JPS5823995B2 - Irosingou Shiyori Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color signal processing circuit applied to demodulate a color signal (RY component and BY component) from a carrier color signal of a PAL color television signal, for example.

In order to facilitate understanding of the present invention, an example of a conventional color signal processing circuit will be described with reference to FIG.
Reference numeral 1 indicates a terminal to which a carrier color signal and a burst signal separated from a PAL composite color television signal are supplied.

This carrier color signal consists of the (R-Y) component of the color signal and the (B-
Y) is a quadrature two-phase balanced modulated wave modulated by the component,
The phase of the carrier wave modulated by the (RY) component is IH (
At the same time, the phase of the burst signal is delayed or advanced by 135° with respect to the (BY) axis for each IH.

This carrier color signal is transmitted to an ACC circuit 2 having a variable gain amplifier configuration.
is supplied to the IH (one horizontal period) delay line 3 via the IH (one horizontal period) delay line 3, and is also supplied to the addition circuit 4 and the subtraction circuit 5, and the output of the IH delay line 3 is supplied to the addition circuit 4 and the subtraction circuit 5. As a result, the (B-Y) component in the carrier color signal is obtained at the output of the adder circuit 4, and the (R-Y) component in the carrier color signal is obtained at the output of the subtractor circuit 5.

These signals are demodulated by, for example, double-balanced demodulation circuits 6B and 6R, and the (B-y:) component chrominance signal and (R-Y) component including the demodulated output of the burst signal are output to terminals IB and 7R, respectively. A color signal will appear.

A carrier wave whose phase coincides with the (BY) axis is supplied from a voltage-controlled variable frequency oscillator 8 to the demodulation circuit 6B.

Therefore, a burst signal is separated from the output of the adder circuit 4 by a burst gate circuit 9, this burst signal is phase detected by a phase detection circuit 10, and the detected output is supplied to the variable frequency oscillator 8 as a control voltage.

A burst flag is supplied to the burst gate circuit 9 from a terminal 11 .

Furthermore, the amount supplied to one input terminal a of the switch circuit 13 is supplied to the other input terminal a of the switch circuit 13.

The switch circuit 13 is an electronic switch controlled by the output of the flip-flop 15.
Switching is performed for each IH by supplying a horizontal synchronizing pulse from 6.

Therefore, for each IH generated at the output terminal C of the switch circuit 13, a carrier wave whose phase is switched to coincide with the (Y) axis or the -(RY) axis is supplied to the demodulation circuit 6R.

Further, the demodulated output of the burst signal obtained at the terminal 7R and the (R-Y) component are supplied to the burst gate circuit 11, and the demodulated output of the burst signal obtained at the output is supplied to the color signal level and polarity control signal generation circuit 18. Supplied.

This circuit 18 is connected to the ACC circuit 2 from the output of the gate circuit 17.
In addition to forming an ACC voltage for the demodulation circuit 6R, it also determines whether the polarity of the (RY) component output from the demodulation circuit 6R is correct or not. If the polarity is incorrect, it sends a correction signal to the flip-flop 15. It is something to give.

In such a color signal processing circuit, if we consider a case where only a burst signal is supplied to terminal 1, as in the case of a monochrome image, only burst signals appear in the outputs of addition circuit 4 and subtraction circuit 5 in principle. It should be, but actually I
The output of the H delay line 3 has a level of 20-30 dB (20-odd B to 30 dB) outside the horizontal blanking period due to unnecessary reflections in the delay medium.
Contains unnecessary signals (with respect to IH-delayed signals).

Since these unnecessary signals are demodulated by the demodulation circuits 6B and 6R, color stripes appear when the screen becomes dark, resulting in a deterioration in image quality.

In consideration of the above points, the present invention provides a gate circuit 19 on the input side of the IH delay line 3 as shown in FIG.
A gate pulse that occurs only during the burst period is supplied from
The burst signal supplied to the IH delay line 3 is cut off or reduced.

An embodiment of the present invention will be described below with reference to FIG. 3. In the figure, 21 indicates a delay medium of the IH delay line 3, and 22 and 23 indicate converters on the input side and output side. , from the electrodes of the respective transducers to the input terminals 24a, 2
4b and output terminals 25a and 25b are led out.

Further, an input terminal 26 to which the output of the ACC circuit 2 is supplied is connected to the base of a transistor 27, its emitter is grounded via a resistor 28, and its collector is connected to a parallel circuit of a resistor 29 and a compensation coil 30. and resistor 3
1 to the power supply terminal (+VCC), and both ends of this resistor 29 are connected to input terminals 24a and 24b of the IH delay line 30, respectively.

Along with this, both ends of the resistor 290 are connected to diodes 32, respectively.
a and 32b, and the cathodes of these diodes are connected via a resistor 33 to the supply terminal 20 of the gate pulse Pg.

The gate pulse Pg is a negative pulse that occurs only during the flyback period, and this gate pulse Pg changes the terminal 20 from a potential higher than the power supply voltage +VCC to a lower potential, and the diodes 32a and 32b are connected only during the flyback period.
is turned on, therefore, the input terminals 24a, 2 of the IH delay line
4b is short-circuited in an alternating current manner.

The gate pulse Pg can be formed from a horizontal flyback pulse or the like.

Further, a compensation coil 34 is connected between the output terminals 25a and 25b of the IH delay line 3, and the output terminal 25a is grounded via a resistor 35, and the output terminal 25b is grounded via a resistor 36. .

A connection point between the output terminal 25a and the resistor 35 is connected to the emitter of the transistor 27 via the resistor 37,
A connection point between output terminal 25b and resistor 36 is connected to the emitter of transistor 27 via resistor 38.

Here, since the output signals generated at the output terminals 25a and 25b are of opposite polarity, the input signal from the terminal 26 and the output signal of the IH delay line 3 are added by the resistors 28, 37.35 to the burst signal 39a. The input signal and the output signal of the IH delay line 3 are subtracted by the resistors 28, 38, 36, and the burst signal and (RY) component are obtained at the terminal 39b. Component carrier color signals are obtained and supplied to demodulation circuits 6B and 6R.

According to the configuration of the embodiment of the present invention described above, since no input voltage is applied to the input side converter 22 during the burst period, the burst signal is sent to the demodulation circuits 6B and 6R without being passed through the IH delay line 3. will be charged.

Therefore, it is possible to prevent unnecessary signals from being demodulated and vertical color stripes from appearing on the screen when the image is black and white.

Furthermore, since a burst signal is present in the output of the adder circuit 4 or the subtracter circuit 5, it is possible to form a carrier wave for demodulation and an AC'C signal based on this burst signal, and also to determine the polarity of the color signal. I can do it.

In addition, in the embodiment of the present invention described above, the supply of the burst signal to the IH delay line 3 is cut off. Alternatively, the signal may be supplied to the IH delay line 3.

Specifically, for example, as shown in FIG. 4, resistors 40a and 40b may be inserted between both ends of resistor 290 and diodes 32a and 32b, respectively, in the configuration of the above-described embodiment.

Note that the present invention is not limited to a PAL color signal demodulation circuit;
Similar benefits can be obtained when applied to cases where the luminance signal and carrier color signal of an NTSC color television signal are separated using a comb filter consisting of an IH delay line.

[Brief explanation of drawings]

Fig. 1 is a system diagram of an example of a color signal processing circuit to which the present invention can be applied, Fig. 2 is a system diagram of main parts of the invention, Fig. 3 is a connection diagram of an embodiment of the invention, and Fig. 4 is a system diagram of an example of a color signal processing circuit to which the present invention can be applied. FIG. 6 is a connection diagram of main parts of another embodiment of the present invention. 1 is a terminal to which a carrier color signal and a burst signal are supplied;
3 is an IH delay line, 6B and 6R are demodulation circuits, and 20 is a gate pulse supply terminal.

Claims (1)

[Claims] 1 A carrier color signal and a burst signal are supplied, and
a gate circuit that removes or reduces the burst signal; a delay line to which the output from the gate circuit is supplied and whose delay time is equal to one horizontal period; a signal on the input side of the gate circuit and a signal on the output side of the delay line; the output carrier color signal and the output burst signal are obtained from the addition circuit and the subtraction circuit, the output carrier color signal is supplied to a demodulation circuit, and the output burst signal is A color signal processing circuit characterized in that the color signal is supplied to a circuit to be used.