JPS60254984A - Signal processor for color television signal - Google Patents

Abstract

PURPOSE:To perform invariably accurate color demodulation in an SECAM color television receiver by demodulating the line identification signal in a color television signal, varying the extent of level shifting according to the level of the demodulated line identification signal, and performing control so that an achromatic part has a specific reference level. CONSTITUTION:The color television signal processor 21 has a sample and hold circuit 22 as a control means between a gate circuit 7 and level shifting circuits 6r and 6b. When a chrominance subcarrier varies in frequency at a transmission side, the line identification signal extracted by the gate circuit 7 also varies in level, so this level variation is sampled and held by the sample and hold circuit 22, thereby varying the extents of level shifting of the level shifting circuits 6r and 6b with the output of the circuit 22. Consequently, even when the chrominance subcarrier varies in frequency, an (R-Y) and a (B-Y) signal outputted by the level shifting circuits 6r and 6b have achromatic parts of white or black coincident with an accurate reference level, so that invariably correct color demodulation is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color television signal processing device suitable for a color signal demodulation circuit of an SEOAM color television receiver.

[Conventional technology]

The 8BCAM color television signal is formed by switching the red and blue color difference signals line-sequentially, applying pre-emphasis and band limiting, and then frequency-modulating the color subcarrier and superimposing it on the luminance signal. Regarding the color subcarrier, when the color difference signal is zero (that is, when the color is achromatic), the carrier frequencies for the red color difference signal (R-y) and the blue color difference signal (B-Y) are 4t, 410421 MHz and g, JtMHz.
becomes. In this case, in order to reduce dot interference, the signal is passed through a bandpass filter called a Bell filter to suppress color subcarriers at levels that are or are close to achromatic colors. Therefore, on the television receiver side, a Bell filter with characteristics opposite to those on the transmitting or encoding side is provided to correct the signal.

Conventional color television signal processing device shown in Figure 1/
extracts the carrier color signal shown in FIG. 3(A) from the SFj OAM color television signal input to the bell filter described above, limits the amplitude in the limiter circuit 3, and then supplies it to the demodulator circuit 3. The color signal shown in FIG. 3 (0) demodulated by the 0 demodulation circuit is de-emphasized by the de-emphasis circuit and then sent to the level shift circuit &
r, supplied to tb. The level shift circuit 6r is
The level of the signal fVr is shifted, and as shown in FIG. Level shift circuit g1. , the signal is level-shifted by Vb and shown in Figure 3 (
As shown in F), v
b Shift it slightly upward.

Here, the level shift operation by the level shift circuits 4b and 6r is controlled by a gate circuit 7 that allows a line identification signal (ident signal) to pass through using an ident gate pulse shown in FIG. 3(B), and is used for this control. Is the line identification signal shown in FIG. 3(D) a line identification circuit? is supplied to In this example, a demodulation circuit having a circuit configuration similar to that of the demodulation circuit is provided between the gate circuit 7 and the limiter circuit 30. is provided, and by gating with the ident gate pulse in the gate circuit 7 which is the output of this demodulation circuit, a pulse whose positive and negative polarities are inverted every horizontal scanning period, that is, a line identification signal is obtained.

The outputs of the level shift circuits 4b and tr are brought to a no-signal zero level during the horizontal retrace period by the horizontal (or vertical) blanking pulse shown in FIG. 3(H) in the blanking circuits 9r and tb, respectively. Both signals thus level-shifted and blanked are supplied to gate circuits 10r and 1Ob, respectively. Gate circuit 10
r, a 7 rig 7 connected to the line identification circuit;
Figure 3 (
With the gate pulse shown in J), the (R-y) component of the (N+1)th line is extracted as shown in (L) of the same figure.
The (B-y) component of the Nth line is removed. Similarly, in the gate circuit 10F), from the free-lag frog circuit /I,
Due to the gate pulse shown in Fig. 3 (1) sent out as the Q output, the Nth line +7) is detected as shown in Fig. 3 (K).
The (B-Y) component is taken out, and the (R-Y) component of the (N+1)th line is removed. In this example, the demodulated (
Since the polarity of the R-y) signal is inverted with respect to the polarity of the B-Y signal, the phase of the R-Y signal is inverted in the phase inversion circuit 12.

The (R-y) signal and (B-Y) signal obtained in this way are respectively transmitted by a synchronization circuit/6b in which the line delay line circuit/3 and the signal line stub are connected in parallel to the combining circuit 15, and/
After undergoing line-sequential and simultaneous processing using Ar,
(This is a predetermined color difference signal that indicates the color difference.)

[Problem that the invention seeks to solve]

In the above conventional color television signal processing circuit, since the level shift amount in Jr is fixed to vl) and Vr, respectively, the frequency of the color subcarrier on the transmitting side of the color television signal is When it fluctuates, it is the output of the level shift circuit db, tr (
The white and black achromatic parts of the B-Y) signal or the (R-Y) signal do not reach the reference level, resulting in problems such as the inability to perform correct color demodulation.

Furthermore, the above-mentioned conventional color television signal processing circuit demodulates the line identification signal using a demodulation circuit separate from the demodulation circuit, which has the problem of complicating the circuit configuration.

[Means for solving problems]

This invention solves the above problems, and S I
The carrier color signal of the O'A M color television signal is demodulated line-sequentially, level-shifted so that the white and black achromatic portions of the color-difference signal components become reference levels, and then line-sequential simultaneous conversion is performed. In the color television signal processing device, the line identification signal included in the color television signal is demodulated, the level shift amount is varied according to the level of the demodulated line identification signal, and the color subcarrier on the transmitting side is The gist of the present invention is to provide a control means for controlling the white and black achromatic portions of the color difference signal components (related to frequency fluctuations) to a predetermined reference level.

[Effect]

This invention demodulates a line identification signal included in a SECAM color television signal, varies the level shift amount of a color difference signal component according to the level of the demodulated line identification signal, and controls the frequency of a color subcarrier on the transmitting side. C1 to set the white and black achromatic parts of the color difference signal components to a predetermined reference level regardless of the fluctuations. [Embodiment] Hereinafter, with reference to FIGS. 1 and 3, the present invention will be described. Let's discuss an example. FIG. 1 is a circuit diagram showing one embodiment of a color television signal processing apparatus of the present invention.

In FIG. 1, the color television signal processing device 21 includes a sample and hold circuit n as a control means between the gate circuit 7 and the level shift circuits 6r and 4b. , gate circuit 7
The peak value of the line identification signal is sampled and held in each horizontal scanning period in response to the positive and negative polarities of the line identification signal, which is sent out from /Outputs a signal whose nine polarities are inverted every horizontal scanning period.This signal corresponds to the frequency fluctuation of the color subcarrier on the transmission side of the color television signal, and is supplied to the level shift circuit Ar, tb. In other words, when the frequency of the color subcarrier changes on the transmitting side of the color television signal, the level of the line identification signal extracted in the gate circuit also changes, so this level fluctuation is detected by the sample and hold circuit. The level shift circuit t is captured by the output shown in Figure 3 (1!it).
The amount of level shift of r, l+b is varied. Therefore, even if the frequency of the color subcarrier varies, the output of the level shift circuit &r, jb remains unchanged.

In the (R-y) signal and the (B-Y) signal, the white or black achromatic portion matches an accurate reference level, which allows correct color demodulation at all times.

In the case of this embodiment, the conventional demodulation circuit is omitted, and the gate circuit 7 is a de-emphasis circuit! Since such a signal is supplied, the circuit configuration is simplified.

Therefore, according to the color television signal processing device 21, the line identification signal included in the BEOAM color television signal is demodulated, and the sample and hold circuit n converts the color difference signal component according to the level of the demodulated line identification signal. The level shift amount is controlled so that the white and black achromatic portions of the color difference signal components are at a predetermined reference level regardless of the frequency fluctuation of the color subcarrier on the transmitting side. Unlike conventional color television signal processing apparatuses in which the color subcarriers are fixed such as VR and VB, accurate color demodulation is always possible even if the frequency of the color subcarrier on the transmitting side changes.

〔Effect of the invention〕

As described above, according to the present invention, the line identification signal included in the SECAM color television signal is demodulated, and the level shift amount of the color difference signal component is varied according to the level of the demodulated line identification signal. The configuration controls the white and black achromatic parts of the color difference signal components to a predetermined reference level regardless of the frequency fluctuation of the color subcarrier on the transmitting side, which is different from the conventional method in which the amount of level shift was fixed. Unlike a color television signal processing device, it has excellent effects such as always being able to perform accurate color demodulation even if the frequency of the color subcarrier on the transmitting side changes.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a color television signal processing device of the present invention, and FIGS. 2 and 3 are circuit configuration diagrams and circuit components, respectively, showing an example of a conventional color television signal processing device. FIG.

Claims (1)

[Claims] A color television that demodulates the carrier color signal of the SKCtAM color television signal line-sequentially, shifts the level so that the white and black achromatic parts of the color difference signal components become the reference level, and then performs simultaneous line-sequential conversion. In the television signal processing device, the line identification signal included in the color television signal is demodulated, and the level shift amount is varied according to the level of the demodulated line identification signal, thereby adjusting the frequency fluctuation of the color subcarrier on the transmitting side. Regardless, the color television signal processing apparatus is provided with a control means for controlling the white and black achromatic portions of the color difference signal components to a predetermined reference level.