JPS59221089A - Video tape recorder - Google Patents

Abstract

PURPOSE:To ensure satisfactory video recording and reproducing operation by recording the character multiplex signal after converting it into a signal of a low transmission rate and superposing repetitively in a prescribed number of times the converted signal onto the vertical blanking flyback time of a video signal and then reproducing the recorded character multiplex signal after converting it into a normal rate signal and superposing the converted signal onto the vertical blanking flyback time. CONSTITUTION:A carrier wave TV signal containing a character multiplex signal which is received through an antenna 1 is demodulated 2 and sent to a gate circuit 6 via a changeover switch 15. Then the character multiplex signal is extracted and stored to an RAM12. The signal read out of the RAM12 is superposed repetitively in a prescribed number of times onto the vertical blanking flyback time in rate lower then the normal transmission rate and then recorded to a magnetic tape 28. In a reproduction mode the character multiplex signal which is contained in the reproduction video signal reproduced from the tape 28 and repeated plural times in a low transmission rate is demodulated 14 and sent to the RAM12. These multiplex signals are read out in parallel to each other in a normal rate and corrected by a majority logical circuit for their errors to be mixed 7 with a video signal containing no character multiplex signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides signal conversion of a text multiplex signal that does not cause signal deterioration of the text multiplex signal in the process of recording and reproducing a video signal containing a text multiplex signal. The present invention relates to a video tape recorder having a device.

Conventional configuration and its problems Compact home video tape recorder (hereinafter referred to as VTR)
Since it was designed with economy in mind, its frequency characteristics and signal-to-noise ratio (S/N) during the recording and reproducing process are not as good as those of broadcasting VTRs. The methods and standards for teletext broadcasting in Japan were deliberated by the Radio Technology Council, and from October 1988, characters or figures were decomposed into pixels, which were then sequentially converted into binary digital signals. Broadcasting begins by superimposing the necessary control signals on the vertical blanking period of the video signal of the television broadcast radio wave (Nolean transmission method). Furthermore, it is expected that a few years later (around 1932), there will be a transition to a system (hybrid transmission system) that combines the Nokuturn transmission system and the function of encoding and transmitting characters, etc. In any case, the character multiplex signal is superimposed on the vertical blanking period of the video signal, and the signal format is also the same. The format of the transmission code is the NRZ system, and the image frequency is 2.86 MHz. As mentioned above, in a small VTR, attenuation is severe at this frequency, making recording and reproduction almost impossible.

Purpose of the Invention The present invention makes it possible to record and reproduce text multiplex signals by eliminating attenuation when recording the above-mentioned text multiplex signals on a VTR, as well as eliminating errors caused by dropouts during recording and playback. The goal is to provide a VTR with a high level of quality.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention converts a character multiplex signal included in a composite video signal into a signal with a transmission rate lower than the normal transmission rate, and repeats it a set number of times. , the character multiplex signal, which is repeated multiple times at a low transmission rate and is included in the reproduced video signal that is reproduced by the recording medium, is recorded on a recording medium superimposed on the vertical blanking period of the video signal. The transmission rate is converted to a transmission rate and this is superimposed on the vertical blanking period of the reproduced video signal to output the video signal.

To explain the specific configuration of the present invention in more detail, for example, a gate circuit extracts a character multiplex signal superimposed in the vertical blanking period from a baseband composite video signal obtained by demodulating received broadcast waves. and a readable and writable memory, a logic circuit that compares the contents of the memory in parallel and performs majority logic, and a control signal generator that generates a control signal to control reading and writing of the memory, and A control signal generator generates a control signal from the clock signal and the periodic signal of the video signal included in the multiplexed signal, reads it into the memory at a regular transmission rate during recording, and at a speed lower than the regular transmission rate. A character multiplex signal is read from the memory a preset number of times, the obtained character multiplex signal is superimposed on the vertical blanking period of the original video signal, and recorded on a recording medium, and when played back, the video is reproduced from the recording medium. The low-rate character multiplex signal superimposed during the vertical blanking period of the signal is extracted by the gate circuit, and is sent to the control signal generator based on the synchronization signal of the reproduced signal and the clock signal of the low-rate character multiplex signal. generates a control signal,
The reproduced multiplexed signal is sequentially written into multiple memories corresponding to a preset number of times in the above memory at a low rate, the memory contents are removed by a majority logic circuit, and then read out at the normal transmission rate. The character multiplex signal is configured to be superimposed on the vertical blanking period of the reproduced video signal and output.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Second
The figure is a circuit diagram showing a VTR which is an embodiment of the present invention, and FIGS. 3 to 6 are schematic waveform diagrams of input and output signals of each part in signal processing of teletext broadcasting of the same VTR.

In FIG. 2, a carrier television signal including a text multiplex signal received by an antenna 1 is applied to a demodulator 2 including a tuner, where it is demodulated into the composite video signal shown in FIGS. 3 to 5a. Ru. This signal indicates the vicinity of the vertical blanking period of the odd field. The teletext signal is from 10H to 21H during this vertical blanking period (even fields are 2H).
73H to 284H; H is one horizontal opening signal period). Figure 3 is superimposed on 10H, Figure 4 is superimposed on 16H, and Figure 5 is 2
1) This shows the case where it is superimposed on 4. Basically, it is superimposed on one horizontal opening period (1H) determined for each program, and there is a character multiplex signal in some horizontal synchronization period for as many programs as there are. What is shown in FIGS. 3 to 5 is the case of one program. FIG. 6d is shown as an example of a case where there are two or more programs. In such a case, the program selected by the program selection switch 23 is caused to generate pulses as shown in FIG. 6 by the control signal generator 10, and is extracted in the form as shown in FIG. 6C.

Now, the composite video signal demodulated in this way passes through the R side of the recording/reproduction changeover switch (hereinafter simply referred to as the switch) 15, and then passes through the gate circuit 3. It is added to the gate circuit 6 and the synchronous separator 4. From the sync separator 4, only a sync signal as shown in FIG. 3 is taken out. And then the third
A vertical synchronizing signal as shown in Figure C is also taken out. A gate signal generator generates a third signal from the synchronization signal and vertical synchronization signal.
A gate signal as shown in Figure d is obtained. This signal is applied to the gate circuit 6, and only the character multiplex signal of the video signal shown in FIG. 3a is gated as shown in FIG. 3e. A gate signal whose phase is inverted from that of FIG. 3d is applied to the gate circuit 3, and video signals other than the character signal among the video signals shown in FIG. 3a are extracted here. On the other hand, the signal shown in FIGS. 3C obtained from the sync separator 4 is applied to the control signal generator 1o. Further, the character multiplex signal from the gate circuit 6 is also applied to this control signal generator 10, which generates address designation and control signals for the storage device 12 (random access memory 1J-RAM) that stores the character multiplex signal. .

The method of generating these signals is very simple. To explain briefly, the character multiplex signal has a signal of 37 bytes in 1H period including the clock line and framing code, so more than 236 bits can be stored. R of the capacity to
With AM, one program can be memorized, but
708 in order to correct the errors by the majority logic circuit 35.
If the RAM has a memory capacity equal to or larger than that of a memory, it is possible to store one program and correct errors. In the example, since one program is shown as an example of repeating recording and reproducing five times, in this case,
This is possible if it is 1180 bits or more.

If the number of programs and the number of duplicate recordings are different, the memory capacity must be greater than the total number of bits in that case.

The addressing and control signals described above can also be created with reference to the clock line and framing pulses at the beginning of each program.

These addressing and control signals are now applied to RAM 12. Also, this RAM1
A character multiplex signal shown in FIG. 3e from the gate circuit 6 is also applied to 2, and the character multiplex signal is written and switched by the above-mentioned address designation and control signals.

At the same time, the character multiplex signal written in the RAM 12 is
It is read out as shown in Figure f. This example is half the transmission speed of the original teletext shown in FIG. 3e, and is in the form of five duplicate outputs. In other words, the read time is 10 times longer than the read time. In this case, the signal frequency is halved compared to the original signal, 9 times, and overlapped 5 times, so the image frequency of the currently scheduled teletext broadcast (2.86 MHz as mentioned above)
The frequency is 1.43MHz, which is half the frequency of become able to.

Now, in order to reduce the readout rate in this way, the signal speed of the address designation and control signals added to the RAM 12 described above can be reduced to half that of the writing speed, and the number of repetitions can be set in the memory of the control signal generator 10. Control may be performed by counting down the number of repetitions written in advance each time the number of repetitions is read. To briefly explain how this signal is generated, this signal is also generated by the control signal generator 10;
Since the above-mentioned synchronization signal from the synchronization separator 4 is added to , the read timing is determined from these signals (11H and 12H in the case of FIG. 3).

13H, 14H, 15H, 16H, 17H, 18H.

19H and 20H), and also create address designation and control signals based on a signal obtained by dividing the signal from the oscillator with the same frequency as the clock signal at the time of writing the above-mentioned i by μ, and also determine the number of repetitions. The countdown may be performed using the fact that the character multiplex signal is composed of a 37-byte signal.

In this way, the character multiplex signal read out from the RAM 12 is mixed with the video signal of the gate circuit 3 in the mixer 7, and the video signal containing the converted character multiplex signal obtained from the mixer 7 is transferred to the magnetic tape. Switch 1 to record to 28
6 and is applied to the modulator 8. Normally, consumer V
In the TR, the luminance signal is frequency modulated and the sub-carrier color signal is low frequency converted and recorded, so this modulator 8 is also constructed from a modulation circuit.

Next, the video signal modulated by the modulator 8 is supplied to the rotary magnet nodes 26 and 27 on the rotary head drum 25 through the R1111 of the switch 19, and is recorded on the magnetic tape 28.

During reproduction, the rotary magnetic heads 26 and 27 reproduce the modulated video signal recorded on the tape. The modulated video signal passes through the P side of the switch 19, is amplified by the regenerative amplifier 13, and is further demodulated by the demodulator 14 into the original video signal shown in FIG. 3q. This signal has the above-mentioned low bit rate character signal, and even if this signal is directly applied to a television receiver with a character multiplex signal reception function, the receiver cannot receive it as a character multiplex signal.

In order to make the signal acceptable to the receiver, it is necessary to convert it to a signal with a normal bit rate of the original character multiplex signal. The method will be explained below.

The video signal obtained from the demodulator 14 is sent to P of the switch 15.
Gate circuit through the side 3. It is supplied to the gate circuit 6 and the synchronous separator 4. The operation of these circuits is similar to that for recording. That is, the reproduced video signal shown in FIG. 3q that has passed through the gate circuit 6 becomes only a low-rate character multiplex signal as shown in FIG. 3f. This signal is the control signal generator 1
0 and RAM 12, and is temporarily stored in RAM 12. At this time, the control signal generator 10 must generate a control signal opposite to that for recording.

That is, during recording, a signal to read a character signal at a normal transmission rate is given to the RAM 12, and reading is performed at a low rate, whereas during playback, a control signal to read at a low rate is given to the RAM 12, and the readout is performed at a low rate. is read out at the normal rate and in parallel output,
A control signal must be generated to be supplied to the majority logic circuit 36. Therefore, a switching signal is applied to the control signal generator 10 so that, for example, a voltage of 10 B is applied from the switch 11 during recording, and GND is applied during reproduction. In this way, the character multiplexed signal read out in parallel (the number of signals corresponds to the number of repetitions) from the RAM 12 at the regular character signal transmission rate and subjected to error correction by the majority logic circuit 35 is applied to the mixer 7.

Since the video signal from which only the text multiplex signal has been removed from the gate circuit 3 is added to the mixer 7, it is mixed with the text multiplex signal converted to the regular rate, and the third video signal, which is similar to the broadcast wave before recording, is mixed. The video signal shown in the figure is obtained.

As shown in the third diagram, the character signal of the reproduced video signal differs from its position before recording. This shift occurs because memory time and read time are required to store and read the data.

However, this shift has no effect on the decoding of the teletext signal in the television receiver. The video signal obtained in this way passes through the P side of the switchboard 16, is outputted to the terminal 18 through the output amplifier 17, and is applied to the television receiver. , text images are projected on the screen.

By the way, teletext broadcasting is scheduled to be broadcast using 16H and 21H (279M and 284H in even fields) for the time being, but it is hoped that eventually it will be possible to broadcast on all available lines H. Conceivable. Therefore, three other embodiments of the present invention will be described below.

The example shown in FIG. 4 is a case where a character multiplex signal is carried on the 16th H. In this case, if you use the same method as shown in Figure 3, reduce the transmission speed to half and repeat it 5 times during recording, you will get 17Hg1 as shown in Figure 4d.
8H, 19H, 20H.

The character multiplex signal will arrive at 21H, 22M, 23H, 24H, 25H, and 26H, and it will exceed the vertical blanking edge determined by the standard after 22H, and will collide with the original video signal. .

Therefore, in this case, the character multiplexed signal after 22H may be sent to the next field as illustrated in FIGS. 4d and 4e. Figure 4q shows the even field 273H, 2.
74H, 275H, 276H.

An example is shown that applies to 277H. Since it is reproduced at the same location during reproduction, the original character multiplex signal is superimposed on the 278th H of the even field as shown in the fourth diagram. In this case, there is a delay of one field, but there is no particular problem. Naturally, the character message originally in the even field will be delayed to the next odd field. The example shown in FIG. 5 is a case where a character multiplex signal is placed on the 21st H.

In this case, if it is recorded in the same manner as shown in Figures 3 and 4, it will go from 2 to 3H to 282H in the next field, and the character multiplex signal that has been reproduced and converted to the original transmission speed will be recorded in the next field. As shown in Figure 5 f, it will be on the 283rd H. The example shown in FIG. 6 shows a case where a teletext signal is carried on all lines H that can be used for teletext multiplex broadcasting within the same field. In this case, if an attempt is made to record all the character signals by reducing the transmission speed, the fields will be recorded one after another with a delay, and the time delay will eventually become so large that recording will not be possible. In order to avoid such a phenomenon, in the present invention, as shown in FIG. 2, the character multiplex signal selected by the program selection switch 23 is recorded and reproduced by the method shown in FIGS. 3 to 5.

We have explained four examples above, including the case in Figure 3, but there are also cases where the number of programs is different from this example, or when the rate is lowered to a lower rate, or when the rate is lowered even further. If you want to use a different number of times than this example, you can also use the RAM12
Various combinations may occur, such as when the readout order of the signals is different, but all of these do not depart from the scope of the present invention.

Effects of the Invention As described above, the present invention has the great effect of being able to faithfully record and reproduce character multiplexed signals without causing extensive deterioration using a relatively simple memory circuit, and has great industrial value. There is something very big about it.

[Brief explanation of the drawing]

Figure 1 shows a small consumer VTR and a broadcasting and industrial VTR.
2 is a circuit block diagram of a VTR which is an embodiment of the present invention, and FIGS. 3, 4, 5 and 6 are diagrams showing various parts of the VTR. FIG. 3 is a θU diagram showing input/output signal waveforms. 1...Anti-two, 2...Demodulator, 3,
6...Gate circuit, 4...Sync separator,
5... Gate signal generator, 7... Mixer, 8... Modulator, 9... Recording amplifier, 1Q...
・・Control signal generator, 11, 15° 16.19.36・
...Selector switch, 12...RAM, 1
3... Regenerative amplifier, 14. T, LJAl device, 1
7...Output amplifier, 18...Video output terminal,
20...Pinch roller, 21...Capstan, 22...Capstan motor, 23...
Program selection switch, 24... Mechanism, 25
...Drum, 26.27...Rotating magnetic head, 28...Magnetic tape, 29...Shaft, 3
0 ・Tram rotation motor, 31. 32...Guide ball, 33...Fixed magnetic head, 34・Mark・
Traveling direction, 35...Majority logic circuit. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure M wave number

Claims (2)

[Claims] (1) The character multiplex signal included in the composite video signal is converted to a signal with a lower rate than the regular transmission rate, and the line is repeated a preset number of times and superimposed on the vertical blanking period to be recorded on the recording medium. A character multiplex signal that is repeated multiple times at a low transmission rate and is included in the reproduced video signal that is recorded on the recording medium and played back from the recording medium during video playback is converted to a regular transmission rate, and this is output as the reproduced video signal. A videotape recorder configured to do this. (2) A gate circuit for extracting a female multiplexed signal superimposed in the vertical blanking period from a baseband composite video signal obtained by demodulating received broadcast waves, a readable and writable memory, and a memory. It has a logic circuit that performs majority logic by comparing the contents of generating a control signal from the signal in the control signal generator, reading it into the memory at a regular transmission rate during recording, and repeatedly reading it from the memory a preset number of times at a speed lower than the regular transmission rate; The obtained character multiplex signal, which is repeated multiple times at a low rate, is superimposed on the vertical blanking period of the original video signal and recorded on a recording medium, and when played back, the video signal reproduced from the recording medium is The gate circuit extracts the low-rate character multiplex signal superimposed during the vertical blanking period and repeats a plurality of times. A control signal is generated by a control signal generator, and the reproduced character multiplex signal to which an erroneous signal generated due to drone knob out etc. is added at a low rate is read into a plurality of memories corresponding to a preset number of times, and the The character multiplex signal from which the error signal has been removed is converted to a normal rate by performing majority logic on the contents of multiple memories in bit units, and the obtained character multiplex signal is used as the vertical blanking line of the reproduced video signal. A video tape recorder configured to output data by superimposing it on a period.