JPH01311688A - Video output circuit with gamma correcting circuit - Google Patents

Abstract

PURPOSE:To completely correct the non-linear luminance characteristic of a cathode ray tube by correcting the luminance signal input output characteristic of a video output circuit only at the time of lighting with high luminance. CONSTITUTION:A gamma detecting circuit 6, only when the level of the inputted luminance signal is the intermediate luminance or above, is operated, the output in proportion to the input signal is outputted to a gain control circuit 7, and the gain control circuit 7, when a luminance signal to exceed a certain constant luminance level is outputted from a video chroma circuit 6, controls the gain of a driving circuit 3. Consequently, the characteristic of the cashode output signal and the luminance signal outputted from an output circuit 4 to a cathode ray tube 5 becomes the non-linear characteristic the more the luminance is increased the more the gain is increased in the part to exceed a certain constant luminance level. Thus, the phenomenon, that the characteristic of the beam current versus light-emitting luminance generated by the performance of the fluorescent substance of the cathode ray tube is saturated at the time of the high luminance and the luminance is reduced, can be corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video output circuit, and more particularly to a video output circuit with a gamma correction circuit that is suitable for correcting the luminance saturation phenomenon of a cathode ray tube. .

[Conventional technology]

When the beam current of the cathode ray tube is increased, the 41 degrees will not follow the beam current above a certain value and will become saturated 2)
, the so-called brightness saturation phenomenon occurs and the beam current is large at brightness 9
■The balance of the three primary colors is disrupted in the area.

This method corrects the once-in-a-day saturation phenomenon of the cathode ray tube.
Conventionally, there is a dynamic white circuit that corrects the gain in the video output circuit2].

FIG. 4 is a circuit diagram explaining an example of a conventional dynamic white circuit, where ■ is a video chroma circuit, 5 is a cathode ray tube, 8.10 is a buffer transistor, 13 is a drive 1 transistor, 14 is an output transistor, TF,
I is a video output type: ゛Hara, E2 is a video output type: 17 power supply,
Er3 is a base bias power supply, and ET 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 1 transistor 13, a luminance signal is input to the base of the buffer transistor 10, and a difference signal between the color difference signal and the luminance signal is input to both ends of the drive resistor 12. When a certain primary color video signal is applied, an emitter current flows through the drive transistor 13, the output transistor 14 connected to the collector of the drive transistor 13 is driven, and the video signal is transmitted from the collector of the output transistor 14 to the cathode ray tube 5. is output, when the voltage across the drive resistor 12 increases due to the resistor 11 connected in series between the emitter of the drive transistor 13 and the emitter of the buffer transistor 10 and the voltage source ET, that is, when the brightness increases, the resistor 12 When the voltage across the resistor 11 exceeds the voltage of the voltage source ET,
A current flows through the drive transistor 13, and the emitter current of the drive transistor 13 increases, operating to increase the video output gain. As a result, 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 1b flowing through the cathode ray tube 5 have a compromise characteristic as shown in FIG.

Note that the video chroma circuit 1 includes a drive transistor 13.
A color difference signal is output to the base of the buffer transistor 8, and a luminance signal is output to the base of the buffer transistor 8. Further, the luminance signal buffered and output from the emitter of the buffer transistor 8 is input to the base of the buffer transistor 1o.

A related circuit of this type is “Hitachi Colorate L
/ Bi, G7-LX (C33-J67S, C29-G6
7S) Service Book (issued June 1986) P-5 can be mentioned.

[Problem to be solved by the invention]

The above conventional circuit is used in a blue circuit to act only on the blue primary color signal and automatically switch the color temperature change at the white peak to a higher side than normal, and is used for the purpose of correcting the brightness characteristics of a cathode ray tube. has the following problems.

In other words, as shown in FIG. 6, when the characteristic of the intensity 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 of increasing the beam current rb by increasing the output by switching the gain of the video output circuit, the beam current Ib of the cathode ray tube with respect to the luminance signal level output from the video chroma circuit is as shown in Fig. 5. , the characteristics change in two stages due to folding and tightening, and the non-linear characteristics of the luminance of the phosphor screen with respect to the beam current 1b of the cathode ray tube shown in FIG. 6 cannot be completely corrected.

SUMMARY OF THE INVENTION An object of the present invention is to provide a video output circuit with a gamma correction circuit configured to completely correct the non-linear brightness characteristics of a cathode ray tube.

[Means to solve the problem]

The above purpose is to provide the video output circuit with a gamma detection circuit for detecting the high luminance level of the input luminance signal that exceeds a certain luminance level, and to detect the level of the luminance signal detected by this gamma detection circuit. If a high brightness signal exceeding a certain brightness level is input by operating the gain control circuit and changing the gain of the video output stage or by changing the gain of the video output stage, the video output will increase as the brightness level increases. This is achieved by using a circuit configuration that performs gun correction that increases the gain.

[Effect]

The gamma correction circuit does not operate below a certain brightness level and the output signal is zero, but if there is an input signal that exceeds the brightness level, it will generate an output signal proportional to the input. This output signal is input to the gain control circuit to change the gain of the video output circuit to increase the gain at high brightness, and by inputting the video output at this time to the cathode ray tube, the beam current at intermediate brightness or higher is suppressed. Can be increased linearly. As a result, it is possible to correct a phenomenon in which the characteristic of beam current versus emission brightness is saturated at high brightness and the brightness is reduced, which occurs due to the performance of the phosphor of the cathode ray tube.

〔Example〕

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

FIG. 1 is a block diagram illustrating an embodiment of a video output circuit with a gamma correction circuit according to the present invention, in which 1 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 gamma detection circuit, 7 is a gain control circuit, and vec is a power supply. Note that in the following explanation, gamma will be abbreviated as γ.

In the figure, a video chroma circuit 1 outputs a color difference signal and a brightness signal, the color difference signal is input to a drive circuit 3, the brightness signal is input to a brightness signal buffer circuit 2, and the brightness signal is buffered and output from the brightness signal buffer circuit 2. is input to the drive circuit 3 at the same time as the color difference signal, and
The signal is input to the γ detection circuit 6. The drive circuit 3 generates a difference signal between a color difference signal and a luminance signal, that is, a primary color video signal,
This signal drives the output circuit 4, and a video output signal is applied from the output circuit 4 to the cathode of the cathode ray tube 5.

The γ 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. γ detection circuit 6
The brightness level at which it operates is an intermediate brightness level, which is set to a certain constant brightness level. Therefore, when a luminance signal exceeding a certain luminance level is output from the video chroma circuit 6, the gain control circuit 7
Controls the gain of drive circuit 3. Due to this operation, the characteristics of the cathode output signal and brightness 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 increases in the portion where the brightness level exceeds a certain level, and the brightness increases. It becomes a non-linear characteristic in which the gain increases as the distance increases.

FIG. 2 is a block diagram illustrating another embodiment of the video output circuit with gamma correction circuit according to the present invention, and the same parts as in FIG. 1 are given the same reference numerals.

The embodiment shown in FIG. 2 differs from the embodiment shown in FIG. The signal is input to the luminance signal buffer circuit 2, and the luminance signal buffered and output from the luminance signal buffer circuit 2 is input to the output circuit 4 and the γ detection circuit 6 at the same time as 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 well, as in the embodiment shown in FIG. Output to gain 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, and controls the input/output characteristics of the cathode output signal and luminance signal output to the cathode ray tube 5. The characteristics shown in FIG. 3 are realized.

In each of the embodiments described above, the cathode ray tube 5
Since the cathode output signal outputted to the cathode output signal can be realized as shown in Fig. 3, the beam current 1b of the cathode ray tube 5 flowing in proportion to the cathode output
As shown in FIG. 6, by correcting the characteristic of the phosphor screen brightness becoming saturated in high-brightness portions, it is possible to obtain the phosphor screen brightness of the cathode ray tube 5 that is faithful to the level of the input brightness signal.

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

〔Effect of the invention〕

As explained above, according to the present invention, the luminance saturation phenomenon in which linearity is impaired and luminance growth decreases as the luminance of the phosphor screen of a cathode ray tube becomes higher can be avoided by adjusting the luminance signal input/output characteristics of the video output circuit at high luminance. For example, in a 3-tube, 3-lens projection TV, the brightness characteristics of each red, green, and blue cathode ray tube can be corrected to improve the brightness of each cathode ray tube that is synthesized on the projection TV screen. The balance of brightness output can be stabilized from low brightness to high brightness, and a video output circuit with excellent functions can be provided without the drawbacks of the above-mentioned prior art.

[Brief explanation of the drawing]

Fig. 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 luminance signal versus cathode output according to the present invention, and Fig. 4 is a conventional diagram. A circuit diagram explaining the technology, FIG. 5 is a characteristic diagram of luminance signal versus beam current in the prior art, and FIG. 6 is a characteristic diagram of beam current of a cathode ray tube versus fluorophore luminance. l......Video chroma circuit, 2...
...Brightness signal buffer circuit, 3...
・Drive circuit, 4... Output circuit, 5.
・・・・・・・・・CRT, 6・・・・・・・・・γ
Detection circuit, 7... Gain control circuit. Figure 1\cc 4 output circuit vcc 'Kake 4 station Figure 2 Figure 3! 〇8 To Fa Transistor E2 Diodeok D
Maden J hole 13 tribe transistor E day °-
Subias Announcement 5) Viewpoint Figure 5 /゛ @ Figure 6

Claims (1)

[Scope of Claims] 1. A video chroma circuit, a luminance signal buffer circuit that inputs and buffers the luminance signal output from the video chroma circuit, and a luminance signal output from the luminance signal buffer circuit and the video chroma circuit. Video output consists of a drive circuit that inputs the color difference signal output from the chroma circuit and drives the output circuit with the difference signal between these two signals, and an output circuit that is driven by this drive circuit and outputs the video signal to the cathode ray tube. In the circuit,
A gamma detection circuit receives the luminance signal output from the luminance signal buffer circuit and detects a white peak signal exceeding a certain luminance level; A video output circuit with a gamma correction circuit, comprising a gain correction circuit that changes the gain of the drive circuit. 2. A video chroma circuit, a brightness signal buffer circuit that inputs and buffers the brightness signal output from the video chroma circuit, and a brightness signal output from the brightness signal buffer circuit and the brightness signal output from the video chroma circuit. In a video output circuit consisting of an output circuit that inputs a color difference signal and outputs the difference signal between these two signals as a video signal to a cathode ray tube, the luminance signal output from the luminance signal buffer circuit is input and the luminance signal is outputted to a certain luminance level. a gamma detection circuit that detects a white peak signal that exceeds
A video output circuit with a gamma correction circuit, comprising a gain correction circuit which inputs the signal detected by the gamma detection circuit and changes the gain of the output circuit according to the level of the signal.