JPS6318263B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides an MFM (Modified
The present invention relates to a digital signal recording and reproducing apparatus using a frequency modulation method, and provides a digital signal recording and reproducing apparatus that can prevent signal deterioration due to waveform distortion.

Many methods for digitizing and recording analog signals have been proposed depending on the type of recording medium or means used.

One of the greatest features of the method of recording and reproducing digital signals from analog signals is that there is no signal deterioration during the recording and reproducing process. However, when simply recording without applying any means, signal deterioration often occurs due to imperfections in the recording medium and means. There are many factors that cause this signal deterioration, such as non-uniformity of the recording medium, signal loss due to scratches, dust, etc., noise within the required frequency band, frequency band limitations related to the recording medium and means, There are waveform distortions due to nonlinearity of phase characteristics, laser beam recording threshold, peak power incident on the disc surface, amount of defocus, and waveform distortions due to incomplete control of wavelength and pit diameter. Each of these factors requires countermeasures, and in general, the advantages of digital recording can only be utilized if these countermeasures are taken.

The present invention provides a digital signal recording and reproducing device that can prevent waveform distortion related to the last of the above factors, and detects a specific code pattern in advance during recording, and detects the ideal desired code pattern when recording and reproducing. It corrects so that a reproduced waveform of
This is applied to the MFM (Modified Frequency Modulation) method. A detailed explanation will be given below with reference to the drawings.

Figure 1 is an example of an MFM modulation circuit, and Figure 2 is its timing chart. In Figure 1, 1
is the modulation circuit input expressed in NRZ, 2 and 3 are clocks, and 4 and 5 are delay type flip-flops (D-
FF), 6 and 7 are NAND gates, 8 and 9 are OR gates, and 10 is an MFM modulation output. Figure 2
As is clear from the MFM data, MFM is
For any combination of code patterns of NRZ data, if the cycle of NRZ "1" or "0" is T, the pulse width has a characteristic that it cannot be anything other than 2T, 1.5T, or T. .

FIGS. 3a to 3h are diagrams showing the basic principle of the present invention, and show the case where the previous MFM data is recorded and reproduced on a recording medium using a laser beam. 31 is the MFM data to be recorded, 32 is the laser beam diameter for recording, 33 is the energy part of the laser beam that is above the recording threshold, and 3 is the actual recording on the recording medium by the laser energy that is above the recording threshold. _t1 is the time difference between the threshold energy and the recorded pit, 35 is the reproduction laser beam diameter for reading out the recorded pit, 36 is the actually read pit reproduction waveform, and 37 is the pulser ( The threshold value 38 of the comparator is the pulse-shaped output of the pit reproduction waveform, and this pulse-shaped output has a wider pulse width than the previous MFM data to be recorded. Due to its nature, the MFM method has T,
Since only three types of pulse widths, 1.5T and 2T, are possible, the discrimination margin for each is ±0.5T, and if this is exceeded, T will be determined to be 1.5T, or 2T will be determined.
It may be determined to be 1.5T, causing signal deterioration.
Therefore, it is necessary to correct the above 38 expanded pulses so that they have a prescribed pulse width as much as possible. Therefore, one method is to reduce and correct the pulse width of "1" or "ON" in advance during recording as shown in 39, and then it is easy to obtain an ideal pulse waveform as shown in 40 during playback. be understood. However, as shown in No. 39, reducing the pulse width will reduce the recording energy of the laser beam, resulting in a further reduction in the pit diameter, which is undesirable. 41, the pulse amplitude is changed for each pulse width.

FIG. 4 is a diagram showing the relationship between the light spot and the recording pit. When a laser beam with a spot diameter of 2W _O hits a recording medium, the portion exceeding the recording threshold power Pth is melted, forming a pit with a width of 2W _P.

2W _P is given by the following equation using Pth, the peak power P incident on the disc surface, the amount of defocus Z, and the wavelength input.

W ² _P = W _O ² /2 {1+(λ/π z/W _O ² ) ² }ln {P/Pth/1+(λ/π z/W _O ² ) ² } The pit diameter W _P is the incident power. Threshold ratio P/
It can be seen that it changes depending on Pth. When the focus is on the disk surface (Z = 0) W _P = W _O /2lnP/Pth If you apply a laser beam with an intensity that makes P/Pth 3, you will get a pit with a width approximately 0.7 times the diameter of the beam spot. be able to. That is, if conditions are selected, it is possible to record pits smaller than the optical spot diameter.

Figure 5 shows P/Pth using W _O as a parameter.
W _P changes are determined, but where the slope of the graph is large, the dependence on P/Pth becomes large, making stable recording difficult. Also, the 6th
The figure is a model of the pulse input and the corresponding recording pit, ignoring the time delay _t1 .

FIG. 7 shows a block diagram of one embodiment of the present invention. 71 is the MFM modulation circuit shown in FIG.
72 is a monostable multivibrator that operates on the rising edge of the pulse; 74 is a monostable multivibrator that operates on the falling edge of the pulse;
75 and 76 are D-FF, 77 is a 4-bit binary counter, 78 and 79 are D-FF, and 80 is a 4-bit digital magnitude comparator, and this digital magnitude comparator 80 has terminals _A0 to _A3 . A = only when the input and preset B ₀ to B ₃ terminals have the same sign.
A matching pulse is output from the B terminal.
81 to 83 and 92 are AND gates, 84 is an inverter, 93 is an OR gate, 85 is an exclusive OR gate, and 86 and 87 are peripheral AND drivers. 88 to 90 are detection circuits for pulse widths T, 1.5T, and 2T, respectively, and 89 and 90 have basically the same configuration as 88, but have different preset values of the digital magnitude comparators.

8 and 9 are timing charts of the circuit shown in FIG. 7. 1 is NRZ data, 2 is MFM modulation output, 17 is pulse width T detection output, 21 is "H" level detection output 2 among pulse width detection outputs
5 is the output after pulse width correction of pulse width T, 26 is the output after pulse width and amplitude correction of pulse width T, 27 is the addition output after pulse width and amplitude correction of pulse width T, 1.5T, and 2T, This is the laser drive circuit input.

As described above, according to the present invention, when an analog signal is digitized and recorded and reproduced, each pulse width of the MFM modulation output is detected and reduced in advance during recording, and the pulse amplitude is changed in accordance with each pulse width. This has the advantage that an ideal desired pulse width can be obtained during reproduction.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the MFM modulation circuit, Figure 2 is a timing chart of the MFM modulation circuit, and Figure 3 is a block diagram of the MFM modulation circuit.
Figures a to h are diagrams showing the basic principle of the present invention, Figure 4 is a diagram showing the relationship between the optical spot and recording pit, and Figure 5 is a diagram showing the relationship between laser incident power and pit width.
Figure 6 is an explanatory diagram of pulse input and recording pit model.
FIG. 7 is a block diagram of a digital signal recording/reproducing device according to an embodiment of the present invention, and FIGS. 8 and 9 are timing charts of the same device. 4, 5...delayed flip-flop (D-FF),
6, 7...NAND gate, 8, 9...OR gate, 7
1... MFM modulation circuit, 72... Monostable multivibrator, 73, 74... Monostable multivibrator, 75, 76... D-FF, 77... 4-bit binary counter, 78, 79... D-FF, 80... Digital magnici Youdo comparator, 81-8
3...AND gate, 84...Inverter, 85...Exclusive OR gate, 86, 87...Peripheral AND driver, 88-90...Pulse width detection circuit.

Claims (1)

[Claims] 1. Digitizing and recording/reproducing analog signals
In a digital signal recording and reproducing device using the MFM variation method, the pulse width T of the MFM modulation output is 1.5T, where T is the period of data before modulation during recording.
2T individually, extract only the "H" level pulses from among the pulses with the corresponding pulse width, reduce the width of each pulse by a predetermined pulse width, and reduce the amplitude of each pulse. A digital signal recording/reproducing device characterized in that the digital signal is amplified by an amount corresponding to the pulse width to be reduced and then added. 2. In the digital signal recording and reproducing device according to claim 1, each pulse width is adjusted so that when the recorded pulse is reproduced, the pulse width becomes the predetermined pulse width of T, 1.5T, and 2T, respectively. A digital signal recording and reproducing device characterized by correcting pulse width and amplitude.