JPH05334681A - Adaptive filter control method - Google Patents

Abstract

PURPOSE:To reduce a decision error by eliminating an output signal from a reference signal used in coefficient control. CONSTITUTION:A delay element 13 between a subtractor 9 and a switch 11 is provided to generate delay for unit time for an error signal selection circuit 10. Accordingly, the delay quantity of a filter input signal inputted to a correlator 12 can be increased by that time. The switch 11 on the feedback route of an error signal is closed only when both the output of the circuit 10 and that of a synchronizing signal detection circuit 19 become active. The coefficient control is performed only by the error signal which satisfies a condition in a training signal period and also provided at the circuit 10. This method is effective when the waveform distortion of an input signal is large, and the decision error obtained from a reproducing signal is large. The coefficient control is performed only by a training signal. Thereby, it is possible to take out satisfactory equivalent output with low decision error even when large amount of nonlinear distortion exists in an optical disk reproducing waveform inputted to an adaptive filter and to reduce the decision error.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to characteristic control of an adaptive filter for removing an interference component from a reproduction signal of an optical disc in which intersymbol interference has occurred.

[0002]

2. Description of the Related Art In an optical disc, an equalizer is provided in a reproducing circuit to compensate for intersymbol interference in a recording sequence in order to remove a waveform distortion generated in a signal passing through a recording / reproducing system. When the transfer characteristic in the recording / reproducing system changes or when the transfer characteristic cannot be specified, a method of adaptive equalization is adopted in which the waveform distortion is estimated from the reproduced signal to determine the characteristic of the equalizer. ..

By setting the response characteristic of the equalizer so that the reproduced signal obtained as an output has an appropriate partial response equalization characteristic, a low error rate can be realized even when high density recording is performed. Partial response equalization is a method of appropriately controlling the intersymbol interference amount in a signal to limit the frequency band of the signal instead of making a pseudo multi-valued determination. In reproduction signal equalization, for example, it is used for the purpose of suppressing enhancement of high frequency components and preventing an error rate from increasing due to noise. For example, when PR (1,1) equalization in the partial response equalization method is used, the required bandwidth of the signal is reduced to about half by quasi-equalizing the binary signal as a ternary signal. be able to.

FIG. 4 shows the configuration of an adaptive filter used conventionally. The signal before equalization is input from the input terminal 1. The input signal is subjected to waveform distortion removal by the transversal filter 2 including the delay element 3, the multiplier 4 and the adder 5, and is output from the output terminal 6. This output signal is fed back to extract the error signal used for updating the tap gain.

When the tap coefficient is not set to the optimum value, a signal with waveform distortion remains is output from the output terminal. When performing ternary equalization by the PR (1,1) method, the ternary decision circuit 7 causes the signal R with the waveform distortion remaining.
Is determined, and the reference level generation circuit 8 outputs the ternary signal D having the reference amplitude. The tap gain coefficient is changed so as to minimize the power of the error signal E obtained by the difference between the output signal R of the transversal filter and the output signal D of the reference level generating circuit 8. Therefore, after the tap coefficient converges to an appropriate value, the filter output signal takes the three values given as the output of the reference level generating circuit.

The error signal is sent to the correlator 12 together with the input signal of the filter, which is delayed by an appropriate time, and the correlator outputs the correlation strength of both. The output signal of the correlator is the integrator 13
Is integrated by and given to the multiplier of each tap as a tap gain coefficient.

In the above example, only the reproduced signal having the waveform distortion is used to judge the data and output the error signal. Therefore, if the distortion is large, an error occurs in the output of the judgment device itself. Correct output cannot be obtained. In order to avoid this, in many cases, the training signal having a predetermined pattern is added to the input signal following the synchronization signal. The tap gain coefficient is modified so that the reproduction signal obtained subsequent to the synchronization signal matches the pattern of the training signal. FIG. 5 shows an example of a circuit that updates coefficients using a training signal.

Transversal filter 2 and correlator 12
The configuration of the integrator 13 is the same as that of the example of FIG. The synchronization signal detection circuit 19 monitors the output R of the transversal filter and determines whether the same training pattern as that included in the reproduction signal is generated for a certain period of time from the time when the synchronization signal that precedes the training signal is detected. Prompt the generation circuit 20. The reference level generation circuit 8 converts the training signal into a ternary signal D and outputs the ternary signal D, and the subtractor 9 outputs E1 as the difference between the transversal filter output signals R and D. At the same time, while the training signal is being output, the switch 11 is closed by the signal from the synchronization signal detection circuit, and the reference error signal E2 is output to the correlator 11. On the other hand, the switch is opened while a signal other than the training signal is being input, and the coefficient update is prohibited by setting the error signal input E2 of the correlator to 0.

Originally, the equalization by the transversal filter aims at removing linear distortion. Therefore, the waveform distortion composed of only linear distortion is effectively removed from the reproduced signal. However, in the case of an optical disc in which thermal recording is performed using a light beam, for example, when recording pits are continuously formed, overlap between the pits occurs as shown by the diagonal lines in FIG. Therefore, the reproduced signal does not have a waveform like the broken line 24 obtained by superposing the reproduced signals 22 by a single pit, but has a reproduced amplitude like the solid line 23. The non-linear distortion component that appears here is left in the output signal because it cannot be removed by the transversal filter,
This will cause the error rate to deteriorate.

The non-linear component contained in the reproduced signal is shown in FIG.
In addition to the component due to the overlapping of pits shown in (1), a component that appears because the size of the leading edge and the trailing edge of the recording pit changes due to the heat flow on the recording medium is also known. However, this non-linear component can be removed by recording power control as disclosed in Japanese Patent Application No. 1-322340.

[0011]

In optical recording and magneto-optical recording, since information is stored by changing the shape of the recording medium and the direction of magnetization, nonlinearity in the input / output characteristics increases as the recording density increases. Appears.

On the other hand, the transversal filter circuit for equalizing the reproduced signal is constituted only by linear operations such as delay of the reproduced signal, multiplication of coefficients, and addition. Therefore, when the signal has nonlinear distortion, Ingredients cannot be removed. Therefore, when the normal coefficient control method is used here, there is a drawback in that the equalization ability is significantly reduced due to the influence of this non-linearity, and the judgment error is increased.

SUMMARY OF THE INVENTION An object of the present invention is to provide a coefficient control method which is less likely to be affected by non-linear distortion in order to solve the above problems, and to suppress the determination error of the filter output signal.

[0014]

According to the present invention, in an adaptive transversal filter for producing an output signal by performing partial response equalization on a reproduction signal of an optical disk, the output signal is a code having a maximum positive or negative amplitude. And the output signal is excluded from the reference signal used for coefficient control when the codes match immediately before and immediately after.

[0015]

Since the non-linear distortion in the digital recording system of the optical disk is mainly caused by the duplication of the recording pits as shown in FIG. 6, it appears characteristically when the same code continues. On the other hand, when determining the reproduction signal, it is more difficult to identify the inversion position when the code is reversed than when the same code is continuous, and it is affected by bit shift due to inter-code interference. easy.

In the present invention, the tap coefficient is controlled by using the error signal before and after the code inversion position, which is relatively susceptible to the intersymbol interference and less affected by the non-linear distortion. As a result, it has good equalization characteristics before and after sign inversion, which is important in data determination.

[0017]

EXAMPLE An example of the present invention will now be described with reference to FIGS.

FIG. 1 is a block diagram showing an embodiment.
The transversal filter 2 has the same configuration as the conventional example. The output signal R of the transversal filter is subjected to ternary decision by the ternary decision circuit 7 and converted into a ternary signal D having a reference amplitude by the reference level generation circuit 8. The output signal R is input to the subtractor 9 together with the ternary signal D, and the output error signal E1 is taken out.

At the same time, the error signal selection circuit 10 extracts the timing at which an effective error signal is output from the output signal of the three-value determination circuit, and outputs the selection signal S. The switch 11 operates according to the selection signal S and serves to send only the valid error signal to the correlator 12 as the reference error signal E2. When S becomes active, switch 11 is closed and the correlator input E2 is equal to E1. As a result, the tap coefficient is adaptively controlled by the correlation between the error signal and the input signal. On the other hand, when the selection signal is inactive, the switch 11 is opened and the reference error signal E2 input to each correlator becomes 0, so that the tap coefficient of the transversal filter 2 does not change.

FIG. 2 is a block diagram showing details of an embodiment of the ternary value judging circuit 7, the reference level generating circuit 8 and the error signal selecting circuit 10. The ternary judgment circuit 7 receives the output signal R of the transversal filter as an input and the resistors R9 and R1.
The determination is made based on the threshold level determined by 0 and R11. Output signals T1, T2 of the three-value determination circuit
Can take three states depending on the level of the input R, that is, both T1 and T2 are inactive, only T1 is active, and both T1 and T2 are active. Reference level generation circuit 8
Generates a ternary signal D having a reference amplitude according to each state of T1 and T2. The signal level is defined by the resistors R1 to R8. The error signal selection circuit 10 determines whether to use the error signal E1 as the reference error signal E2. When T1 is inactive three times or more in succession, or when T2 is active three times or more in succession, S is inactive in order to exclude the error signal E1 from the reference error. To be done.

In this configuration, since the error signal selection circuit 10 has a unit time T delay, the subtractor 9 and the switch 11 are connected.
The delay element 3 is required between the and. With this,
The delay amount of the filter input signal input to the correlator is also the time T
Just more.

FIG. 3 shows a block diagram when the equalization method of this system is applied to a recording signal to which a training signal is added. The synchronization signal detection circuit 19 monitors the output signal R from the transversal filter as in the conventional example, and during the training period that appears after the synchronization signal,
Promotes the generation of training signals. The output of the training signal generation circuit 20 is sent to the subtractor 9, is used to extract the error signal E1, and is also passed to the error signal selection circuit 10.

The switch 11 provided in the error signal feedback path is closed only when the outputs of both the error signal selection circuit 10 and the synchronization signal detection circuit 19 are both active. The coefficient control is performed only by the error signal satisfying the condition provided in the selection circuit. This is effective when the waveform distortion of the input signal is large and the judgment error obtained from the reproduced signal is large.

In this circuit, coefficient control is performed only by the training signal. Therefore, when the recording code such as the RLL code is used, it is more preferable that the training signal also satisfies the similar RLL rule.
Further, it is preferable that the training signal and the actual data are simultaneously recorded when the actual signal is recorded, because the same recording condition is given to the training signal and the actual data.

In the above embodiment, the case of using the ternary partial response equalization signal has been described.
A similar circuit can be used when a partial response signal other than three values is used.

[0026]

By using the control method of the present invention, it is possible to extract a good equalized output with few decision errors even when the optical disk reproduction waveform input to the adaptive filter has a large amount of nonlinear distortion.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a system diagram showing details of a three-value determination circuit, a reference level generation circuit, and an error signal selection circuit.

FIG. 3 is a system diagram showing another embodiment of the present invention.

FIG. 4 is a system diagram showing a configuration of a conventional adaptive filter.

FIG. 5 is a system diagram showing the configuration of another conventional adaptive filter.

FIG. 6 is a diagram for explaining a cause of non-linear distortion.

[Explanation of symbols]

 1 Input Terminal 2 Transversal Filter 6 Output Terminal 7 Ternary Judgment Circuit 8 Reference Level Generation Circuit 9 Subtractor 10 Error Signal Selection Circuit 12 Correlator 13 Integrator 19 Sync Signal Detection Circuit 20 Training Signal Generation Circuit 21 Recording Pit 22 Single Pit response waveform 23 Playback waveform

Claims (1)

[Claims] 1. An adaptive transversal filter for generating an output signal by performing partial response equalization on a reproduction signal of an optical disk, wherein the output signal is a code having a positive or negative maximum amplitude, and is provided with a code immediately before and immediately after. An adaptive filter control method, wherein the output signal is excluded from a reference signal used for coefficient control when they match.