JPS6025191Y2 - hue correction device - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a hue correction device for a color television receiver, and provides a device suitable for integration into an integrated circuit.

Conventional Structures and Their Problems Recently, various methods have been considered as means for correcting color signals of color television receivers.

As an example, as described in Japanese Patent Application Laid-Open No. 144523/1982, the phase component of a specific color, for example, skin color, of the chroma signal is detected, and the phase of the demodulation color subcarrier is detected using the detected output. By correcting the phase of the chroma signal with a hue near the skin tone and demodulating the color, even if there is a slight phase shift in the signal sent from the broadcasting station or relay station, the receiver can automatically correct it. It is conceivable that the image can be reproduced in a hue that is almost skin-colored.

First, let's talk about the basic configuration and specific circuit of such a device. This will be explained with reference to FIG.

In the figure, reference numeral 1 denotes a chroma signal amplification circuit, in which a chroma signal (carrier color signal) of a television signal received is extracted, amplified, and applied to a sampling circuit 2.

On the other hand, 3 is a color subcarrier oscillation circuit that generates a color subcarrier for color demodulation in synchronization with a burst signal. Generate color subcarriers.

The l-axis color subcarrier is applied to a sampling circuit 2, which samples the chroma signal at this l-axis phase to detect the skin color phase component in the chroma signal.

In other words, the output of the sampling circuit 2 is a signal that detects how much the received chroma signal deviates from the phase of the skin color, and becomes larger as it approaches the phase of the skin color.

This output is applied to the modulation circuit 4 as a control signal without being filtered.

A chroma signal made to a constant amplitude by an amplitude control circuit 5 is also added to the modulation circuit 4, and the above-mentioned sampling circuit 2
The amount of passage of this chroma signal is modulated according to the detection output from the chroma signal.

That is, the closer the phase of the received chroma signal is to the phase of skin color, the more chroma signal components are modulated to be passed.

However, if the phase is shifted by more than ±90° (or an angle smaller than that) with respect to the skin color phase, no output is output from the modulation circuit 4.

Further, the output of this modulation circuit 4 is applied to a synthesis circuit 6, where it is synthesized with the color subcarrier of the l axis which has been amplified by the amplifier circuit 7 and has a constant amplitude, thereby producing a color subcarrier. is shifted slightly in the direction of the phase of the chroma signal that is being received at the time.

That is, the color demodulation phase of the chroma signal is slightly rotated in the l-axis direction, and the demodulation phase of colors near skin color is automatically corrected.

The color subcarrier whose phase has been corrected in this way is applied to the color demodulation circuit 8, and a color demodulation operation is performed.

The amplifier circuit 7 naturally forms part of the color subcarrier oscillation circuit 3, and may be omitted if unnecessary.

In this way, the chroma signal whose phase is shifted from the skin color phase is corrected in the direction of the skin color phase and demodulated, so that even if phase distortion etc. occur during the transmission of the television signal, the chroma signal is corrected in the direction of the skin color phase and demodulated. It is capable of always reproducing skin tones well.

A detailed circuit diagram of a conventional example of such a device is shown in FIG.

In the figure, reference numeral 9 denotes a subcarrier input terminal, to which a color subcarrier of l-axis phase is added, and transistor 10.1 of the amplifier circuit 7
1 and simultaneously constitute the double-balanced differential amplifier of the axis sampling circuit 2.
It is also added to transistors 13 and 14 of 5.

Further, 16 and 16 are input terminals for chroma signals, and chroma signals φ and -φ, which are in opposite phases to each other, are applied to the bases of transistors 17 and 18 of the sampling circuit 2, and this chroma signal is transmitted to the l-axis by the above-mentioned color subcarrier. sampled.

Its output is applied to the base of transistor 20 of modulation circuit 4.

On the other hand, the chroma signal φ and a portion thereof are applied to transistors 21 and 22 of the amplitude limiting circuit 5 and amplified.

Since this transistor 21 serves as a current source for the transistors 19 and 20, the amplitude-limited chroma signal φ is modulated by the output component sampled on the l axis and extracted as an output at the collector of the transistor 19. can get.

The axial subcarrier from the collector of the transistor 11 of the amplifier circuit 7 and the modulated chroma signal from the collector of the transistor 19 of the modulation circuit 4 are connected to a common load resistor 23.
and an external W resonant circuit 24 to obtain a phase-corrected l-axis color subcarrier.

Therefore, this phase-corrected output is transferred to a buffer amplifier circuit 26 consisting of a transistor 25 connected as an emitter follower.
By extracting the chroma signal and demodulating the chroma signal using it as a color subcarrier for color demodulation, distortion of the transmitted hue can be corrected and demodulated.

In addition, 27 is a bias capacitor, 28, 29.30 is an external lead terminal of the IC element 31 including the above circuit, and 32 to 3
6 is a transistor for constant current, and 37 is a Zener diode for level shift.

Hue correction is performed in this way, but if there is almost no phase shift or phase distortion in the received television signal, colors may be reproduced more faithfully by disabling this hue correction function. become.

Therefore, a switch is required to switch between operating and stopping this device.

Conventionally, a switch 38 is used as the switch, as shown in FIG. 2, which sets the bases of constant current transistors 34 to 36 to the low position to cut them off.

However, with such a configuration, the value of the current flowing through the device changes significantly between when the switch 38 is closed and when it is opened. Significant changes in current value are disadvantageous because they cause instability in operation.

OBJECTS OF THE INVENTION It is an object of the present invention to eliminate such conventional drawbacks and to provide an apparatus in which the current value does not change much even when the hue correction function is switched on and off.

Structure of the invention In this invention, a double-balanced differential amplifier configured so that the output current is constant is provided in the middle of the chroma signal transmission path, and during hue correction operation, the double-balanced differential amplifier performs chroma signal processing. In addition to removing the burst signal from the signal and supplying a chroma signal that does not contain the burst signal, by operating a switch, both the double-balanced differential amplifier and the sampling circuit are configured to stop transmitting the chroma signal at least during the scanning period. The present invention is characterized in that the hue correction function is stopped by operating to prevent the hue correction function.

DESCRIPTION OF THE EMBODIMENTS FIG. 3 shows a block diagram of an apparatus according to an embodiment of the present invention, and FIG. 4 shows its detailed circuit diagram.

In the figure, 39 is a control signal generation circuit, and a terminal 40
The burst gate pulse applied to the amplitude limiting circuit 5 switches a circuit composed of a double-balanced differential amplifier in the amplitude limiting circuit 5 to remove the burst signal from the chroma signal, and converts the chroma signal not containing the burst signal into the modulation circuit 4.
The purpose is to supply

In this device, the control signal generation circuit 39 is provided with a switch 41, and when the switch 41 is closed, the control signal generation circuit 39 operates continuously during the entire period including the scanning period. A circuit made up of an amplifier is similarly switched to block the supply of all chroma signals other than the burst signal.

When this chroma signal is blocked, no modulated output is generated in the modulation circuit, so the hue correction operation is stopped.

Note that during hue correction operation, the burst signal is removed,
The chroma signal that does not include the burst signal is supplied to the modulation circuit 4 for the following reason.

Normally, the color subcarrier oscillation circuit 3 is controlled using a voltage obtained by phase-detecting the burst signal in the input color signal and the color subcarrier signal of the output signal of the combining circuit 6 for only the burst signal period (APC circuit).

For this reason, if hue correction is also performed during the burst signal period, the color subcarrier signal will be modulated by the burst signal and form a loop in which the phase changes, making it impossible to generate the color subcarrier correctly, and the hue Correction cannot be performed correctly.

Furthermore, there may be a problem that the hue changes significantly when the switch 41 is opened and closed.

Therefore, in this device, the burst signal is removed during the burst period, and a chroma signal containing no burst signal is supplied.

FIG. 4 shows one specific circuit.

This circuit is partially composed of differential amplifiers, but the second
Components similar to those in the drawings are designated by the same reference numerals, and description thereof will be omitted.

First, in this circuit, a synthesis circuit 6 for synthesizing a color subcarrier and a modulation signal is constituted by a resistance matrix of resistances 42 and 43.

The amplitude limiting circuit 5 includes a transistor 44 for removing a burst signal during hue correction operation. 44 at 44
b, 45° A double-balanced differential amplifier consisting of 45a and 45b, and this double-balanced differential amplifier 4
In order to keep the output current of 4.45 degrees constant, a current source transistor 46 is provided which supplies a current of 12 times the current of the current source transistor 36.

That is, the double-balanced differential amplifier has a constant current source transistor 46 connected to the common emitters of transistors 44a and 44b, and transistors 45a and 45b.
The common emitter of the transistor 21 is connected to the collector of the transistor 21 whose base is supplied with a chroma signal, and a bias voltage is applied from the transistor 53 to the bases of the transistors 44b and 45a through the resistor, and from the transistor 54 to the base of the transistor 44a through the resistor. , 45b are configured such that a bias voltage is supplied to the bases of the transistors 44a* and 45b, and the collector connection points of the transistors 44a* and 45a are connected to the modulation circuit via a resistor as an output terminal.

Further, 47 is a terminal for connecting the switch 41.

Assuming that the switch 41 is now open and hue correction is being performed, when a positive burst gate pulse is applied to the terminal 40, the transistors 48, 49, 50
conducts, and the base voltage of transistors 44b and 45a becomes lower than the base voltage of transistors 44a+45b, so that the chroma signal is blocked by transistor 45a during this burst pulse period, and the burst signal is removed.

During periods other than the burst gate pulse, the transistor 48
, 49.50 are cut off, so the transistor 44b,
The base voltage of transistor 45a becomes higher than the base voltage of transistors 44a and 45b, and the chroma signal is applied to transistor 4.
5a, a hue correction operation is performed.

On the other hand, when the switch 41 is closed, the transistor 51
As the base voltage of the transistor 52 decreases and its collector voltage increases, the transistor 52 becomes conductive, resulting in a state similar to the pulse period of the burst gate pulse, and the transistor 50 continues to conduct continuously.

Therefore, the base voltages of the transistors 44b and 45a become lower than the base voltages of the transistors 44a and 45b, and the chroma signal is blocked by the transistor 45a for the entire period including the scanning period.

This causes the hue correction function to be stopped.

Note that 53, 54, 55, and 56 are buffer transistors, and 57 is a chroma signal amplification transistor.

When the hue correction function is stopped in this way, there is an increase in the current of the transistors 52 and 54 and a decrease in the current of the transistor 51 when the function is stopped, and the current increase is slightly large. Since the increase is small, it has almost no effect on the whole, making extremely stable and accurate operation possible.

Since such a configuration can be easily incorporated into an integrated circuit element, a device suitable for integrated circuit elements can be obtained.

Furthermore, in order to reduce (offset) the increase in current in the transistors 51 and 52, the constant current source transistor 34 and the constant current source transistor 35 for level shifting the sampling output are cut off via the transistor 58, as shown in the figure. The operation of the sampling circuit 2 is also stopped.

In this way, the overall current change can be further reduced.

Moreover, there is an advantage that leakage transmission of chroma signals and color subcarriers when no hue correction is performed can be completely eliminated.

It goes without saying that transmission of the chroma signal may be blocked only during the scanning period by using the Miburst gate pulse or a pulse obtained by inverting the Miburst gate pulse.

Effects of the invention As described above, according to the invention, the sampling circuit samples the phase component of a specific color, such as skin color, from the chroma signal, modulates the chroma signal with the output, and combines the modulation output with the color sub-color. In a device that corrects the hue of a chroma signal by combining it with a carrier wave, a double-balanced differential amplifier configured to keep the output current constant is installed in the transmission path of the chroma signal, and the hue correction operation is performed using a double-balanced differential amplifier configured to keep the output current constant. When not being performed, both the double-balanced differential amplifier and the sampling circuit are operated to stop signal transmission at least during the scanning period, and the hue correction operation is stopped by blocking the chroma signal during at least the scanning period. Therefore, even if the device is switched from the hue correction operating state to the state in which the hue correction operation is stopped, there is little change in the current value between the operating state and the stopped state, making it possible to obtain a device suitable for integrated circuit elements. Moreover, when the hue correction operation is stopped, leakage of the chroma signal and the color subcarrier from both the chroma signal transmission path and the sampling circuit can be prevented, and an adverse effect can be eliminated.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional hue correction device, Fig. 2 is a detailed circuit diagram of the same device, Fig. 3 is a block diagram of a hue correction device according to an embodiment of the present invention, and Fig. 4 is a block diagram of a hue correction device of a conventional example. It is a detailed circuit diagram of the same device. 1...Chroma amplification circuit, 2...Sampling circuit, 3...Color subcarrier oscillation circuit, 4...
... Modulation circuit, 5 ... Amplitude limiting circuit, 6
...Synthesis circuit, 7...Amplification circuit, 8.
...Color demodulation circuit, 12, 13, 14.15...
...Double balanced differential amplifier, 17.18...
... Differential amplifier, 21, 22 ... Differential amplifier, 34, 35, 36, 46 ... Constant current source transistor, 44a, 44b, 45a, 45b = double balanced type difference dynamic amplifier, 39... control signal generation circuit, 40, music/burst gate pulse input terminal, 41...
...Switch, 48, 49, 50, 51.52.5
8...Transistor.

Claims (1)

[Scope of utility model registration request] a color subcarrier oscillation circuit that oscillates a color subcarrier for color demodulation; Second. Third. A double-balanced differential amplifier configured with a fourth transistor; The common base of the fourth transistor and the second . 180° to each other corresponding to the phase of the specific color to the common base of the third transistor
Color subcarriers with different phases are input, and the first . Connect the collector of one transistor of the differential amplifier to the common emitter of the second transistor to the base of which the chroma signal is applied; the third. A collector of the other transistor of the differential amplifier to which a DC voltage is applied to the base is connected to the common emitter of the fourth transistor, and a first constant current source transistor of the differential amplifier is provided. a sampling circuit for sampling phase components of colors; 7th. an eighth transistor; The common base of the 8th transistor and the 6th and 7th transistors
A double-balanced differential amplifier is provided, in which a bias voltage is applied to the common base of each transistor, and a DC voltage is applied to the bases of three transistors, and the chroma signal is applied to the base of the other transistor. The collector of the transistor of
．． The eighth transistor is connected to the common emitter of the differential amplifier, the second constant current source transistor is connected to the common emitter of the differential amplifier, and the fifth. A double-balanced type difference between an amplitude control circuit in which a third constant current source transistor that supplies 1/2 of the current of the second constant current source transistor is connected to the common emitter of the sixth transistor, and the sampling circuit. The sampling output from the dynamic amplifier allows the above-mentioned 5. a modulation circuit that modulates the chroma signal obtained from the common collector of the seventh transistor; a synthesis circuit that synthesizes the modulation output signal of the modulation circuit and the color subcarrier to correct the phase of the color subcarrier; The switch for stopping the correction operation is electrically connected during the burst gate pulse period, and the switch for stopping the correction operation is turned on during the burst gate pulse period. The base potential of the seventh transistor is set to 5. lower than the base potential of the eighth transistor,
A first switching element that is cut off during periods other than the pulse period to set the two base potentials in an opposite relationship; a first switching element that is cut off when the switch is open and conducts when the switch is closed; A second switching element that is continuously made conductive, and a fourth constant current source h transistor that is made conductive by the conduction of the second switching element and that shifts the level of the first constant current source transistor and the sampling output. and a control signal generation circuit including a third switching element to transmit a chroma signal, which removes the burst signal during the burst gate pulse period and transmits a chroma signal that does not include the burst signal, and when the switch is turned on, the chroma signal A hue correction device that blocks signal transmission and stops the operation of the sampling circuit.