JPH0754609B2 - PCM recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PCM recording / reproducing apparatus, and more particularly to a PCM for a video signal.
The present invention relates to a PCM recording / reproducing device suitable for multiple recording of audio signals or digital information.

[Background of the Invention]

Conventionally, as a method for recording an audio signal of a home-use VTR for the purpose of improving sound quality, a technical research report of the Institute of Electronics and Communication Engineers
MR83-20 (1983) "HiFi V" by Miura and 5 others
As described in the document entitled "HS VTR system development", a method of multiplexing FM audio signals using a dedicated rotary audio head for recording audio signals on a video signal track for recording video signals is adopted. However, with the spread of digital audio disc players using compact discs and the start of broadcasting high-quality digital audio by satellite broadcasting, VTR has become an era in which digitization is required for higher quality recording.

[Object of the Invention]

It is an object of the present invention, in response to the demands of such an era, to enable digital recording in a domestic VTR and, in that way, a PCM that does not interfere with the video signal.
It is to provide a recording / reproducing apparatus.

[Outline of Invention]

The present invention, after converting an audio signal or information to a PCM digital signal, or a signal modulated by an input PCM digital signal, outside the occupied band of the video signal,
Alternatively, the signal is frequency-multiplexed and recorded and reproduced in the occupied band of the low carrier FM luminance signal and the low frequency conversion chromaticity signal, and the signal modulated by the PCM digital signal is a video signal or the low carrier FM luminance signal and low A magnetic head that records and reproduces the area-converted chromaticity signal is one that records and reproduces with a magnetic head having a different azimuth angle.

Furthermore, the frequency multiplexing and the azimuth angle difference are used together to reduce the mutual interference between video and audio and record and reproduce. Further, as the modulation method of the signal modulated by the PCM digital signal, an offset type 4-phase PS that phase-modulates each of two orthogonal carriers with two lines of data strings whose code change points differ from each other by 1/2 data period
The K (hereinafter referred to as O-QPSK) method is used.
Furthermore, the amplitude of this modulated output signal is limited and recorded and reproduced.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. First
In the figure, 1 is a video signal input terminal, 10 is an LPF that separates a luminance signal, 11 is an FM modulator that receives a luminance signal as input, 12
Is a BPF for separating the chromaticity signal, 13 is a frequency converter for converting the chromaticity signal into the low frequency range, 14 is an adder for adding the FM-modulated luminance signal and the low-frequency converted chromaticity signal, and 15 is Recording amplifiers, 16a and 16b are recording / reproducing heads for video signals, 2 is an audio signal input terminal, 20 is an A / D converter, 21 is a digital processing circuit, 22 is an O-QPSK modulation circuit, 23 is a limiter circuit, and 24 is Recording amplifiers, 25a and 25b are recording / playback heads dedicated to audio signals, 30 is a playback amplifier, 31 is a BPF for separating luminance signals, 32 is an FM demodulation circuit, and 33 is an LP for separating chromaticity signals.
F and 34 are frequency conversion circuits, 35 is an adder that adds a luminance signal and a chromaticity signal, 3 is a video signal output terminal, 40 is a reproduction amplifier, 41 is a BPF that separates audio signals, and 42 is O-QPSK.
Demodulation circuit, 43 digital processing circuit, 44 D / A converter,
Reference numeral 4 is an audio signal output terminal.

The operation will be described below. The video signal is separated into a luminance signal and a chromaticity signal by LPF10 and BPF12, and then FM modulated and low-frequency converted to the bands shown in FIG. Recording is performed on the tape by the two recording heads 16a and 16b. Head 1 during playback
The signals reproduced by 6a and 16b are separated into a luminance signal and a chromaticity signal by BPF31 and LPF33, respectively, and FM demodulator 32 and frequency converter 34
To return to the video frequency band before recording and adder 35
To demodulate into a video signal.

On the other hand, the audio signal is once converted into a digital signal by the A / D converter 20, and then the digital processing circuit 21 adds a synchronizing signal and a correction code, and interleaves the signal.
Input to the SK modulation circuit 22. The second in the O-QPSK modulation circuit 22
As shown in the figure, O-QPSK modulation is performed so that the spectrum falls within the occupied band of the low-frequency conversion chromaticity signal and the low carrier FM luminance signal in the recording signal spectrum. And this O
-Amplify the QPSK modulation signal by the limiter circuit 23, and record on the video track prior to the video recording using the dedicated audio heads 25a and 25b whose azimuth angles are different from those of the video heads 16a and 16b. . The recorded O-QPSK modulated signal is erased at the surface layer portion by the video signal to be recorded later and remains in the deep layer portion.

At the time of reproduction, the signal reproduced by the dedicated audio heads 26a and 26b is subjected to O-QPSK after extracting the audio modulation signal with the BPF41.
The demodulation circuit 42 and the digital processing circuit 43 demodulate the original digital signal, and the D / A converter 44 demodulates the original audio signal.

In this way, once the audio signal is converted into a digital signal and recorded, higher quality voice transmission is possible without being affected by the distortion of the recording medium. Furthermore, the C / N ratio of the reproduced O-QPSK modulated signal can be improved by O-QPSK modulating the digital signal and limiting the amplitude of the digital signal before recording. Hereinafter, this will be described in detail.

FIG. 3 shows an example of actual measurement of recording current vs. reproduction output level characteristics of the audio dedicated heads 25a and 25b. In general, not only for audio, but also for video, the magnetic head increases the reproduction output level in proportion to the recording current up to a certain level, but it does not increase even if the recording current is further increased. There is a saturation point. Then, normally, the recording current is set to this saturation point in order to improve the S / N ratio. However, this saturation distorts the recorded waveform,
There is a risk of generating unnecessary spectrum and interfering with the video signal. In particular, the 4-phase PSK (hereinafter referred to as QPSK) system, which is used in various fields as a digital modulation system, is substantially equivalent to the amplitude modulation (AM) system. It was

Therefore, in the present invention, in the QPSK system, by adopting the offset QPSK system in which the code change points of the 2-bit parallel data are modulated by shifting each other by 1/2 data period, the amplitude change of the recording waveform is reduced and the distortion due to the saturation is adopted. The occurrence of was suppressed.

FIG. 4 and FIG. 5 show this state. Fourth
In the figure, A and B are envelope waveforms of O-QPSK and QPSK modulated waves, respectively. In this way, the O-QPSK system has less amplitude fluctuation than the QPSK system. Saturation of these waveforms is equivalent to clipping of the waveforms at the level indicated by the alternate long and short dash line in the figure, for example. FIG. 5 shows the spectrum at this time, the solid line is the O-QPSK spectrum, and the broken line is the QPSK spectrum.
Also, the chain double-dashed line shows the spectrum at the time of non-saturation without clipping, which is the same spectrum in both the O-QPSK and QPSK systems. As described above, the O-QPSK system has an advantage that the spectrum is not spread even if the waveform is clipped. Therefore, even if the digital audio signal is recorded by using this system, the interference to the video signal is hardly given.

Further, in the present invention, attention is paid to the fact that the spectrum does not spread even if the O-QPSK modulated signal is clipped, and the amplitude fluctuation remaining in the O-QPSK modulated signal is limited by the limiter circuit 23 and recorded at a constant amplitude. As a result, complete saturation recording is possible, so that the C / N ratio of the reproduced signal is improved and the code error rate of the demodulated data is reduced.

FIG. 6 shows a specific example of the O-QPSK modulation circuit 22. In FIG. 6, reference numeral 50 is an input terminal for digital data (DATA), 51 is an input terminal for a clock (DCK) bit-synchronized with the digital data, and 52 is input 2-bit parallel data (X-DATA). , Y-DATA), and 53a and 53b are differential encoding circuits for encoding so that the parallel data converted into 2 bits each have a code change, in other words, a phase change of a modulated wave, to carry information. Is a delay circuit that delays one data by 1/2 data cycle, 55a, 5
5b is an LPF that shapes the waveform of the digital signal to limit the band of the modulated wave, 56a and 56b are balanced modulators that modulate the carrier with the shaped digital signal, 57 is a carrier oscillator, and 58 is to obtain a quadrature carrier. 90 degree phase shifter, 59 is adder and 60
Is an O-QPSK signal output terminal. Figure 7 shows this modulation circuit
FIG. 13 is a waveform chart showing the operation of each part of 22. In this way O-QPSK
In the method, X-DATA and Y-DATA converted into 2 bits in parallel are
Amplitude fluctuation is suppressed by shifting 1/2 parallel data period.

FIG. 8 is a circuit diagram showing a specific example of the limiter circuit 23. In the figure, the signal input to the input terminal 80 is a resistance
Both the positive and negative amplitudes are limited to the threshold voltage (about 0.7V) of the diode by 81 and the diodes 82 and 83, and the output terminal
It is output from 84. FIG. 9 is a circuit diagram showing another specific example of the limiter circuit 23. Here, transistors 85 and 86 are used.
The limiter effect of the differential amplifier configured by is used.

As described above, various circuit systems are conceivable for the limiter circuit 23, but the present invention is not limited to this circuit system and is characterized in that the limiter circuit is inserted.

FIG. 10 is a block diagram showing a specific example of the O-QPSK demodulation circuit 42. In the figure, 61 is an input terminal for the reproduced O-QPSK signal, 62a and 62b are phase detectors for phase-detecting the reference carrier wave signal and the input modulated wave signal reproduced by the carrier reproduction circuit 63,
64 is a 90-degree phase shifter, 65a and 65b are LPFs that remove unnecessary harmonic components generated by the phase detectors 65a and 65b, and 66a and 66b are comparators that determine whether the detected signal is positive or negative and convert it to a digital signal. ,
67a and 67b are latch circuits which strobe the digital signals from the comparators 66a and 66b at the timing of the clock reproduced by the clock reproducing circuit 68, 69 are inverter circuits, and 70a and 70b are also data strings encoded on the modulator side. , A differential decoding circuit for decoding into a data string, 71 is a circuit for converting 2-bit parallel data into original serial data, 72 is an output terminal of demodulated data, and 73 is an output of a reproduction clock bit-synchronized with the demodulated data. It is a terminal. Figure 11 shows the operation waveforms of these parts.
In this way, I-DATA and Q-DATA are obtained by synchronously detecting the input modulated wave with the reproduced reference carrier wave and strobing the detected signal with the reproduced clock,
Further, by differentially decoding each, X-DATA and Y
-DATA is obtained. Then, by converting these parallel data into serial data, final demodulated data can be obtained.

As described above, as one embodiment of the present invention, the case where the video signal is the low carrier FM luminance signal and the low frequency conversion chromaticity signal, and the so-called deep recording method in which the video and audio dedicated heads different in azimuth angle from each other perform the overlap recording Although shown, the purpose of the present invention is to reduce the occupied bandwidth of the digital audio recording signal as much as possible to suppress mutual interference with the video recording signal. Therefore, the recording method is not the deep layer recording but the normal frequency multiplex recording. May be Further, when the video signal is a luminance / chromaticity time division multiplexing system, the occupied band of the digital audio recording signal may be placed outside the occupied band of the low carrier FM video signal and frequency-multiplexed.
When the chromaticity signals are recorded in different tracks in parallel, the chromaticity signals may be frequency-multiplexed and recorded so that the occupied bands do not overlap in any one of the tracks.

〔The invention's effect〕

According to the present invention, a PCM-converted audio signal or digital data can be multiplexed and recorded without disturbing a video signal, and the C / N ratio of a reproduced signal can be improved. Alternatively, digital data can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a spectrum of a data recording signal, FIG. 3 is a diagram showing recording current vs. reproduction output level characteristics of an audio dedicated head, and FIG. O
− Waveform diagram showing the envelope of QPSK modulated wave, FIG.
-Figure showing the spectrum of QPSK modulated wave, Figure 6 shows O-QPSK
FIG. 7 is a configuration diagram showing a specific example of the modulation circuit, FIG. 7 is a waveform diagram showing the operation of each part of the circuit shown in FIG. 6, FIG. 8 is a circuit diagram showing a specific example of the limiter circuit, and FIG. 9 is a limiter circuit. FIG. 10 is a circuit diagram showing another specific example of the above, FIG. 10 is a configuration diagram showing one specific example of the O-QPSK demodulation circuit, and FIG. 11 is a waveform diagram showing the operation of each part of the circuit shown in FIG. 11 …… FM modulator, 32 …… FM demodulator, 16,17 …… Recording / reproducing head, 20 …… A / D converter, 44 …… D / A converter, 21,43 …… Digital processing circuit, 22 …… O-QPSK modulation circuit, 42 …… O-QPSK demodulation circuit, 23 …… Limiter circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoji Kobayashi, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture Home Appliances Research Laboratory, Hitachi, Ltd. (72) Inventor Takao Arai, 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside the Hitachi Electric Appliances Research Laboratory (72) Inventor Yasushi Yumi, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Shares Inside Hitachi Electric Appliances Research Laboratory (72) Kuniaki Miura, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa (56) References JP 60-1651 (JP, A) JP 60-30241 (JP, A) JP 60-50604 (JP, A)

Claims (5)

[Claims] 1. A device for multiplex recording and reproducing a video signal and a digital information signal on the same track of a magnetic tape, and means for converting the video signal into a video recording signal having a predetermined frequency band, and the digital signal. Means for digitally phase-modulating an information signal in a carrier frequency band, and having a first azimuth angle and recording the amplitude-limited, ratio-modulated digital information signal in a deep portion of a magnetic layer of the magnetic tape, A first magnetic head for reproducing a signal, and a second azimuth angle, and the video recording signal is superposed and recorded on a surface portion of a magnetic layer above a track formed by recording the modulated digital information signal, A second magnetic head for reproducing the recorded signal and the demodulated digital information signal reproduced by the first magnetic head are demodulated to obtain the original data. And means for generating a digital information signal, means for converting said video recording signal reproduced by said second magnetic head on the basis of the video signal, offset 4 as a system for the digital phase modulation and demodulation
A PCM recording / reproducing apparatus characterized by using phase modulation / demodulation. 2. The offset 4 as a method of the digital phase modulation / demodulation according to claim 1.
A PCM recording / reproducing apparatus characterized by using a phase differential phase modulation / demodulation method. 3. The digital signal processing apparatus according to claim 1 or 2, wherein the means for converting the video signal into the video recording signal includes means for frequency-modulating a luminance signal into a predetermined carrier frequency band. The PCM recording / reproducing apparatus, wherein the phase modulating means outputs the modulated digital information signal in a carrier frequency band lower than the carrier frequency band of the modulated luminance signal. 4. The digital signal processing apparatus according to claim 3, wherein the means for converting the video signal into the video recording signal includes means for converting a sub-carrier frequency band of a color signal into a low carrier frequency band. The PCM recording / reproducing apparatus, wherein the means for phase modulating outputs the modulated digital information signal in a carrier frequency band higher than the carrier frequency band of the color signal converted into the low frequency band. 5. The analog-to-digital conversion means for converting an audio signal into a digital audio signal by pulse code modulation according to any one of claims 1, 2, 3, and 4, wherein the digital audio signal Is recorded as the digital information signal, and the digital information signal demodulated by the digital demodulating means is digital-analog converted to generate the original audio signal.
PCM recording / playback device.