JPH077569B2 - Recording / playback processing method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording / reproducing processing method in a signal recording / reproducing apparatus such as a video tape recorder or a signal transmitting apparatus.

2. Description of the Related Art When a signal such as a video signal containing a direct current component is passed through a transmission system such as a magnetic tape, which has a large fluctuation in amplitude, it is generally considered effective to transmit the signal by frequency modulation (FM). ing. In fact, it is well known that FM is mostly used for recording video signals in video tape recorders.

Currently, FM modulators and demodulators used in video tape recorders are processed in the form of analog signals. As for the method, the astable multivibrator type is widely used as the modulator and the pulse count type is widely used as the demodulator. Has been.
FIG. 6 shows an example of the configuration. A recording system 51 surrounded by a broken line frame supplies the video signal applied to the input terminal 52 to capacitors 53, 54, 55, transistors 56, 57, resistors 58, 59, 60, 61, 62.
And a multivibrator type F consisting of variable resistors 63 and 64
FM is performed by the M modulator, and the output is amplified by the recording amplifier 65. F
The M modulator directly oscillates a carrier wave with a multivibrator and modulates this with a video signal to obtain an FM-RF signal at the collector of the transistor 57. The input voltage at the connection point P and the oscillation frequency of the output are shown in FIG. It is a kind of V (voltage) -F (frequency) converter having a relationship as shown in FIG. Variable resistor 64
Is for setting the carrier frequency, and 63 is for adjusting the balance of FM modulation. It is the output of the recording amplifier 65.
The FM modulated wave passes through the recording / playback switch 66 and the magnetic head 67.
It is recorded on the magnetic tape 68 by. The FM modulated wave recorded on the magnetic tape 68 is reproduced by the head 67 and given to the reproduction amplifier 70 of the reproduction system 69 via the switch 66 and amplified.
The limiter 71, the delay circuit 72, the EXOR circuit 73 and the low pass filter 74 form an FM demodulator. The operation is, as shown in FIG. 7 (b), a delay circuit 72 produces a signal (b) delayed for a fixed time with respect to an FM wave (a) having a constant amplitude, which is a limiter output, and takes an EXOR of both signals. As a result, the signal is converted into the pulse density signal as shown in (c), the signal component (d) is taken out by the low pass filter 74, and the video signal output is obtained at the output terminal 75. In this way, FM is conventionally used for recording and reproducing video signals.
Modulation and demodulation were used, and the signal processing was performed in analog form. (For example, "Recording and Reproduction of Video Signals" Shozo Nakagawa, Journal of the Television Society, Volume 34, No. 12, pages 1102-1110) Problems to be Solved by the Invention Images using the conventional analog modulator / demodulator as described above When recording a signal, beat components other than the modulated signal appear in the demodulated signal band obtained by reproduction. This unnecessary beat component appears as an unpleasant noise in the reproduced image and is one of the major causes of deterioration of the image quality. There are various causes of the beat component, but the following three are the main ones. One is due to mutual leakage between video and modulated signals, which occurs in both FM modulators and demodulators. It can be reduced by the circuit configuration, placement of circuit parts, and wiring, but it cannot be completely eliminated, which is a fate in analog processing. Second, the distortion of the circuit system,
This is especially due to even-order distortion, which occurs when the balance adjustment by the variable resistor 63 shown in Fig. 6 is insufficient in the modulator or when there is a change over time.
Occurs when 71 is out of balance. For analog circuits, this requires subtle adjustments. The third is a demodulation operation mechanism, which is an unavoidable problem in a pulse counter type demodulator. The disturbance will be described with reference to FIG. If the balance of the modulator and limiter is good, the original carrier component (fc) will disappear in the output of the demodulator, and 2fc,
A sideband spectrum centered around 4fc appears.
As is well known, since FM includes not only the first sideband but also higher-order sidebands, the lower sideband of the FM signal that has been doubled is mixed into the demodulated video signal band, causing a so-called moiré phenomenon beat. Occurs. FIG. 8 (a) is an example of the case where the carrier fc is located near the maximum frequency fm of the input video signal, and as is clear from the figure, the lower sideband of twice the carrier is greatly mixed in the video signal. Cause a big beat disturbance. (b) is an example when the carrier is doubled with respect to the maximum frequency fm of the input signal. In this case, the component that falls in the original video signal in the lower sideband of the carrier due to doubling is It has become very small. However, since the carrier (fc) is set high, a wide band is required for FM signal transmission (recording / reproducing system).

Generally, the allowable limit of the beat due to the doubled component in the FM recording / reproduction of the video signal is such that the second lower side wave of the maximum frequency fm does not fall within the original video signal band. In this case, the carrier frequency is It is selected according to the following formula.

fc1.5fm (1) In other words, it is impossible to lower fc from Eq. (1), and if fc is chosen high, there is a problem that the transmission system becomes wideband and expensive.

Means for Solving the Problems In order to solve the above-mentioned problems, a recording / reproducing processing method of the present invention provides an arithmetic unit for giving a digital input signal information of a modulation index and a carrier frequency to perform a digital operation; A signal is recorded by the first system having a frequency modulating means in the form of a digital signal, which comprises an integrator for integrating the output of the detector and a sine wave generator for generating a frequency modulated wave corresponding to the integrated output, and the frequency is recorded. The modulated digital signal and the signal obtained by phase-shifting it by 90 ° are divided, the instantaneous phase of the frequency-modulated wave is calculated using the inverse trigonometric function circuit, and the instantaneous phase is differentiated by the differentiator. It is characterized in that the signal is reproduced by a second system having a frequency demodulation means in the form of a signal.

The input signal is converted into a digital signal, and in the digital signal form
By using FM, it is possible to eliminate the mutual leakage between the modulated signal and the modulated signal, and to eliminate the fine adjustment for the balance. In addition, by performing demodulation using the inverse triangular function in digital signal form, it is possible to eliminate the leakage of the doubled lower sideband component into the baseband, which occurs in the pulse count type demodulator, and to perform FM modulation. It is possible to avoid mutual leakage between the wave and the demodulated signal and distortion caused by imbalance, and it is possible to perform high quality signal transmission in a relatively narrow band.

Examples Examples will be described below with reference to the drawings. FIG. 1 is a block diagram showing the principle of the present invention. An input signal is given to a terminal 1 and converted into a digital signal by an AD converter 2. AD
The signal converted into discrete values on the time axis and the amplitude axis by the converter 2 is FM-modulated by the digital frequency modulator 3. The FM modulator 3 gives information on a modulation index and a carrier frequency to an input signal and directly generates an FM modulated wave by digital calculation. The digitally modulated signal is guided to the inverse triangular function demodulator 4 via a transmission system (shown by a broken line). The inverse trigonometric function demodulator 4 processes the digital signal form and calculates the instantaneous phase of the input modulated signal using an inverse trigonometric function such as tan ^-1 or sin ^-1 and demodulates the original signal from the instantaneous phase. is there. The demodulated digital signal is converted into an analog signal by the DA converter 5 and output to the output terminal 6.

In the configuration of FIG. 1, modulation / demodulation is performed in the form of digital signals. Therefore, there is no leakage between the baseband signal and the FM modulated wave signal. In other words, beats do not occur at all due to mutual influences or direct jumps through the power supply and ground lines as in the case of the analog type. In addition, there is no concern that distortion will occur due to subtle shifts in balance adjustment, and changes with time will hardly occur.

The demodulation with inverse trigonometric function, equation shows the FM modulated wave _{F (nT) = cos [2πf} C T + 2πf d Vi (nT) θ
{(N-1) T}] (2) is calculated so that the modulated signal is directly output, so that the lower sideband of the doubled carrier generated by the analog pulse count demodulator is modulated. It does not fall into the signal baseband and cause moire interference.
FIG. 2 shows the demodulation output spectrum of the inverse triangular function demodulator, and beat interference does not occur even if the carrier frequency fc close to the maximum input frequency fm is selected. This means that FM modulated waves can be transmitted by a narrow band transmission system. In other words, a low-band FM with little moire interference is possible. Therefore, according to the present invention, it is possible to select the carrier frequency fc according to the relationship of the following equation: fc1.5fm (3)

FIG. 3 and FIG. 4 are configuration examples of the digital modulator and the inverse triangular function demodulator. In FIG. 3, the video signal input provided to the terminal 7 is multiplied by the deviation (frequency shift) fd information that determines the modulation index by the bundle calculator 8 and added to the information of the carrier frequency fc. This signal is integrated by the adder 10 and the delay circuit 11 to output the instantaneous phase θ of the modulated signal. 12 is a circuit that generates cos θ for input θ
Etc. Therefore, a sine wave corresponding to the instantaneous phase θ, that is, an FM output whose frequency changes according to the instantaneous amplitude of the video signal input is obtained at the terminal 13. If this is expressed by an equation, the FM wave of equation (2) is obtained.

In Fig. 4, the FM wave applied to terminal 14 is divided by dividers 16 and 90.
The output of 90 ° phase shifter 15 reaches the divider 16
Added to. The 90 ° phase shifter 15 is a circuit that changes the phase of the input signal by 90 °, and a Hilbert transformer is used. Now FM
If the input is asin θ, the output of 90 ° phase shifter 15 is acos
If θ is a quotient, it becomes tan θ, and the amplitude term a is canceled out. If this is passed through the inverse triangular function circuit 17, the instantaneous phase θ
Is required. That is, the inverse trigonometric function circuit 17 only needs to output a table of tan ⁻¹ for given data, and is composed of a ROM or the like. The obtained instantaneous phase θ is differentiated by the delay circuit 18 and the difference calculator 19, and the video signal is demodulated and output to the terminal 20 by the reverse operation of the modulator shown in FIG.

The demodulator shown in Fig. 4 uses a tan ^-1 circuit, but the input FM
It is also possible to use a high-speed AGC (automatic gain control) to make the signal constant in amplitude and demodulate it using a sin ^-1 circuit. In this case, the 90 ° phase shifter is not needed. Of course, the effect of not producing a beat component of carrier multiplication is the same.

FIG. 5 is a block diagram showing an embodiment according to the present invention.
The video signal applied to the terminal 21 is converted into a digital signal by the AD converter 22 and is emphasized by the emphasis circuit 23. Emphasis raises the high band by utilizing the fact that the high band energy of the video signal is small in order to reduce the effect of triangular noise (in this case, the high band noise of the video signal) in the FM transmission system. E / P signal is W / D
The clipping circuit 24 clips the white and dark portions, adds them to the frequency modulator 25, FMs them, and then returns them to analog signals by the DA converter 26. The FM analog signal is recorded by the head 29 and the tape 30 via the recording amplifier 27 and the changeover switch 28. When the switch 28 is switched to the reproduction mode, the signal picked up by the head 29 is reproduced by the reproduction amplifier 31.
Amplified by and converted into a digital signal by the AD converter 32. This is demodulated by the FM demodulator 33 using an inverse trigonometric function, is returned to an analog signal by the DA converter 35 via the de-emphasis circuit 34 having a frequency characteristic opposite to the emphasis characteristic, and the reproduced video signal is output to the terminal 36. Will be done. In this embodiment, since the recording system performs FM in the form of a digital signal and the reproducing system performs inverse triangular function demodulation, there is no problem with leakage or distortion of the video signal and FM wave in the modulation / demodulation process, and the FM carrier frequency. Since the input signal can be selected to be 1.5 times or less of the maximum frequency, the recording band of the tape and head system can be narrowed, and a VTR for obtaining a high-quality reproduced image on a small scale can be realized.

EFFECTS OF THE INVENTION As is apparent from the above description, the recording / reproducing processing method of the present invention integrates the arithmetic unit for giving a digital input signal with information of the modulation index and the carrier frequency for digital arithmetic operation and the arithmetic unit output. A signal is recorded by a first system having frequency modulating means in the form of a digital signal, which comprises an integrator and a sine wave generator for generating a frequency modulated wave corresponding to the integrated output, and the frequency modulated digital signal is recorded. And a signal obtained by phase-shifting this by 90 ° are subjected to division, the instantaneous phase of the frequency-modulated wave is calculated using an inverse trigonometric function circuit, and the instantaneous phase is differentiated by a differentiator. By reproducing the signal by the second system having the means, it is possible to obtain an excellent effect that the generation of the beat component which is a problem in recording and reproducing the video signal is significantly reduced.
Due to the effect of the format that has been decided from the past
In the VTR, the image quality can be greatly improved.

When determining a new format, the present invention can be used to set the carrier frequency to 1.5 with respect to the maximum frequency of the input signal.
Since it can be selected less than double, it is possible to realize a high-quality VTR with a narrow band.

[Brief description of drawings]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a spectrum diagram of a demodulation output according to the present invention, FIG. 3 is a block diagram of an embodiment of a digital frequency modulator used in the present invention, and FIG. FIG. 5 is a block diagram of an embodiment of an inverse triangular function demodulator used in the present invention, FIG. 5 is a block diagram of an embodiment in which the present invention is applied to a magnetic recording / reproducing apparatus, and FIG. 6 is a circuit diagram of a conventional FM modulator / demodulator circuit. FIG. 7 is a diagram of their operating principle, and FIG. 8 is a spectrum diagram of the demodulator. 1 ... AD converter, 3 ... Digital frequency modulator, 4
…… Inverse triangular function demodulator, 5 …… DA converter, 9,10 ……
Adder, 8 ... multiplier, 11 ... delay circuit, 12 ... cos θ
Generator, 15 …… 90 ° phase shifter, 16 …… divider, 17 …… Inverse triangular function circuit, 18 …… Delay circuit, 19 …… Difference calculation circuit.

Claims (3)

[Claims] 1. An arithmetic unit for digitally calculating a digital input signal by providing information on a modulation index and a carrier frequency,
A signal is recorded by the first system having a frequency modulating means in the form of a digital signal, which comprises an integrator for integrating the output of the arithmetic unit and a sine wave generator for generating a frequency modulated wave corresponding to the integrated output. , Frequency modulated digital signal and this
A frequency demodulating means in the form of a digital signal is provided, which divides a signal phase-shifted by 90 °, calculates an instantaneous phase of a frequency-modulated wave using an inverse trigonometric function circuit, and differentiates the instantaneous phase by a differentiator. A recording / reproducing processing method characterized in that a signal is reproduced by a second system. 2. The first system AD-converts an input signal to convert it into a digital signal, modulates it by a frequency modulating means in the form of a digital signal, and further DA-converts it for recording. Characterized in that the reproduced signal is AD-converted into a digital signal, then demodulated using an inverse trigonometric function by a frequency demodulating means in digital signal form, and further DA converted to obtain a reproduced output signal. The recording / reproducing processing method according to claim 1. 3. The input signal is a video signal, and when the included maximum frequency is fm, the carrier frequency fc is fc ≦ 1.5f.
2. The recording / reproducing processing method according to claim 1, wherein the relationship is set to m and recording is performed by frequency modulating means in the form of a digital signal.