JPS59103489A - Circuit for eliminating carrier chrominance signal - Google Patents

Abstract

PURPOSE:To reduce the effect of a luminance signal component on a frequency band of a carrier chrominance signal by designing the circuit that only a PAL color video signal is applied and the PAL color video signal not including the carrier chrominance signal is outputted as it is, when no chrominance carrier signal exists. CONSTITUTION:When no color difference signal is included in the PAL color video signal, that is, the signal level of the carrier chrominance signal is zero, a color difference signal detecting signal is annihilated, an analog switch 11 is opened, an output of a two-multiplication circuit 6 is not applied to a multiplier circuit 7 and no signal is outputted from the multilier circuit 7, resulting that only the PAL color video signal is applied to an adder circuit 2 to which the output of the multiplier circuit 7 is applied via a low pass filter 8. Thus, when the PAL color video signal not including the carrier chrominance signal is applied to a band pass filter 1 and the adder circuit 2, the supplied PAL color video signal is outputted from the adder circuit 2 as it is.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a carrier color signal removal circuit, and in particular to a PAL (
The present invention relates to a carrier color signal removal circuit that removes a carrier color signal to obtain a luminance signal included in a color video signal based on the Phase Alternation Line (Phase Alternation Line) method.

Such a carrier color signal removal circuit is configured to completely remove the carrier color signal from a color video signal using a band rejection filter having an IE band approximately equal to the frequency band of the carrier color signal, or a carrier color signal in an HPAL color video signal. By using the fact that the phase of is shifted by 90° every IH (one horizontal scanning period), two
There is a known structure in which the carrying color signals of each of the scanning lines of a book are completely synthesized having a phase difference of 180° to cancel the carrying color signals. However, when the luminance signal obtained by the former circuit is supplied to the video output circuit that amplifies the luminance signal and applies it to the cathode of the picture tube, the luminance signal components near the frequency of the carrier color signal are also removed, so the horizontal resolution This causes an inconvenience in that the value decreases. Furthermore, when the luminance signal obtained by the latter circuit is supplied to the video output circuit, color video signals corresponding to two scanning lines separated by 2 H from each other are synthesized, resulting in a significant decrease in vertical resolution. occurs.

Therefore, a circuit as shown in FIG. 1 has already been devised as a carrier color signal removal circuit that does not reduce horizontal resolution or vertical resolution. In FIG. 1, a PAL color video signal is fed to a bandpass filter l and a summing circuit 2. In FIG. The bandpass filter 1 is configured such that its passband is approximately equal to the frequency band of the carrier color signal included in the PAL color video signal. This bandpass filter I
Accordingly, the carrier color signal component is extracted and supplied to the 11-T delay circuit 3 and the burst gate 4. The IH delay circuit 3 is composed of, for example, a delay line whose signal delay time is equal to the time corresponding to IH. The burst gate 4 is supplied with the output of a pulse generator (not shown) configured to obtain a pulse that exists for approximately the same period as the color burst signal by delaying the horizontal synchronization signal, for example, as a burst gate pulse. .Perst Gate 4
is composed of an analog switch circuit that is turned on and off in response to the burst gate pulse, for example, and separates the color burst signal from the carrier color signal and supplies it to a subcarrier generation circuit 5 based on, for example, an APC (automatic phase side rUI) system. The subcarrier generation circuit 53- generates a color subcarrier signal synchronized with the color burst signal and supplies it to a color demodulation circuit (not shown) and the like, as well as to the doubling circuit 6. The doubler circuit 6 has a configuration similar to, for example, a double-wave rectifier (b) circuit, and outputs a signal obtained by fully doubling the frequency of the color subcarrier signal. The output of this doubler circuit 6 is supplied to a multiplier circuit 7. Multiplier circuit 7 J: ri, output of doubler circuit 6 and i
A signal obtained by multiplying the output of the H delay circuit 3 is output and supplied to the low-pass filter 8. In the low-pass filter 8, components with frequencies twice and three times the frequency of the color subcarrier signal included in the output of the multiplication circuit 7 are removed, and only components with a frequency equal to the frequency of the color subcarrier signal are output. The signal is supplied to the adder circuit 2. In the adder circuit 2, the PAL color video signal and the output of the low-pass filter 8 are added together to cancel the carrier color signal component. The output of this adder circuit 2 is supplied to a video amplification circuit or the like.

In the above configuration, the PAL color video signal EMrL corresponding to n (n is a natural number) grain scanning lines is expressed as a quartic equation.

EMn = I”y(t) +EU(t)cosωot
10Ev (sinω, 1・・・・・・・・・(1) ωc=2π(284−′/4) fH−=−(2) Here, EY(ri is the luminance signal, Ev(t) and EU(t) indicate color difference signals R=Y and B-Y-i, respectively.

Further, fH is a horizontal scanning frequency.

Here, EY(ri is the fundamental frequency component of the luminance signal ￥1■s
(2πfH・1・t) and its high frequency component Y2coS
(2rrfH・2・t) , ・＋・++−+YZ
cQS (2ttfu・L・t).

Since it can be considered as the sum of..., EY(ri) is expressed as the following formula.

EY(S=ΣYtcO8(2πfH・t・t) ・
......(3) is similarly expressed as EU(su, Ev(ri) as shown in the following formula.

EU(t)=ΣAmcos (2π9・m・t)...
・・・・・・(4)n Ev(LiniΣBga CO3(2π9・rt)・・
(5) Next, (n-1) the main PAL color video signal EM (7L-1) is expressed as shown in the following equation.

EM (nt) - EY (t"H) + EU (t tH) C1O5ω, (t-1H) -
Evsinωo(j-tH) 2EY(LeeEU(t) SinωctEy(t)
cO8ωc1 −・・・(6) Here,
tH indicates time equivalent to iHK.

Therefore, the signal sin 2ωo1 obtained by doubling the frequency of the color subcarrier signal and (n-1') main P
The signal sin 2ωct' EM Cn-1) obtained by multiplying the AL color video signal EM (nt) is as follows: 0 sin 2ωct'' EM Cn-5) = Ey Ct
) ・sin 2 ω, tEU (t) Sin ω, t
* sin 2ωo1−Ev(t) CO8ωct −
sin 2ωct Substituting equation (3) into equation (7) and rearranging, we get the following equation: 0sin 2ωct” EM(n-
1) = (EY7 CO8 (2πfH11 or t)) sir + z
ω, 1-EU (sinωo1・sin 2ω, 1-E
v(s cosωot * sin 2ωo1−(′/2
)ΣYz[sin (2ω, +2πtH−t'tt−1
-8in(zωc-2π9・t'(t ] + ('A)
EU(su(CQS 3ω, t-cosωct)+('
A) Ev(su(sin 3ω, t +sinωct)
......(8) Signal EM(n-1) obtained by removing components of frequencies twice and three times the frequency of the color subcarrier signal from this signal Sin 2ωct" EM(n-1) is O EM (n-1) = ('I/L2)ΣYz sin (2
ωo−2π9・1)1−(a)EU(scO8ωct(V2)By(t)sinω,17− Substituting the formula (2) into the formula (9) and reorganizing it, the following formula is obtained.

EM (71, -1) - (3/2) EU (t) wω. t(/2)E
v (t) 8111 ωot...(lO) (1), equation (lO), and J: the ninth-order equation holds true.

E engineering+2Epoi-1)-EY(su+ΣY7 Sin 27C(2X284-t/2) f
H@L... (11) According to equation (11), it is possible to completely cancel the carrier color signal component in the output of the adder circuit 2 that combines the PAL color video signal and the output of the low-pass filter 8. However, in the conventional luminance signal separation circuit as described above, when the luminance signal component in the frequency band of the carrier color signal passes through the bandpass filter, the luminance signal output from the adder circuit 2 is given the equation (11). Unnecessary components as shown in item 2 will be mixed in. This 8----(Since the angular frequency of the fundamental frequency component in the component indicated by the second term of Equation 10 is different from the angular frequency of the fundamental frequency component in the luminance signal EY(t), there is interference due to the component indicated by the second term. Although it is thought that the influence of the above factors is small, it is desirable to further reduce the influence by reducing unnecessary components as shown in the second term.

SUMMARY OF THE INVENTION An object of the present invention is to provide a carrier color signal removal circuit that can reduce the influence of the luminance signal component in the frequency band of the carrier color signal than in conventional circuits.

A carrier color signal removal circuit according to the present invention includes a bandpass filter means for passing only components within the frequency band of the carrier color signal from a PAL color video signal, a signal delay means for delaying the output of the bandpass filter means for a predetermined time, and a color frequency doubling means for generating a signal with a frequency twice the frequency of the subcarrier; multiplication means for multiplying the output of the signal delay means and the output of the frequency doubling means; A low frequency component extracting means for extracting and outputting all low frequency components, and a signal synthesizing means for adding or subtracting the output of the low frequency component extracting means and the PAL color video signal to synthesize the PAL color video signal. It is configured to supply only video signals.

Hereinafter, the present invention will be explained in detail with reference to FIG. 2.As shown in FIG.
Delay circuit 3. Purst Gate 4. Subcarrier generation circuit 5, double times N6. The multiplier circuit 7° low-pass filter 8 is the first
Connected as shown.

However, in this example, the output of the bandpass filter 1 is supplied to one input terminal of the subtraction circuit 9. The output of the lH delay circuit 3 is supplied to the other input terminal of the subtraction circuit 9. The IH delay circuit 3 and the subtraction circuit 9 form a so-called comb-shaped filter, and the subtraction circuit 9 cancels the luminance signal component and outputs a signal containing only the carrier color signal component. The output of this subtraction circuit 9 is supplied to a color difference signal detector 10. The color difference signal detector 10 separates each of the EU(R) component and the Ev(t) component from a signal containing only the carrier color signal component, and sends the signals to the B-'Y demodulator and R.
-Y demodulators, and when a signal is output from either or both of these B-'Y demodulators and R-Y demodulators, outputs a color difference signal detection signal consisting of a high level signal, for example. It is configured to do this. The output of this color difference signal detector 10 is supplied to a side input terminal of an analog switch 11 serving as signal supply stopping means. The analog switch llu is connected to the output end of the two-way digital sound circuit 6 and the multiplier circuit 7 so that it becomes open when the color difference signal detection signal disappears and stops supplying the output of the two-way signal circuit 6 to the multiplication circuit 7.
0 input terminal.

In this configuration, if the PAL color video signal includes a color difference signal, that is, if the signal level of the carrier color signal is not zero, a color difference signal detection signal is generated, the analog switch 11 is closed, and the doubler circuit 6 is closed. The output is supplied to a multiplication circuit 7, where the carrier color signal is removed by K, similar to the circuit of FIG. Next, if the PAL color video signal does not include a color difference signal, that is, if the signal level of the carrier color signal becomes zero, the color difference signal detection signal disappears, the analog switch 11 becomes open, and the 2-way transmitter circuit 6 The output of the multiplication circuit 7 is no longer supplied to the multiplication circuit 7, and no signal is output from the multiplication circuit 7. As a result, only the PAL color video signal is supplied to the adder circuit 2 to which the output of the multiplier circuit 7 is supplied via the low-pass filter 8. Therefore, when a PAL color video signal that does not include a carrier color signal is supplied to the band filter 21 and the adder circuit 2, the supplied PAL color video signal is output from the adder circuit 2 as is.

As described above, according to the present invention, when there is no carrier color signal component, only the PAL color video signal is supplied to the adder circuit 2 as a signal combining means, and the PAL color video signal containing no carrier color signal is supplied to the adding circuit 2 as a signal combining means.
Since the AL color video signal is output as is, even if a luminance signal component exists in the frequency band of the carrier color signal, the influence of the brightness signal component can be reduced.

In addition, by sharing the comb-shaped filter section consisting of the 1I-I delay circuit 3 and the subtraction circuit 9 and the color difference signal detector 10 with the color demodulation circuit, the number of component parts of the device for reproducing video according to the PAL color video signal is increased. can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional luminance signal separation circuit;
FIG. 2 is a block diagram showing one embodiment of the present invention. Explanation of symbols of main parts 1...Band filter 2...Addition circuit 3...
IH delay circuit 4... Burst gate 5... Subcarrier generation circuit 6... Double multiplier circuit 7... Multiplier circuit 8...
Low-pass filter 9...Subtraction circuit lO...Color difference signal detector 11...Analog switch applicant Pioneer Corporation agent Patent attorney Motohiko Fujimura

Claims (1)

[Claims] (il) removing the carrier color signal to obtain a luminance signal contained in a PAL color video signal in which one of the carrier color signals and the color burst signal are phase-inverted every other horizontal scanning period; A carrier color signal removal circuit, comprising: bandpass filter means for passing all of the components within the frequency band of the carrier color signal from the PAL color video signal; and signal delay means for delaying the output of the bandpass filter means for a predetermined time;
a frequency doubling means for generating a signal with a frequency twice the frequency of a color subcarrier; a multiplication means for multiplying the output of the signal delay means by the output of the frequency doubling means; and a comparison of the outputs of the multiplication means. low frequency component extracting means for extracting and outputting low frequency components, and signal synthesizing means for adding or subtracting and synthesizing the output of the low frequency component extracting means and the PAL color video signal; a difference signal generating means for generating a difference signal according to a difference between an input and an output of the means; a color difference signal detecting means for generating a color difference signal detection signal when the difference signal includes a color difference signal; and a color difference signal detecting means for generating a color difference signal detection signal. and supply signal control means for supplying only the PAL color video signal to the signal synthesis means in accordance with a detection signal. (2) The supply signal control means comprises signal supply stop means for completely stopping the supply of the output of the frequency doubling means to the multiplication means in accordance with the color difference signal detection signal. A carrier color signal removal circuit according to scope 1.