JPS61294665A - Pcm recording and reproducing device - Google Patents

Abstract

PURPOSE:To permit digital recording with a home VTR and to prevent the inter-disturbance with a video signal by subjecting the PCM digital signal of an audio signal to prescribed modulation to limit the output amplitude and recording and reproducing said signal by frequency multiplexing between the occupying bands of a low carrier wave FM luminance signal and low range conversion chromaticity signal. CONSTITUTION:The audio signal is subjected to interleaving by adding a synchronizing signal and correction code thereto in a digital processing circuit 21 via an analog-to-digital converter 20 and is inputted to an O-QPSK conversion circuit 22. The signal is converted by an offset QPSK system and the spectra of the recording signal are subjected to O-QPSK modulation so as to be recorded between the low range conversion chromaticity signal and the low carrier wave FM luminance signal in the circuit 22. The modulation signal is amplitude- limited by a limiter circuit 23 and is recorded on the video tracks by heads 25a, 25b to be exclusively used for audio having the azimuth angles different from the azimuth angles of video heads 16a, 16b in precedence to the video record. The signal is erased in the surface layer part by the video signal to be recorded afterward and remains in the deep layer part.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a PCM recording and reproducing apparatus, and particularly to a PCM recording and reproducing apparatus suitable for multiplex recording a PCM audio signal or digital information on a video signal.

[Background of the invention]

Conventionally, as a home VTR (7) audio signal recording method for the purpose of improving sound quality, the Institute of Electronics and Communication Engineers Technical Research Report MR85-20 (1983) [r HiFi VH8 VTR by Eura et al. As described in the document titled ``System Development'', a system is adopted in which an FM audio signal is multiplexed onto a video signal track for recording a video signal onto a rotary audio signal for recording a dedicated audio signal. However, with the spread of digital audio disc players using compact discs and the start of high-quality digital audio broadcasting through satellite broadcasting, the era has come when VTRs must be digitized for even higher-quality recording.

[Purpose of the invention]

An object of the present invention is to provide a PCM recording and reproducing device that enables digital recording in home VTRs to be performed to the greatest extent possible in response to the demands of the times, and that does not cause mutual interference with video signals in the method. It is in.

[Summary of the invention]

The present invention converts an audio signal or information into a PCM digital signal, or converts a signal modulated by an input PCM digital signal to a signal outside the occupied band of a video signal, or a low carrier FM luminance signal and a low frequency signal. Frequency multiplexing is performed between the areas occupied by the converted chromaticity signal for recording and reproduction.

The signal modulated by the PCM digital signal is recorded by a 6-chip head that has a different azimuth angle from the magnetic head that records and reproduces the video signal, low carrier wave FM luminance signal, and low frequency conversion chromaticity signal. It is something to be regenerated.

Alternatively, the above-mentioned frequency multiplexing and azimuth angle difference may be used in combination to record and reproduce video and audio with less mutual interference. Furthermore, the modulation method for the signal modulated by the PCM digital signal is an offset type in which two orthogonal carrier waves are phase-modulated using two data streams whose sign change points differ from each other by 1/2 data period. A 4-phase PSK (hereinafter referred to as 0-QPSK) system is used. Furthermore, the imaging width of this modulated output signal is limited for recording and reproduction.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. IE
In Figure 1, 1 is a video signal input terminal, 10 is an LPF that separates the luminance signal, and 11 is an FM that inputs the luminance signal.
A modulator, 12 is a BPF that separates the chromaticity signal, 1M is a frequency converter that converts the chromaticity signal to low frequency, and 14 is an adder that adds the FM modulated luminance signal and the low frequency converted chromaticity signal. 15 is a recording amplifier, 16a and 16b are video signal recording and reproducing heads, 2 is an audio signal input terminal, 20 is an A/D converter, 21 is a digital processing circuit, 2
2 is a 0-QPSK modulation circuit, 23 is a limiter circuit, 2
4 is a recording amplifier, 25a and 25b are recording and reproducing heads dedicated to audio signals, 3o is a reproduction amplifier, 51 is a BPF that separates the luminance signal, 32 is an FM demodulation circuit, 55 is an LPF that separates the chromaticity signal, and 34 is a frequency Conversion circuit, 35
4 is an adder that adds the luminance signal and the chromaticity signal, 3 is a video signal output terminal, 40 is a playback amplifier, 41 is a BPF that separates and separates the audio signal, 42 is a 0-QPSK demodulation circuit, 4
3 is a digital processing circuit, 44 is a D/A converter, and 4 is an audio signal output terminal.

The operation will be explained below. The video signal is LPFlo.

After the luminance signal is separated into two chromaticity signals by B P F12,
Two video recording heads 16a facing each other are subjected to FM modulation and low frequency conversion into bands as shown in FIG. 2 by an FM modulator 11 and a frequency converter 13.

16b on the tape. Head 16 during playback
&, the signals reproduced by 16b are BPF51, respectively.
LP F55 separates the luminance signal and chromaticity signal, and converts them to FM
A demodulator 32 and a frequency converter 34 each restore the video frequency band before recording, and an adder 55 demodulates it into a video signal.

On the other hand, the audio signal is first converted into a digital signal by the A/D converter 20, then added with a synchronization signal and a correction code by the digital processing circuit 21, subjected to an ink 1 knob, and then converted to a 0-QPSK conversion circuit 22. Enter. 0-QPS
In the K modulation circuit 22, as shown in FIG.
PSK modulation. Then, the amplitude of this 0-QPSK modulated signal is limited by a limiter circuit 23, and the video head 1
6a, 16b are used to record audio on the video track using dedicated audio heads 25a, 25b having different azimuth angles.
Record prior to video recording. This recorded 0-Q
The surface layer of the PSK modulated signal is erased by the video signal recorded later, and remains in the deep layer.

During reproduction, the signals reproduced by the audio dedicated heads 26a and 26b are sent to the BPF 41 to extract the audio modulation signal, and then sent to the 0-QPSK demodulation circuit 42 and the digital processing circuit 43.
The D/A converter 44 demodulates the original digital signal, and the D/A converter 44 demodulates the original audio signal.

In this way, once an audio signal is converted into a digital signal and recorded, it is not affected by the distortion of the recording medium, making it possible to transmit higher quality audio. Furthermore, the digital signal was 0-QPSK modulated, and its amplitude was limited while being recorded and reproduced. -C/N of qpsx modulation signal
ratio can be improved. This will be explained in detail below.

FIG. 3 shows an example of an actual measurement of the recording current versus reproduction output level characteristics of the audio dedicated heads 25a and 25b. In general, not only for audio but also for video, the playback output level of magnetic heads increases in proportion to the recording current up to a certain level, but does not increase even if the recording current is increased beyond that level. There is a saturation point. In order to improve the S/N ratio, the recording current is usually set at this saturation point. However, due to this saturation, the recorded waveform is distorted and unnecessary spectra are generated, which may interfere with the Eirin signal.

In particular, the four-phase PSK (hereinafter referred to as QPSK) method, which is used in various fields as a digital modulation method, is essentially equivalent to the amplitude modulation (AM) method, so this saturation causes the problem that the side lobe spreads. was there.

Therefore, in the present invention, in the QPSK method, the recording waveform is The amplitude change was reduced to suppress distortion caused by saturation.

Figure fa4 and Figure 5 show this situation. In Figure 4, A and B are 0-QPSK and Q
This is an envelope waveform of a PSK modulated wave. 0 like this
-The QPSK method has less amplitude fluctuation than the QPSK method. The fact that these waveforms become saturated is equivalent to the waveforms clipping, for example, at the level shown by the dashed line in the figure. Figure 5 shows the spectrum at this time, where the solid line is 0-QPSK and the broken line is QPSK.
This is a PSK spectrum. In addition, the dashed-two dotted line shows the unsaturated spectrum without clipping, which is Q-Q
Both PSK and QPSK systems have the same spectrum.

As described above, the 0-QPSK system has the advantage that the spectrum does not widen even if the waveform is clipped once, so even if a digital audio signal is recorded using this system, it will hardly interfere with the audio signal.

Furthermore, the present invention focuses on the fact that the spectrum does not expand even if the 0-QPSK modulation signal clips, and
The amplitude fluctuation remaining in the modulated signal is limited by the limiter circuit 23 so that it is recorded at a constant amplitude. This enables complete saturation recording, improving the C/N ratio of the reproduced signal and reducing the code error rate of demodulated data.
A specific example of this 0-QPSK modulation circuit 22 is shown in the figure.

In FIG. 6, 50 is digital data (DATA
), 51 is an input terminal for a clock (DOK) that is bit synchronized with the digital data, and 52 is an input terminal for converting the input digital data into 2-bit parallel data (X-DA).
T.A.

53a and 55b are differential code circuits that encode so that the sign change of each parallel data converted to 2 bits, in other words, the phase change of the modulated wave carries information; A delay circuit that delays one data by 172 data cycles; 55a and 55b are LPFs that shape the waveform of the digital signal and limit the band of the modulated wave;
56a and 56b are balanced modulators that modulate carrier waves with waveform-shaped digital signals; 57 is a carrier wave oscillator;
8 is a 90-degree phase shifter for obtaining orthogonal carrier waves, 59 is an adder, and 60 is a 0-QPSK signal output terminal. FIG. 7 is a waveform diagram showing the operation of each part of this modulation circuit 22. In this manner, in the 0-QPSK system, amplitude fluctuations are suppressed by shifting X-DATA and Y-DATA converted into 2-bit parallel data by 1/2 parallel data period.

FIG. 8 is a circuit diagram showing a specific example of the limiter circuit 23. In the figure, a signal input to an input terminal 80 is outputted from an output terminal 84 with its amplitude, both positive and negative, limited to the threshold voltage of the diode (about α7V) by a resistor 81 and diodes 82 and 83. FIG. 9 is a circuit diagram showing another specific example of the limiter circuit 23, in which the limiter effect of a differential amplifier composed of transistors 85 and 86 is used. .

As described above, although the limiter circuit 23 can be implemented using various circuit systems, the present invention is not limited to this circuit system, but is characterized in that this limiter circuit is inserted.

FIG. 10 is a configuration diagram showing a specific example of the 0-QPSK demodulation circuit 42. In the same figure, 61 is the regenerated 0-QP
SK signal input terminals, 62a and 62b are phase detectors for phase detecting the basic carrier signal and input modulated wave signal regenerated by the carrier regeneration circuit 63, 64 is a 90 degree phase shifter, 65a and 6
5b is an LPF that removes unnecessary harmonic components generated by the phase detectors 65a and 65b.

66a and 66b are comparators that determine whether the detected signal is positive or negative and convert it into a digital signal; 67a and 67b are comparators 66
a, a latch circuit that strobes the digital signal from 66b at the timing of the clock reproduced by the clock recovery circuit 68; 69 is an inverter circuit; 70a, 70b decodes the data string encoded on the modulator side into the original data string. 71 is a circuit for converting 2-bit parallel data into original serial data, 72 is an output terminal for demodulated data, and 73 is an output terminal for a recovered clock that is bit synchronized with the demodulated data. FIG. 11 shows operating waveforms of each of these parts. In this way, by synchronously detecting the input modulated wave with the regenerated fundamental carrier wave and data strobe the detected signal with the regenerated clock, I-DATA and Q-D
ATA is obtained, and X-DATA and Y-DATA are obtained by differentially decoding each of them. Then, final demodulated data is obtained by converting these parallel data into serial data.

As described above, as an embodiment of the present invention, the Eirin signal is a low carrier FM signal.
Although the case of the so-called deep layer distribution method is shown, in which an 11 degree signal and a low frequency conversion chromaticity signal are used and overlapping recording is performed using dedicated video and audio heads with different azimuth angles, the gist of the present invention is to record digital audio recording signals. Since the purpose is to narrow the occupied bandwidth of the video signal as much as possible to suppress mutual interference with the video recording signal, the recording method may be ordinary frequency multiplexing recording instead of deep N-recording.

In addition, if the video signal is of the luminance, chromaticity, time and minute overlap method, the occupied band of the digital audio recording signal may be placed outside the occupied band of the low carrier FM Eirin signal, and frequency multiplexing may be performed. When recording one chromaticity signal in parallel on separate tracks, the signals may be frequency-multiplexed and recorded so that the occupied bands do not overlap on any one of the tracks.

〔Effect of the invention〕

According to the present invention, it is possible to multiplex and record a PCM audio signal or digital data without interfering with a video signal, and it is also possible to improve the C/N ratio of the reproduced signal, thereby producing high-quality audio. A signal or digital data is obtained.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing a spectrum of a tape recording signal, Fig. 3 is a diagram showing recording current versus reproduction output level characteristics of an audio-only head, and Fig. 4 is a diagram showing an example of the present invention. is 0
-A waveform diagram showing the envelope of the QPSK modulation wave, Figure 5 is a diagram showing the spectrum of the 0-QPSK modulation wave, Figure 6 is a configuration diagram showing an example of a 0-QPSK modulation circuit, and Figure 7 is a diagram showing the spectrum of the 0-QPSK modulation wave. Figure 6 is a waveform diagram showing the operation of each part of the circuit, faB diagram is a circuit diagram showing one specific example of a limiter circuit, @ Figure 9 is a circuit diagram showing another specific example of a limiter circuit,! 10 figure is 0
- A configuration diagram showing a specific example of a QPSK demodulation circuit, and FIG. 11 is a waveform diagram showing the operation of each part of the circuit shown in FIG. 11...FMy & modulator, 52...FM demodulator,
16, 17...recording/reproducing head, 20...A/D converter, 44...D/A converter,
21.43...Digital processing circuit, 22...0-
QPSK modulation circuit, 42...0-QPSK demodulation circuit, 23... Limiter circuit.

Claims (1)

[Claims] 1. A signal processing circuit that encodes and formats a PCM audio signal or digital data, a circuit that performs offset four-phase phase modulation of the output signal of the digital signal processing circuit onto a carrier band, and the offset. 4
A device for multiplex recording the output signal of a phase modulation circuit and a video signal, a device for reproducing the recorded offset four-phase phase modulation signal and the video signal, and a device for demodulating the reproduced offset four-phase phase modulation signal. In a device comprising a circuit and a circuit that performs decoding processing to return the output signal of the demodulation circuit to the original PCM audio signal or digital data, the offset four-phase phase modulation signal is recorded via a limiter circuit. A PCM recording and reproducing device characterized by the following. 2. The PCM recording and reproducing apparatus according to claim 1, characterized in that the multiplex recording device and the reproducing device are a video tape recorder using a magnetic head. 3. In claim 2, in addition to the magnetic head for recording and reproducing the video signal, a dedicated magnetic head for recording and reproducing the offset four-phase phase modulation signal is provided as the magnetic head, and the deep part of the magnetic tape is A PCM recording and reproducing device characterized by recording on. 4. A PCM recording and reproducing apparatus according to claim 1, 2, or 3, characterized in that the offset four-phase phase modulation circuit is provided with a differential encoder.