JPS6362824B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a video signal recording and reproducing apparatus that frequency-multiplexes and records two frequency-modulated video signals on the same track.

Conventional Structure and Problems It has been known that when two video signals are recorded on a magnetic recording medium, frequency multiplexing is performed on the same track from the viewpoint of efficient use of the magnetic surface.

FIG. 1 shows a conventional example of a video signal magnetic recording and reproducing device that performs frequency multiplexing. In Fig. 1, input terminals 1 and 2 are applied with two video signals to be recorded, input terminals 3 and 4 are low-pass filters (LPF), 5 and 6 are band-pass filters (BPF), and 7 and 8 are modulators. (MOD), 9 and 10 are demodulators (DEMOD), 11 and 12 are magnetic heads, 13 is a mixer, 14 is a recording amplifier (AMP), 15 is a reproduction amplifier (AMP), and 16 and 17 are output terminals. Here, the video signal input to input terminal 1 is assumed to be the first video, and input terminal 2
The video signal input to the second video signal is assumed to be a second video signal. The first video signal becomes a first modulation signal in the modulator 7 and enters the bandpass filter 5. On the other hand, the second video signal also becomes a second modulation signal in the modulator 8 and enters the low-pass filter 3. Here, in order to enable frequency multiplexing of the first modulation signal and the second modulation signal, for example, the first carrier frequency ₁ of the modulator 7 is selected to be higher than the second carrier frequency ₂ of the modulator 8. . In addition, the first modulation signal and the second modulation signal are
Each of the signals is guided to a bandpass filter 5 and a lowpass filter 3 to limit the band. After this,
The first modulated signal and the second modulated signal are mixed in the mixer 13 to form a mixed signal. The mixed signal is amplified by a recording amplifier 14 and recorded on a magnetic recording medium (not shown) via a magnetic head 11.

On the other hand, during reproduction, a mixed signal is reproduced from the magnetic recording medium by the magnetic head 12, amplified by the reproduction amplifier 15, and input to the band pass filter 6 and the low pass filter 4. The bandpass filter 6 extracts the first modulated signal from the mixed signal, returns it to the first video signal in the demodulator 9, and outputs it to the output terminal 1.
Output to 6.

Furthermore, the low-pass filter 4 extracts the second modulation signal from the mixed signal, returns it to the second video signal in the demodulator 10 , and outputs it to the output terminal 17 .

[FIG. 2] shows the frequency allocation of the mixed signal obtained with the configuration shown in [FIG. 1]. The horizontal axis is the frequency axis, and the vertical axis is the power density. 18 is a power density distribution of the first modulation signal, 19 is a power density distribution of the second modulation signal, and 20 is an unnecessary component.

By the way, the power density distribution 18 of the first modulation signal
is the frequency _1L , which is the frequency deviation width of the first modulated wave
The carrier part of the first modulated wave from to frequency _1H ,
Upper sideband of the first modulation wave from _1H to _1U and _1S
It consists of lower sideband waves from to _1L . Furthermore, _1S and _1U are expressed by the first equation and the second equation, respectively, based on the bandwidth _1B considered when demodulating the first modulated wave. _1S = _1L − _1B ...(1) _1U = _1H + _1B ...(2) On the other hand, the power density distribution 19 of the second modulation signal is from frequency _2L , which is the frequency deviation width of the first modulation wave, to frequency _2H. The carrier part of the first modulated wave of , from _2H
Upper sideband of the first modulation wave up to _2U and from _2S
Consists of lower sideband waves up to _2L . _2S and _2U are expressed by the third and fourth equations using the bandwidth _2B considered when demodulating the first modulated wave. _2S = _2L − _2B ...(3) _2U = _2H + _2B ...(4) Also, the unnecessary component 20 spans from frequency _DL to frequency _DU , and _DL and _DU are defined by the fifth and sixth equations. _DL = _1L −2 _2H ...(5) _DU = _1H −2 _2L ...(6) The unnecessary component 20 is generated due to magnetic odd-order distortion in the transmission system, and the principle of its generation will be explained below.

In order to briefly explain the principle of generation of the unnecessary component 20, consider a non-modulation model in which no video signal is input to input terminals 1 and 2 in [Fig. 1].

Here, the first modulation signal and the second modulation signal at an arbitrary time t are respectively expressed as X ₁ as a function of time t.
(t), X ₂ (t), then X ₁ (t), X ₂ (t) are
Using the first carrier frequency ₁ and the second carrier frequency ₂ ,
They can be expressed by the seventh and eighth equations, respectively.

X ₁ (t) = acos (2π ₁ t) ……(7) X ₂ (t) = bcos (2π ₂ t) ……(8) Here, a and b are the first modulation signal and the second modulation signal, respectively. is the amplitude coefficient of the signal.

On the other hand, as mentioned above, the transmission system has magnetic odd-order distortion, and the mixed signal X(t) (=X ₁ (t) + X ₂
(t)) passes through this transmission system, the output Y(t) is the 9th
It can be expressed as an expression.

Y(t)= _∞ 〓 ^i-1 C _2i-1 X ^(2c+i) (t) ...(9) However, i is an integer.

Here, C ₁ is a response coefficient for the first modulation signal X ₁ (t) and the second modulation signal X ₂ (t),
C _2i-1 is a response coefficient for the (2i-1) order distortion component. In the ninth equation, the first modulation signal X ₁
( _t ), _the response coefficient C ₁ for _the second modulation signal 1 modulation signal X ₁ (t)
If only the second modulation signal X ₂ (t) and third-order distortion are considered, the output Y(t) will be as shown in Equation 10.
Note that d ₁ to _{d 6} in Equation 10 are respective frequency response level coefficients when the input X(t) enters this transmission system.

Y(t) = d ₁ cos (2π ₁ t) + d ₂ cos (2π ₂ t) + d ₃
cos3 (2π ₁ t) + d ₄ cos3 (2π ₂ t) + d ₅ cos [2π (2 ₁ − ₂ ) t] + d ₆ cos [2π ( ₁
−2 ₂ )t]...(10) In the 10th equation, the first term and the second term are the first modulation in the 7th and 8th equations, if the frequency response level coefficients d ₁ and d ₂ are ignored. components corresponding to the signal X ₁ (t) and the second modulated signal X ₂ (t), respectively;
The third to sixth terms are unnecessary components.

By the way, it is not impossible to select a frequency allocation in which the unnecessary components from the third term to the sixth term do not overlap with the signal band (i.e., the first and second terms in Equation 10), but as a practical matter, When the transmission system is a magnetic head/magnetic recording medium, there is a limit to the frequency band, and from the viewpoint of band efficiency utilization, the power density distribution 18 of the first modulation signal and the power density distribution 18 of the second modulation signal are It is normal that the power density distribution 19 of the modulated wave signal is allocated relatively close to each other. When choosing such an allocation, experiments have shown that the unnecessary components of the 6th and 4th terms in Equation 10 have relatively large levels,
In particular, the sixth term has the disadvantage of deteriorating the S/N ratio of the screen and causing beat disturbance.

By the way, the unnecessary component 20 in FIG. 2 is the unnecessary component in the sixth term of equation 10 for the first and second modulated signals modulated by the first and second video signals.

Also, the unnecessary component 20 in [Figure 2] overlaps both the lower side band of the first modulated wave and the upper side band of the second modulated wave, but in reality, the unnecessary component 20 and the first modulated wave The overlap with the lower sideband wave is not very important, and the overlap between the unnecessary component 20 and the upper sideband wave of the second modulation wave is a particularly important problem, causing S/N degradation and beat interference on the screen. This often occurs.

Purpose of the Invention The present invention suppresses unnecessary components 20 (unnecessary components in the 6th term of equation 10) to the upper sideband of the second modulation signal, improves the S/N ratio on the screen, and eliminates beat interference. The present invention also provides a video signal magnetic recording and reproducing device that aims to efficiently utilize the bandwidth of a transmission system.

Structure of the Invention The present invention emphatically records the upper sideband of a second modulated signal during recording, and suppresses the opposite characteristic of the emphasis during recording during reproduction, thereby creating a desired first modulated signal and a second modulated signal. The objective is to faithfully reproduce the modulated signal and suppress only unnecessary odd-order distortion components.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. 3, FIG. 4, FIG. 5, and FIG. 6.

[Fig. 3] is a configuration block diagram of one embodiment. In this drawing, 21 and 22 are video signal input terminals to be recorded, 23 and 24 are low pass filters (LPF), and 25 and 26 are band pass filters (BPF). ), 27 and 28 are modulators (MOD), 29 and 30 are magnetic heads, 31 and 32 are demodulators (DEMOD), 33 and 34
is an output terminal, 35 is a mixer, 36 is a recording amplifier (AMP), 37 is a regenerative amplifier (AMD), 38 is an emphasizer (EMP), and 39 is a suppressor (DEEMP).

Here, the first video signal is input to the input terminal 21, and the second video signal is input to the input terminal 21.
A video signal is applied to input terminal 22.

[Fig. 3] has exactly the same configuration and function as [Fig. 1] except for the emphasizing device 38 and the suppressor 39, and only the emphasizing device 38 and the suppressor 39 will be explained here.

As mentioned above, the suppressor 39 suppresses unnecessary odd-order distortion components and the upper sideband of the second modulation signal during reproduction, and the enhancer 38 has exactly opposite characteristics to the suppressor 39. , the upper side wave of the second modulated signal is emphasized and recorded.

[Fig. 4] and [Fig. 5] show the above suppressor 3.
9 shows detailed circuits and frequency characteristics of the emphasizer 38. In FIG. 4, 40 and 41 are transistors 42, 43, 44, 45, 46 and 4.
7 is a resistor, 48 and 49 are capacitors, 50 and 51 are inductors, 52 and 53 are input terminals, 54 and 55 are output terminals, 56 and 57
is a power supply terminal, and 58 and 59 are ground terminals. 4A is a detailed circuit diagram of the emphasizer 38, and FIG. 4B is a detailed circuit diagram of the suppressor 39.

A and B in [Fig. 5] correspond to A and B in [Fig. 4], respectively, and indicate the transfer characteristics from the input terminal 52 or 53 to the output terminal 54 or 55 of the respective circuit. The horizontal axis shows frequency, and the vertical axis shows transfer characteristics. [A in Figure 5
The frequency _C in and B is the peak frequency of each characteristic, and the frequency _F is the frequency to which no emphasis characteristic or suppression characteristic is applied.

Set the resistance values of resistors 42, 44 and 45 to the same value.
R ₁ (Ω), the resistance values of resistors 43 and 46 are the same R ₂ (Ω), the capacitances of capacitors 48 and 49 are the same C(F), and the inductances of inductors 50 and 51 are the same L( H), and the Laplace operator S is used as a means of frequency analysis of the circuit.

[Figure 4] Input-output transfer function H _B of suppressor B of B
(S) is H _B (S)=S ² LC+SR ₂ C+1/S ² LC+S(R ₁ +R ₂ )C+
1...(11) Equation 11 is obtained, and the input/output transfer characteristic H _A (S) of the enhancer A in Fig. 4A is H _A (S) = S ² LC + S (R ₁ + R ₂ ) C + 1/ S ² LC+SR ₂ C+
It can be expressed as 1...(12). From equations 11 and 12, H _A (S) x H _B (S) = 1...(13) It can be understood that the relationship shown in equation 13 exists. From the above, the emphasizer A and the suppressor B have opposite characteristics. In particular, in the enhancer A and the suppressor B, the series resonance frequency of the inductor 50 or 51 and the capacitor 48 or 49 corresponds to the frequency _C at A or B in FIG. 5. Furthermore, the frequency _C and the frequency _F in [Fig. 5] are respectively the upper limit frequency _2U and the lower limit frequency of the upper sideband wave of the second modulation signal in [Fig. 2].
Set around _2H .

[FIG. 6] shows a comparison between the conventional method and the present method using the power density of a mixed signal of the first modulation signal and the second modulation signal during recording and reproduction. [6th
In the figure, the horizontal axis represents frequency, and the vertical axis represents power density. a is the power density distribution of the mixed signal during recording in the conventional method, b is the power density distribution of the mixed signal during reproduction in the conventional method, and C is
d represents the power density distribution of the mixed signal during recording in this method, and d represents the power density distribution of the mixed signal during reproduction in this method. 60, 61, 62, 63 are the first
Modulation signal, 64, 65, 66, 67 are second modulation signals, 68, 69 are unnecessary components, 70 is emphasizer characteristic,
71 is a suppressor characteristic.

As mentioned above, when the first modulated signal 60 and the second modulated signal 64 are frequency multiplexed and recorded as shown in a, in the conventional method, the mixed signal at the time of reproduction is
Unnecessary component 68 is added. In this method, the upper sideband of the second modulation signal was raised due to the enhancer characteristic 70. When the signal is recorded in the state and is reproduced, the first modulated signal 63, the second modulated signal 67, and the unnecessary component 69 are reproduced by the suppression characteristic 71. The first modulation signal 63 and the second modulation signal 67 are the same as the first modulation signal 61 and the second modulation signal 65 in the conventional method, but in this method, the unnecessary component 69 is extremely suppressed. Become.

In the above, the unnecessary component of the 6th term in Equation 10 is
Countermeasures were taken only for the allocation between the modulation signal and the second modulation signal, but depending on the allocation, the unnecessary component in the sixth term of Equation 10 may become the second modulation signal.
There is an allocation that falls into the lower frequencies of the modulating signal. Even in such cases, the emphasis recording and suppressed reproduction of this method can be applied. That is, when recording, the second
The lower sideband of the modulated signal is emphasized, and the lower sideband and unnecessary components of the second modulated signal are suppressed during reproduction.

Furthermore, in the above explanation, only the suppression of unnecessary components in the 6th term of Equation 10 was dealt with, but as a practical matter,
Even in cases where the unnecessary component in the fourth term of Equation 10 is more important than the unnecessary component in the sixth term of Equation 10 in terms of image quality deterioration,
The present invention can be applied, and the problem can be solved by emphasizing in advance the vicinity of the frequency where the unnecessary component in the fourth term of Equation 10 occurs during recording, and then performing suppression having the opposite characteristics during reproduction.

Effects of the Invention As described above, the present invention, in a frequency multiplexing magnetic recording device, emphasizes and records the upper sideband of the second modulation signal in advance during reproduction, so that during reproduction the upper sideband wave of the second modulation signal is recorded with an opposite characteristic to that during recording. By suppressing
It does not affect the desired first modulation signal and second modulation signal, and suppresses only the unnecessary odd-order distortion components generated by the frequency multiplexing magnetic recording/reproducing device, which is the problem of the conventional method. It is possible to significantly improve the S/N deterioration due to
It is possible to widen the bands of the first video signal and the second video signal more than before.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional frequency multiplexing video signal magnetic recording and reproducing device, FIG. 2 is a diagram showing frequency allocation in the configuration of FIG. 1, and FIG. 3 is an implementation of the video signal recording and reproducing device of the present invention. An example block diagram, FIG. 4 is an electric circuit diagram showing the specific configuration of the emphasizer and suppressor used in the present invention, and FIG.
FIG. 6, which is a transfer characteristic diagram of the same circuit, is a diagram showing frequency allocation used to explain the effects of the present invention. 18, 60, 61, 62, 63...Power density distribution of the first modulated wave, 19, 64, 65, 66, 67
... Power density distribution of second modulated wave, 38 ... Emphasis device, 39 ... Suppressor, 70 ... Emphasizer characteristics, 71
... Suppressor characteristics, 43 ... First resistance, 48 ...
Capacitor, 50...Inductor, 44...Second
resistor, 40...transistor, 42...third resistor.

Claims (1)

[Claims] 1 Frequency modulation of the first and second video signals,
a first modulated wave and a second modulated wave, respectively, the center frequency ₁ of the first modulated wave is higher than the center frequency ₂ of the second modulated wave, and the lower sideband wave of the first modulated wave and the second modulated wave. This is an allocation in which the upper sideband waves of the waves do not overlap and frequencies ₁ - 2 ₂ fall between center frequencies ₁ and ₂ , and a mixed signal in which the first modulated wave and the second modulated wave are frequency multiplexed is magnetically generated. When recording on the same track of a recording medium, the recording circuit system is provided with an emphasizing device for emphasizing the upper sideband of the second modulated wave, and the reproducing circuit system is provided with a suppressor having characteristics opposite to those of the emphasizing device. A video signal magnetic recording and reproducing device characterized by: 2. The intensifier connects a series resonant circuit consisting of a first resistor, a capacitor, and an inductor and a second resistor in parallel between the emitter terminal of a transistor and ground, and inputs a second modulation signal from the base terminal of the transistor. , the video signal according to claim 1, wherein the video signal is configured to obtain an output emphasizing the upper sideband of the second modulation signal from the collector terminal of the transistor loaded with the third resistor. Magnetic recording and reproducing device.