JP2002032958A - Reproduced signal processing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve wrong binarization due to amplitude variation resulting from a flaw or defect of a disk without varying binarization characteristics in normal reproduction. SOLUTION: In this reproduced signal processing circuit, a peak envelope detector 13 detects the peak value of a reproduced signal and attenuates the peak value with the time constant determined on the basis of the time-constant variation signal from a control means and the envelope output having the peak value is supplied to an intermediate value detecting circuit 16. A bottom envelope detector 14 detects the bottom value of the reproduced signal and attenuates the bottom value with the time constant determined on the basis of the time-constant variation signal from a control means not shown in Fig., and the envelope output of the bottom value is supplied to the intermediate value detecting circuit 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a reproduction signal processing circuit, and more particularly to a reproduction signal processing circuit suitable for reproducing information from a recording medium such as an optical disk on which high density recording is performed.

[0002]

2. Description of the Related Art As a conventional optical disk device, for example,
There is a mark position recording system in which a recording mark is formed by emitting a laser beam in a pulse corresponding to the information bit 1. In this recording method, since the position of the center of a recording mark has information, the center of the mark, that is, the peak position of the reproduced signal is 1 and the rest is 0 in the case of reading.

In recent years, in order to improve the recording density of an optical disk, a mark edge recording type optical disk apparatus which gives meaning to an edge portion of a recording mark has been put into practical use. In this recording method, since the information bit 1 corresponds to the edge of the recording mark, it is possible to record twice the information with the same mark length as compared with the mark position recording method.

In the mark edge recording method, as a method of extracting the original information of 1, 0 from a recording mark, a slice level method in which a reproduction signal is sliced at a certain level and binarized, or a reproduction signal is differentiated by differentiating the reproduction signal. Although a differential method for detecting a peak point is known, for example, in magneto-optical recording and the like, the rotation angle of the polarization plane due to the magnetic Kerr effect is small, and the amplitude of a reproduced signal obtained is small. A method is used.

As such a slice level method, for example, Japanese Patent Application Laid-Open No. 55-150645 discloses a positive / negative peak hold circuit, which detects a positive / negative envelope of a reproduced signal, and calculates an intermediate value between these positive / negative envelopes. The reproduced signal is binarized as a slice level, and
There is disclosed a technique in which a time constant in a positive / negative peak hold circuit is controlled based on the frequency of a digitized signal so that a slice level follows amplitude fluctuation, bias fluctuation and frequency fluctuation of a reproduction signal.

[0006] Japanese Patent Application Laid-Open No. Hei 5-81677 discloses that
A maximum value of a reproduction signal in a single recording period signal for PLL pull-in (hereinafter referred to as a VFO unit) recorded at a data start portion of a data recording area on a recording medium is detected, and data following the data start portion is detected. The maximum value of the same polarity of the reproduced signal in the VFO section is detected, and the slice level is set based on the difference between the maximum value in the VFO section and the maximum value in the data section. , In which the reproduced signal in the data section is binarized.

Further, Japanese Patent Application Laid-Open No. 62-254514 discloses that a reproduced signal is binarized by a slice level based on the positive and negative envelopes of the reproduced signal, and the binarized signal is
A final binary signal is obtained by latching with a clock synchronized with the binary signal, and a phase comparison between the final binary signal and a binary signal obtained by slicing at a slice level is performed. A technique has been disclosed in which a slice level is corrected based on the above, thereby compensating for amplitude fluctuations of a reproduced signal.

On the other hand, in the mark edge recording system using the 1-7 modulation system which is currently being standardized by the ISO,
Since the signal recorded on the disk is not a DC free code, it is necessary to use a head amplifier having a time constant that can be regarded as DC coupling or DC coupling for a certain period (specifically, the period of a resync signal). However, a disk substrate used for a magneto-optical disk or the like is generally made of a plastic typified by polycarbonate, and has a birefringence. Therefore, when a magneto-optical signal is detected using a polarizing optical system, the disk substrate is often used. , The envelope of the reproduced signal fluctuates under the influence of the birefringence. Although the frequency of this fluctuation is sufficiently lower than that of the reproduced signal, it cannot be cut by a high-pass filter or the like because a DC component is required in the reproducing system for the reason described above. For this reason, the technique described above is required to make the slice level follow the fluctuation of the envelope.

However, using the above-mentioned known technique,
Even if the slice level is made to follow the fluctuation of the envelope, the intermediate value of the envelope of the reproduction signal does not always match the optimum slice level for the reason described below, and therefore, the reproduction signal cannot be accurately binarized. there were.

That is, the resolution of an optical system for reading a recording mark on a recording medium is limited, and the amplitude of a reproduced signal of a short mark is different from that of a reproduced signal of a long mark. For example, when recording is performed with a recording power lower than the regular recording power or when recording is performed with a recording power higher than the regular recording power, the reproduction signal of the shortest mark 1 and the reproduction signal of the long mark 2 The middle values of those envelopes are shifted.

In such a case, if the slice level is set to the intermediate value of the envelope of the long mark, the detected mark will be short in the case of low power recording, and will be detected in the case of high power recording. Mark becomes longer. For this reason, even if the slice level is set to the intermediate value of the envelope of the reproduction signal and the slice level is controlled to follow the amplitude fluctuation, bias fluctuation and frequency fluctuation of the reproduction signal as in the related art, the recording power is not increased. If the fluctuations match, the length of the mark cannot be accurately detected.

Therefore, for example, in Japanese Patent Application Laid-Open No. 8-287606, after determining the intermediate value between the envelope of the peak value and the bottom value of the reproduction signal of the VFO section as the slice level, the determined slice level is used as the reproduction signal of the data section. There has been proposed a reproduction signal processing circuit that can follow the envelope fluctuation of the peak value and the bottom value and binarize the reproduction signal of the data portion at the slice level obtained therefrom.

[0013]

The envelope detector usually has a small time constant during an attack (in a direction in which the amplitude increases) and a time constant in a decay (in a direction in which the amplitude decreases).
Is generally set to be large.

[0014] As shown in FIG.
If there is a defect, the amplitude may fluctuate at the wound part. As described above, the envelope detector responds to a wave of increasing amplitude. The operation of the bottom envelope detector responds to an increase in amplitude due to flaws or the like, and the output of the bottom envelope detector outputs a value larger than that at the time of normal amplitude even after the influence of amplitude fluctuation due to flaws or the like is eliminated.
On the other hand, the operation of the peak envelope detector has the same output as that in the normal state because the peak side is not affected by flaws or the like.

In order to set the intermediate value of the peak and bottom envelope detectors to the slice level, FIG.
As shown in (b), there is a problem that the slice level is affected after the amplitude of a flaw or the like fluctuates and cannot be binarized.

To solve this problem, it is conceivable to reduce the time constant at the time of decay of the envelope detector. Although less, as shown in FIG. 5, the envelope detector reacts to a long pattern and the slice level fluctuates even in a normal state. In other words, there is a problem that the slice level fluctuates due to the previous mark pattern and the jitter at the time of binarization increases.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to improve erroneous binarization due to amplitude fluctuation with respect to a scratch or defect on a disk without changing the binarization characteristic during normal reproduction. It is an object of the present invention to provide a reproduction signal processing circuit that can perform the reproduction.

[0018]

According to the present invention, there is provided a reproduction signal processing circuit comprising: a synchronization pull-in VFO section in which a shortest pattern is continuously recorded; and a data having a recording mark recorded by a mark edge recording method. And a first envelope detecting means for detecting an envelope of a peak value of the reproduction signal when binarizing a reproduction signal obtained by reading a recording medium having a format including a section and an envelope of a bottom value of the reproduction signal. , Second value detecting means for detecting an intermediate value between the outputs of the first and second envelope detecting means, and binarizing means for setting the output of the intermediate value detecting means to a slice level. Wherein the first and second envelope detecting means include a time constant varying means for varying a time constant. And configured.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

1 to 3 relate to an embodiment of the present invention. FIG. 1 is a block diagram showing a configuration of a reproduction signal processing circuit, and FIG. 2 shows a specific configuration of the reproduction signal processing circuit of FIG. FIG. 3 is a diagram for explaining the operation of the reproduction signal processing circuit of FIG.

The present embodiment is applied to a magneto-optical disk drive. A magneto-optical disk (not shown) has a synchronization pull-in VFO section in which the shortest mark is continuously recorded, and a VFO section following the synchronization. Information is recorded in a format including a data portion having a recording mark recorded by a -7 modulation type mark edge recording method, and is read by a known optical pickup 11 shown in FIG.

In the reproduction signal processing circuit, as shown in FIG. 1, a reproduction signal obtained from the optical pickup 11 is converted into a DC signal.
The signal is amplified by a head amplifier 12 having a time constant that can be regarded as coupling or DC coupling for a certain period, and supplied to a peak envelope detector 13, a bottom envelope detector 14, and a binarization circuit 15.

The peak envelope detector 13 detects a peak value of the reproduced signal and attenuates the peak value with a time constant determined by an external signal (variable time constant signal) from control means (not shown). The envelope output of the peak value is supplied to the intermediate value detection circuit 16.

Similarly, the bottom envelope detector 14
Is configured to detect the bottom value of the reproduction signal and attenuate the bottom value by a time constant determined by a time constant variable signal from control means (not shown), and the envelope output of the bottom value is an intermediate value. It is supplied to the detection circuit 16.

The intermediate value detecting circuit 16 detects an intermediate value between the envelope output of the peak value and the envelope output of the bottom value and supplies it to the binarization circuit 15 as a slice level. And binarizes the reproduced signal. The binarized output is converted into reproduction data by a demodulation circuit (not shown).

FIG. 2 shows a specific configuration of the light receiving section, head amplifier 12, peak envelope detection circuit 13, bottom envelope detection circuit 14, and intermediate value detection circuit 16 of the optical pickup 11 shown in FIG. The current output signals of the photodiodes 11a and 11b are converted into the IV converters 12a and 12b in the head amplifier 12 by using the orthogonal components of the return light from the magneto-optical disk.
Is converted to a voltage signal, and is differentially amplified by the differential amplifier 12c.
Thereby, a reproduced signal is obtained.

The peak envelope detection circuit 13 includes a peak hold circuit 13a having a diode 13b connected in the forward direction, a time constant variable circuit 13c including a plurality of sets of capacitors and resistors, a buffer 13d, and a low-pass filter having resistors and capacitors. 13e. The peak hold circuit 13a can change the time constant by selecting one of a plurality of sets of capacitors and resistors in the time constant variable circuit 13c based on the time constant variable signal.

Similarly, the bottom envelope detector 14
Is composed of a peak hold circuit 14a having a time constant variable circuit 14c composed of a plurality of sets of capacitors and resistors connected in the opposite direction, a buffer 14d, and a low-pass filter 14e having resistors and capacitors. The peak hold circuit 14a can change the time constant by selecting one of a plurality of sets of capacitors and resistors in the time constant variable circuit 14c based on the time constant variable signal.

Further, the intermediate value detection circuit 16 includes a resistor 16
a, 16b, and these resistors 16a, 16b
Is configured to output an intermediate voltage (intermediate value) from the peak envelope output by the divided voltage.

When the scratch or defect is read out, a reproduced signal as shown in FIG. 3 is obtained from the head amplifier 12.

During normal reproduction, the peak envelope detector 13, the bottom envelope detector 14, and the intermediate value detector 1
6 (slice level) fluctuates as shown in FIG. After passing through the flaw or defect, the output of the bottom envelope detector 14 fluctuates greatly due to the flaw and holds a value lower than usual. The time constant at this time is set to be relatively large. Under the influence of the output of the bottom envelope detector 14, the output of the intermediate detector 16 outputs a slice level lower than usual. As a result, in the reproduced signal of this figure, erroneous binarization of the mark immediately after the scratch continues for a long time, and a demodulation circuit (not shown) cannot read data correctly.

Therefore, in the present embodiment, data is reproduced again by a control system (not shown) (retry reproduction). At that time, the control system uses a time constant variable signal
The time constants of the peak envelope detector 13 and the bottom envelope detector 14 are set smaller than those at the time of normal reproduction. The output (slice level) of the peak envelope detector 13, the bottom envelope detector 14, and the intermediate value detector 16 at that time fluctuates as shown by the dotted line in FIG.

After passing through the flaw or defect portion, the output of the bottom envelope detector 14 is largely fluctuated by the flaw as in the case of normal reproduction, and holds a lower value than the normal portion which is not a flaw or defect portion.

In this embodiment, since the time constants of the peak envelope detector 13 and the bottom envelope detector 14 are set smaller than those in the normal reproduction, the slice levels return to the original slice level earlier than in the normal reproduction. 3 (b)
As shown by the broken line, erroneous binarization of the mark immediately after the scratch is improved.

In the above-described embodiment, the case of reading a magneto-optical disk has been described. However, another recording medium on which information is recorded in a format including a data portion having a recording mark recorded by a mark edge recording method is read. In this case, the present invention can be applied effectively.

[0036]

As described above, according to the present invention, it is possible to improve erroneous binarization due to amplitude fluctuation with respect to scratches and defects on a disk without changing the binarization characteristics during normal reproduction. effective.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a reproduction signal processing circuit according to one embodiment of the present invention.

FIG. 2 is a configuration diagram showing a specific configuration of a reproduction signal processing circuit of FIG. 1;

FIG. 3 is a diagram for explaining the operation of the reproduction signal processing circuit of FIG. 1;

FIG. 4 is a first diagram illustrating the operation of a conventional reproduction signal processing circuit.

FIG. 5 is a first diagram illustrating the operation of a conventional reproduction signal processing circuit.

[Explanation of symbols]

 Reference Signs List 11 optical pickup 11a, 11b photodiode 12 head amplifier 12a, 12b IV converter 12c differential amplifier 13 peak envelope detector 13a, 14a peak hold circuit 13b, 14b diode 13c, 14c Time constant variable circuit 13d, 14d Buffer 13e, 14e Low-pass filter 14 Bottom envelope detector 15 Binarization circuit 16 Intermediate value detection circuit 16a, 16b Resistance

Claims (2)

[Claims] 1. A recording medium which is obtained by reading a recording medium of a format including a VFO section for synchronization pull-in in which shortest patterns are continuously recorded, and a data section having recording marks recorded by a mark edge recording method. In binarizing the reproduction signal, a first method for detecting an envelope of a peak value of the reproduction signal
And a second detecting means for detecting an envelope of a bottom value of the reproduced signal.
A reproduced signal comprising: an envelope detecting means; an intermediate value detecting means for detecting an intermediate value between outputs of the first and second envelope detecting means; and a binarizing means for setting an output of the intermediate value detecting means to a slice level. In the processing circuit, the first and second envelope detecting means include a time constant varying means for varying a time constant. 2. The reproduction signal processing circuit according to claim 1, wherein the time constant changing means changes the time constant between normal reproduction and retry reproduction.