a Viterbi decoding process for the equalized signal. A path metric difference detecting means for detecting a path metric difference between the signal and a path metric difference of the detected equalized signal and performing an adaptation by updating an equalization characteristic based on an error with respect to a target value. And an equalization update amount evaluation means for evaluating the update amount of the equalization characteristic. The equalization adaptation means performs the adaptation process based on the evaluation result by the equalization update amount evaluation means. It is the structure to control.

  The waveform equalization method according to the present invention includes an equalization step for generating an equalized signal by performing waveform equalization on an input signal, and a correct path and an error path in a Viterbi decoding process for the equalized signal. And a post-equalization path metric difference detection step for detecting a path metric difference between the first and second signals, and an adaptation by updating an equalization characteristic based on an error of the detected equalized signal with respect to a target value of a path metric difference. And an equalization update amount evaluation step for evaluating the update amount of the equalization characteristic. In the equalization adaptation step, the adaptation process is performed based on the evaluation result in the equalization update amount evaluation step. How to control.

  In the above configuration and method, the signal quality of the input signal or the equalized signal, or the update amount of the equalization characteristic reflecting them is evaluated, and the adaptation process is controlled based on the evaluation result. It is like that. As a result, when the signal quality of the input signal or the equalized signal or the update amount of the equalization coefficient is deteriorated from a predetermined standard, the adaptation is performed so that the convergence of the equalization characteristic is not adversely affected. The process can be controlled.

  As a result, the convergence of the equalization characteristic is impaired or the equalization characteristic is prevented from diverging, and the waveform equalization can be performed more appropriately.

Embodiment 1
An embodiment of the present invention will be described with reference to FIGS. 1 to 5 as follows.

  FIG. 1 is a block diagram showing a configuration of an optical disc reproducing apparatus 20 to which a waveform equalizing apparatus and a waveform equalizing method according to the present invention are applied. In addition, about the component which has a function equivalent to the component in the optical disk reproducing | regenerating apparatus 50 demonstrated based on FIG. 7 in the above-mentioned background art section, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  The optical disc playback apparatus 20 is different from the optical disc playback apparatus 50 in that the optical disc playback apparatus 20 further includes a pre-equalization SAM value calculation circuit 10 and a pre-equalization SAM value determination circuit 11.

  The pre-equalization SAM value calculation circuit 10 receives the reproduction signal sequence u (i, n), and based on the input reproduction signal sequence u (i, n), the pre-equalization SAM value s ′ (n ) Is calculated and output. Further, the pre-equalization SAM value determination circuit 11 determines whether or not the pre-equalization SAM value s ′ (n) is within a predetermined range.

  The FIR filter 4 is equalization means, the tap coefficients of the FIR filter 4 are equalization coefficients (equalization characteristics), the Viterbi decoding circuit 5 is equalization path metric difference detection means, and the tap coefficient update circuit 9 is equalization adaptation. The pre-equalization SAM value calculation circuit 10 corresponds to a pre-equalization path metric difference detection means, and the pre-equalization SAM value determination circuit 11 corresponds to a signal quality evaluation means. Further, in the optical disk reproducing apparatus 20 of FIG. 1, the configuration excluding the optical disk 1, the optical pickup 2, and the A / D converter 3 corresponds to the waveform equalizer.

  Now, a reproducing operation by the optical disk reproducing apparatus 20 having the configuration shown in FIG. 1 will be described with reference to FIG. FIG. 2 is a flowchart showing the reproduction operation of this embodiment.

  A reproduction waveform output from the optical pickup 2 by irradiating a light beam onto the optical disc 1 is converted into a reproduction signal sequence u (i, n) by the A / D converter 3 and is transmitted to the Viterbi decoding circuit 5 via the FIR filter 4. The path metric difference s (n) and the decoded bit string b (i) are output (step S1). Then, in the specific pattern detection circuit 8, the decoded bit strings b (i-4), b (i-3),..., B (i) are specific patterns “00111”, “00011”, “11000”, “11100”. ”Is determined (step S 2), and a specific pattern determination signal indicating“ match ”/“ mismatch ”as the determination result is transmitted to the tap coefficient update circuit 9. Since the operation so far is the same as that of the prior art, a detailed description thereof is omitted.

  On the other hand, the reproduction signal sequence u (i, n) is also input to the pre-equalization SAM value calculation circuit 10, and the pre-equalization SAM value calculation circuit 10 calculates and outputs the pre-equalization SAM value s' (n). (Step S3). The pre-equalization SAM value s ′ (n) is a SAM value obtained by Viterbi decoding the input signal sequence before equalization, and is an evaluation value indicating the signal quality of the input signal sequence before equalization.

  Note that the pre-equalization SAM value calculation circuit 10 may be the same as the Viterbi decoding circuit 5, but in this case, since two complicated Viterbi decoding circuits must be provided, the circuit load increases. End up. Therefore, as shown in FIG. 3, instead of executing Viterbi decoding itself, a circuit 10a that simply calculates a partial response characteristic of an input signal and only a SAM value corresponding to a specific pattern may be used. This circuit 10a can be realized by applying, for example, a circuit disclosed in Japanese Patent Application Laid-Open No. 2004-62998, and an adder 14 and a multiplier 13 (because of double multiplication, can be realized only by bit shift) Since it can be configured by the delay elements 15 and 15, it can be mounted very easily compared to mounting the Viterbi decoding circuit itself.

  The pre-equalization SAM value s ′ (n) output from the pre-equalization SAM value calculation circuit 10 is input to the pre-equalization SAM value determination circuit 11. The pre-equalization SAM value determination circuit 11 determines whether or not the input pre-equalization SAM value s ′ (n) is within a predetermined range (allowable range) (step S4), and the determination result A pre-equalization SAM value determination signal indicating “within allowable range” / “out of allowable range” is transmitted to the tap coefficient update circuit 9.

  If the allowable range is set too narrow, the tap coefficient may not be updated with respect to the input signal that should originally be the adaptation target. On the other hand, if the setting is too wide, the update is delayed when the input signal becomes abnormal, and the effect of preventing divergence cannot be obtained. Therefore, the allowable range must be set to an appropriate value.

  In the tap coefficient update circuit 9 to which the specific pattern determination signal and the pre-equalization SAM value determination signal are input, the specific pattern determination signal indicates “match” (step S2, YES), and the pre-equalization SAM value determination signal Indicates “within allowable range” (step S4, YES), the tap coefficient c (k, n) is updated by executing the calculation of the expression (1) described in the background art section (step S5). That is, in the optical disc reproducing apparatus 20, even when the specific pattern determination signal indicates “match”, when the pre-equalization SAM value determination signal indicates “out of allowable range”, the tap coefficient c (k, n ) Is different from the conventional optical disk reproducing device 50 in that it is not updated.

  Thereby, in the optical disc reproducing apparatus 20, when the reproduction signal becomes an abnormal signal due to a defect of the disc or the like, the pre-equalization SAM value s ′ (n) corresponding to the signal quality of the reproduction signal becomes an abnormal value and is within an allowable range. Therefore, the tap coefficient c (k, n) is not updated, and the previous value is held. Therefore, since the updating of the tap coefficient c (k, n) is stopped while the reproduction signal is abnormal, the risk of the tap coefficient c (k, n) being diverged can be reduced or eliminated. .

  As described above, the updating of the tap coefficient c (k, n) is stopped, or the adaptation operation is interrupted by not updating (skipping) the updating of the tap coefficient c (k, n). . If the reproduction signal eventually returns to normal, the pre-equalization SAM value s ′ (n) falls within the allowable range again, so that updating of the tap coefficient is resumed, and convergence converges again toward the optimum value. The above process is repeated until the end of the reproduction operation (step S6).

  Here, the reason why the pre-equalization SAM value s ′ (n) is outside the allowable range when the reproduction signal becomes abnormal and an example of a method for setting the allowable range will be described.

  FIG. 4A is a graph showing a path metric difference histogram obtained for an ideal waveform having no noise assumed in the PR (1, 2, 1) characteristic based on the bit pattern of the (1, 7) RLL code. is there. The ideal value of the path metric difference is 1.5, 2.5, 3.5, 4.5, 5, 6, 7, 8, 9,... (PR (1, 2, 1) maximum amplitude of sample level) It can be seen that a plurality of discrete values are obtained. The ideal values take various values because, in the trellis diagram, the path metric difference from the error path that starts from the same state as the correct path corresponding to the ideal waveform and merges into the same state differs depending on the bit pattern. is doing. The frequency of each ideal value is different because the frequency of appearance of each bit pattern is different in the bit pattern of the (1,7) RLL code in addition to the number of types of bit patterns taking each ideal value. Because. The specific patterns “00111”, “00011”, “11000”, and “11100” are bit patterns that take the minimum ideal value 1.5 of the path metric difference.

  On the other hand, when the histogram of the path metric difference of the reproduction signal sequence before equalization obtained by actually reproducing the bit pattern of the (1,7) RLL code recorded on the optical disk is examined, as shown in FIG. The distribution is such that the path metric difference varies around each ideal value. This is due to various noises on the reproduced signal, but since it is due to natural noise, the distribution has a shape close to a normal distribution.

  However, when the reproduced waveform becomes abnormal due to the influence of a defect or the like, the path metric difference becomes a value greatly deviated from the ideal value. Therefore, if the allowable range is set to, for example, 0 to 3.0 based on the actually measured data in FIG. 4B, the deterioration of the path metric difference due to natural noise becomes an adaptation target for equalization, and the reproduced waveform is abnormal. It is considered that the deterioration of the path metric difference due to the above is out of the above-mentioned allowable range and is not subject to equalization adaptation.

  FIGS. 5A and 5B are graphs showing the results of confirming the tap coefficient divergence preventing effect by the experiment according to the present embodiment. FIG. 5 (a) shows the result when the optical disk reproducing apparatus 20 of the present embodiment is used, and FIG. 5 (b) shows the case where the conventional optical disk reproducing apparatus 50 is used for the same input waveform for comparison. The results are shown. In both cases, the horizontal axis is the tap coefficient update count (unit: 100), the vertical axis is the tap coefficient, and it has been confirmed that the input waveform contains a waveform abnormality that seems to be affected by a defect. Yes.

  5 (a) and 5 (b), it can be seen that the tap coefficient starts to diverge after several hundred updates in the conventional example, whereas in the present embodiment, the tap coefficient continues to converge without divergence. In the circuit configuration used in this experiment, since the range of the tap coefficient is limited to ± 8, the coefficient exceeding this is fixed to ± 8.

  As described above, in the optical disc reproducing apparatus 20, when the signal quality of the input signal is deteriorated from a predetermined reference, the adaptation process can be controlled so that the convergence of the equalization coefficient is not adversely affected. become able to. As a result, the convergence of the equalization coefficient is impaired, or the equalization coefficient is prevented from diverging, and the waveform equalization can be performed more appropriately.

  The optical disc playback apparatus 20 can be modified like an optical disc playback apparatus 20 'shown in FIG.

  The optical disc playback apparatus 20 ′ is different from the optical disc playback apparatus 20 in that the optical disc playback apparatus 20 ′ includes a tap coefficient update circuit 9 ′ instead of the tap coefficient update circuit 9, and an update pause circuit 16 further. It is a point that is provided.

  In the optical disc reproducing apparatus 20 ′, the pre-equalization SAM value determination signal indicating the determination result of the pre-equalization SAM value determination circuit 11 is not directly transmitted to the tap coefficient update circuit 9 ′, but is temporarily transmitted to the update pause circuit 16. Reportedly. The update suspension circuit 16 updates the update stop signal only when the determination result is “outside the allowable range” in accordance with the determination result of the pre-equalization SAM value determination circuit 11 “inside the allowable range” / “outside the allowable range”. Is output to the tap coefficient update circuit 9 '. The tap coefficient update circuit 9 ′ does not perform the tap coefficient update operation during the period when the update stop signal is received from the update pause circuit 16.

  As described above, the optical disc playback apparatus 20 ′ has a part of the function of the tap coefficient update circuit 9 in the optical disc playback apparatus 20 in the external update pause circuit 16, and the overall operation is the optical disc playback apparatus. 20 is the same.

  The tap coefficient update circuit 9 'corresponds to equalization adaptation means, and the update pause circuit 16 corresponds to adaptation pause means.

  As described above, the waveform equalization apparatus of the present embodiment is a waveform equalization apparatus that applies equalization characteristics to an input signal while equalizing the waveform of the input signal, and performs waveform equalization on the input signal. Performing equalization means for generating a post-equalization signal, path metric difference detection means before equalization for detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the input signal, and the post-equalization An equalized path metric difference detecting means for detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for a signal, and based on an error with respect to a target value of the detected path metric difference of the equalized signal Equalization adaptation means for performing adaptation, and based on the path metric difference value of the input signal detected by the pre-equalization path metric difference detection means, the equalization adaptation means Controlling the execution of the serial adaptation operation.

  The waveform equalization method of the present embodiment is a waveform equalization method that adapts the equalization characteristics while equalizing an input signal, and performing the waveform equalization on the input signal. Generating an equalized signal; detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the input signal; and a correct path and an error path in a Viterbi decoding process for the equalized signal; Detecting the path metric difference of the input signal, performing the adaptation based on an error with respect to a target value of the detected path metric difference of the equalized signal, and based on the value of the path metric difference of the input signal Controlling execution of the adaptation operation.

  In the above configuration and method, the tap coefficient is updated only when the path metric difference obtained from the input signal before waveform equalization is within a predetermined range. As a result, when the input signal temporarily becomes an abnormal value, the path metric difference obtained from the abnormal input signal is out of the allowable range, and during that time, the tap coefficient update operation is stopped and the previous normal input signal is Since the obtained tap coefficient is held as it is, there is an effect that divergence of the tap coefficient can be prevented.

[Embodiment 2]
In the first embodiment described above, the tap coefficient is updated only when the path metric difference obtained from the input signal before waveform equalization is within the allowable range. For this purpose, the SAM value calculation circuit 10 before equalization is used. Was needed.

  However, if the input signal becomes abnormal, the signal after waveform equalization naturally also becomes abnormal. Therefore, the same effect can be obtained even in a configuration in which the path metric difference obtained from the equalized signal sequence after waveform equalization is to be determined. It is thought that. In other words, the tap coefficient may be updated only when the path metric difference obtained from the equalized signal sequence is within the allowable range.

  FIG. 6 is a block diagram showing a configuration of an optical disc reproducing apparatus 21 to which the waveform equalization apparatus and the waveform equalization method of the present invention are applied. In FIG. 6, components having the same functions as those in the optical disc playback apparatus 20 of the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  The optical disc playback device 21 is different from the optical disc playback device 20 in that the pre-equalization SAM value calculation circuit 10 is omitted in the optical disc playback device 21 and equalization is performed instead of the pre-equalization SAM value determination circuit 11. The post-SAM value determination circuit 12 is provided.

  The post-equalization SAM value determination circuit 12 receives the post-equalization SAM value s (n), which is a path metric difference of the post-equalization signal sequence, from the Viterbi decoding circuit 5, and s (n) is within an allowable range. And the result is output to the tap coefficient update circuit 9.

  The FIR filter 4 is equalization means, the tap coefficients of the FIR filter 4 are equalization coefficients (equalization characteristics), the Viterbi decoding circuit 5 is equalization path metric difference detection means, and the tap coefficient update circuit 9 is equalization adaptation. The post-equalization SAM value determination circuit 12 corresponds to a signal quality evaluation unit. Further, in the optical disk reproducing apparatus 21 of FIG. 6, the configuration excluding the optical disk 1, the optical pickup 2, and the A / D converter 3 corresponds to the waveform equalizer.

  The playback operation of the optical disk playback device 20 configured as described above will be described with reference to the block diagram of FIG.

  A reproduction waveform output from the optical pickup 2 by irradiating a light beam onto the optical disc 1 is converted into a reproduction signal sequence u (i, n) by the A / D converter 3 and is transmitted to the Viterbi decoding circuit 5 via the FIR filter 4. The path metric difference s (n) and the decoded bit string b (i) are output. Further, the specific pattern detection circuit 8 determines whether the decoded bit string b (i-4), b (i-3),..., B (i) matches any of the specific patterns. A specific pattern determination signal indicating a certain “match” / “mismatch” is transmitted to the tap coefficient update circuit 9. The operation so far is the same as in the first embodiment.

  The equalized SAM value s (n) output from the Viterbi decoding circuit 5 is a SAM value obtained by Viterbi decoding the equalized signal sequence, and is an evaluation value indicating the signal quality of the equalized signal sequence. . The post-equalization SAM value s (n) is input to the post-equalization SAM value determination circuit 12. The post-equalization SAM value determination circuit 12 determines whether or not the post-equalization SAM value s (n) is within the allowable range, and indicates the determination result “within allowable range” / “outside of allowable range”. The equalized SAM value determination signal is transmitted to the tap coefficient update circuit 9. The permissible range needs to be set to an appropriate value as in the case of the first embodiment.

  In the tap coefficient update circuit 9, when the specific pattern determination signal indicates “match” and the equalized SAM value determination signal indicates “within tolerance”, the equation (1) described in the background art section When the tap coefficient c (k, n) is updated by performing the calculation, but the SAM value determination signal after equalization indicates “outside the allowable range”, that is, the SAM value s (n) after the equalization is out of the allowable range If it is, the tap coefficient c (k, n) is not updated.

  As a result, also in the optical disc reproducing apparatus 21, when the reproduction signal becomes an abnormal signal due to a defect of the disc, the equalized SAM value s (n) corresponding to the signal quality of the equalized signal sequence also becomes an abnormal value. Therefore, the tap coefficient c (k, n) is not updated and the previous value is held. Therefore, since the updating of the tap coefficient is stopped while the reproduction signal sequence is abnormal, the risk of divergence can be reduced or eliminated. If the reproduced signal eventually returns to normal, the SAM value s (n) after equalization falls within the allowable range again, so that updating of the tap coefficient is resumed and convergence toward the optimum value again proceeds.

  As described above, the optical disc reproducing apparatus 21 is configured to update the tap coefficient only when the path metric difference obtained from the equalized signal sequence is within the allowable range, thereby preventing the tap coefficient from being diverged. In addition to the effect of the first aspect, since only one circuit for calculating the path metric difference is required, the circuit scale can be reduced.

  Also for the optical disc playback apparatus 21, the optical disc playback apparatus 21 'shown in FIG. 10 can be configured by performing the same modification as the modification from the optical disc playback apparatus 20 to the optical disc playback apparatus 20' in the first embodiment.

  The optical disc playback device 21 ′ is different from the optical disc playback device 21 in that the optical disc playback device 21 ′ is provided with a tap coefficient update circuit 9 ′ instead of the tap coefficient update circuit 9, and an update pause circuit 16 is further provided. It is a point that is provided. Note that the tap coefficient update circuit 9 'and the update pause circuit 16 are the same as those described using the same reference numerals in the first embodiment, and thus description thereof is omitted here.

  As described above, the waveform equalization apparatus of the present embodiment is a waveform equalization apparatus that applies equalization characteristics to an input signal while equalizing the waveform of the input signal, and performs waveform equalization on the input signal. An equalization means for generating an equalized signal by performing, and an equalized path metric difference detection means for detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the equalized signal, Equalization adaptation means for performing the adaptation based on an error of the path metric difference of the equalized signal with respect to a target value, and the equalized signal detected by the post-equalization path metric difference detection means Based on the value of the path metric difference, the equalization adaptation means controls execution of the adaptation operation.

  The waveform equalization method of the present embodiment is a waveform equalization method that adapts the equalization characteristics while equalizing an input signal, and performing the waveform equalization on the input signal. A step of generating an equalized signal, a step of detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the equalized signal, and a target of a path metric difference of the detected equalized signal Performing the adaptation based on an error with respect to the value, and controlling the execution of the adaptation operation based on a path metric difference value of the equalized signal.

  In the above configuration and method, the tap coefficient is updated only when the path metric difference obtained from the equalized signal obtained by equalizing the waveform of the input signal is within a predetermined range. When the input signal temporarily becomes an abnormal value, the equalized signal also becomes an abnormal value, and the path metric difference obtained from the abnormal equalized signal is outside the predetermined range. Then, during that period, the updating of the tap coefficient is stopped, and the tap coefficient obtained from the immediately preceding normal input signal is held as it is, so that it is possible to prevent divergence. Furthermore, since only one circuit for calculating the path metric difference is required, the circuit scale can be reduced.

[Embodiment 3]
In the waveform equalization apparatus described in the first and second embodiments, the SAM value based on the input signal or the equalized signal is used as an evaluation value indicating the signal quality of the input signal or the equalized signal. The signal quality is evaluated by the above, and the updating of the tap coefficient in the tap coefficient updating circuit 9 may be controlled based on the evaluation result. As another evaluation method of signal quality, for example, a method in which an error with respect to a target value of a SAM value based on an input signal or an equalized signal, an update amount of a tap coefficient, or a change amount thereof is used as an evaluation value. Below, the case where the update amount of a tap coefficient is made into an evaluation value is demonstrated.

  FIG. 11 is a block diagram showing a configuration of an optical disc reproducing apparatus 22 to which the waveform equalization apparatus and the waveform equalization method of the present invention are applied. In FIG. 11, components having the same functions as those in the optical disc playback apparatus 20 '(see FIG. 9) of the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  The optical disc playback device 22 is different from the optical disc playback device 20 ′ in that the pre-equalization SAM value calculation circuit 10 is omitted in the optical disc playback device 22, and the pre-equalization SAM value determination circuit 11 is replaced with the same. The update update amount determination circuit 17 is provided.

  The equalization update amount determination circuit 17 receives the tap coefficient update amount μ {s (n) −ds} {u (−2−k, n) + 2u (−1−k, n) from the tap coefficient update circuit 9 ′. + U (−k, n)} is input, and the equalization update amount determination circuit 17 determines whether or not this value is within the allowable range, and outputs the result to the update pause circuit 16. Yes. Since the step gain μ is a constant, a value obtained by dividing both the value of the update amount and the allowable range by μ in advance may be used. In this case, the circuit configuration can be simplified.

  Here, the FIR filter 4 is equalization means, the tap coefficients of the FIR filter 4 are equalization coefficients (equalization characteristics), the Viterbi decoding circuit 5 is equalization path metric difference detection means, and the tap coefficient update circuit 9 'is equalization. The adaptation means, the equalization update amount determination circuit 17 corresponds to the equalization update amount evaluation means, and the update pause circuit 16 corresponds to the adaptation pause means. Further, in the optical disk reproducing device 22 of FIG. 11, the configuration excluding the optical disk 1, the optical pickup 2, and the A / D converter 3 corresponds to the waveform equalizer.

  The playback operation of the optical disk playback device 22 configured as described above will be described with reference to the block diagram of FIG.

  A reproduction waveform output from the optical pickup 2 by irradiating a light beam onto the optical disc 1 is converted into a reproduction signal sequence u (i, n) by the A / D converter 3 and is transmitted to the Viterbi decoding circuit 5 via the FIR filter 4. The path metric difference s (n) and the decoded bit string b (i) are output. Further, the specific pattern detection circuit 8 determines whether the decoded bit string b (i-4), b (i-3),..., B (i) matches any of the specific patterns. A specific pattern determination signal indicating a certain “match” / “mismatch” is transmitted to the tap coefficient update circuit 9 ′. The operation so far is the same as in the first embodiment.

  Tap coefficient update amount μ {s (n) −ds} {u (−2−k, n) + 2u (−1−k, n) + u (−k, n) output from the tap coefficient update circuit 9 ′ } Is input to the equalization update amount determination circuit 17. The equalization update amount determination circuit 17 determines whether or not the tap coefficient update amount is within an allowable range, and an equalization update amount determination indicating “within allowable range” / “outside of allowable range” as the determination result. The signal is transmitted to the update pause circuit 16. The permissible range needs to be set to an appropriate value as in the case of the first embodiment.

  The tap coefficient update circuit 9 ′ executes the calculation of the equation (1) described in the background art only when the specific pattern determination signal indicates “match” and the update stop signal is not input. When the tap coefficient c (k, n) is updated, but the equalization update amount determination signal indicates “out of allowable range”, that is, when the update amount of the tap coefficient is out of the allowable range, the update stop signal is Since it is input, the tap coefficient c (k, n) is not updated.

  Thereby, also in the optical disc reproducing apparatus 22, when the reproduction signal becomes an abnormal signal due to a defect of the disc or the like, the post-equalization SAM value s (n) corresponding to the signal quality of the post-equalization signal sequence also becomes an abnormal value. Since the update amount of the tap coefficient reflecting both these values is outside the allowable range, the tap coefficient c (k, n) is not updated and the previous value is held. Therefore, since the updating of the tap coefficient is stopped while the reproduction signal sequence is abnormal, the risk of divergence can be reduced or eliminated. If the reproduction signal eventually returns to normal, the update amount of the tap coefficient falls within the allowable range again, so that the update of the tap coefficient is resumed and the convergence proceeds toward the optimum value again.

  As described above, the optical disk reproducing apparatus 22 is configured to update the tap coefficient only when the tap coefficient update amount is within the allowable range, in addition to the effect of the first embodiment that prevents the tap coefficient from diverging. Thus, since only one circuit for calculating the path metric difference is required, the circuit scale can be reduced. Further, since updating and stopping of the tap coefficient are controlled based on the evaluation value reflecting both the reproduction signal and the equalized SAM value, there is an effect that more accurate control is possible.

[Embodiment 4]
In the waveform equalizer described in the first to third embodiments, the tap coefficient update is stopped only when the signal value reflecting the abnormality of the reproduction signal is out of the allowable range. When it is outside, it is good also as a structure which stops update of the following tap coefficient only predetermined times.

  For this purpose, as shown in FIG. 12, a retriggerable down counter 18 may be used in place of the update pause circuit 16. FIG. 12 is a block diagram showing a configuration of an optical disc playback apparatus 23 configured by applying the above modification to the optical disc playback apparatus 22 (see FIG. 11) of the third embodiment. Here, the description will be made on the assumption that the optical disk reproducing apparatus 22 of the third embodiment is used, but the same modification can be applied to the optical disk reproducing apparatus 20 'of the first embodiment and the optical disk reproducing apparatus 21' of the second embodiment.

  In the optical disc reproducing device 23, an equalized update amount determination signal indicating “within allowable range” / “outside allowable range”, which is a determination result by the equalized update amount determination circuit 17, is provided instead of the update pause circuit 16. Input to the retriggerable down counter 18.

  The retriggerable down counter 18 initializes the counter value to a predetermined value N when a signal indicating “out of allowable range” is input from the equalization update amount determination circuit 17. Then, it decrements from the predetermined value N at every channel clock timing, and outputs an update stop signal to the tap coefficient update circuit 9 until the counter value becomes zero. The retriggerable down counter 18 corresponds to an adaptive pause means.

  Here, “retriggerable” has a function of reinitializing the counter value to a predetermined value N when a new signal indicating “out of tolerance” is input before the counter value reaches 0. Means.

  Normally, even if an abnormal signal due to a defect is included in the input signal, the equalization update amount does not always become “outside the allowable range” throughout the period of the abnormal signal. It is. However, even if it is “within the allowable range” during the abnormal signal period, it only appears to be “within the allowable range”. When the update is stopped, if the signal quality of the abnormal signal is very poor, the tap coefficient may be updated in the wrong direction based on the update amount reflecting the abnormal signal. There is a risk that the tap coefficient will diverge as a result.

  On the other hand, by adopting the above-described configuration using the retriggerable down counter 18, even when a signal indicating “out of the allowable range” is intermittently input, N is set to a value larger than the interval. Is set, the stop of updating in the tap coefficient updating circuit 9 ′ is continued.

  This will be described with reference to FIGS. 13 (a) and 13 (b). As shown in FIG. 13 (a), when the update amount of the tap coefficient is “outside the allowable range” due to normal noise that is not a defect, down-counting is performed N times for each, Update will be suspended only during that period. On the other hand, as shown in FIG. 13B, when an “out of tolerance” signal is intermittently generated due to a defect, re-triggering is repeated during the defect period, and the count value is reinitialized to N each time. Therefore, the update stop signal is continued, and the update is restarted after N updates are stopped from the last “out of tolerance” signal.

  FIGS. 14A to 14C are graphs showing the results of confirming the tap coefficient divergence prevention effect according to the present embodiment by experiments. As shown in FIG. 10 (a), when a signal including a period in which the amplitude is abnormal due to a defect is input, the tap coefficient update amount is changed during the abnormal period as shown in FIG. 10 (b). The range of variation increases.

  Therefore, if the allowable range is set to ± 0.00667, as shown in FIG. 10 (c), when N = 200, the tap coefficient (here, the central tap coefficient c ( In the graph of (1, n) only), updating is stopped during the defect period, and when the defect period is over, the update is resumed and the convergence is resumed.

  On the other hand, when N = 1 (corresponding to a configuration in which updating of the tap coefficient is stopped only when the update amount is “outside the allowable range”), it appears to be “within the allowable range” at the defect location. However, since the tap coefficient is actually updated based on the update amount reflecting the abnormal signal, it can be seen that the tap coefficient has diverged (converged in an abnormal direction).

  In addition, the update amount may be “outside the allowable range” due to noise even at a non-defect location, and at N = 200, the update is stopped during the period of 199 times when a normal signal is input. However, since updating of the tap coefficient is performed minutely, stopping updating about 200 times hardly affects the convergence performance. This can be confirmed by comparing the convergence state before the defect with N = 1.

  In this way, when the coefficient update amount is out of the allowable range, a signal indicating “out of the allowable range” is intermittently input by stopping the update of the subsequent tap coefficient by a predetermined number of times. However, since the updating of the tap coefficient is continued during the period of abnormal input, it is possible to more reliably prevent the tap coefficient from diverging.

  14 (a) to 14 (c) show the results under conditions in which tap coefficient divergence is very likely to occur. Therefore, the divergence prevention effect in the case of N = 1 should be denied with this result. Absent. That is, when N = 1, the divergence prevention effect may not be sufficient under conditions where divergence is very likely to occur. However, even when N = 1, FIG. ) As explained based on (b), it has a divergence prevention effect in comparison with the prior art.

  In the waveform equalization apparatus described in the first to fourth embodiments, the case where the tap coefficient immediately before the tap coefficient is maintained after the update of the tap coefficient has been described has been described. A configuration may be adopted in which a predetermined tap coefficient stored, a tap coefficient recorded in advance on a disc, or the like is reset as an initial value. Thereby, when an abnormality of the input signal occurs rapidly, the pre-equalization SAM value calculation circuit 10, the pre-equalization SAM value determination circuit 11, the post-equalization SAM value determination circuit 12, or the equalization update amount determination circuit 17 Even if an abnormal tap coefficient is retained due to a delay in the coefficient update due to the time lag due to the processing time, the tap coefficient is reset to the initial value, so there is a risk of being played back with an abnormal tap coefficient. It becomes possible to prevent.

  In the waveform equalizers described in the first to fourth embodiments, the configuration for stopping the updating operation of the tap coefficient when the evaluation value is out of the allowable range has been described. However, the effect of preventing the divergence can be obtained. All that is necessary is not limited to this. For example, instead of stopping the update operation, the step gain is reduced or the update frequency is reduced (the tap coefficient is not updated every time a specific pattern is detected, but is updated only once at a plurality of times). Also good. As a result, the responsiveness of the update can be delayed, so that the effect of preventing divergence can be obtained similarly.

  In addition, each block of the waveform equalizer described in the first to fourth embodiments may be configured by hardware logic, or may be realized by software using a computer as follows. That is, the waveform equalizer (the optical disc 1, the optical pickup 2, and the A / D conversion among the optical disc reproducing devices 20, 21, 20 ′, 21 ′, 22, 23 of FIGS. 1, 6, and 9 to 12) The apparatus excluding the device 3) develops a central processing unit (CPU) that executes instructions of a waveform equalization program that implements each function of the apparatus, a read only memory (ROM) that stores the program, and the program. It can also be realized by a computer having a RAM (random access memory), a storage device (recording medium) such as a memory for storing the program and various data. That is, an object of the present invention is to provide a computer with a recording medium in which a program code (execution format program, intermediate code program, source program) of a waveform equalization program, which is software that realizes the functions described above, is recorded in a computer-readable manner. This can also be achieved by supplying and executing the program code recorded in the recording medium by the computer.

  Thus, in this specification, the means does not necessarily mean physical means, but includes cases where the functions of the means are realized by software. Further, the function of one means may be realized by two or more physical means, or the functions of two or more means may be realized by one physical means.

  In each of the above embodiments, the ideal value of the path metric difference is obtained because the ideal sample level is normalized to ± 1 in the reproduction system combining the PR (1, 2, 1) characteristic and the (1, 7) RLL code. For example, in the first embodiment, an example in which the allowable range is 0 to 3.0 is given based on this, but the gist of the present invention is that it does not depend on the PR characteristics or the encoding method. Of course, it goes without saying that the allowable range should be set to an appropriate value accordingly.

  In any of the above-described embodiments, the optical disc reproducing apparatus has been described as an example of the information reproducing apparatus. However, the present invention is not limited to this, and the same effect can be achieved in an apparatus that performs PRML signal reproduction. That is, the present invention can be applied not only to a magnetic recording / reproducing apparatus such as a hard disk apparatus or a magnetic tape apparatus as another information reproducing apparatus but also to a communication apparatus such as a communication data receiving apparatus.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Of course, it is included in the technical scope of the present invention.

  According to the waveform equalization apparatus, the waveform equalization method, and the waveform equalization program of the present invention, waveform equalization can be appropriately performed. Therefore, the signal reproduction apparatus such as an optical disk reproduction apparatus that reproduces a PRML system signal or a communication apparatus can be used. Applicable.

1 is a block diagram showing a configuration of an optical disk reproducing device according to a first embodiment of the present invention. 3 is a flowchart showing a playback operation of the optical disk playback device in FIG. 1. FIG. 2 is a block diagram showing a configuration example of a pre-equalization SAM value calculation circuit in the optical disc playback apparatus of FIG. (A) is a histogram of the path metric difference of the ideal waveform, and (b) is a histogram of the path metric difference of the actual reproduction signal. (A) is a graph which shows the result which confirmed the divergence prevention effect of the tap coefficient by the optical disk reproducing apparatus of FIG. 1 by experiment, (b) is the result of having conducted the same experiment by the conventional optical disk reproducing apparatus as a comparative example. It is a graph to show. It is a block diagram which shows the structure of the optical disk reproducing | regenerating apparatus in the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the conventional optical disk reproducing | regenerating apparatus. It is a figure for demonstrating the correspondence of decoding bit string "00111", a recording mark, a reproduction | regeneration waveform, and its sample level. It is a block diagram which shows the modification of the optical disk reproducing | regenerating apparatus of FIG. It is a block diagram which shows the modification of the optical disk reproducing | regenerating apparatus of FIG. It is a block diagram which shows the structure of the optical disk reproducing | regenerating apparatus in the 3rd Embodiment of this invention. It is a block diagram which shows the structure of the optical disk reproducing | regenerating apparatus in the 4th Embodiment of this invention. (A) And (b) is a timing chart which shows operation | movement of the optical disk reproducing | regenerating apparatus of FIG. (A) is a graph showing the signal level input to the optical disc playback apparatus of FIG. 12, (b) is a graph showing the tap coefficient update amount in the optical disc playback apparatus of FIG. 12, and (c) is a graph of FIG. It is a graph which shows the change of the tap coefficient in an optical disk reproducing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk 2 Optical pick-up 3 A / D converter 4 FIR filter (equalization means)
5 Viterbi decoding circuit (path metric difference detection means after equalization)
6 delay adjustment circuit 7 delay adjustment circuit 8 specific pattern detection circuit 9 tap coefficient update circuit (equalization adaptation means)
10 Pre-equalization SAM value calculation circuit (pre-equalization path metric difference detection means)
11 Pre-equalization SAM value determination circuit (signal quality evaluation means)
12 SAM value determination circuit after equalization (signal quality evaluation means)
13 Multiplier (Double multiplier)
14 adder 15 delay element 16 update pause circuit (adaptive pause means)
17 Equalization update amount judgment circuit (equalization update amount evaluation means)
18 Retriggerable down counter (Adaptive temporary stop means)
20 Optical disc playback device 20 ′ Optical disc playback device 21 Optical disc playback device 21 ′ Optical disc playback device 22 Optical disc playback device 23 Optical disc playback device

Claims (19)

In the waveform equalization device that adapts the equalization characteristics while equalizing the waveform of the input signal,
Equalization means for generating a post-equalization signal by performing waveform equalization on the input signal;
An equalized path metric difference detecting means for detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the equalized signal;
Equalization adaptation means for performing the adaptation based on an error with respect to a target value of a path metric difference of the detected post-equalization signal;
Signal quality evaluation means for evaluating the signal quality of the input signal or the equalized signal,
The waveform equalization apparatus, wherein the equalization adaptation unit controls the adaptation process based on an evaluation result by the signal quality evaluation unit. Further comprising pre-equalization path metric difference detecting means for detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the input signal,
2. The waveform equalization according to claim 1, wherein the signal quality evaluation unit evaluates signal quality based on a path metric difference value of the input signal detected by the pre-equalization path metric difference detection unit. apparatus. The signal quality evaluation means determines whether the value of the path metric difference of the input signal is within an allowable range;
The equalization adaptation unit temporarily stops the adaptation process when the signal quality evaluation unit determines that the value of the path metric difference of the input signal is outside the allowable range. The waveform equalization apparatus according to claim 2.   An adaptation pause means for temporarily stopping the adaptation process in the equalization adaptation means when the signal quality evaluation means determines that the value of the path metric difference of the input signal is outside the allowable range. The waveform equalizer according to claim 3.   The pre-equalization path metric difference detecting means executes an arithmetic expression of a path metric difference set in advance corresponding to a specific partial response characteristic and a specific decoding pattern of an input signal. Item 5. The waveform equalization apparatus according to any one of Items 2 to 4.   2. The signal quality evaluation unit according to claim 1, wherein the signal quality evaluation unit evaluates signal quality based on a value of a path metric difference of the equalized signal detected by the equalized path metric difference detection unit. Waveform equalizer. The signal quality evaluation means determines whether a value of a path metric difference of the equalized signal is within an allowable range;
The equalization adaptation unit temporarily stops the adaptation process when the signal quality evaluation unit determines that the value of the path metric difference of the equalized signal is out of an allowable range. The waveform equalizer according to claim 6.   An adaptation pause means for temporarily stopping the adaptation process in the equalization adaptation means when the signal quality evaluation means determines that the value of the path metric difference of the equalized signal is outside the allowable range The waveform equalization apparatus according to claim 7, comprising: In the waveform equalization device that adapts the equalization characteristics while equalizing the waveform of the input signal,
Equalization means for generating a post-equalization signal by performing waveform equalization on the input signal;
An equalized path metric difference detecting means for detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the equalized signal;
Equalization adaptation means for performing the adaptation by updating the equalization characteristic based on an error with respect to a target value of a path metric difference of the detected post-equalization signal;
Equalization update amount evaluation means for evaluating the update amount of the equalization characteristic,
The waveform equalization apparatus, wherein the equalization adaptation unit controls the adaptation process based on an evaluation result by the equalization update amount evaluation unit. The equalization update amount evaluation means determines whether the update amount of the equalization characteristic is within an allowable range,
The equalization adaptation unit temporarily stops the adaptation process when the equalization update amount evaluation unit determines that the update amount of the equalization characteristic is out of an allowable range. The waveform equalization apparatus according to claim 9.   An adaptive pause means for temporarily stopping the adaptation process in the equalization adaptation means when the equalization update quantity evaluation means determines that the update amount of the equalization characteristic is out of an allowable range; The waveform equalization apparatus according to claim 10.   The waveform equalization apparatus according to any one of claims 4, 8, and 11, wherein the adaptation pause means stops the adaptation process a plurality of times. The equalization means associates each equalization coefficient with each equalization coefficient while sequentially associating a plurality of equalization coefficients with a digital input signal sequence obtained by A / D converting the input signal. A digital filter that generates an equalized signal sequence by performing a convolution operation with each digital input signal sequence,
The equalization adapting means updates the equalization coefficients with a minute width so that a function representing the mean square value of the error created using the respective equalization coefficients as a variable approaches a minimum value. The waveform equalization apparatus according to claim 1, wherein the waveform equalization apparatus performs adaptation.   A waveform equalization program for operating the waveform equalization apparatus according to any one of claims 1 to 13, wherein the waveform equalization program causes a computer to function as each of the means.   A computer-readable recording medium on which the waveform equalization program according to claim 14 is recorded. In the waveform equalization method that adapts the equalization characteristics while equalizing the waveform of the input signal,
An equalization step of generating a post-equalization signal by performing waveform equalization on the input signal;
A post-equalization path metric difference detection step of detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the post-equalization signal;
An equalization adaptation step for performing the adaptation based on an error with respect to a target value of a path metric difference of the detected post-equalization signal;
An input signal evaluation step for evaluating the signal quality of the input signal,
In the equalization adaptation step, the adaptation process is controlled based on the evaluation result in the input signal evaluation step. A pre-equalization path metric difference detecting step of detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the input signal;
The waveform equalization according to claim 16, wherein in the input signal evaluation step, signal quality is evaluated based on a path metric difference value of the input signal detected in the pre-equalization path metric difference detection step. Method.   The signal quality is evaluated based on a path metric difference value of the post-equalization signal metric detected in the post-equalization path metric difference detection step in the input signal evaluation step. Waveform equalization method. In the waveform equalization method that adapts the equalization characteristics while equalizing the waveform of the input signal,
An equalization step of generating a post-equalization signal by performing waveform equalization on the input signal;
A post-equalization path metric difference detection step of detecting a path metric difference between a correct path and an error path in a Viterbi decoding process for the post-equalization signal;
An equalization adaptation step for performing the adaptation by updating the equalization characteristic based on an error with respect to a target value of a path metric difference of the detected post-equalization signal;
An equalization update amount evaluation step for evaluating an update amount of the equalization characteristic,
In the equalization adaptation step, the adaptation processing is controlled based on the evaluation result in the equalization update amount evaluation step.

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