JPH0376554B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention records analog signals sequentially and continuously on helical scan recording tracks sequentially formed by a plurality of rotating heads, and utilizes the overlap recording portion thereof. The present invention relates to a rotary head type magnetic recording/reproducing device that intermittently inserts and records digital signals.

[Background of the invention]

The above-mentioned rotating head type magnetic recording/reproducing apparatus records, for example, an FM-modulated video signal sequentially and continuously on a helical scan recording track, and also records a PCM-modulated, time-axis compressed burst signal in the overlap recording portion. A rotary head type video tape recorder has already been proposed in which audio signals are inserted and recorded intermittently. First, such a conventional example will be explained using FIGS. 1 to 4.

FIG. 1 shows a pattern of helical scan recording tracks recorded and formed on the magnetic tape 1. Each helical scan recording track P, as is well known, crosses the magnetic tape 1 running in the direction of the arrow X.
The rotary heads are formed by sequentially and alternately rotating and scanning in the direction of the arrow Y. In this case, before one rotary head finishes forming a recording track, the other rotary head comes into contact with the magnetic tape 1 and starts forming the next recording track, and both rotary heads simultaneously overlap for a predetermined period of time. It is now possible to perform rotational scanning of the recording trunk, so that during this overlap period, one of the rotating heads, for example the one that starts forming a new recording track, receives an FM modulated video signal instead of an FM modulated video signal. P.C.M.
If the audio signal is time-compressed and switched and supplied, the FM video signal can be recorded continuously in time in the scanning section _t2 of the helical scan track P that is formed sequentially, and the time can be changed in the scanning section _t1 . Compressed
PCM audio signals can be inserted and recorded intermittently.

Figures 2a and 2b show reproduced waveforms obtained by alternately rotating and scanning the helical scan recording track P recorded with the track pattern shown in Figure 1 with two rotating heads. 3 is
FM modulated video signal, 4 and 5 are time axis compressed
It is a PCM audio signal. FM modulated video signal 2, 3
are alternately reproduced by the two rotary heads every interval _t2 shown in FIG. 1, and are alternately switched at the dotted line portion where they overlap each other, and are extracted as a continuous reproduced FM modulated video signal. P.C.M.
The audio signals 4 and 5 are alternately and intermittently reproduced by two rotary heads in each interval _t1 in FIG.
After being separated from the FM modulated video signals 2 and 3 and expanded on the time axis, it is PCM demodulated and restored to the original temporally continuous analog audio signal.

FIG. 3 is a block diagram showing the configuration of a recording circuit for recording an FM modulated video signal and a time-base compressed PCM audio signal using the helical scan recording track pattern shown in FIG. 3 is a diagram showing operating waveforms of each part, and signals corresponding to those in FIG. 3 are given the same reference numerals. In FIG. 3, 6 is an input terminal for audio signal A, 7 is an input terminal for FM modulated video signal D, 8 is an input terminal for head switching position control signal F, 10 is a PCM processor, 20 is a transmission cable, 30 , 31 are AC coupling capacitors, 40 and 41 are changeover switches, 5
0 is an inverter, 51 and 52 are AND circuits, 6
0 and 61 are recording amplifiers, 70 and 71 are rotating heads, and 80 is a magnetic tape.

In FIGS. 3 and 4, the audio signal A input from the terminal 6 is PCM modulated by the PCM processor 10, and compressed on the time axis to generate a burst-like PCM signal.
It is output as audio signal B. This burst shape
During the generation period of the PCM audio signal B, the rotating head 70,
It is assumed that the magnetic tape 71 is appropriately controlled so as to overlap the magnetic tape 80 and scan it within a period, that is, to coincide with the scanning section _t1 in FIG.

The PCM audio signal B is waveform-transmitted by the transmission cable 20, and the transmitted PCM audio signal C is
The signal is supplied to terminals c ₁ and c ₂ of changeover switches 40 and 41 via an AC coupling capacitor 30, respectively. On the other hand, the FM modulated video signal D input from the terminal 7 is transmitted to the respective terminals of the changeover switches 40 and 41 via the AC coupling capacitor 31.
Supplied to d ₁ and d ₂ . Changeover switch 40, 41
are controlled by switching control signals G and H that are 180° out of phase with each other as shown in FIG. The terminals c _{1 and} c ₂ are switched to the terminals c 1 and c 2 , and during the low level period, the terminals d ₁ and d 2 are switched to the respective terminals d 1 and d ₂ to which the FM modulated video signal D is supplied. The switching control signals G and H for performing such switching are the head switching position control signal F input from the terminal 8 and the PCM processor 1.
It is generated as follows based on the gate signal E output from 0. That is, the gate signal E is
This is a signal that is generated corresponding to the generation period of the burst-like PCM audio signal B. As mentioned above, the generation period of the PCM audio signal B is a signal that is generated when the scanning period _t1 of the recording track shown in FIG. 70 and 71 coincide with the scanning period, so the gate signal E also corresponds to the scanning period of the rotary heads 70 and 71.
71 is generated every time the scanning section t ₁ of _the recording track shown in FIG _. supplied to On the other hand, the head switching position control signal F is applied to the rotating heads 70, 7.
This is a rectangular wave signal with a duty ratio of 50% synchronized with the rotational phase of 1, and its polarity is at a low level during the period when one of the rotary heads 70 is scanning the scanning section _t1 of the recording track shown in FIG. In addition, during the period when the other rotary head 71 is scanning the scanning section _t1 , the head switching position control signal is set to be at a high level, and the head switching position control signal is applied to the other input terminal of the AND circuit 52. As well as being fed to f ₂ ,
It is supplied to the other input terminal f ₁ of the AND circuit 51 via the inverter 50 . Therefore, now,
If the rotary head 70 is scanning the scanning section _t1 of the recording track shown in FIG. Since the signal supplied to the input terminal _e1 of the AND circuit 51 is at a high level, and the gate signal E supplied to the input terminal e1 of the AND circuit ₅₁ is also at a high level, the AND circuit 51 switches the changeover switch 40 to the terminal _c1 side. A switching control signal G is output. When the rotary head 71 is scanning the scanning _{section t1} of the recording track shown in FIG _. Both will be supplied with high-level signals,
Therefore, from the AND circuit 52, the changeover switch 4
A switching control signal H for switching the terminal C1 to the terminal _C2 side is output. By switching the changeover switches 40, 41 using these changeover control signals G, H, the output of the changeover control signals G, H causes the rotary heads 70, 71 to change over the output period of the changeover control signals, that is, the scanning period t ₁ of FIG.
The signal I, in which the PCM audio signal is switched and inserted instead of the FM modulated video signal, is inserted every alternate period of scanning.
Since signal J is obtained, the signals I and J are recorded in the recording amplifier 6.
By supplying the PCM audio signal to the rotary heads 70, 71 through the PCM audio signals 0 and 61, it is possible to intermittently insert and record the PCM audio signal into the FM modulated video signal in a track pattern as shown in FIG.

By the way, such conventional rotating head type magnetic recording and reproducing devices have the following drawbacks (a) and (b).

(b) When the PCM audio signal B output from the PCM processor 10 is transmitted through the transmission cable 20, the transmission band is limited by the stray capacitance of the transmission cable 20, so the transmission waveform is distorted, and the PCM A mismatch between the output impedance of the processor 10 and the characteristic impedance of the transmission cable 20, as well as a mismatch between the characteristic impedance of the transmission cable 20 and the load impedance at the output end of the transmission cable 20, causes reflections, causing waveforms in the transmitted PCM audio signal. Since distortion occurs, the code error rate increases, making it impossible to reproduce a correct audio signal and deteriorating the sound quality.

(b) PCM processor 10 is usually CMOS, TTL
In this case, the output PCM audio signal B is a large amplitude signal that varies from the power supply voltage level of the PCM processor to the ground level, and therefore the transmission cable 20
The fundamental wave component and harmonic component of the PCM audio signal B emitted from the PCM audio signal B are large and interfere with the FM modulated video signal D recorded at the same time as the transmission of the PCM audio signal B, degrading its image quality.

[Purpose of the invention]

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art,
When a digital signal transmitted via a transmission system is intermittently inserted and recorded into an analog signal that is sequentially and continuously recorded on a helical scan recording track by a plurality of rotating heads, the overlapping recording portion is used to record the digital signal. To provide a rotating head type magnetic recording and reproducing device which can faithfully transmit digital signals without interfering with analog signals and by reducing the code error rate of the digital signals themselves.

[Summary of the invention]

In order to achieve this object, the present invention provides an attenuator on the input side of a transmission line in a recording digital signal transmission system and a limiter circuit on the output side, and uses the attenuator to adjust the level of the digital signal propagating through the transmission line. The present invention is characterized in that it is attenuated to such an extent that no interference waves are generated to the analog signal, and that distortion in the transmission waveform of the digital signal due to the transmission path is removed by a limiter circuit.

[Embodiments of the invention]

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

FIG. 5 is a block diagram showing an embodiment of the recording circuit of the rotary head type magnetic recording/reproducing apparatus according to the present invention, and FIG. 6 is a diagram showing the transmission waveform of the recording digital signal transmission system. Signals corresponding to are given the same symbols. The embodiment shown in FIG.
The conventional transmission cable 20 shown in FIG. 7 is provided with an attenuator 12 on the input side, a limiter circuit 35 and a recording equalization circuit 36 on the output side, and the other configuration is the same as the conventional example shown in FIG. 3. The same components are given the same reference numerals as in FIG. 3, and their explanation will be omitted.

To explain the operation of the embodiment shown in FIG. 5, the audio signal A inputted from the terminal 6 is PCM modulated by the PCM processor 10, compressed on the time axis, and output as the PCM audio signal B. The PCM audio signal B is input to the attenuator 12 and its amplitude level is attenuated, and then transmitted through the transmission cable 20. FIG. 6B' shows the waveform of the attenuated PCM audio signal. The transmitted PCM audio signal C has a waveform that is blunted due to transmission band limitations due to stray capacitance of the transmission cable 20, etc.
Mismatch between the output impedance of 2 and the characteristic impedance of the transmission cable 20, the transmission cable 20
Reflection occurs due to a mismatch between the characteristic impedance of the transmission cable and the load impedance at the output end of the transmission cable, and waveform distortion occurs in the transmitted PCM audio signal C.
FIG. 6 C ₁ is a waveform diagram of a PCM audio signal _whose waveform has been distorted due to the transmission band limitation characteristic of the transmission cable 20, and FIG. Ta
FIG. 3 is a waveform diagram of a PCM audio signal.

However, although the PCM audio signal C after transmission has undergone waveform rounding or waveform distortion, the shift on the time axis at its rise and fall is clear from C ₁ and C ₂ in Fig. 6. The amplitudes are almost the same at the mid-amplitude position shown by the dotted line, and therefore, at the mid-amplitude position of the PCM audio signal C after transmission, the duty ratio of the PCM audio signal B' before transmission is maintained. Therefore, if the transmitted PCM audio signal C is supplied to the limiter circuit 35 through the AC coupling capacitor 30, and the limiter circuit 35 limits the amplitude around the amplitude intermediate level of the PCM audio signal,
As shown in Figure 6 C', the PCM audio signal before transmission
B′ can be restored.

The fundamental wave component and the harmonic component of the PCM audio signal radiated from the transmission cable 20 during the transmission of the PCM audio signal C transmitted by the transmission cable 20 are simultaneously recorded by the attenuator 12. It is sufficiently attenuated so as not to interfere with the FM modulated video signal. In this case, naturally the transmission
Although the S/N of the PCM audio signal deteriorates, there is no particular problem because the noise component superimposed on the PCM audio signal is removed by the limiter circuit 35.

Now, the PCM audio signal C', which has been waveform-shaped into a rectangular wave by the limiter circuit 35, is further inputted to a recording equalization circuit 36 as required. This recording equalization circuit 36 converts the PCM audio signal into the optimum waveform for recording, for example,
As described in Vol. J64-C No. 11, pages 762 to 768, a rectangular wave PCM signal is converted into a waveform with overshoot. The PCM audio signal output from the recording equalization circuit 36 is transferred to the changeover switch 4.
0 and 41 are input to terminals c ₁ and c ₂ , respectively.
On the other hand, the FM modulated video signal D input from terminal 7
is input to terminals d ₁ and d ₂ of the changeover switches 40 and 41 via the AC coupling capacitor 31. In this embodiment, the recording equalization circuit 36 is connected between the limiter circuit 35 and the changeover switches 40 and 41.
Since it is installed in the PCM audio signal transmission system, PCM
The audio signal is waveform-shaped by the limiter circuit 35 and then recorded and equalized, so that simple and stable equalization can be performed without being affected by the characteristics of the transmission cable 20. Optimum recording equalization can be independently performed on the PCM audio signal without affecting the FM modulated video signal D in any way.

Respective terminals of changeover switches 40 and 41
PCM audio signals input to c ₁ , d ₁ and c ₂ , d ₂
The FM modulated video signal D is switched by switching control signals G and H, as in the conventional example shown in FIG.
0 and 71 and recorded on the magnetic tape 80, the details of which have already been explained and will be omitted here.

In the embodiments described above, the digital signal was explained as a time-base compressed PCM audio signal output from the PCM processor 10, and the analog signal was explained as an FM-modulated video signal, but in general, the digital signal is It may be generated from any digital signal generation circuit, and any analog signal such as an AM modulated signal or an audio signal may be used, and in either case, the scope of the present invention is not exceeded. Further, in the above embodiment, a case where a transmission cable is used as a transmission path for digital signals has been described, but the present invention is equally applicable to cases where a transmission path such as a normal transmission line or a wiring pattern on a board is used. Needless to say.

〔Effect of the invention〕

As explained above, according to the present invention, by providing a limiter circuit on the output side of the transmission path for recording digital signals, the transmission band limiting characteristics of the transmission path can be improved.
Since it is possible to recover the waveform distortion of the transmitted digital signal due to impedance mismatch, etc., it is possible to significantly reduce code errors in the digital signal during playback. By inserting an attenuator on the input side of the transmission line to sufficiently attenuate the recorded digital signal before transmitting it,
It is possible to prevent the transmitted digital signal from interfering with the analog signal recorded at the same time, and if necessary, by providing a recording equalization circuit on the output side of the limiter circuit, the above-mentioned The present invention is superior in that it can perform recording equalization that is optimal for recording digital signals regardless of the characteristics of the transmission path and without affecting the equalization characteristics of recorded analog signals. It is possible to provide a rotary head type magnetic recording and reproducing device with various functions.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the pattern of a helical scan recording track recorded on a magnetic tape, Fig. 2 is a reproduction waveform diagram of the helical scan recording track, and Fig. 3 is a diagram showing recording in a conventional rotating head type magnetic recording/reproducing device. FIG. 4 is a block diagram showing the configuration of the circuit; FIG. 4 is a diagram showing the operating waveforms of each part thereof; FIG. 1 is a diagram showing a transmission waveform of the transmission system of the recorded digital signal. 10...PCM processor, 12...attenuator,
20...Transmission cable, 35...Limiter circuit,
36... Recording equalization circuit, 40, 41... Changeover switch.

Claims (1)

[Claims] 1. Analog signals are sequentially and continuously recorded on a helical scan recording track sequentially formed by a plurality of rotating heads, and at the same time, analog signals are transmitted from a digital signal generation circuit via a transmission system to the overlap recording portion. In a rotating head type magnetic recording/reproducing device that records digital signals by intermittently inserting them using switching means, the digital signal transmission system includes an attenuator on the input side of the transmission line and a waveform shaping circuit on the output side. A rotary head type magnetic recording/reproducing device characterized in that: 2. The rotating head type magnetic recording and reproducing apparatus according to claim 1, wherein a direct current or disconnection circuit is provided between the transmission line and the waveform shaping circuit. 3 The digital signal generation circuit suppresses the DC component of the digital signal.
3. A rotating head type magnetic recording/reproducing apparatus according to claim 2, characterized in that PCM modulation is performed. 4. A rotary head type magnetic recording and reproducing apparatus according to any one of claims 1 to 3, characterized in that an equalization circuit is provided on the output side of the waveform shaping circuit.