JP2000276849A - Equalizing device and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waveform equalizing device, with which a high frequency is not emphasized even when the number of taps is increased, concerning the waveform equalizing device using a transversal filter. SOLUTION: Concerning an equalizer 11 using the transversal filter serially connecting (n-1) pieces of delay elements DE, when there are 11 pieces of central sampling taps(ST) (n) among (n) pieces of ST located before and after the delay elements DE, for example, ST 5 and 7 located symmetric to the center are not connected to an output part 19 except ST 6. Thus, the high frequency is not emphasized, the sampling taps can be increased and the output signal of a little equalization error can be outputted. Therefore, the reproducing device having a high decoding ability can be provided by performing tolerant (viterbi) decoding to the output signal of a waveform equalized by using the equalizing device.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a waveform equalizer used for reproducing digital data recorded on a recording medium such as an optical disk, and a reproducing apparatus using the same.

2. Description of the Related Art As an optical recording medium for recording digital data, a compact disk (CD) and a mini disk (M
D), and 130 mm and 90 mm optical disk cartridges and the like according to the standards of the International Organization for Standardization (ISO) have been commercialized. In recent years, DVD-standard optical discs having a recording capacity about seven times as large as CDs have appeared, and are attracting attention as recording media for moving image data whose data amount will increase in the future. Conventionally, in a CD or the like, if the read analog signal is larger than a predetermined level, "1";
Although a bit-by-bit decoding method in which the value is determined to be "0" if the value is small is adopted, it is difficult to reproduce digital data with high reliability on a recording medium having a greatly improved recording density according to the DVD standard. For this reason, recently, as a method of reproducing digital data, a partial response method (P
RML or PR) and the maximum likelihood decoding method (ML method or ML) using the Viterbi decoding method.
The method is receiving attention. FIG. 5 is a block diagram showing a general configuration of the disk device 1 using the PRML method. The processing in the optical disk device 1 is performed along the arrows in the block diagram, and the disk data recorded on the optical disk medium 2 is read and reproduced. First, the optical pickup 3 irradiates the optical disc medium 2 with laser light to read digital data recorded on the optical disc medium 2 as an analog signal, and the reproduced signal φ1 is amplified by the preamplifier circuit 4. The amplified analog signal is shaped by a waveform shaping circuit 5 having a function of a low frequency pass filter (LPF) and an equalizer (EQ) for shaping the waveform, and then analog / digital (A / D).
D) The signal is converted into a digital signal by the converter 6. The digitized reproduction signal is further equalized by an equalization circuit 11 into a waveform of a preset partial response characteristic (PR characteristic). In this way, the output signal φs is obtained by the PR equalization processing, which is Viterbi-decoded by the maximum likelihood decoding circuit 20, and the digital data recorded on the optical disk medium 2 is reproduced. In the PRML optical disk device 1, the transfer characteristic of the signal reproduction system 10 is a predetermined PR characteristic, for example, PR (1), until the reproduction signal is read from the optical disk medium 2 and supplied to the maximum likelihood decoding circuit 20.
221) The maximum likelihood decoding circuit 20 is assumed to have characteristics.
Performs Viterbi decoding. Therefore, the equalizer 11
Is adjusted so as to output an output signal φs whose waveform is shaped into a predetermined PR characteristic, for example, a PR (1221) characteristic. FIG. 6 shows an example of the waveform equalizer 11. The waveform equalizer 11 includes an equalizing filter, a transversal filter,
Alternatively, also called a FIR (Finite Impulse Response) filter, a plurality of delay elements 15 connected in series,
A sampling tap 16 for outputting values before and after these delay elements 15, and a weight coefficient (tap coefficient) C according to an equalization method based on the value obtained by the sampling tap 16.
, And outputs an output signal φs. The output unit 19 generally includes a multiplier 17 corresponding to each sampling tap 16 and an adder 18 that adds the multiplication results of the multipliers 17 and outputs a sample value. The delay time of the delay element 15 is set to the delay time of the bit period of the reproduced signal φ1, that is, the delay time D for one bit. In order to obtain n samplings, n-1 delay elements 15 are used. Connected in series.

As shown in FIG. 7, the 8/16 optical disk used in the DVD standard optical disk is used.
Code and bit error rate (B
According to the evaluation of ER), the PR (1221) method has the smallest error rate. Also, it can be seen that the PR (1221) method becomes more advantageous as the S / N ratio increases. This is based on the MTF (Modulation Transfer Function) which is the frequency characteristic of the optical system of the DVD standard.
This is probably because the frequency characteristics of the (1221) method are similar. Therefore, it is desirable to employ the PR (1221) method in the reproducing apparatus of the optical disk apparatus that handles the DVD standard optical disk, and the waveform equalizer 11 can obtain the output signal φs according to the PR (1221) characteristic. And the tap coefficient C is determined.
(1221) It is important to minimize the equalization error from the characteristics. In general, it is known that the number of taps 16 should be increased in order to reduce the equalization error of the equalizer 11. However, when the number of taps 16 is increased, high-frequency noise is emphasized, and as a result, the equalization error does not decrease. In FIG. 8, the number of taps is one.
A Gaussian waveform (4T waveform, T is 1
PR (1221)
The state of waveform shaping is shown in the characteristics. PR (122
1) In the characteristic, a response of “01356310” is obtained by the 4T digital signal “011110”, and it can be seen from the equalized waveform that the detected point has a value corresponding to those predicted values. Therefore, an output signal with almost no equalization error is obtained. When a Gaussian waveform (4T waveform) on which noise of a sine wave having a frequency of 1 / 2T and an amplitude of 0.03 is input is input to this equalizer, the noise component is emphasized as shown in FIG. Otherwise, the equalization error becomes very large. Furthermore, originally, the predicted value 0
A noise component reaching the predicted value of about 3 also appears in a region stabilized at the level of. Therefore, if the detection timing is slightly deviated due to clock deviation, etc.,
Since the error of the output signal φs is very large, data corresponding to the predicted value may be detected as appearing,
This leads to decoding errors. As described above, in the equalizer, even if the number of taps is increased, the high frequency band is emphasized and the equalization error is not improved.Therefore, an equalizer having a small number of taps that is advantageous in terms of the circuit configuration scale and power consumption is used. Has been adopted. Therefore, Viterbi decoding is performed on the output signal containing an appropriate equalization error. Therefore, in the present invention, by increasing the number of taps, the equalization error is reduced, the noise is prevented from being enlarged by emphasizing the high frequency range, and the equalization error is reduced throughout after the waveform is equalized. It is an object of the present invention to provide an equalizer capable of supplying an output signal. The PR (122) is supplied by supplying a signal having a small equalization error over the entire area, not limited to the planned detection points.
It is another object of the present invention to provide a reproducing apparatus having a high decoding ability based on a signal having a predetermined PR characteristic such as 1).

For this reason, in the present invention, a high frequency range is prevented from being emphasized by removing a sampling tap at a predetermined position of the equalizer, and noise is reduced even if the number of taps is increased. The present invention provides an equalizer that is not emphasized and has less equalization error than ever before. That is, in the waveform equalizer of the present invention for waveform-equalizing and outputting a reproduced signal obtained from a recording medium on which digital data is recorded, an integer n sampling taps for sampling the reproduced signal in time series And n-1 delay elements for connecting each sampling tap, and an output for multiplying each of the sample values obtained by these sampling taps by a predetermined tap coefficient and then adding the resultant to output a waveform-equalized output signal And at least one set of symmetrical positions except for a central sampling tap when n is an odd number and a central pair of sampling taps when n is an even number. The tap is not connected to the output unit. By not allowing the sampling tap at an appropriate position to contribute to the output signal, it is possible to suppress the high-frequency fluctuation of the output signal caused by reflecting the component of the sampling tap. In particular, taps on both sides of the center sampling tap, that is, sampling taps on both sides of the center sampling tap when n is odd, and sampling taps on both sides of the center pair of sampling taps when n is even. The component has a high possibility that high-frequency noise is emphasized by reflecting it in the output signal. Therefore, it is effective not to connect the sampling tap at this position to the output unit. Of course, it is also affected by a transfer function of an amplifier or the like that supplies a reproduction signal to the waveform equalizer, and it is not always effective to not use the sampling taps on both sides at the center. However, the central sampling tap,
That is, when n is odd, the value of the center sampling tap is important, and when n is even, the value of the center pair of sampling taps is important for waveform equalization, and these sampling taps are connected to the output unit. I do. In addition, if the sampling taps at the asymmetric positions are not connected to the output unit, the function as a low-pass filter cannot be realized. Therefore, it is necessary to eliminate the contribution of the sampling taps at the symmetric positions. Further, even if the number of taps is increased by the equalizer of the present invention, the effect of noise is small, and an output signal with a small equalization error over the entire area can be obtained. For this reason, it is possible to provide a reproducing apparatus having a high decoding capability by a reproducing apparatus having maximum likelihood decoding means for performing maximum likelihood decoding on an output signal output from the equalizer using a plurality of prediction values and reproducing digital data. Can be.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of an equalizer 11 according to the embodiment of the present invention. This equalizer 11
Constitutes the optical disk device 1 described above with reference to FIG. 5, and a detailed description of the optical disk device 1 will be omitted below. The equalizer 11 of this example includes n (integer) -1 delay elements DE (i) (i = 1) connected in series.
To n-1) and n sampling taps ST (j) (j) for outputting values before and after these delay elements DE (i).
= 1 to n) and their sampling taps S
An output unit 19 is provided which multiplies the value obtained at T (j) by a weighting coefficient (tap coefficient) C (j) according to the equalization method, adds the result, and outputs an output signal φs. The output unit 19 generally includes a multiplier 17 corresponding to each sampling tap ST (j), and an adder 18 that adds the multiplication results of the multipliers 17 and outputs a sample value. . FIG.
Is an example where n is 11, and the multiplier 17 is not connected to the sampling taps ST (5) and ST (7) on both sides of the central sampling tap ST (6). , Are not connected to the adder 18. Therefore, the sampling tap ST is output from the output unit 19.
An output signal φs to which the values of (5) and ST (7) do not contribute is output. Therefore, the tap coefficient C (j) applied to the sampling tap ST connected to the output unit 19 is calculated excluding the sampling taps ST (5) and ST (7). FIG. 2 shows that the waveform equalizer 11 of this example has a Gaussian Ann waveform (4T
Output signal (equalized waveform) when the waveform and original waveform are input
φs is shown. As can be seen from the figure, even if sampling taps ST (5) and ST (7) are removed, PR
(1221) An output signal φs having almost no equalization error with respect to characteristics can be obtained. That is, the tap coefficient Cj can be determined so that there is no equalization error. Further, FIG. 3 shows that the waveform equalizer 11 of the present example in which the tap coefficient Cj is determined in this manner is provided with the same frequency 1 / 2T as in FIG.
5 shows an output signal (equalized waveform) φs when a Gaussian waveform (4T waveform) on which noise of a SIN wave having an amplitude of 0.03 is superimposed is input as an original waveform. As can be seen from this figure, there is almost no emphasis on the high frequency range, and even at positions other than the detection points, an output signal with little deviation from the output signal shown in FIG. Can be
In particular, even in the region of the bottom 0 level, some vibration appears, but the level is sufficiently smaller than 1. Therefore, even if the detection timing is shifted for some reason, it is not recognized as a significant value, and a decoding error can be prevented. As can be seen from the comparison between the output signal shown in FIG. 3 and the output signal shown in FIG.
By not connecting (5) and ST (7) to the adder 18, it is possible to prevent high-frequency noise from being emphasized despite the large number of taps of 11. As a result, by increasing the number of taps, the reproduction signal φ1 can be equalized in waveform to an output signal φs having a small equalization error with respect to a predetermined PR characteristic and supplied to the maximum likelihood decoding circuit 20. Further, since the high frequency range is not emphasized, the fluctuation width of the output signal φs is small even at positions other than the detection point. Therefore, the maximum likelihood decoding circuit 20 accurately evaluates the waveform-shaped output signal φs with respect to a predicted value, for example, six values (0, 1, 3, 5, 6) in PR (1221). It is possible to do. For this reason, by employing the equalizer 11 of the present example, it is possible to provide a reproducing apparatus with few decoding errors, high decoding speed, and high decoding capability. In particular, as described above, by employing the PR (1221) method, it is possible to extremely reduce the error rate in an optical disc device or the like, and to provide a reproducing device that is resistant to noise and has a high reproducing capability. Can be provided. The equalizer 11
Of course, the number of sampling taps is not limited to an odd number. In the equalizer 11 shown in FIG.
And the sampling taps ST on both sides of the center sampling taps ST (6) and ST (7).
The multiplier 17 is not connected to (5) and ST (8), and is not connected to the adder 18. Therefore,
The output unit 19 outputs an output signal φs to which the values of the sampling taps ST (5) and ST (8) do not contribute. Therefore, the tap coefficient C applied to the sampling tap ST connected to the output unit 19
(J) shows sampling taps ST (5) and ST
It is calculated excluding (8). As described above, when the number of sampling taps is an even number, the sampling taps at symmetrical positions on both sides thereof are not connected to the output unit 19 except for the sampling tap of the center pair, so that high-frequency noise Can be suppressed. Of course, the phenomenon in which high-frequency noise is emphasized can be suppressed by not connecting sampling taps to the output unit 19 at symmetrical positions outside the sampling taps, not limited to sampling taps on both sides of the center sampling tap. However, unless the sampling taps at positions symmetric with respect to the center sampling tap (a pair of sampling taps at the center in the case of an even number) are not connected, the coefficients (tap coefficients) of the sampling taps will not be even symmetric. An equalizer (transversal filter) having a function as an LPF filter cannot be realized. Further, in this specification, as shown in FIG. 5, the reproduced signal is A / D converted and the waveform is equalized by the equalizer. However, the A / D conversion may be performed after the waveform equalization. good. Further, in the above description, an example is shown in which the number of sampling taps is 11 and 12, but it is needless to say that the number of sampling taps is not limited to this. Further, in this example, the equalization method is PR (122
Although the reproduction apparatus of 1) is described as an example, the present invention can be applied to other equalization schemes. And
It is possible to provide a reproducing apparatus having a high decoding capability with an output signal having a small equalization error while suppressing high-frequency noise. However, as described above, it has been found from the experimental results of the inventors of the present application that this equalization method is suitable for an optical disk, particularly an optical disk according to the DVD standard.

As described above, in the present invention, n
In an equalizer using a transversal filter in which a delay element of -1 is connected in series, of n sampling taps located before and after the delay element, a position symmetrical with respect to the center except for a center sampling tap. Are not made to contribute to the output signal output from the equalizer. Then, it is possible to output an output signal with a small equalization error without using a sampling tap located at a symmetrical position, and to prevent noise from being emphasized even when noise is present.
Therefore, even if the number of sampling taps is increased, the high frequency range is not emphasized, and an output signal with a small equalization error for a predetermined PR characteristic can be obtained. Therefore, by performing maximum likelihood decoding (Viterbi decoding) on the output signal waveform-equalized using the equalizer of the present invention, the DVD or M
In a signal reproducing apparatus such as an optical drive such as an OD or a magnetic disk drive such as an HDD or a ZIP, a reproducing apparatus having a high decoding capability can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an equalizer according to an embodiment of the present invention.

FIG. 2 is a graph showing a waveform obtained when a Gaussian Ann waveform is input as an original waveform into the equalizer shown in FIG.

FIG. 3 is a graph showing a waveform obtained when a Gaussian waveform with noise is input as an original waveform to the equalizer shown in FIG. 1;

FIG. 4 is a block diagram showing an equalizer according to another embodiment of the present invention.

FIG. 5 is a block diagram illustrating a general configuration of a PRML-type playback device.

FIG. 6 is a block diagram showing a configuration of a conventional equalizer.

FIG. 7 is a graph showing an error rate when 8/16 modulation data is reproduced by various PRML systems.

8 is a graph showing a waveform obtained when a Gaussian Ann waveform is input as an original waveform into the equalizer shown in FIG. 6;

9 is a graph showing a waveform obtained when a Gaussian waveform with noise is input as an original waveform to the equalizer shown in FIG. 6;

[Explanation of symbols]

 Reference Signs List 1 optical disk apparatus 2 optical disk 3 optical pickup 4 preamplifier 5 waveform shaping circuit 6 A / D conversion circuit 10 system showing PR equalization characteristics 11 equalizer 20 maximum likelihood decoding circuit 16, ST sampling tap 15, DE delay element 17 multiplier 18 Adder 19 Output section

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D044 BC06 CC04 FG01 GL32 5D090 AA01 BB04 CC04 DD03 EE13 FF41 5K046 AA01 EE06 EE51 EF17 EF46

Claims (3)

[Claims] 1. A waveform equalizer for waveform-equalizing a reproduced signal obtained from a recording medium and outputting the equalized signal, comprising: an integer n sampling taps for sampling the reproduced signal in time series; It has n-1 delay elements connected in series, and an output unit for multiplying each of the sample values obtained by these sampling taps by a predetermined tap coefficient and then adding and outputting a waveform-equalized output signal. And, among the sampling taps, at least one set of sampling taps at symmetric positions except for a central sampling tap when the n is odd and a pair of central sampling taps when the n is even Is not connected to the output unit. 2. The sampling tap according to claim 1, wherein when n is an odd number, sampling taps on both sides of a central sampling tap are provided, and when n is an even number, sampling taps on both sides of a central pair of sampling taps are provided. An equalizer that is not connected to the output unit. 3. An equalizer according to claim 1, further comprising: a maximum likelihood decoding unit that performs maximum likelihood decoding on an output signal output from the equalizer using a plurality of prediction values and reproduces digital data. Playback device.