JP2583974B2 - Video output circuit with white balance correction circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video output circuit, and more particularly to a video output circuit with a light balance correction circuit suitable for correcting a luminance saturation phenomenon of a cathode ray tube.

[Conventional technology]

When the beam current of the cathode ray tube is increased, the luminance saturates without following the beam current exceeding a certain value, that is, a so-called luminance saturation phenomenon occurs. In a luminance region where the beam current is large, the balance of the three primary colors is lost. I will.

As a device for correcting the luminance saturation phenomenon of the cathode ray tube, there has conventionally been a dynamic white circuit for correcting a gain in a video output circuit.

FIG. 4 is a circuit diagram for explaining an example of a conventional dynamic white circuit, wherein 1 is a video chroma circuit, 5 is a cathode ray tube, 8 and 10 are buffer transistors, 13 is a drive transistor, 14 is an output transistor, and E1 Is a video output power supply, E2 is a video chroma power supply, EB is a base bias power supply, and Eγ is a voltage source.

In the figure, a color difference signal is input from the video chroma circuit 1 to the base of the drive transistor 13, and a luminance signal is input to the base of the buffer transistor 10. Both ends of the drive resistor 12 are the difference signal between the color difference signal and the luminance signal. When a certain primary color video signal is applied, an emitter current flows through the drive transistor 13 and an output transistor connected to the collector of the drive transistor 13
When the video signal is output from the collector of the output transistor 14 to the cathode-ray tube 5, the drive resistor 14 is driven by the resistor 11 and the voltage source Eγ connected in series between the emitter of the drive transistor 13 and the emitter of the buffer transistor 10. When the voltage between both ends of the resistor 12 becomes large, that is, when the voltage between both ends of the resistor 12 exceeds the voltage of the voltage source Eγ when the luminance increases, the current also flows through the resistor 11 and the emitter current of the drive transistor 13 increases to increase the video. Operates to increase the output gain. This allows, for example,
When there is no color difference output, that is, when the base of the drive transistor 13 is at a constant voltage, the characteristics of the luminance signal level and the beam current Ib flowing through the cathode-ray tube 5 are broken-line characteristics as shown in FIG.

The video chroma circuit 1 has a drive transistor 13
And a luminance signal to the base of the buffer transistor 8. The luminance signal buffered from the emitter of the buffer transistor 8 is input to the base of the buffer transistor 10.

Related circuits of this type include those described in P-5 of "Hitachi Color Television, G7-LX (C33-J67S, C29-G67S) Service Book (issued in 62.6)".

[Problems to be solved by the invention]

The above-mentioned conventional circuit is used for a blue circuit to automatically switch the color temperature at a white peak to a higher side than a normal time by acting only on a blue primary color signal. Has the following problems.

That is, as shown in FIG. 6, when the characteristic of the luminance of the phosphor screen with respect to the beam current Ib of the cathode-ray tube is a nonlinear saturation characteristic, as shown in FIG. In the method in which the beam current Ib is increased by switching the gain of the circuit to increase the output, the beam current Ib of the CRT with respect to the luminance signal level output from the video chroma circuit is a polygonal line as shown in FIG. Therefore, the non-linear characteristic of the luminance of the phosphor screen with respect to the beam current Ib of the CRT shown in FIG. 6 cannot be completely corrected.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a video output circuit with a white balance correction circuit configured to completely correct the non-linear luminance characteristics of a cathode ray tube.

[Means for solving the problem]

An object of the present invention is to provide a video output circuit with a detection circuit for detecting a level on the high-luminance side exceeding a certain luminance level of an input luminance signal, and using a level of the luminance signal detected by the detection circuit. A drive circuit that drives the video output stage by operating the gain control circuit, or if a high-luminance signal exceeding a certain luminance level is input by changing the gain of the video output stage, the video output increases as the luminance level increases. It is configured by a circuit configuration for performing gain correction for increasing the gain.

[Action]

The gain correction circuit does not operate below a certain luminance level, and the output signal is zero. However, if there is an input signal exceeding the luminance level, an output signal proportional to the input is generated. This output signal is input to the gain control circuit, and the gain of the video output circuit is changed to increase the gain at the time of high luminance. By inputting the video output at this time to the cathode ray tube, the beam current of the intermediate luminance or higher is prevented. It can be increased linearly. Thereby, it is possible to correct the phenomenon that the characteristics of the beam current versus the light emission luminance generated by the performance of the phosphor of the cathode ray tube are saturated when the luminance is high and the luminance is reduced.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram for explaining an embodiment of a video output circuit with a white balance correction circuit according to the present invention.
Is a video chroma circuit, 2 is a luminance signal buffer circuit, 3
Is a drive circuit, 4 is an output circuit, 5 is a cathode ray tube, 6 is a detection circuit, 7 is a gain control circuit, and V _CC is a power supply.

In the figure, a color difference signal and a luminance signal are output from a video chroma circuit 1, a color difference signal is input to a drive circuit 3, a luminance signal is input to a luminance signal buffer circuit 2, and a luminance signal output from the luminance signal buffer circuit 2 is output from the luminance signal buffer circuit 2. Are input to the drive circuit 3 at the same time as the color difference signal, and are also input to the detection circuit 6. The drive circuit 3 produces a difference signal between the color difference signal and the luminance signal, that is, a primary color video signal, and drives the output circuit 4 with this signal to drive the output circuit 4.
Is applied to the cathode of the cathode ray tube 5.

The detection circuit 6 operates only when the level of the input luminance signal is equal to or higher than the intermediate luminance, and outputs an output proportional to the input signal to the gain control circuit 7. The luminance level at which the detection circuit 6 operates is an intermediate luminance level, and is set to a certain luminance level. Accordingly, the gain control circuit 7 controls the gain of the drive circuit 3 when a luminance signal exceeding a certain luminance level is output from the video chroma circuit 6. By this operation, the characteristics of the cathode output signal and the luminance signal output from the output circuit 4 to the cathode ray tube 5 are as shown in FIG. 3, and the gain of the cathode output is increased in a portion exceeding a certain luminance level, and the luminance is increased. As the gain increases, the characteristic becomes nonlinear.

FIG. 2 is a block diagram for explaining another embodiment of a video output circuit with a white balance correction circuit according to the present invention.
The same parts as those in FIG. 1 are denoted by the same reference numerals.

The embodiment shown in FIG. 2 is different from the embodiment shown in FIG. 1 in that a drive circuit is not provided. A color difference signal and a luminance signal are output from the video chroma circuit 1, and the color difference signal is input to an output circuit 4. The signal is input to the luminance signal buffer circuit 2, and the luminance signal output from the luminance signal buffer circuit 2 is input to the output circuit 4 and the detection circuit 6 simultaneously with the color difference signal. The output circuit 4 amplifies the difference signal between the color difference signal and the luminance signal, that is, the primary color video signal, and outputs it to the cathode of the cathode ray tube 5 as a video output signal. In this case, as in the embodiment shown in FIG. 1, the detection circuit 6 operates only when the level of the input luminance signal is equal to or higher than the intermediate luminance to generate an output proportional to the input signal, and Output to the control circuit 7.
The gain control circuit 7 controls the gain of the output circuit 4 when a luminance signal exceeding a certain luminance level is output from the video chroma circuit 1 to control the cathode output signal output to the cathode ray tube 5 and the input / output characteristics of the luminance signal. It is realized as the characteristic shown in FIG.

In each of the embodiments described above, the cathode output signal output to the cathode ray tube 5 can be realized as shown in FIG. 3, so that the beam current Ib of the cathode ray tube 5 flowing in proportion to the cathode output signal and As shown in FIG. 6, it is possible to correct the characteristic that the phosphor screen luminance of the cathode ray tube 5 is saturated in a high luminance portion to obtain the phosphor screen luminance of the cathode ray tube 5 which is faithful to the level of the input luminance signal. it can.

Note that the characteristic diagrams in FIGS. 3 and 6 show an example in which only the luminance signal is output from the video chroma circuit 1.

〔The invention's effect〕

As described above, according to the present invention, the luminance saturation phenomenon in which the linearity is impaired and the luminance extension decreases as the phosphor screen luminance of the cathode ray tube becomes higher, the luminance signal input / output characteristic of the video output circuit is increased when the luminance is high. It can be improved by correcting only the brightness of the red, green, and blue CRTs, for example, using a three-tube three-lens projection TV and synthesizing them on the projection TV screen. The balance of the luminance output of each CRT can be stabilized from low luminance to high luminance, and a video output circuit having excellent functions can be provided except for the above-mentioned disadvantages of the prior art.

[Brief description of the drawings]

1 is a block diagram of one embodiment of the present invention, FIG. 2 is a block diagram of another embodiment of the present invention, FIG. 3 is a characteristic diagram of a luminance signal versus a cathode output according to the present invention, and FIG. FIG. 5 is a circuit diagram for explaining the technology, FIG. 5 is a characteristic diagram of a luminance signal versus a beam current in the prior art, and FIG. DESCRIPTION OF SYMBOLS 1 ... Video chroma circuit, 2 ... Luminance signal buffer circuit, 3 ... Drive circuit, 4 ... Output circuit, 5 ... CRT, 6 ... Detection circuit, 7 ... Gain control circuit.

Claims (2)

(57) [Claims] 1. A luminance signal buffer circuit for inputting and buffering a luminance signal output from a video chroma circuit, a luminance signal output from the luminance signal buffer circuit, and a color difference signal output from the video chroma circuit. And a drive circuit that outputs a difference signal between the two input signals; an output circuit that is driven by the drive circuit and outputs a video signal to a cathode ray tube; and a luminance signal that is output from the luminance signal buffer circuit. A detection circuit that detects a white peak signal exceeding a predetermined luminance level; and a gain correction circuit that receives a signal detected by the detection circuit and changes a gain of the drive circuit according to the input level. The gain correction circuit corrects a non-linear saturation characteristic of the phosphor screen luminance with respect to the beam current of the CRT. It has the feature that a straight line characteristic Te, white balance correction circuit with video output circuit, characterized in that. 2. A luminance signal buffer circuit for inputting and outputting a luminance signal output from a video chroma circuit, and a luminance signal output from the luminance signal buffer circuit and a color difference signal output from the video chroma circuit. And an output circuit for outputting a difference signal between the two input signals to the cathode ray tube as a video signal, and a luminance signal output from the luminance signal buffer circuit and detecting a white peak signal exceeding a predetermined luminance level. And a gain correction circuit that receives the signal detected by the detection circuit and changes the gain of the output circuit in accordance with the input level. It has a function of correcting a non-linear saturation characteristic of surface luminance so that the characteristic becomes a linear characteristic. White balance correction circuit with video output circuit.