JPH0347617B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a demodulation method for extracting data from a modulated signal, such as a reproduced signal of an optical disk.

[Technical background of the invention]

In recent years, image information storage and retrieval devices have been developed and put into practical use that store the increasing amount of image information such as documents in large-capacity storage signals, and retrieve and read out the required image information from the storage device as needed. has been done.

In such an image information storage and retrieval device,
Optical disk devices are often used as mass storage devices. This optical disk device uses, for example, the well-known Modified FM (hereinafter referred to as
It uses a modulation/demodulation method (abbreviated as MFM). this
MFM modulation modulates data (binarized signals) consisting of all combinations of "0" and "1" in accordance with the following regulations. That is,
(a) If the data is “1”, the same timing as the data generation timing (hereinafter referred to as data timing) is considered “1”; (b) if the data is “0”
In this case, the timing corresponding to the data boundary (hereinafter referred to as clock timing) is set to "1" only when the previous data is "0", and the other timings are set to "0" as a modulation signal. be. As a result, in the modulated signal by the MFM modulation method, if the data is the same as the previous state, the signal is always changed at an interval of "1", and if the data is inverted from the previous state, the signal is changed at an interval of "1.5". changed,
Further, when the data continues as "1", "0", and "1", the signal is changed at intervals of "2". Data is recorded (stored) by forming pits corresponding to changing points of the modulated signal along groups on the optical disk. On the other hand, in MFM demodulation, clock signals and data are extracted from the reproduced signal according to the mutual interval of pulse signals (pit signals) included in the reproduced signal (modulated signal) from the optical disk, for example, the interval from rear end to rear end. This is for extracting signals.

[Problems with background technology]

By the way, in such MFM demodulation, if dust X adheres to the optical disk as shown in Figure 2, for example, the dust X will be reproduced as pits, so that a completely different data signal will be generated after that. There is a problem with extraction.

[Purpose of the invention]

This invention was made in view of the above circumstances,
The purpose is to provide an excellent demodulation method that can accurately extract data without being affected by, for example, dust on an optical disk.

[Summary of the invention]

This invention determines that when the width of a pulse contained in a modulated signal, such as a reproduced signal from an optical disk, exceeds a certain value, the pulse is caused by dust on the optical disk, and the pulse is invalidated. The data is extracted as follows. In addition, in the modified FM demodulation method, when extracting data “0”, the modulated signal has an interval of “2”.
The data is extracted as “0” even if it changes, and when the change of interval “2” continues twice, the data is changed to “1”.
This prevents data extraction errors based on the interval "2".

[Embodiments of the invention]

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

In FIG. 3, 1 is an optical disk, and information on this optical disk 1 is reproduced by a pickup (using a laser beam) 2. In FIG. The reproduced signal (modulated signal) is amplified by an amplifier 3 and waveform-shaped by a waveform shaping circuit 4, and then supplied to a pulse width detector 5 and a pulse trailing edge detector 6. Pulse width detector 5
When the width of the pulse included in the reproduced signal is greater than a certain value, that is, when it does not correspond to the size of the pit on the optical disk 1, this information is sent to the pulse trailing edge detector 6. Pulse trailing edge detector 6
detects the trailing edge of the pulse included in the reproduced signal and outputs a trailing edge signal synchronized with the trailing edge position, but the width of the pulse is set to a constant value by a command from the pulse width detection circuit 5. If this is the case, the trailing end signal for that pulse is not output. Thus, the trailing edge signal obtained by the pulse trailing edge detector 6 is supplied to the MFM demodulation circuit 7 and the 10101 detection circuit 8. The 10101 detection circuit 8 detects when the mutual interval between the supplied trailing end signals is "2" and the mutual interval "2" continues twice. The MFM demodulation circuit 7 extracts a clock signal and a data signal from the supplied rear end signal. In other words, if the mutual interval between trailing end signals is "1", the same data signal as in the previous state is generated, and if the mutual interval is "1.5", a data signal inverted from the previous state is generated, and the mutual interval is If it is "2", data signals of "1", "0", and "1" are generated. On the other hand, as mentioned above, the MFM demodulated signal is
In the case of a data signal of "1", "0", "1", the mutual interval between the pulses is always "2", and conversely, when the pulse interval of the modulation signal is "2", the data is " 1”, “0”, and “1”. Therefore,
When the MFM demodulation circuit 7 receives the output of the 1010101 detection circuit 8 and outputs the data signal "0" instead of the data signal "1", the mutual interval "2" is set thereafter.
Even if this occurs, it is a signal sequence that cannot occur in the MFM demodulated signal described above, and it is judged as an error, and the signal is set to “1”.
Similarly, the mutual interval "2" occurs twice and it is
When the 10101 detection circuit 8 detects it, it emits a data signal "1". The extracted data signal is then outputted to the outside via the error correction circuit 9. This error correction circuit 9 employs a fire code correction method, and is capable of correcting errors of up to 3 bits of the supplied data signal.

Therefore, as shown in Fig. 4, if dust X is attached to pit B, a pulse corresponding to dust X will be generated in the reproduction signal, but since this pulse has a width of more than a certain value, The pulse width detector 5 and the pulse trailing edge detector 6 make this invalid. Therefore, data is extracted assuming that pit B and dust X do not exist. In this case, the data will have an error of only one bit compared to the normal case shown in FIG. 1, but no error will occur in the subsequent data. Moreover, since a 1-bit error is corrected by the error correction circuit 9 at the subsequent stage, reliable data can be obtained.

By the way, when the data continues to be logic "0",
The pits are formed with a mutual spacing of "1", but if dust adheres to any of the pits, the following problem may occur if the pulse signal invalidation control is performed as described above. That is, as shown in FIG. 5, pits G, H, I, J, K, L, M,
When N is formed with a mutual interval of "1" and the data should continue to be logic "0", if dust X adheres to pit I, that pit I and dust
The pulse corresponding to is invalidated by the action of the pulse width detector 5 and the pulse trailing end detector 6, and a mutual interval of "2" is created by the pits H and J. However, conventional MFM demodulation has the disadvantage that the data becomes a logic "1" and an error occurs, as shown by the two-dot chain line in the figure, and the error continues. However, due to the balance with the 10101 detection circuit 8, the MFM demodulation circuit 7 of the present invention does not emit the data signal "0" even if the pulse interval is "2" when the data signal "0" is being emitted. , the data signal "1" is generated when the mutual interval "2" continues twice, so even if the pulse corresponding to pit I becomes invalid, the data signal becomes "0" as shown by the solid line in the figure.
maintained and error-free.

In the above embodiment, demodulation of a reproduced signal from an optical disk has been described, but the present invention can be similarly implemented when demodulating a signal obtained from another device. In addition, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without changing the gist.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an excellent demodulation method that can perform accurate data extraction without being affected by, for example, dust on an optical disk.

[Brief explanation of drawings]

Fig. 1 is a time chart for explaining the MFM demodulation method, Fig. 2 is a time chart for explaining the problems that occur in the conventional MFM demodulation method, and Fig. 3 is for explaining an embodiment of the present invention. 4 and 5 are time charts for explaining the operation of the same embodiment, respectively. 1... Optical disk, 5... Pulse width detector, 6
...Pulse trailing edge detector, 9...Error correction circuit,
7...MFM demodulation circuit, 8...10101 detection circuit.

Claims (1)

[Claims] 1. A modulation signal that is recorded as data on a recording medium, has a constant width corresponding to the width of a pit, and is composed of a pulse train having intervals according to the data value. In a demodulation method that extracts data based on the interval, a pulse detection signal corresponding to each of the pulse trains is generated only when the width of the pulse included in the modulation signal is equal to or less than a certain value, and the pulse detection signal A demodulation method characterized in that data is extracted based on the interval between each of the pulses detected based on. 2. The demodulation method according to claim 1, wherein the extracted data is outputted via an error correction circuit. 3. Claim 2, characterized in that the error correction circuit employs a fire code correction method.
Demodulation method described in section.