JP2529335B2 - Digital signal recording / reproducing system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a digital signal recording / reproducing system such as a helical scan type digital magnetic recording / reproducing system.

2. Description of the Related Art The need for recording and storing digital information has increased in recent years. Various methods and devices are being studied depending on the nature and usage of the data to be handled.

Therefore, a helical scan type magnetic recording / reproducing device is used as a recording device for a video signal digitized as digital information, and a conventional method in this field will be described first.

FIG. 3 is a block diagram showing a conventional device. In the figure, 32 is an input terminal, 33 is an analog / digital converter (hereinafter referred to as an A / D converter, and is also referred to as an A / D converter in the drawing), 34 is a recording side processor, and 35 is a modulator. 36, 38 are magnetic heads, 37 is a magnetic tape, 39 is a demodulator, 40 is a reproducing side processor, and 41 is a digital / analog converter (hereinafter referred to as a D / A converter). Also, in the drawing, it is described as a D / A converter), and 42 is an output terminal.

The video signal to be recorded is input to the A / D converter 3 via the input terminal 32.
Supply to 3. The A / D converter 33 digitizes the applied analog video signal and sends the data to the recording side processor 34. The recording side processor 34 subjects the received digital data to predetermined digital processing. For example, data formatting, error correction coding, band compression, etc. are executed. The result is digitally modulated by the modulator 35 and recorded on the magnetic tape 37 via the magnetic head 36.

At the time of reproduction, the signal recorded on the magnetic tape 37 is read out via the magnetic head 38 and decoded by the demodulator 39.
The reproduction side processor 40 subjects the output of the demodulator 39 to predetermined digital processing. Here, data de-formatting, error correction decoding, band expansion, error correction, error correction, etc. are executed. The result is inversely converted into an analog signal by the D / A converter 41, and an analog reproduced video signal is transmitted via the output terminal 42.

Next, the conventional tape pattern shown in FIG. 3 will be described with reference to FIG.

FIG. 4 is a tape pattern diagram of the above-mentioned conventional method. In the figure, 43 is a magnetic tape and 44 to 47 are tracks. In the helical scan type magnetic recording / reproducing apparatus, the magnetic heads 36 and 38 are mounted on a rotary cylinder, and a magnetic tape 37 wound around the surface of the rotary cylinder with a slight inclination.
The recording / reproducing method is as follows. As a result, the formed track pattern is in a direction licking the magnetic tape 43 like the tracks 44 to 47.

By the way, when the recording density is increased, track 44
The track width (track pitch) of .about.47 becomes very narrow, which makes it difficult to accurately trace the magnetic heads 36 and 38 on the tracks 44 to 47.

As one means to solve this, a method of recording multiple pilot signals, extracting this pilot signal at the time of playback, detecting track deviation and correcting the trace has been put to practical use in analog recording VTRs. ing.

FIG. 5 shows the frequency spectrum of the recording signal in this analog recording VTR. In the figure, the horizontal axis represents frequency and the vertical axis represents level. 54 is the video signal component, 50-
53 is a pilot signal. In an analog recording VTR, after subjecting a video signal to a predetermined process, FM modulation is performed to create a video signal component 54 (in a VTR for home use, a carrier color signal is converted to a low frequency band to a low frequency band). It has been recorded, but omitted here.). In addition, the space of the spectrum is made in the low frequency band, and the pilot signal 50 ~
53 is frequency-multiplexed and recorded. 4 pilot signals 50
.About.53 are used in a predetermined manner for each track. For example, the pilot signals 50 for the tracks 44 to 47 in FIG.
~ 53 is used. As a result, since the pilot signal frequencies are different between adjacent tracks, if a tracking error occurs during reproduction, the pilot signal changes and the tracking state can be detected. The tracking is corrected based on this result.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention By the way, in the case of digital recording, the above pilot signal insertion method cannot be adopted.

FIG. 6 is a frequency spectrum diagram when, for example, NRZ is adopted as the digital modulation method. In the figure, the horizontal axis represents frequency and the vertical axis represents level. Reference numeral 61 is an output signal component of NRZ modulation, and 57 to 60 are pilot signals. Third
When the modulator 35 in the figure is NRZ-modulated, if the input data to the modulator 35 is random, energy uniformly exists up to a low frequency band like 61. Here, if the pilot signals 57 to 60 are inserted as in the above analog recording VTR,
Crosstalk occurs between the pilot signals 57-60 and the output signal component 61 of the modulator 35, which adversely affects both. As a result, it becomes impossible to detect a tracking error, or even if accurate tracking is possible, the error rate of reproduced data increases extremely.

On the other hand, the modulator 35 has no direct current component and has a very low level in the low frequency band (hereinafter referred to as "DC free modulation").
It is written. ) Will be described with reference to FIG. In the figure, the horizontal axis is frequency, the vertical axis is level, 68 is the output component of the modulator, and 64 to 67 are pilot signals. Since it is DC-free modulation, there is no energy in the low frequency band like the output component 68, and it is considered that the pilot signals 64-67 can be frequency-multiplexed in this portion. However, in this case, although crosstalk to the pilot signals 64 to 67 does not occur, the output waveform of the modulator 35 is recorded by vibrating up and down at a low frequency by the pilot signals 64 to 67. As a result, a zero-cross shift or the like occurs at the time of recording, and the data error rate increases.

FIG. 8 is a waveform diagram when the pilot signal is frequency-multiplexed on the DC-free modulation output. In the figure, 69 is a recording current waveform of the magnetic head, 70 and 71 are signal waveforms corresponding to pilot signals, 73 to 78 are zero cross points, and 72 is a zero level. Reference numeral 69 denotes an output waveform in which the modulator 35 outputs 1010 ... And undulates up and down by the pilot signals 70 and 71. As a result, it can be seen that the interval between the zero cross points 73 to 78 fluctuates.

Thus, there is a problem in digital recording that a pilot signal insertion method such as analog recording VTR cannot be introduced.

In view of this problem, the present invention provides a digital signal recording / reproducing system capable of accurately detecting tracking information without affecting digital information to be recorded.

Therefore, in the present invention, the data to be recorded is normally subjected to DC free modulation so that the DC free modulation is disturbed in places on the track, and if this disturbing method is different between adjacent tracks, By doing so, the spectrum of the low frequency band is made different between the adjacent tracks, and tracking information is obtained according to the state of the spectrum of the low frequency band at the time of reproduction.

By such a method, the digital information to be recorded is not adversely affected, unnecessary data is not additionally recorded, and the tracking information can be accurately detected.

In the embodiments, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is a video signal input terminal, 2 is an A / D converter, 3 is a recording side processor, 4 is a modulator, 5 is a modulation controller, 6 and 8 are magnetic heads, 7 is a magnetic tape. , 9 is a demodulator, 10 is a demodulation controller, 11 is a reproduction side processor, 12 is a D / A converter, 13 is a video signal output terminal, 14 is a wave device, 15 is a track error detector, 16
Is a track error output terminal.

The video signal to be recorded is applied to the A / D converter 2 via the input terminal 1 and digitized. The output of the A / D converter 2 is subjected to predetermined digital processing by the recording side processor 3 and sent to the modulator 4. The modulator 4 performs DC-free modulation, and is composed of, for example, an 8/10 conversion block code. Normally, the output of this modulator 4 is DC free, and DSV (Digital Sum Variation) for each block.
Is 0. However, the modulator 4 outputs the output data whose DSV is not 0 according to the instruction from the modulation controller 5 in a predetermined period. The output of the modulator 4 is recorded on the magnetic tape 7 via the magnetic head 6.

At the time of reproduction, the signal recorded on the magnetic tape 7 is read out to the demodulator 9 via the magnetic head 8. The demodulator 9 normally operates to demodulate the input data. By the way, DSV is 0 in some places of the truck.
The signal which is not recorded is recorded, and the data which is out of the modulation rule is applied to the demodulator 9. During this period, demodulation controller 10
The correct data is restored by performing an irregular demodulation operation. The output of the demodulator 9 is the processor on the reproduction side.
Predetermined digital processing is performed at 11, converted into an analog signal at the D / A converter 12, and a video signal is sent from the video signal output terminal 13. On the other hand, the output of the magnetic head 8 is a wave
It is also supplied to 14, and low-frequency band components are extracted. The low frequency band component extracted by the wave filter 14 is sent to the tracking error detector 15. The tracking error detector 15 detects the status of the tracking error from the spectrum of the applied signal, and sends the result through the tracking error output terminal 16.

By the way, if the digital information is recorded on the magnetic tape 7 as shown in FIG. 4, it is necessary to operate the reproduction side processor 11 while recognizing which place on the track or what kind of data is being reproduced. There is. Therefore, it is usual to record beforehand some data indicating the start of a track, a sync signal indicating the start of each predetermined data block, and the like. Of course, a controller for detecting such data and sync signal and controlling the processing of the entire reproducing system is required, but FIG. 1 is omitted for simplification of the drawing and description. Needless to say, the demodulation controller 10 receives the signal from this controller, estimates the period when DSV becomes non-zero, and informs the demodulator 9 of it.

Although FIG. 1 shows the case where the demodulation controller 10 controls the demodulator 9, such a demodulation controller 10 is not always necessary depending on the configuration method of the demodulator 9. What happens is that, as an example of the case where a DC-free 8/10 block code is adopted as the modulation method, there are 252 patterns of normal codewords with a DSV of 0 and codewords with a non-DSV of 0. There are also 772 patterns. That is, if a code word whose DSV is not 0 is assigned in advance, even if the modulator 4 adopts the code word whose DSV is not 0, the demodulator 9 can perform normal demodulation without any abnormality.

Now, an example of how the DSV is disturbed by the modulator 4 will be described with reference to FIG. In the figure, 17 is a data string to be recorded in one track length, 18 is an output data string of the modulator 4, and 19 to 27.
Is the period during which the modulation rule is disturbed, 28 and 29 are DS in block units
V, 30 and 31 show the undulations of DSV, respectively. A data string to be recorded in one track length created by the magnetic head 6 of FIG. 1 in one trace (that is, the recording side processor 3
The data sequence (17) output by the modulator 4 is modulated by the modulator 4, but the modulation rule is disturbed in the periods 19 to 27 as shown in the modulation output 18. The modulator 4 is basically DC-free modulation, and is assumed to be realized by, for example, an 8/10 block code. In this case, DSV of each block of modulation output is 0
However, in 19 to 27, the modulation rule is disturbed, and the DSV at this timing is not 0 but changes like DSV28. DS
V28 and 29 show the DSV states of two adjacent tracks, respectively, and the modulation rules are disturbed differently between adjacent tracks. It can be said that the undulations 30 and 31 of the DSVs 28 and 29 are low frequency band components, and the undulation 31 has a frequency component that is 30 times as high.

At the time of reproduction, as shown in FIG. 1, the signal read out through the magnetic head 8 is guided to the demodulator 9 and wave device 14.
By the way, the modulator 4 operates in a DC-free state for almost the entire period, and the DSV changes for a very limited period. Therefore,
The output signal spectrum of the modulator 4 has a tendency similar to that shown in FIG. 7 (however, the appearance of the low frequency band depends on how the undulation of the DSV is made). Therefore, different signals are obtained from the wave device 14 between adjacent tracks. This works in the same way as the pilot signals 50 to 53 in FIG.

Furthermore, an example of how to disturb the modulation rule is given below. Assuming an 8/10 block code as DC-free modulation, the DSV of a 10-bit codeword is as shown in Table 1. Of the modulator output data 18 shown in FIG. 2, a code word having a DSV of 0 is converted in a period other than 19 to 27, and a code word having a DSV of not 0 may be selected in a period of 19 to 27.

Although the present invention has been described above with reference to the embodiments, it is needless to say that the present invention is not limited to the helical scan type digital recording VTR and can be applied to other scanning methods and information other than video.

Further, the period in which the modulation system rule is disturbed is not particularly specified in FIG. The reason is that the effect of the present invention can be basically obtained anywhere. However, in a digital recording VTR, there are various advantages when the modulation rule is disturbed during the sync data section. For example, the sync data part is intended to detect the sync, and does not transmit other information in this part. Therefore, any codeword other than 0 for DSV in Table 1 can be used freely.
Also, the sync data section is regularly arranged, and both sync and pilot information can be transmitted in the sync data section. There are such merits.

Further, in addition to the sync data section, the amble data section and the edit gap section can be used.

Further, the method of disturbing the DSV between adjacent tracks does not always have to be the same data position as in FIG. 2, and a method of varying the frequency and length of disturbing the modulation rule between the adjacent tracks is also possible. .

In addition, as the DC-free modulation, the 8/10 block code is taken as an example, but it is not necessary to limit to this method, and the effect of the present invention can be exerted even in other DC-free modulation.

EFFECTS OF THE INVENTION As is clear from the above description, the present invention does not need to purposely insert or superpose another signal in order to detect a tracking error during reproduction, and has no adverse effect on original digital data recording / reproduction. Without giving it, the tracking error can be correctly detected while maintaining the efficient recording / reproducing function of digital data.

High-density recording is indispensable for digital recording VTRs, etc., and the track pitch is naturally narrowed. Therefore, tracking at a narrow track pitch is an important key technology, and recording / reproduction with a low error rate and a highly accurate tracking error detection capability are required. From this point of view, the present invention exerts an extremely high effect.

[Brief description of drawings]

FIG. 1 is a block diagram showing a digital signal recording / reproducing system according to an embodiment of the present invention, FIG. 2 is a pattern diagram showing changes in a data string and DSV for explaining FIG. 1, and FIG. A block diagram showing an example, FIG. 4 is a tape pattern diagram, FIG. 5 is a frequency spectrum diagram of a recording signal in an analog recording VTR, FIG. 6 is a frequency spectrum diagram in digital modulation, and FIG. FIG. 8 is a frequency spectrum diagram for explaining FIG. 3, and FIG. 8 is a recording current waveform diagram in the case where the conventional system is introduced into the digital recording. 2 ... A / D converter, 3 ... recording side processor, 4 ... modulator, 5 ... modulation controller, 6,8 ... magnetic head, 7 ... magnetic tape, 9 ... demodulator, 10 ... Demodulation controller, 11 ... Reproduction processor, 12 ... D / A converter, 14 ... Wave device, 15 ... Track error detector.

Claims (1)

(57) [Claims] 1. Data to be recorded is normally subjected to DC-free modulation, and the DC-free modulation is disturbed everywhere on a track, and the disturbing manner of the DC-free modulation is made different between adjacent tracks. A digital signal recording / reproducing system characterized in that the spectrum of the low frequency band is made different between tracks and the tracking information is obtained according to the state of the spectrum of the low frequency band during reproduction.