JPS5923993A - Circuit for improving signal-to-noise ratio of video signal - Google Patents

Abstract

PURPOSE:To improve the signal-to-noise ratio of video signals, by relatively increasing the signal component against noises contained in demodulated signals of video signals, such as carrier chrominance signals, luminance signals whose frequency is modulated, etc., in color video signals. CONSTITUTION:Mixed signals reproduced from a magnetic tape 14, on which video signals of SECAM system are recorded, by a magnetic head 13 are divided into two parts after passing through a front amplifier 15 and one part is supplied to a high-pass filter 16 having a cut-off frequency of 1.5MHz and luminance signals, whose frequency is to be modulated, are separated and filtered. The other part is passed through a low-pass filter 17 and low frequency converting carrier chrominance signals are separated. The output of the filter 16 is demodulated at an FM demodulator 18 and returned to luminance signals, and then, inputted into a mixer 19. One part of the outputs of the filter 17 remains intact, and the other part is converted by the converter 21 after it is changed into two signals delayed by two horizontal scanning periods (2H), and a low frequency carrier converting chrominance signal whose carrier frequency shift and center frequency are reduced to 1/2 is obtained as the output of the converter 21. The frequency and shift are doubled at the next double-multiplying circuit and color video signals are obtained after the low frequency carrier chrominance signals are passed through a filter 24 and mixer 19.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a signal-to-noise ratio improvement circuit for video J8J signals;
In particular, the signal components 5-
The present invention relates to a circuit that improves the signal-to-noise ratio by relatively enhancing the signal-to-noise ratio.

Prior Art Conventionally, when recording a color video signal on a magnetic recording medium such as a magnetic tape, a luminance signal and a carrier chrominance signal are separated from the color video signal, and a wideband luminance signal is recorded using a low carrier frequency of 4! ;: It is converted into a harmonic signal and recorded using the vestigial sideband method, and the comparatively narrow band carrier color signal is processed to stabilize the phase of the color signal against 1uJ '+dl fluctuations when writing. The frequency modulated wave signal is converted to a frequency band lower than the frequency band of the wax signal, and this low frequency converted carrier color signal is multiplexed and distributed on the frequency modulated luminance signal, and this is reproduced. The Machio method of magnetically recording video signals is widely known. Depending on the magnetic recording and reproducing method,
The frequency-modulated luminance signal acts like a high-frequency bias, and the low-frequency conversion carrier color signal can be recorded with good linearity.

FIG. 1 shows a block system diagram of an example of a recording system of the SECAM color video signal recording and reproducing system, which was previously proposed by the present applicant in Japanese Patent Application Laid-Open No. 4-37426.

In the figure, the S E CAM color video signal input to the input terminal 1 is divided into two parts, one of which is converted into a 2tP wave by the low-pass filter 2, and the other is filtered by the bandpass filter 31 (
The carrier color signal is separated into P waves. The luminance signal is supplied to a frequency modulator 4, where it is converted into a frequency modulated wave signal of a predetermined band (hereinafter also referred to as rFM modulation H), and then passed through a high-pass filter 5 that removes unnecessary components and then sent to a mixer 6. On the other hand, J-, Ki (# power transmission signal is 1 as well known).
A 1.M modulated wave (with a center frequency of approximately 4.4
MHz), automatic chroma control! ] The signal is supplied to an ACC circuit 7, where it is set at a predetermined constant level, and then limited by a limiter 8 to the maximum width of 4 to remove the unconnected AM component. The carrier color signal taken out from the limiter 8 is supplied to a flip-flop 9, which is an example of a frequency step-down path, where it is counted down and the frequency is stepped down. The carrier color signal taken out from the flip-flop 9 has a center frequency of approximately 221 to IHz and a frequency of 1
, whose frequency deviation has been reduced to one of that of the input carrier chrominance signal of flip-flop 9.

Is the above carrier color signal inserted from flip-flop 9 a circle? , l&g'l$ converter 10, where the tube wave number is changed by the oscillation frequency of, for example, 2.8 MJ''z from the local oscillator 11, and then the cut-off frequency 1. , 5 Pv
The center frequency is approximately 600 through IHz low-pass filter 2.
The signal is extracted as a kHz low-frequency conversion carrier color signal, and is then supplied to the AiJ mixer 6 where it is mixed with the elementary signal which has been made into the FM modulated wave. The output mixing coefficient of the mixer 6 is recorded by a rotating magnetic head 13 onto a magnetic tape 14 over an inch. Here, the band of the mixed signal recorded on the magnetic tape 14, that is, the recording band, is made small as the frequency shift of the low frequency conversion carrier color signal by the flip-flop 9 is reduced.

The video signal recorded by this recording system is
The brightness symbol, which is the M modulated wave, is F M1, tl, (
), J- band brightness) is converted to f signal, while 1・λ
・Since the reproduced low-frequency carrier color vibration, which is one modulated wave, is restored to its original state by frequency conversion by a heterogeneous inverter and a doubling circuit, the recording band is Even when applied to a narrow-band general urine VTR, a good reproduction image can be obtained with almost no h-ler inversion phenomenon.・ Also, those who do not publish r'rlr should first read the F Japanese Patent Application Publication No. 54-37531.
By providing a flip-flop in place of the frequency converter 10 and station 41j excavator 111 shown in FIG. ) At the time of production, IM proposed a wiring regeneration method that uses a quadrupling circuit to return to the original frequency shift and band.

According to this proposed method, it has the same features as the above-mentioned applicant's 4 easy recording/reproducing method, and also has a frequency multiplier circuit and a frequency converter that can be converted into a sandalwood circuit in V using frequency conversion by heterogain. Since the frequency expansion of the carrier color signal is performed using a multiplier circuit, the circuit configuration is simple and the table can be made compact.

Problems to be Solved by the Invention However, both of the above proposed methods are excellent, although the 8/N ratio of the after-tone output of the reproduction 1.M change decirculation is not as good as 2.2. In particular, there was a problem in that the S/N ratio of the FM demodulated output of the carrier color signal, which is an FM modulated wave, was poor.

Therefore, the purpose of the present invention is to delay the FM modulated video signal by two horizontal scanning periods. The frequency with the output delay signal of the mother-in-law circuit? By adding the frequency η, the S/N ratio of the demodulated signal (video signal) of the F1ν1 modulated wave is improved, and the S
It is an object of the present invention to provide a signal-to-noise ratio improvement circuit for a single video word that is suitable for application to a reproduction processing system for ECAIM carrier color signals.

Means for Solving the Problems The present invention provides a delay circuit that delays a frequency-modulated video signal by two horizontal scanning periods, and a frequency-modulated video signal that is an input signal to the delay circuit. The output frequency modulated wave 43 of the delay circuit is received as an input signal, respectively, and the frequency 7 AC harmonics of the same frequency are received as the sum of the frequencies of the input signals in ζ.
Due to the configuration of the frequency converter that controls No. 1,
The above-mentioned r1.] attack [1 point name-- has been solved, and each embodiment thereof will be described below with reference to FIGS. 2 to 41.

Example 2
] is shown in the block system diagram in which the recording endogenous method proposed by the author is applied to the middle thread. In the figure, the same reference numerals are given to the same components as those in FIG. 1. Second
The circuit 20 surrounded by a broken line at T shows the first part of the signal-to-noise ratio numerical circuit for the video signal, which will become clear in this case.

The p gosengo reproduced by IjB ki head 13 is %ii
Divided into two through R amplification 15, one side is j1 place cut li
'; 3 high-pass filters 161ζ with wave numbers 1, 5 Ml (z are supplied and the frequency-modulated luminance signal is divided into σ5 waves, and the other is supplied with low-pass filters 171 with cut-off frequencies 1, 5 M, Hz and the low The range-transformed carrier chrominance signal is separated into a P wave.The output wave frequency modulated luminance signal of the high-pass filter 16 is supplied to an FM demodulator 18, where it is FM demodulated and converted into a luminance signal (P wave).
Mixer 19 after being returned to number i? This one is dressed up.

On the other hand, the low-pass converted carrier color signal with a center frequency of approximately 600 kl-1z, which is a phase-modulated wave of 1·' taken out from the low-pass filter 7, is divided into two parts, one being supplied to the frequency converter 21, and the other being (21 (2 horizontal scans 1o1r4 by delay circuit 22) (2H) Frequency converter 2 after being delayed
] and be cured. Frequency fact: Izumi 21 is 2H slow (・1
Hidden W4-raw low range change j! 41jli, the +4 color signal and the non-delayed endogenous low-pass conversion carrier color No. 41 are combined with 111S, and the 11th frequency of both −fg signals (one range change of the same frequency: "1" Output h-transfer and e-mail '?1-
Ru. Here, the low-pass replacement carrier color number supplied to the frequency conversion 2 and 21-Q is the same as the 11th 4) i14 [
.

As shown in S E CAhj', the carrier color/signal wave frequency of the 13th expression was converted to 4 das to 1'
Since it is a 1 blind code, by adding the frequencies in the upper 601 frequency converter 21, the frequency converter 2J to 1.4 (low frequency conversion carrier in which the carrier wave center frequency is doubled while the general transmission frequency deviation remains the same) p, enlightenment, that is, a low-pass conversion carrier color signal whose aligned frequency shift and center frequency are both J-ζ·=9] is output rfJ!9 with respect to the carrier color signal of the 5ECAhl system.

4. Input low-frequency disguise tQ'i included signal of the converter 21 IJSI: '
IR7H, the same as the S ECAM system's hook feed color signal.
r-? The first one with this color difference signal>i(+?-Y) as the modulation signal
A second 1.M modulated color difference signal that modulates the 1-tone color difference width signal and the color difference signal ()i-Y). j scarcity is t
Since these are sequential signals that are synthesized in time series for each H period, the color information between 211 and 211 is very similar to each other. This two-line phase [η property is 5f]
In other words, the frequency change 46 and the frequency conversion 21 are carried out by each other, and the frequency conversion is carried out between the two H females and the scale range, and the frequency is converted between the two aunts. 1V,
be taken out.

In this way, after frequency conversion, the output low frequency and converted carrier color No. 44 of T+421 are outputted from I~, and the output low range/converted carrier color No. 44 is later stored in a monitor television receiver as if ] The signal is obtained by improving the S/N ratio of the color signal demodulated by the P/M demodulation circuit, and is supplied to the doubling circuit 23. This doubler circuit 23 is constructed, for example, from a double-wave rectifier circuit, and as is well known, Yoshikawa ζζ doubles the center plane of one input FM wave, and the frequency F at each instantaneous time.
By doubling A as well, H1θν and 9 deviation are also 24@
Outputs the FM modulated wave. The IPA signal extracted through the bandpass filter 244 which removes unnecessary frequency components from the above-mentioned double multiplication filter 23 has both the center frequency and the frequency deviation. l':
To C, one method of Takao's color signal is good. This horse owner conveyance color signal is transmitted to the mixed fortune 19 (A4), and here P Ju
! It is mixed with the reproduction purity signal from the demodulator 18 and outputted from the output terminal 25 as a color video signal to the 8ECA 81.

Next, the S/N ratio improvement operation by the signal-to-noise ratio improvement circuit 20 will be explained. Now, the modulation signal V of the output low-pass conversion carrier color signal of the low-pass filter] 7, (t) and the noise component V. ([) and are respectively shown in the following formulas.

Vl(t) = A, crsω1t
(1) V, (11=Ancy-ω.t
(2+ However, in the formula 111 and (2+, A t l 7Vn is the scratch width, ω1゜ω (J angular frequency. = Adjustment Vl (
tl and noise [component Vn(t) (actual transmission wave f. 5-to F obtained by frequency modulation 1 modulation: harmonic M (tl, 7th ζ] and this) parameter λ1 Modulation θ>, [(tl 11 and γS.t), In formula (3), Ao is F
With an amplitude of eP, I(11), ω0 is 2πfo and is also 1(·J constant.

On the other hand, the output FM modulation S of the 2H predetermined circuit 22 which extends this Fhl modulation M(tl by 14 units in 2H period) is transferred to 4(tj
' and 1-Rokichi, M(ti' is)-r, C, and the noise component becomes a random.

Therefore, the output FM modulated wave ■t) of the frequency converter 21 is expressed by (F'M modulated wave M(1) expressed by equation 31) and (4
) is expressed as the component of the sum of the products of the F PJ modulated wave M(t)', so the component 2 of the sum of V(tl=(M(t)xM(t)') has A .

#, ko'-cm(2ω.1+rsinω,tl) This FM modulated wave V(tl is demodulated by the PM demodulation circuit in the monitor television receiver, 2A,
sinω1t + Aocpsωni + An' cos
ω,' t (6). here,(
6) Assuming that the width An' of the noise component in the equation is approximately equal to A, the effective value of the noise component is ρ-A. However,
As shown in equation (6), the imaging width A1 of the signal component is doubled. This means that the output FM modulation V(t) of the frequency converter 21 is equal to This means that the ratio has been recast.

Next, a second embodiment of the circuit of the present invention will be described with reference to the block system diagram shown in FIG. 3. In FIG. 3, the same components as those in FIG. 2 are given the same reference numerals, and their explanations will be omitted. In FIG. 3, a circuit 26 surrounded by a broken line represents a second embodiment of the circuit of the present invention. The reproduced low-pass converted carrier color signal extracted from the low-pass filter 17 is supplied to a doubling circuit 27, where the carrier frequency shift and center frequency are each doubled. As a result, for the carrier color signal of the SECAM system,
The carrier frequency deviation is the same, only the carrier center frequency is 1
The low-frequency conversion carrier electric signal, which has been doubled in frequency, is transmitted to the doubling circuit 2.
Taken out from 7 I! The signal is supplied to a 1 wave number converter 28 and a 2H delay circuit 29, respectively.

The frequency converter 28 performs frequency conversion between the input low-band converted carrier color signal of the 2H delay circuit 29 and the output low-band converted carrier color signal, and adds the frequencies of both signals to obtain SECA of the original band.
Outputs an M system carrier color signal.

Further, since the frequency converter 28 and the 2H delay circuit 29 perform the same operation as the frequency converter 21 and the 2H delay circuit 22, the transmitted color signal with an improved S/N ratio is passed through the bandpass filter 24 to the mixer. 19.

Next, 43 embodiments of the circuit of the present invention will be explained together with the block system diagram shown in FIG. In FIG. 4, the same components as those in FIG. 2 are designated by the same reference numerals, and their explanations will be omitted. In FIG. 4, a circuit 32 surrounded by a broken line shows a third embodiment of the circuit of the present invention. M! The present applicant previously proposed the tape 30 in Japanese Patent Application Laid-Open No. 54-37531. m like, SID
The carrier signal signal in the CAM system color video signal is converted into a low frequency converted carrier color signal in which the carrier frequency shift and center frequency are reduced and changed by the l+3 frequency down-down circuit. The brightness of the lake has been recorded.

Therefore, the low-pass converted carrier color signal that is frequency-selected and extracted by the low-pass filter 7 is the carrier wave ■ whose center frequency is also approximately 1.1 Ml-1x of the frequency of 7, 5
This is the signal that was sent. This reproduced low-pass conversion carrier color signal is supplied to the equalizer circuit 31, where it has a frequency characteristic that is opposite to the frequency characteristic of the recording system equalizer circuit (a frequency characteristic that attenuates the level of both upper and lower side bands of the low-pass conversion carrier color signal). )
is applied to make the sideband at a substantially constant level, and then the signal is sequentially supplied to doubler circuits 33 and 34 and multiplied by 4. 2
A circuit section 14 consisting of multiplier circuits 33 and 34, for example, a circuit consisting of a half-wave rectifier circuit and a bandpass filter, which extracts the fourth-order harmonic component of the half-wave rectified output to increase the quadrupled output by r%, or a phase-locked loop ( PLL) etc., and as is well known, the input F M '& F
By quadrupling the center frequency of the wave, by quadrupling the number of cycles at each instant, the frequency deviation also quadruples.
Return to the original carrier color signal. Therefore, the signal is output through the doubler circuit 34. (No. g is the reproduced carrier color signal of the CAM method, which has been compressed for both Nakagami frequency and frequency shift. This raw carrier color signal is processed by the frequency converter 35 and the 2H delay. are supplied to circuits 36, respectively.

The frequency converter 35 performs frequency conversion to obtain the frequency of the sum of the above-mentioned reproduced carrier color signal and the 4 general color feed signals outputted from the 2H delay circuit 36.

As a result, the frequency converter 35 outputs 8
An improved reproduction carrier color signal with a 7N ratio is retrieved. However, since this reproduced carrier color signal is a carrier color signal in which only the center frequency of the carrier wave is twice that of the carrier color signal of the SECAM system, the frequency conversion circuit 37 in the next stage converts the carrier wave center frequency to 7. After being converted back to the carrier color signal of the SECAM system, it is passed through the bandpass filter 24 and sent to the mixer 1.
9.

In the above embodiments, the case where the circuit of the present invention is provided in one regenerative carrier chrominance signal transmission system has been explained, or in the case where the circuit of the present invention is provided in one regenerative carrier chrominance signal transmission system. The S/N ratio can be improved in the same way by adding a frequency converter circuit that returns the center frequency to the original value, or by adding a frequency a conversion circuit to return the center frequency Is it necessary to change the configuration of the demodulation circuit 18 itself to transmit a frequency-modulated luminance signal that has a center frequency or two?

Effectively, the circuit for improving the signal-to-noise ratio of video signals according to the present invention is capable of converting frequency-modulated video signals having a time difference of two horizontal scanning periods from each other to a sum of 1 or 2 times. ,
Since the frequency is converted so that the signal component is relatively enhanced compared to the noise component of the FM demodulated detailed signal, the signal-to-noise ratio (S/N ratio) can be improved, especially for magnetic recording media. 5IDCA that is reproduced from It is suitable because it can improve the S/N ratio of the phrase tone output of the cover color hakumei where the deterioration of the lid color is easily noticeable.

[Brief explanation of the drawing]

Figure 1 shows S)′; CA ht originally proposed by the applicant.
Figures 2 and 3 are block system diagrams showing an example of the 6-recording system of the color video signal recording and reproducing system. 11 is a block system diagram in which the method is applied to a reproducing system of a recording/reproducing method proposed by the applicant. 14.30... S E CAM color video No. 1 recorded magnetic tape, 1G... Bright band filter for frequency modulation luminance signal separation, 17 - Low frequency modulation single carrier color signal separation low cut Filter, 18...FM qshiXWj, 19
---Mixer, 20, 26.32--Signals 4 Usui ratio improvement circuit, 21, 28, 35--Frequency converter,
22.29.36--2H delay circuit, 23, 27
. 33.34...2 multiplication circuit, 25...Reproduction S B
CAM color video signal output terminal. Procedure room rli hlE Shu'I, lli display Showa 5) 7 (11+i'l Application No. 134269 2, name of invention video iba) 4 signal S・1 force ratio improvement circuit 3, n+Ii
If-Oral fortune 4'l i:'lApplicant 1 location 3 Moriya-cho, Yamakana-ku, Yokohama, Kanagawa Prefecture 221
]l'' Address name 12 (432) l] Ki Victor Co., Ltd. 71 Representative Director N1 Ai Shishi Michi - Department 4, Dai J (11 people 11 locations 102 Higashikoto Chiyo 11) 5-7 Kojimachi, Ward
Address 6, column for detailed description of the invention of the specification to be amended. Otsu? Ifi positive contents (1) Specification Yamanaka, page 4, No. 10? 'l of j' 2.8J
``3,3J, (2) Same, page 4, 12?j, ε3 shell, 5?i] (
ioOkl-1z J is 1+, 1MI-IZ j etc. are corrected. 1013

Claims (1)

[Claims] +1+ +,'il A delay circuit that delays a wave number modulated video signal by two horizontal scanning periods, the frequency modulated video signal that is an input coefficient of the :N delay circuit, and the delay circuit. The output frequency-modulated frequency signal and the frequency-modulated frequency signal of the receiver are respectively input signals, and the receiver is composed of a frequency converter that obtains a frequency-modulated wave signal of a frequency equal to the sum l of the frequency of the input signal (!:f-
Improving the signal-to-noise ratio of the FI signal (ILit)
Road. (2) The frequency-modulated image signal is reproduced from the magnetic recording medium (41). 1. It changes to the low frequency with a modulus of 1. 2. The signal-to-four-tone ratio improvement circuit of claim 1, which initially recognizes that the signal is a SECAM system carrier I arrow color signal that has been returned to a normal band.