JPH0265594A - Disturbance reducing device - Google Patents

Abstract

PURPOSE:To eliminate the deterioration in the vertical resolution and to realize an excellent reproduction pattern by extracting an unbalanced spectral component to a carrier so as to apply FM detection and eliminating the disturbing component through the arithmetic processing between the extracted disturbing component and the result of FM detection. CONSTITUTION:An output of an equalizer 1 is branched into an FM detection path and an AM detection path and the AM detection path is provided with a band pass filter 4 extracting a frequency band with arranged upper and lower side waves, a square device 5 to apply AM detection, a low pass filter 6 to eliminate a carrier component having a double frequency generated from the square device 5 and a frequency characteristic correction circuit 7 having a frequency characteristic of 6dB/oct for FM detection. An output of a delay correction circuit 8 and an output of a frequency characteristic correction circuit 7 are given to an adder 9, and an FM demodulation wave from which a disturbing component is eliminated and subject to arithmetic processing is obtained. Thus, although the disturbing component in the FM modulation wave is reduced but the vertical resolution is not deteriorated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a disturbance reduction device, and more particularly,
The present invention relates to an interference reduction device for reducing interference caused by crosstalk and the like in an FM transmission line used in a VTR, etc., and obtaining a high quality signal.

[Prior Art] Video signal recording and reproducing apparatuses, such as consumer VTRs, perform guard panless recording, so that the signal of the main track and the signal of the adjacent track are simultaneously taken into the head during reproduction. Therefore, although it is not noise, the signal from the adjacent track interferes with the signal from the main track. this is,
This is a phenomenon called crosstalk. In order to reduce this crosstalk, the "H alignment", Hf) 1 carrier shift, H
A number of interference reduction methods have been employed, such as correlated noise reduction and tilted azimuth recording as described on pages 78 to 89 of the same book.

FIG. 5 is a block diagram showing the configuration of a conventional interference reduction device called H-correlated noise reduction. This interference reduction device includes an amplifier 11 and one horizontal scanning period (hereinafter referred to as I
H) delay line 12, subtracter 13, and limiter 14
, an amplifier 15 with a gain of 1/2, and an adder 16.

On a consumer VTR (VHS format), when guard panless recording is performed, the carrier in FM modulation is recorded every track 1, -1 (this -Σ"fH/). -Σ-f is called carrier shift.Here, f is the horizontal frequency, which is 15.734kHz in the NTSC system.The crosstalk component of the adjacent track has a frequency of Tfs with respect to the signal of the main track. Figure 7 (a
) is the spectral distribution shown. When a signal with this spectral distribution is demodulated (the frequency of the modulated signal is S), it becomes a signal with the spectral distribution shown in FIG. 7(b). In the absence of crosstalk, only the signal of frequency S is demodulated. Therefore, the frequency components of -fH, s-T's, and S+f8 are superimposed after demodulation due to Talostalk. These components are hereinafter referred to as Talostok components.

S has a spectral component that is an integer multiple of fN.
1 + strongly, above lower fN, S5-7f, S+-Σ-f. is fH(n
+ above) times the frequency (where n is an integer).

On the other hand, the frequency characteristics of the circuit shown in FIG. 5 would be the characteristics shown in FIG. 6 without the limiter 14. The characteristic shown in Fig. 6 has a valley at the frequency of (n + L) of fH,
Talostok components are removed.

Next, it will be explained that the characteristics of the circuit shown in 1 and 5 become the characteristics shown in FIG. 6.

In FIG. 5, if the output of the adder 16 is Eo (t) and the output of the amplifier 11 is Ei (t), then Eo (t)
= Ei (t) 1 ± 1 Ei (t − T) − Ei (t) 1 1 1 .

,', Eo (t) −7E i (t) +τE l
(t - T) holds true. However, it is T-IH. Also, limiters are not taken into account.

When the above formula is Z-transformed, E o (z) = −E i (z) +7Z−TE
i (z)−Z (1+Z −”) E i (z
). Therefore, the transfer function H(z) is −−(
1+ e ='''7) 2°=-H(1+coscuT -j slnωT). Therefore, the frequency-gain characteristic is IH(z) l
=1+cos cl, IT. However, ω−2πf
, T-1/fy, so I H(z) I =1+cos 2yr (f
/fs). This shows that when fm (n + engineering) fu, the value becomes 0. That is, it shows that the characteristics shown in FIG. 6 are obtained. This characteristic eliminates crosstalk components.

[Problem to be solved by the invention] As mentioned above, the conventional FM modulated wave interference reduction device has two problems.
Since this is equivalent to finding the sum between E, there is a drawback that the vertical resolution deteriorates, which becomes a big problem in the current demand for high image quality. In addition, using H-correlation means that among the noise components, those with H-correlation remain, resulting in problems such as the screen being played back as if it were raining, making the screen visually unsightly. There was a point.

This invention was made to solve the above-mentioned problems, and aims to provide a completely new interference reduction device that reduces interference components in FM modulated waves and does not cause deterioration of vertical resolution. do.

[Means for Solving the Problems] The interference reduction device according to the present invention extracts interference waves mixed into FM waves by AM detection means, and performs arithmetic processing with a demodulated signal containing the FM detected interference components. , the interference components contained in this demodulated signal are reduced.

[Effects] The interference waves mixed in the FM transmission line do not have a spectral distribution in which the upper and lower side waves are symmetrical with respect to the carrier, unlike normal FM modulated waves, The spectral distribution is asymmetrical (unbalanced). By extracting the unbalanced component with respect to this carrier by the AM detection means and performing arithmetic processing (for example, addition/subtraction) with FM demodulation No. 13, FMm;
This is to remove the interference wave components contained in the signal.

[Embodiment] FIG. 1 is a schematic block diagram showing the configuration of an embodiment of the present invention. In the figure, an FM modulated wave on an FM transmission path is applied to an equalizer 1, and its frequency characteristics are corrected. The output of equalizer 1 is the FM detection path and AM
The detection path is branched into a detection path. The FM detection path includes an FM demodulator 2 that performs FM demodulation of the FM modulated wave, a low-pass filter 3 that removes carrier components after FM demodulation, and A
A delay correction circuit 8 is provided to correct the delay time between the M detection path and the FM detection path. On the other hand, the AM detection path includes a band pass filter 4 that extracts a frequency band in which upper and lower side waves are aligned, and a band pass filter 4 that extracts a frequency band in which upper and lower side waves are aligned, for devices that use a residual side wave transmission method of FM waves such as a VTR. , a low-pass filter 6 that removes a carrier component of twice the frequency generated by the squarer 5, and a frequency characteristic correction circuit 7 that provides a frequency characteristic of 6 dB10ct for FM detection. ing. The output of the delay correction circuit 8 and the output of the frequency characteristic correction circuit 7 are provided to an adder 9 for arithmetic processing (addition processing).

From this adder 9, an FM demodulated wave from which interfering components have been removed is obtained.

Next, the operation of each block in FIG. 1 will be explained using mathematical formulas.

FIGS. 2(a) to 2(e) show the process in which the Talostok component is removed in FIG. 1.

FIG. 2(a) shows that the frequency component f2 is a signal from the main track, and the frequency component f is a crosstalk component that causes interference.

In other words, the signal mixed with crosstalk components is expressed as E(t)
, if the mixing ratio is k, then E (t) −cos (2πf2t)+kcos
(2πf, t) (provided that f2>f). First, A.M.
Consider the Fft wave path. It is assumed that f, , f2 are the passbands of the bandpass filter 4, respectively.

E (t) is squared by $5, so E2 (t) = (cos (2πf2 [) + k
cos C2yr f + t) l 2-co
s2 ('2rf2 t) +2kcos (2πf,,t) cos (21f, t) +2cos2 (2πf+ t) = I + cos (4TCfzt) + kcos
12π (f, +f2)tl+kcos12yr
(f2−f+)) Therefore, this spectrum becomes as shown in FIG. 2(b).

Here, E2 (t) is changed to 2 by the low-pass filter 6.
Since the carrier component of twice the frequency is removed, if the signal after passing through a of the low-pass filter 6 is EL2(1), it is expressed as EL2(t)=(1+2)+kcos12π(f2−f+)tl.

f2-f, is set as Δf, and the DC component 1T (2 to 1+) can be ignored, so EL2 (t)-kcos(2
πΔft) Also, if the signal after passing through the 6dB10ct frequency characteristic correction circuit 7 is ELE2 (j), then E
LE2 (t)- to Δf cos(2WΔft)...
(1) The signal is expressed as: This is because the frequency characteristic of 6dB10ct has a gain characteristic proportional to the frequency.
, 2 (t) is Δf, which means that the gain is also proportional to Δf.

When this ELE2 (t) is expressed on the frequency axis, it becomes as shown in FIG. 2(C). On the other hand, in the FM detection path, the FM demodulator 2 is equipped with an amplitude limiter, usually called a limiter, as shown in FIGS. 10(a) and 10(b). FIG. 10(b) shows F Mi:i! using an amplitude limiting method called the DL-FM method described in pages 98 to 100 of "NHK Home Video Technology" by Katsuya Yokoyama, published by Japan Broadcasting Publishing Association. It is a J device. In the case of FIG. 10(a) and FIG. 10(b), the amplitude limiting method uses a limiter. By passing through the limiter, the upper and lower FM side waves are aligned, and the second The spectrum distribution becomes as shown in Figure (d).

The positive and negative spectra represent the phase relationship of the side waves.

This can be expressed mathematically as shown below.

E(t)=cos(2yr f 2t )+kcos
(2x f + t) cos (2πf2 t) + kcos12 yr (f 2 - Δf) t) =
f 1 +kcos(2wΔf t) 1cos(2π
f2 t) +ksin(2πΔf t ) 5in(2πf2 t
) and is separated into AM and FM components.

The AM component is removed when it passes through the limiter, so the AM
If the signal from which the component has been removed is EL+M (t), then EL + n (t)-cos12πf2 t+
φ (t)). Now, if we consider the case where k is infinitesimal, the approximation φ(t) # −k 5in(2πΔft) holds, so EL I M (t) = cos(:2r f2t−
ks1 mouth (2πΔ [t)). Since FM demodulation operates to differentiate the phase,
If the signal one week after returning to FM is Ern(t), Ern
(t)−k2πΔf cos(2yrΔft)...
(2), and the spectral distribution after FMllJ and modulation is shown in Figure 2 (
It becomes as shown in e).

The above equation (1) is the demodulated waveform by the AM detection path,
Equation (2) is the demodulated waveform by the FM detection path. Also,
Equation (2) includes a beat component generated by interference such as crosstalk. If the signal of equation (1) and the signal of equation (2) are added by an adder 9 that adds them at a ratio of 2π:1, this beat component will disappear.

Therefore, FIG. 1 shows a device that can reduce interference below the carrier component (low frequency side) of an FM modulated wave. Among beat disturbances caused by crosstalk between adjacent tracks, this method is effective against beats caused by crosstalk of signals in the horizontal synchronization portion. Because, VT
This is because the synchronization signal such as R is a negative polarity synchronization, and the carrier of the synchronization signal portion is on the lower side (lower frequency side) than the carrier of a normal video signal. Also, if Δf is constant, 6d
The frequency characteristic correction circuit 7 of B10ct is not necessary.

Next, consider a case where interference is mixed into the upper side (high frequency side) of the carrier of the FM modulated wave. That is, Fig. 4 (a
) We will discuss the case where a waveform with a spectral distribution as shown in is input. This reduction device is shown in FIG.

The only difference from FIG. 1 is that a subtracter 10 is provided in place of the adder 9.

FIGS. 4(a) to 4(e) show the process by which crosstalk components are removed in the embodiment of FIG. 3.

If the signal mixed with crosstalk components is E (t) and the mixing ratio is k, then E (t) = cos (2πf2 t) + k cos (
2πf,t) (however, f, > f2). First, consider the AM detection path. f, , f2 are each bandpass filter 4
Assume that the passband is . E (t) is determined by 2 dye type 5, E2 (t) = (eos (2πf2 t) + kcos
(2πf, t) l 2-earth (2 to 1+) +k
cos t2π(f, -f2) tl +kcos 2π (2π(f, +f2)(1 +cos(4π[2t) + 2cos(4πf, t)) Therefore, this spectrum is as shown in Figure 4(b). Become.

Next, E2 (t) is passed through the low-pass filter 6 to remove the twice the frequency carrier component, so if the signal after passing through the low-pass filter 6 is EL2 (t), then EL2 (t) - ± (1 + 2 ) +kcos12π(f
, -f2)tl. Let f and -f2 be Δf, and since the DC component (1+2) can be ignored, it becomes EL′ (t)−kcos(2πΔft). Moreover, the signal after passing through the 6dB10ct frequency characteristic correction circuit 7 is ELE2 (t)=IcΔf cos(2yrΔft)
...(3) The signal is expressed as follows. This is 6 dB/o
Since the frequency characteristic of ct has a gain characteristic proportional to frequency, the frequency component of E% (t) is Δf, which means that the gain is also proportional to Δf.

This ELE2 (j) is expressed on the frequency axis as shown in Figure 4 (
c).

On the other hand, in the FM detection path, the upper and lower side waves are aligned by the limiter included in the FM demodulator 2, resulting in a spectrum distribution as shown in FIG. 4(d). Upper side of carrier (high frequency side)
When interference is mixed in, the limiter output is E (t) − cos (2rr f2 t) + k cos
(2yr f, t) −cos (2πf2 t) +kcos12π(f2
+Δf)t) −(1+kcos(2yrΔf t))cos(2y
r f2 t) −ksln(2yrΔf t) si
n<2πfz t) = l+Ic +2kcos(2πΔft)・co
Since it can be transformed as s(2xf2 t+φ(t)), if the limiter output is EL+nCt), then EL + n (t) −cos12πf2 t+
φ (t)). Now, considering the case where k is infinitesimal, the approximation φ(t) = ksln(2πΔft) holds, so EL + n (t) = cos12πf2 tl
k 5in(2xΔft) 1 , and the spectrum distribution after FM demodulation is as shown in FIG. 4(e). Since the FM demodulator operates to differentiate the phase, the signal after FMI modulation is converted into E.

M (t), EF M (t)− has 2πΔfcos(2πΔft)
... (4) becomes.

The above equation (3) is the demodulated waveform by the AM detection path,
Equation (4) is the demodulated waveform by the FM detection path. Also,
Equation (4) includes a beat component caused by interference such as crosstalk. (3).

Comparing equations (4), we find that if we subtract the signal from equation (3) and the signal from equation (4) using a subtracter 10 that subtracts the signal from equation (4) at a ratio of 2π:1, we get
This is a device that reduces interference on the upper side of the carrier.

From the above, it has been proven that the interference component extracted by the AM detection means can be reduced by adding and subtracting from the waveform after FM detection. Extracting interference in the FM transmission path using AMI waves is a completely new extraction method.

Unlike noise reduction using H correlation, this type of interference reduction device does not use the Ht (j function), so it does not involve deterioration of vertical resolution, and also reduces noise reduction caused by rain caused by residual noise with H correlation. This has the advantage that the screen does not appear in such a state.

Further, if such an interference reduction device is configured as shown in FIG. 8, it is possible to reduce noise remaining in the transient portion of the video signal.

FIG. 8 is a schematic block diagram showing the configuration of still another embodiment of the present invention. As shown in the figure, this embodiment includes an equalizer 1 for correcting frequency characteristics, an FM demodulator 2, and an FM demodulator 2.
Low-pass filter 3 that removes the carrier component of the M demodulated wave
, a band pass filter 4 for extracting a frequency band in which upper and lower side waves are aligned for a transmission line that uses a residual side wave transmission method such as a VTR, and a double dye type 5 for AM detection;
and a low-pass filter 6 for removing a carrier component of twice the frequency generated by the double dyeing type 5, and a 6 dB/.

a frequency characteristic correction circuit 7 that gives a frequency characteristic of ct;
one code control circuit that controls the code of the AM detection path; and a low-pass filter 17 that removes high-frequency components to prevent the code control circuit from malfunctioning when a high-frequency signal is present.
A bypass filter 18 that performs a differential operation to detect the rising and falling portions of the video signal, a delay correction circuit 8 that corrects the delay time difference between the AM detection path and the 1M detection path, and an adder 9. including.

First, the generation of noise in the transient portion of a video signal due to crosstalk will be explained with reference to FIG. FIG. 9(a) shows a transient portion of the video signal, and FIG. 9(b) shows the FM modulated wave of FIG. 9(a).

Devices that record on magnetic tape, such as VTRs, produce jitter due to their mechanism.

Jitter refers to expansion and contraction of the time axis or deviation in the time axis direction. Therefore, crosstalk components from adjacent tracks include a signal as shown in FIG. 9(c) having a time difference due to jitter with respect to the main signal. If we consider this by dividing the video signal into a flat part and a transient part, the flat part will have a single spectrum as shown in Figures 9(d) and (f), but the transient part will have a second spectrum. As shown in FIG. 4(a) and FIG. 4(a), the spectrum becomes unbalanced between the upper side (high frequency side) and the lower side (low frequency side) with respect to the carrier. That is, in the transient portion, when the signal 73 is rising, crosstalk is mixed into the lower side (low frequency side) of the carrier, and when the signal is falling, crosstalk is mixed into the upper side (high frequency side) of the carrier. Since interferences below the carrier can be added by the adder 9 as shown in FIG. 1, and interferences above the carrier can be subtracted by the subtracter 10 as shown in FIG. Interference can be reduced by controlling the sign of the path by distinguishing whether crosstalk is mixed above or below the carrier. Since it is possible to distinguish whether the crosstalk is mixed in the upper or lower side by checking whether the video signal is rising or falling, if the bypass filter 18 is used for first differentiation, the rising part will have a positive sign and the falling part will have a negative sign. The sign can be controlled by the positive or negative sign. Note that the video signal is transmitted up to a very high frequency, and in order to prevent high frequency signals from erroneously controlling this control, a low pass filter 17 that removes high frequencies is used to filter out the rising edge of the signal only at low frequencies. It is only necessary to control the falling part. The sign control circuit 19 only needs to switch the sign depending on whether the control signal is positive or negative, and can be realized by a circuit as shown in FIG. 14, for example. To detect whether it is a rising part or a falling part,
A circuit with differential characteristics may be used. The differential characteristic is a characteristic that changes the waveform shown in FIG. 12(a) to the waveform shown in FIG. 12(b).

Note that code control does not necessarily have to be performed using transient information; other code control may be performed, for example, using the video signal level. When the video signal level is high, there is a high probability that interference waves from the lower side will mix with the carrier, and when the level of the video signal is low, there is a high probability that interference waves from the upper side will mix with the carrier. It is.

In such a case, for example, 7! If the video signal level is higher than the quasi-potential, it is positive, and if it is lower than the quasi-potential, it is negative, and so on.

The interference reduction device of the embodiment shown in FIG. 8 is also effective against the generation of ghosts in video signals due to the contour effect, which is a problem unique to magnetic heads characterized by forming a metal layer in the gap. There is.

The contour effect refers to crosstalk between the main gap 31 and the pseudo gap 30 in a magnetic head as shown in FIG. 15, and this causes a ghost-like waveform to occur immediately after a transient.

This is the same as noise occurring in the transient section due to the above-mentioned crosstalk, so it will be explained with reference to FIG. The pseudo gap 30 is created in the space created between the metal layer 29 and the ferrite 32. That is, the main gap 31 and the 5iJ-like gap 30 are located apart by the thickness of the metal layer 29. That is,
The signal entering the pseudo gap 30 has a time difference with respect to the main gap 31 by a time represented by the thickness of the metal layer/relative velocity between the tape heads.

If the signal entering the main gap 31 is designated as 91Z (b), the signal entering the pseudo gap 30 is expressed as shown in FIG. 9(c). Therefore, the transient portion of the video signal is mixed with interference waves as shown in FIG. 9(e). The noise in the transient section caused by the above-mentioned crosstalk looks like noise because the time difference is caused by jitter where the time axis shift is not constant, but in the case of a ghost due to the contour effect, it is different from the position of the main gap 31. Since the position of the pseudo gap 30 is fixed and the time difference is constant, it appears as a ghost. However, both have the same cause and can be removed using similar equipment.

In addition, although we have only dealt with interference in the residual sidewave transmission method, the same applies to the double-sided transmission method, and in this case,
As shown in FIG. 11, there is no need for a bandpass filter 4 that extracts only the band in which the upper and lower side waves are aligned. Further, even in the vestigial sidewave transmission method, if the passband of the low-pass filter 6 is narrow, the band-pass filter 4 is not necessary.

Furthermore, although a squarer is used as the AMtA wave method, the squarer may be configured as shown in FIG. 13 in order to increase the sensitivity of the squarer. In FIG. 13, a squarer is configured using a balanced modulator 28.

When using a balanced modulator in this way, the original signal and π/
Since it is most sensitive to manually input a signal phase-shifted by 2, a π/2 phase shifter 26 is provided in FIG. Also,
Any AM detection method that extracts unbalanced components with respect to the carrier may be used without using a squarer.

Further, a limiter or a slicer may be inserted to limit the amplitude of the control signal manually input to one code control circuit in order to prevent malfunction due to noise or the like.

[Effects of the Invention] As described above, according to the present invention, an unbalanced spectrum component with respect to a carrier is extracted by AM detection, and the extracted interference component and the FM detection result are subjected to arithmetic processing. Since the interference component is removed, if it is applied to reduce the interference generated in the FM transmission line, such as in a consumer VTR, the interference can be reduced without using H-correlation, thereby reducing the deterioration of vertical resolution. This makes it possible to achieve a good playback screen.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an interference reduction device according to an embodiment of the present invention. FIG. 2 is a spectrum distribution diagram showing the process of reducing interference by the apparatus shown in FIG. FIG. 3 is a block diagram showing an interference reduction device according to another embodiment of the present invention. FIG. 4 is a spectrum distribution diagram showing the process of reducing interference by the device shown in FIG. 3. FIG. 5 is a block diagram showing a conventional interference reduction device. FIG. 6 is a frequency characteristic diagram of the device shown in FIG. 5. FIG. 7 is a spectrum distribution diagram showing the process of reducing interference by the device shown in FIG. FIG. 8 is a block diagram showing an interference reduction device according to still another embodiment of the present invention. FIG. 9 is a diagram showing the process of signal quality deterioration in the transient portion due to interference. FIG. 10 is a block diagram showing an amplitude limiting method in an FM demodulator. FIG. 11 is a block diagram showing an interference reduction device according to still another embodiment of the present invention. FIG. 12 is a diagram showing a differential waveform of a transient portion. FIG. 13 is a block diagram in which the sensitivity of the squarer is increased. FIG. 14 is a circuit diagram showing an example of the configuration of a code control circuit and a balanced modulator. FIG. 15 is a diagram showing a magnetic head characterized in that a metal layer is formed in the gap portion. In the figure, 1 is an equalizer, 2 is an FM demodulator, 3.6
and 17 is a low-pass filter, 4 is a band-pass filter, 5 is a multiplier, 7 is a frequency characteristic correction circuit, 8 is a delay correction circuit, 9 is an adder, 16 is a subtracter, 18 is a bypass filter, and 19 is a code control circuit shows. Agent Masuo So ((C) ↑ Δf Jealousy 5 times [T 89 times・(吋Mゑめ120 (a) (b) PF Next deception is hot〃 14th Ri 3rd sword t

Claims (1)

[Claims] In a signal transmission device using an FM transmission path, the FM
AM detection means for extracting interference components mixed into the transmission path; FM detection means for demodulating the FM modulated signal in the FM transmission path; and interference components extracted by the AM detection means and the FM detection means.
1. A disturbance reduction device comprising: a signal containing a disturbance component that has been FM demodulated by a detection means; and arithmetic processing means for removing the disturbance component from the FM demodulated signal.