JPH0314395B2 - - Google Patents

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 a SECAM type color television receiver.

[Conventional technology]

A SECAM color television signal is formed by switching red and blue color difference signals line-sequentially, applying pre-emphasis and band limiting, then frequency modulating the color subcarrier and superimposing it on the luminance signal. In this color subcarrier, when the color difference signal is zero (that is, in achromatic color), the carrier frequency for the red color difference signal (R-Y) and the blue color difference signal (B-Y) is
4.40625MHz and 4.25MHz. 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.

The conventional color television signal processing device 1 shown in FIG.
From the SECAM color television signal, the third
The carrier color signal shown in Figure A is extracted and the limiter circuit 3
After limiting the amplitude at , the signal is supplied to the demodulation circuit 4.
The color signal shown in FIG. 3C demodulated by the demodulation circuit 4 is de-emphasized by the de-emphasis circuit 5 and then supplied to level shift circuits 6r and 6b. The level shift circuit 6r converts the signal to V _r
As shown in FIG. 3G, the white and black achromatic color levels of the (RY) signal of the (N+l)th line are at the reference level (zero level in this example).
Shift it downward so that Further, the level shift circuit 6b level-shifts the signal by V _b ,
As shown in FIG. 3F, the levels of the white and black achromatic portions of the (B-Y) signal of the Nth line are shifted upward by _Vb so that they become the reference level.

Here, the level shift operation by the level shift circuits 6b 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. 3B, and is used for this control. The line identification signal shown in FIG. 3D is supplied to the line identification circuit 8. In addition, in the case of this example, between 7 and limiter circuit 3,
A demodulation circuit 9 having a circuit configuration similar to that of the demodulation circuit 4 is provided, and by gating the output of this demodulation circuit 9 with an ident gate pulse in a gate circuit 7, positive and negative polarities are determined every horizontal scanning period. A pulse in which the line is inverted, that is, a line identification signal is obtained.

The outputs of the level shift circuits 6b and 6r are brought to a no-signal zero level during the horizontal retrace period by a horizontal (or vertical) blanking pulse shown in FIG. 3H in blanking circuits 9r and 9b, respectively. Both signals thus level-shifted and blanked are sent to gate circuits 10r and 10, respectively.
b. In the gate circuit 10r, as shown in FIG. 3L, the gate pulse shown in FIG. 3J sent as an output from the flip-flop circuit 11 connected to the line identification circuit 8 causes
The (RY) component of the (N+l)th line is taken out, and the (BY) component of the Nth line is removed. Similarly, in the gate circuit 10b, the flip-flop circuit 11 sends out the Q output as shown in FIG.
By using the gate pulse shown in FIG. 3, the (B-Y) component of the Nth line is taken out and the (RY) component of the (N+l)th line is removed, as shown in FIG.
In this example, since the polarity of the demodulated (RY) signal is inverted with respect to the polarity of the (B-Y) signal,
A phase inversion circuit 12 inverts the phase of the (RY) signal.

The (RY) signal thus obtained and (B-Y)
The signals are subjected to line-sequential/synchronization processing by synchronization circuits 16b and 16r, each of which has a one-line delay line circuit 13 and a signal line 14 connected in parallel to a synthesis circuit 15, and is processed into predetermined signals as shown in FIG. 3M and N. color difference signal.

[Problem that the invention seeks to solve]

The above conventional color television signal processing circuit 1
Since the level shift amounts in the level shift circuits 6b and 6r are fixed to _Vb and _Vr , respectively, when the frequency of the color subcarrier changes on the transmission side of the color television signal, the level shift circuit 6
(B-Y) signal or (R-
Y) There were problems such as the white and black achromatic parts of the signal did not reach the reference level, making it impossible to perform correct color demodulation.

Further, in the conventional color television signal processing circuit 1, the line identification signal is demodulated by a demodulation circuit 9 that is separate from the demodulation circuit 4, which has the problem of complicating the circuit configuration.

[Means for solving problems]

This invention solves the above problems, and demodulates the carrier color signal of a SECAM color television signal line-sequentially, so that the white and black achromatic parts of the color difference signal components are at the reference level. In a color television signal processing device that performs line-sequential simultaneous conversion after level shifting so that a level shift circuit that level-shifts the white and black achromatic portions of the color difference signal components to a predetermined reference level regardless of frequency fluctuations of the color subcarrier on the transmitting side; and a line output from the demodulation circuit. The gist of the present invention is to include a control means that outputs a level shift signal corresponding to the level of the identification signal and controls the level shift circuit so that it reaches the 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. Regardless of fluctuations, white and black achromatic parts of color difference signal components are made to reach a predetermined reference level.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 and 3. FIG. 1 is a circuit diagram showing an embodiment of a color television signal processing device of the present invention.

In Fig. 1, color television signal processing device 2
1 is a gate circuit 7 and a level shift circuit 6r, 6
A sample-and-hold circuit 22 as a control means is provided between the lines 1 and 2b. As shown in FIG. 4, this sample and hold circuit 22 includes, for example, a clamp diode 100 and a clamp diode 1.
The capacitor 101 is connected to the cathode side of the clamp diode 100 to hold the peak value of the line identification signal, and the discharging resistor 102 is connected to the cathode side of the clamp diode 100 to discharge the charge stored in the capacitor 101. The peak value of the line identification signal is sampled and held every horizontal scanning period, and the peak value of the line identification signal is sampled and held every horizontal scanning period, corresponding to the positive or negative polarity of the line identification signal which is sent out from the gate circuit 7 and whose polarity is inverted every horizontal scanning period. A signal whose polarity is inverted every horizontal scanning period as shown in FIG. E is output. 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 circuits 6r and 6b.
The amount of shift is varied.

The level shift circuit 6r includes a diode 106 that becomes conductive when a hold signal of the (RY) signal output from the sample and hold circuit 22 is input, and voltage dividing resistors 103 and 104 connected to the de-emphasis circuit 5. and an amplifier 105 for amplifying the (RY) signal, and the diode 106 is connected to the connection point between the voltage dividing resistors 103 and 104. The level shift circuit 6b also includes a diode 110 that becomes conductive when a hold signal of the (B-Y) signal output from the sample and hold circuit 22 is input, and a voltage dividing resistor 107 and a diode 1 connected to the de-emphasis circuit 5.
08, and an amplifier 109 that amplifies the (B-Y) signal.
The diode 110 is connected to the connection point between the voltage dividing resistors 107 and 108.

That is, when the frequency of the color subcarrier changes on the transmission side of the color television signal, the level of the line identification signal extracted by the gate circuit 7 also changes, so this level fluctuation is stored in the capacitor 101 of the sample and hold circuit 22. Level fluctuations are held and the amount of level shift of the level shift circuits 6r, 6b is varied by the output shown in FIG. 3E.

Therefore, even if the frequency of the color subcarrier changes, the (RY) and (B-Y) signals output from the level shift circuits 6r and 6b will have their white or black achromatic parts at the reference level. , which allows accurate color demodulation at all times.

In the case of this embodiment, the conventional demodulation circuit 9 is omitted and the gate circuit 7 receives a signal from the de-emphasis circuit 5, so that the circuit configuration is simplified.

As described above, according to the color television signal processing device 21, the line identification signal included in the SECAM color television signal is demodulated, and the sample and hold circuit 22 extracts 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 parts 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 the conventional color television signal processing device 1 in which the quantities are fixed such as V _r and V _b , accurate color demodulation is always possible even if the frequency of the color subcarrier on the transmitting side varies.

〔Effect of the invention〕

As explained above, according to this 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, regardless of the frequency fluctuation of the color subcarrier on the transmitting side. Unlike conventional color television signal processing devices in which the amount of level shift is fixed, the control is performed so that the white and black achromatic portions of the color difference signal components are at predetermined reference levels.
Even if the frequency of the color subcarrier on the transmitting side fluctuates, excellent effects such as always accurate color demodulation are achieved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of a color television signal processing device of the present invention, and FIG.
The figures are a circuit configuration diagram and a signal waveform diagram of each part of the circuit, respectively, showing an example of a conventional color television signal processing device, and FIG. 4 is a circuit configuration diagram showing the main parts of the color television signal processing device of FIG. 1. be. 6b, 6r...Level shift circuit, 7...Gate circuit, 16b, 16r...Synchronization circuit, 21...
...color television signal processing device, 22...sample hold circuit.

Claims (1)

[Claims] 1. After demodulating the carrier color signal of a SECAM system color television signal line-sequentially and level-shifting the white and black achromatic portions of the color difference signal components to the reference level, A color television signal processing device that performs simultaneous line-sequential conversion includes a demodulation circuit that demodulates a line identification signal included in the color television signal, and a demodulation circuit that demodulates the line identification signal output from the demodulation circuit into a color subcarrier on the transmitting side. a level shift circuit that level-shifts the white and black achromatic portions of the color difference signal components to a predetermined reference level regardless of frequency fluctuation; 1. A color television signal processing apparatus, comprising: control means for outputting a level shift signal to control the level shift circuit so that it reaches the predetermined reference level.