JP2569469B2 - Magnetic recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus, and more particularly, to a television in which a digital signal is superimposed in a predetermined number of horizontal scanning signal periods, such as a text multiplex broadcast signal. The present invention relates to a magnetic recording / reproducing apparatus for recording and reproducing a John signal on a magnetic recording medium.

[Prior Art] FIG. 9 is a block diagram showing a schematic configuration of a conventional VTR which is an example of a magnetic recording / reproducing apparatus. In the figure, an antenna 1 is for receiving a television signal,
The received output is supplied to a tuner / intermediate frequency amplifier circuit 2. The output of the tuner / intermediate frequency amplifier circuit 2 is supplied to a video signal recording circuit 4 via a video detection circuit 3. The video signal recording circuit 4 is for FM-modulating the video signal so that it can be recorded on a magnetic tape. The output of the video signal recording circuit 4 is provided to an FM amplifier 5 for amplifying the FM signal. The output of the FM amplifier 5 is given to the recording side terminal of the mode switch 6. This mode switch 6
Is switched according to the recording mode and the reproduction mode of the VTR. In the recording mode, the switching contact is connected to the recording terminal, and in the reproduction mode, the switching contact is connected to the reproduction terminal. The changeover contact of the mode changeover switch 6 is connected to the magnetic heads VR and VL. These magnetic head VR
And VL are provided so as to face the rotating drum 100 by 180 °. The magnetic head VR records and reproduces video signals of odd fields, and the magnetic head VL records and reproduces video signals of even fields. On the other hand, the reproduction side terminal of the mode changeover switch 6 is connected to the input terminal of the video signal reproduction circuit 101. The video signal reproducing circuit 101 is for demodulating an FM signal reproduced from a magnetic tape (not shown) by the magnetic heads VR and VL into an original television signal. The output of the video signal reproduction circuit 101 is output terminal 1.
Given to 09.

Next, the operation of the conventional example shown in FIG. 9 will be described. First, the operation in the recording mode will be described. In this case, Anthena 1
Is selected by the tuner in the tuner / intermediate frequency amplifier circuit 2 and further converted into an intermediate frequency signal by the video intermediate frequency amplifier circuit. Then, it is detected by the video detection circuit 3 and becomes a composite video signal. This composite video signal is output to the video signal recording circuit 4
Is converted into a signal recordable on a magnetic tape.
In general, the color signal of the composite video signal is low-frequency converted, and the monochrome luminance signal is 3.4MHz to 4.
Receives 4MHz FM modulation. That is, the video signal recording circuit 4
Then, the signal conversion operation is performed in a manner as shown in FIG. 4 (a). The output of the video signal recording circuit 4 is an FM amplifier 5
And amplified. Here, in the case of the recording mode, the changeover contact of the mode changeover switch 6 is connected to the recording terminal side. Therefore, the output of the FM amplifier 5 is applied to the magnetic heads VR and VL via the mode changeover switch 6 and recorded on a magnetic tape (not shown). The magnetic heads VR and VL are attached to the rotary drum 100 with an azimuth angle of ± 6 °, and crosstalk between adjacent tracks of low frequency components is eliminated by so-called azimuth loss. The magnetic heads VR and VL have a narrow gap width (0.3 μm) and a relatively small recording current, and are surface recording heads for recording on the surface (about 1 μm) of a magnetic tape.

On the other hand, in the reproduction mode, the mode changeover switch 6
Switches to the reproduction terminal side. Then, the FM signal and the reduced color signal recorded on the magnetic tape are picked up by the magnetic heads VR and VL, amplified by a head amplifier unit (not shown), and then sent to the video signal reproducing circuit 101 via the mode switch 6. Given. The video signal reproduction circuit 101 demodulates the applied FM signal and reduced color signal and returns the composite video signal to the original.

[Problems to be Solved by the Invention] Since the conventional VTR is configured as described above, it is generally possible to record and reproduce normal television signals with high quality. By the way, recently, a character or a figure is decomposed into pixels, which are sequentially scanned and converted into binary digital signals, together with necessary synchronization codes and control codes. A so-called teletext multiplex broadcasting is performed in which the broadcast is superimposed on the vertical blanking period. As shown in FIG. 2, a television signal in such a teletext multiplex broadcast has lines (10H to 21H) after the vertical synchronizing signal and before the video signal is inserted.
H) is superimposed on the character signal in a discidal form. This character signal is a binary digital signal whose fundamental frequency is 2.86 MHz. To record and play back this 2.86MHz digital signal without deteriorating the quality, at least double 5.73.
MHz band must be guaranteed. However,
The conventional VTR as shown in FIG. 9 cannot guarantee a signal in the band of 5 to 6 MHz due to the relationship between the material of the magnetic tape, the gap of the magnetic head, the relative speed between the magnetic tape and the magnetic head, and the like.

Therefore, the conventional VTR has a problem that the recording and reproduction of the digital signal as described above is not performed well. When recording and reproducing are actually performed, a part of the digital signal is dropped, so that the signal becomes a completely erroneous signal unlike the analog signal, and the character signal malfunctions and does not become a character.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a magnetic recording / reproducing apparatus capable of accurately recording and reproducing a digital signal superimposed on a certain horizontal scanning signal. I do.

[Means for Solving the Problems] A magnetic recording / reproducing apparatus according to the present invention separates a digital signal from a television signal in which a digital signal is superimposed on a certain horizontal scanning signal. In the same way as a recording / reproducing device, a surface layer is recorded on a magnetic recording medium, the separated digital signal is reduced in frequency, and is then deep-recorded on the magnetic recording medium by a dedicated magnetic head using the entire field period of a television signal. It was done.

[Operation] In the magnetic recording / reproducing apparatus according to the present invention, the digital signal is separated from the television signal by the separating means, and the frequency of the digital signal is reduced by the frequency reducing means. And a television signal is surface-recorded on the magnetic recording medium by a surface recording / reproducing magnetic head.

Embodiment FIG. 1 is a schematic block diagram showing an embodiment of the present invention. In the figure, a reception output of an antenna 1 is supplied to a video detection circuit 3 via a tuner / video intermediate frequency amplification circuit 2. The output of this video detection circuit 3 is
The signal is supplied to the recording side terminal of the mode switch 6 via the video signal recording circuit 4 and the FM amplifier 5. The changeover contact of the mode changeover switch 6 is connected to magnetic heads VR and VL provided on the rotary head 100 '. The reproduction side terminal of the mode switch 6 is connected to the input terminal of the video signal reproduction circuit 101. The output of the video signal reproducing circuit 101 is supplied to a synchronizing signal separating circuit 107 and to a character signal inserting circuit 108. The synchronization signal separation circuit 107 is a video signal reproduction circuit 1
This is a circuit for separating a synchronizing signal from the composite video signal reproduced in step 01. The synchronization signal separated by the synchronization signal separation circuit 107 is supplied to a character signal insertion circuit 108 and to a character signal generator 105 described later. The character signal insertion circuit 108 includes a character signal generator 1 described later.
The character signal created in 05 is placed at the same position as the video signal at the time of receiving the text multiplex broadcast (line 16 and line 279 of the horizontal scanning signal).
This is a circuit to be inserted at line (2). The output of character signal insertion circuit 108 is provided to output terminal 109. The composite video signal derived from the output terminal 109 is the same as the output signal of the video detection circuit 3 at the time of receiving the teletext broadcast.

The output of the video detection circuit 3 is supplied to the clamp circuit 21 and to the synchronization signal separation circuit 28.
The clamp circuit 21 employs a kind of pedestal clamp circuit. The synchronizing signal separation circuit 28 separates the horizontal synchronizing signal and the vertical synchronizing signal from the video detection signal, and creates an HD pulse signal synchronizing with the horizontal synchronizing signal and a VD pulse signal synchronizing with the vertical synchronizing signal. Circuit. The HD pulse signal is applied to a line counter 29. The line counter 29 is a circuit for generating a sampling pulse by counting the line number where the character signal is inserted.
The VD pulse signal is supplied to the read clock generator 30. This read clock generator 30 is a circuit for generating a 100 kHz read clock based on a VD pulse signal.

On the other hand, the output of the clamp circuit 21 is given to the character signal separation circuit 22. The character signal separation circuit 22 extracts the 16th and 279th (the character signal is superimposed) of the horizontal scanning signal period of the television signal based on the extraction pulse from the line counter 29 described above. Circuit. The output of the character signal separation circuit 22 is provided to a sampling circuit 23 and to a sampling clock generation circuit 24. The sampling clock generation circuit 24 generates a 5.8 MHz sampling clock based on the color bust signal included in the horizontal scanning signal period separated by the character signal separation circuit 22. The 5.8 MHz sampling clock is supplied to the sampling circuit 23 and to the buffer memory 25. The sampling circuit 23 is a circuit for extracting only the character signal from the output signal of the character signal separation circuit 22 in synchronization with the sampling clock (5.8 MHz) from the sampling clock generation circuit 24. The output of the sampling circuit 23 is provided to the buffer memory 25 and stored. The writing speed of the buffer memory 25 is controlled by the sampling clock from the sampling clock generation circuit 24. In the buffer memory 25,
The read clock from the read clock generator 30 (100 k
Hz) and its readout speed is controlled. The character signal read from buffer memory 25 is applied to bi-phase modulation circuit 26. This bi-phase modulation circuit 26
Is a circuit for digitally modulating the character signal read from the buffer memory 25. The output of the bi-phase modulation circuit 26 is applied to an amplifier 27 and amplified, and then applied to a recording-side terminal of a mode switch 31. The switching contact of the mode switching terminal 31 is connected to magnetic heads VR 'and VL' provided on the rotating drum 100 '. The magnetic heads VR 'and VL' are deep recording / reproducing heads that perform deep recording of character signals at an angle of about several tens of degrees. That is, in this embodiment, the conventional V
In addition to the magnetic heads VR and VL for surface recording and reproduction provided in the TR, magnetic heads VR 'and VL' for deep recording and reproduction are provided.

On the other hand, the reproduction-side terminal of the mode switch 31 is connected to the input terminal of the digital signal demodulation circuit 102. The digital signal demodulation circuit 102 is a circuit for demodulating a digital signal recorded by BI-PHASE modulation. The output of the digital signal demodulation circuit 102 is provided to a buffer memory 103 and stored. The calling circuit 1 is stored in the buffer memory 103.
04 is connected. This calling circuit 104 has a buffer memory 1
This is a circuit for returning the text signal information stored in 03 to the same frequency of 2.86 MHz as that of the text signal at the time of text multiplex broadcast reception.
The output of the calling circuit 104 is provided to a character signal generator 105.
The character signal generator 105 is a circuit for regenerating a signal output from the calling circuit 104 into a character signal conforming to a broadcasting standard. Note that a clock signal (5.73 MHz) from the clock signal generation circuit 106 is given to the calling circuit 104 and the character signal generator 105, and their operations are controlled. Character signal generator
The output of 105 is supplied to a character signal insertion circuit 108.

 Next, the operation of the embodiment shown in FIG. 1 will be described.

First, as shown in FIG. 2, the text multiplex broadcast signal in Japan is a binary digital signal as a text signal at the 16th (odd field) and 279th (even field) counting from the equivalent pulse before the vertical synchronization signal. Sent by The frequency of this character signal is 2.86 MHz. On the other hand, the video signal is 22
It exists in the period from the 263rd to the 284th and the 284th to the 525th,
Moreover, it is an analog signal.

First, in recording mode, antenna 1, tuner
The text multiplex broadcast signal received and amplified by the video intermediate frequency amplification circuit 2 is detected by the video detection circuit 3 and led out to the connection point a shown in FIG. Therefore,
At this connection point a, a television signal on which a character signal is superimposed as shown in FIG. 2 is generated. This television signal is amplified by a video amplifier circuit 7 and then supplied to a video signal recording circuit 4, where a conventional VTR is used as shown in FIG.
Is modulated in accordance with the recording method. The modulated FM signal and the low-frequency converted color signal are mixed and supplied to the FM amplifier 5. At this time, since the VTR is in the recording mode, the changeover contact of the mode changeover switch 6 is connected to the recording side terminal. Therefore, the FM signal amplified by the FM amplifier 5 is applied to the magnetic heads VR and VL via the mode changeover switch 6 and recorded on a magnetic tape (not shown).

Here, according to the current magnetic tape material technology and magnetic head technology, the relative speed between the magnetic head and the magnetic tape is
In the range of 5 m / sec to 7 m / sec, the deterioration is remarkable in the frequency region of 7 MHz or more, and the high frequency component in the side band of the modulated FM signal of the video signal shown in FIG. High frequency components of the video signal are hardly recorded. Therefore, the 2.86 MHz character digital signal is significantly deteriorated, and cannot be reliably recorded by the magnetic heads VR and VL. On the other hand, the luminance signal and the color signal, which are analog signals, are recorded without any problem, although there is some deterioration.

Next, the television signal shown in FIG.
Given to 21 and pedestal clamped. Thereafter, the character signal separating circuit 22 extracts the signal in the horizontal scanning signal period where the character signal is superimposed. Therefore, the output of the character signal separation circuit 22 is as shown in FIG. As shown in FIG. 3, the character signal is composed of a header part (control signal) of 48 bits and a character information data part of 248 bits, and the digital data signal format is a binary NRZ pulse. I have. The clock frequency of the digital data signal is
364f is _H (8 / 5f _SC) [at a bit rate 5.727272Mb / s]. Where f _H is the frequency of the horizontal sync pulse and f _SC
Is the frequency of the color subcarrier. The sampling clock generation circuit 24 generates a 5.8 MHz sampling clock based on the color burst signal included in the output of the character signal separation circuit 22. The sampling circuit 23 extracts only a 296-bit digital signal of a header portion and a character information data portion in synchronization with the sampling clock. The buffer memory circuit 25 sequentially stores the output of the sampling circuit 23 in synchronization with the sampling clock from the sampling clock generation circuit 24. Then, it is assumed that the digital signal stored in the buffer memory 25 is read by a low-speed read clock of 100 kHz from the read clock generator 30. That is, the read clock generator 30 operates at 100 kHz with the vertical synchronization signal separated by the synchronization signal separation circuit 28 as a start reference, and the read clock generator 30 reads information stored in the buffer memory 25 at 100 kHz. An example of the read digital character signal is shown in FIG. This FIG. 5 (a)
In order to reduce the fluctuation of the direct current component of the original signal shown in FIG. Therefore, the original signal shown in FIG. 5A is as shown in FIGS. 5B and 5C. FIG. 5 (b) shows the BI-PHASE
This shows the logical value of the signal after modulation, and the actual recording signal after modulation is as shown in FIG. 5 (c). The output of the bi-phase modulation circuit 26, that is, the signal shown in FIG.
To the magnetic heads VR 'and VL' for deep recording and reproduction. The frequency spectrum of the recording signal at this time is the sixth
As shown in the figure.

Here, the azimuth angles of the magnetic heads VR and VL for surface recording / reproducing are respectively ± 6 °, and the magnetic heads for deep recording / reproducing.
The azimuth angles of VR ′ and VL ′ are selected to be ± 30 °, and crosstalk interference is prevented so that the signals recorded on the magnetic tape hardly interfere with each other. Next, the actual recording on the magnetic tape will be described with reference to FIGS. 7 and 8. FIG.

First, the magnetic heads VR 'and VL' for deep recording / reproduction have an azimuth angle of ± 30 °, a large head gap width g '(about 2 μm), and a digital signal of about 75 kHz with a large current (see FIG. 4B). Is recorded in a deep layer as shown in FIG. That is, recording is performed up to the full magnetic layer (4 μm). Thereafter, a television signal is recorded on the surface layer of the magnetic layer by about 1 μm with the magnetic heads VR and VL for recording and reproducing on the surface layer (azimuth angle ± 6 ° and the gap width g is as narrow as about 0.3 μm).
The magnetic heads VR and VL operate in the same manner as the conventional VTR magnetic head, and superimpose a low-frequency converted color signal (analog) and an FM-modulated luminance signal as shown in FIG. Then, surface recording is performed.

Therefore, the recording pattern of the magnetic tape on which both signals are recorded by the magnetic heads VR, VL and VR ', VL' is as shown in FIG.

Next, in the reproduction mode, the changeover contacts of the mode changeover switches 6, 31 are switched to the reproduction terminal side. Therefore, the video signal recorded on the surface of the magnetic tape is picked up by the magnetic heads VR and VL, and then supplied to the video signal reproducing circuit 101 via the mode changeover switch 6 to be demodulated to the original video signal. On the other hand, the digital signal deep-recorded on the magnetic tape is picked up by the magnetic heads VR 'and VL' and then applied to the digital signal demodulation circuit 102 via the mode switch 31 to be demodulated to the original digital signal. Then, the output of the digital signal demodulation circuit 102 is given to the buffer memory 103 and stored. The calling circuit 104
The contents stored in the buffer memory 103 are called in synchronization with a high-speed clock signal (5.73 MHz) from the clock signal generation circuit 106, and a digital signal (100 k
Hz) for digital signals (2.86 MHz
Return to z). The output of the calling circuit 104 is supplied to a character signal generator 105, and is re-created to a character standard conforming to the broadcasting standard.
The output of character signal generator 105 is provided to character signal insertion circuit. The character signal insertion circuit 108 is
The character signal from the character signal creator 105 is inserted into the 16th line and the 279th line of the horizontal scanning signal period of the demodulated video signal given from. Therefore, the signal output from the character signal insertion circuit 108 is a signal similar to the original television signal as shown in FIG.

As described above, in the above-described embodiment, the frequency of the 2.86 MHz digital signal is reduced to a 100 kHz digital signal, and the information signal of one scan line is extended to 525/2 scan lines in one field period and written on a magnetic tape. The digital signal can be recorded slowly and accurately.

When the frequency of a 2.86 MHz digital signal is reduced to a 100 kHz digital signal as in the above embodiment,
About 28 scan lines will be used. Also, 100kHz
When the digital signal whose frequency is reduced is read with a 2.86 MHz clock signal, all the character signals can be read and written in one scan line period, but all the character signals in one scan line period are written with a 0.1 MHz clock signal. So, 2
It takes 8.6 times the scan line period.

Although the above embodiment has been described with reference to the example of teletext broadcasting actually broadcast in Japan, the present invention is generally applied to a digital signal (for example, a test system) superimposed on a certain horizontal scanning line and transmitted. Signal etc.) can be applied when recording and reproducing.

Further, in the above embodiment, the frequency of the read clock of the buffer memory 25 is selected to be 100 kHz, but the frequency of the read clock is not limited to 100 kHz, and may be selected to any other value. Basically, when recording and reproducing a text multiplex broadcast signal, a 296-bit signal (about 50 μsec) may be written in one field period (1/60 sec = 16.6 msec). It is possible to improve the write reliability twice or three times, and it is also possible to add a new signal separately.

[Effects of the Invention] As described above, according to the present invention, a digital signal transmitted by being superimposed on a predetermined scanning line of a television signal is separated, and the frequency of the digital signal is reduced.
Since this is extended to one field period and deep recording is performed on the magnetic tape, it is possible to record accurately without error and without interference with other video signals. Therefore, the quality of digital signal recording / reproduction is significantly improved as compared with the prior art.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing one embodiment of the present invention. FIG. 2 is a diagram showing a television signal in teletext broadcasting. FIG. 3 is a character signal separation circuit shown in FIG.
FIG. 4 is a diagram showing signals extracted during a character signal period by a signal 22; FIG. 4 is a diagram showing a frequency band of a video signal recorded on a surface layer of a magnetic tape and a frequency band of a character signal recorded deeply. FIG. 5 is a diagram showing a modulation mode in the bi-phase modulation circuit 26 shown in FIG. FIG. 6 is a diagram showing a frequency spectrum of an output signal of the bi-phase modulation circuit 26 shown in FIG. FIG. 7 is a diagram showing a state where video signals and character signals are recorded on a magnetic tape according to the embodiment shown in FIG. FIG. 8 is a view showing a recording pattern of a magnetic tape recorded by the embodiment shown in FIG. FIG. 9 is a schematic block diagram of a conventional VTR. In the figure, 1 is an antenna, 2 is a tuner / video intermediate frequency amplification circuit, 3 is a video detection circuit, 4 is a video signal recording circuit, 6 and 31 are mode changeover switches, 21 is a clamp circuit, 22 is a character signal separation circuit, 23 is a sampling circuit, 25
Is a buffer memory, 26 is a bi-phase modulation circuit, 28 is a synchronization signal separation circuit, 29 is a line counter, 30 is a read clock generator, 101 is a video signal reproduction circuit, 102 is a digital signal demodulation circuit, 103 is a buffer memory, 104 is a calling circuit,
Reference numeral 105 denotes a character signal generator, and reference numeral 108 denotes a character signal insertion circuit.

Claims (4)

(57) [Claims] 1. A magnetic recording / reproducing apparatus for recording a television signal on which a digital signal is superimposed in a horizontal scanning signal period of a predetermined number on a magnetic recording medium, wherein the digital signal is separated from the television signal. Separating means for reducing the frequency of the digital signal separated by the separating means; a modulating means for converting the television signal into a signal recordable on a pre-recording medium; A rotating drum provided with a pair of a magnetic head and a deep recording / reproducing magnetic head, wherein during recording, a digital signal whose frequency is reduced by the frequency reducing means is applied to the deep recording / reproducing magnetic head. And a signal applying means for applying the output of the modulating means to the magnetic head for recording and reproducing the surface layer. After reduced digital signal of the frequency is deep recorded on the recording medium I, the output of said modulating means, characterized in that it is surface recorded on the recording medium, a magnetic recording and reproducing apparatus. 2. The frequency reduction means includes: storage means for storing the digital signal separated by the separation means; and reading means for reading the digital signal stored in the storage means with a low-speed read clock. The magnetic recording / reproducing apparatus according to claim 1. 3. The magnetic recording / reproducing apparatus according to claim 1, wherein said digital signal is a character signal. 4. The apparatus according to claim 1, further comprising frequency return means for returning a digital signal reproduced by said deep recording / reproducing magnetic head to an original frequency during reproduction. A magnetic recording / reproducing device according to any one of the above.