JP2591778B2 - Image quality correction circuit for CRT - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a CRT that requires relatively high resolution and good image quality, such as for a computer terminal, and its peripheral portion is compared with the central portion. CRT that can compensate for the low brightness, poor focus, and large beam spot diameter to obtain almost uniform image quality over the entire screen
And an image quality non-uniformity correction circuit.

[Conventional technology]

At present, most commonly used CRTs, both color and monochrome, have an electron gun structure called a cathode modulation type. In the case of the cathode modulation type electron gun, there are various names of the electron gun depending on the structure and the like. However, basically, in the case of the cathode modulation type, the anode current Ib of the CRT, that is, the luminance of the screen changes according to the voltage between the first grid G1 and the cathode K.

Similarly, the spot diameter of the electron beam on the phosphor screen of the CRT and the anode current Ib change according to the voltage between the first grid G1 and the second grid G2, and the voltage between the first grid G1 and the third grid G3 changes. Focus changes.

Currently, TV-grade monitors are the first to third grids G
1, an appropriate DC bias voltage is applied to G2 and G3. In a monitor with relatively high resolution, horizontal or horizontal and vertical parabolic voltages are applied only to the third grid G3 for controlling the focus. Superimposition was used in a method called dynamic focus.

FIG. 2 is a configuration diagram showing an example of a conventional dynamic focus circuit of a CRT.

In this figure, reference numerals 1 and 2 denote first and second voltage generating circuits for generating horizontal and vertical parabolic waveform voltages, respectively. Reference numeral 3 denotes an adding circuit, reference numeral 4 denotes an amplifier circuit, reference numeral 5 denotes a CRT, and reference numeral AMP1 denotes both horizontal and vertical directions. Is a differential amplifier to which a parabolic waveform voltage is input, R1 is a feedback resistor for an adder of the differential amplifier AMP1, and AMP2 is a differential amplifier that amplifies an output of the differential amplifier AMP1 to a drive voltage of a third grid G3. , R2 is a feedback resistor for determining the gain of the differential amplifier AMP2,
VR1 is a variable resistor for adjusting the voltage of the parabolic waveform required for the third grid G3. C1 is a decoupling capacitor which transmits only the AC component of the voltage of the parabolic waveform to the third grid G3 in the output signal of the differential amplifier AMP2. E1 is third
DC bias power supply for grid G3, R3 is the differential amplifier
A load resistor for stabilizing the output of AMP2, and R4 is a resistor for bias.

[Problems to be solved by the invention]

Conventionally, a CRT with a relatively round tube surface was used,
In recent years, FS tubes have been widely used in order to improve the visibility of the screen.

In the FS tube, the difference between the distance from the electron gun to the phosphor screen in the center part and the peripheral part becomes extremely large.
If it is a TV grade FS tube CRT, the third grid G3 can be used sufficiently by a DC voltage application method (called static focus for dynamic focus), but the FS tube for computer terminals has a higher resolution than the TV grade. As for the CRT, practical image quality cannot be obtained unless dynamic focus similar to that of the related art (parabolic voltage is superimposed only on the third grid G3) is used. But,
The parabolic modulation of only the third grid G3 only corrects that the focus at the peripheral portion of the screen is deteriorated as compared with the central portion, and does not correct the brightness reduction and the beam spot diameter deterioration. Has a lower image quality than the central portion.

Especially in computer terminal displays etc., the number of display dots is increasing and the use of multi-windows etc. is increasing.However, when windows are displayed at the periphery of the screen, they are compared with those at the center. There was a problem that it became difficult to see.

The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a CRT image quality unevenness correction circuit that can correct image quality unevenness of a CRT and can obtain substantially uniform image quality over the entire screen.

[Means for solving the problem]

The image quality non-uniformity correction circuit of the CRT according to the present invention includes a first voltage generation circuit that generates a parabolic waveform voltage that increases in voltage toward the periphery of the screen in synchronization with horizontal deflection, and a first voltage generation circuit in synchronization with vertical deflection. A second voltage generation circuit that generates a parabolic waveform voltage that increases in voltage toward the periphery of the screen;
An adding circuit for adding the voltages output from the first and second voltage generating circuits;
And a driving circuit for supplying the grid.

[Action]

In the present invention, the spot diameter is narrowed down as the beam goes to the peripheral portion by the output supplied to the second grid from the drive circuit, and the luminance is increased.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of a circuit for correcting image quality unevenness of a CRT according to the present invention.

In this figure, the same reference numerals as those in FIG. 2 denote the same components, 6 is a drive circuit, VR2 is a variable resistor, and a differential amplifier AMP is used.
2 for output stabilization and at the same time
This is for obtaining the parabola voltage necessary for 2 from the output of the differential amplifier AMP2. C2 is a decoupling capacitor for the second grid G2, and E2 is a DC bias power supply for the second grid G2.

For example, in the case of a color CRT with a 21 ″ 90 ° deflection, the DC bias voltage of the third grid G3 is 6000 V with a general electron gun.
By applying a parabolic voltage value of dynamic focus of about 200 to 700 Vp-p to the third grid G3, a substantially uniform focus screen can be obtained on the entire screen.

Even in the circuit for correcting the image quality unevenness of the CRT of this embodiment, since the voltages of the horizontal and vertical parabolic waveforms are added and supplied to the third grid G3, a uniform focus screen is obtained.

Also, the DC bias voltage value of the second grid G2 is generally smaller than the 6000V to 8000V of G3 in the third grid.
Although fixed at 500 to 800 V, in the present invention, the parabolic modulation component of the third grid G3 is divided and applied to the second grid G2 via the variable resistor VR2. That is, the second
A parabolic waveform similar to that of the third grid G3 is superimposed on the grid G2.

Accordingly, the spot diameter of the beam becomes smaller from the center of the screen toward the periphery, and the spot diameter can be made substantially uniform over the entire screen by correction with the parabolic waveform voltage just like dynamic focus. As for the brightness, the brightness increases in a parabolic manner from the center of the screen toward the periphery, similarly to the change in the spot diameter, and correction is performed in the same manner as in the case of the beam diameter.

However, the luminance of the screen is originally affected by the voltage between the first grid G1 and the cathode K, so that the second grid G2
The optimum value of the correction amount of the beam diameter and the correction amount of the luminance by the above voltage do not always coincide with each other and depend on the structure of the electron gun and the like. However, by applying a parabolic waveform voltage to the second grid G2, it is possible to simultaneously correct the beam diameter and the luminance, and the effect is large.

In general, the spot shape of the beam at the periphery of the screen becomes larger not only due to the electron gun structure of the CRT, but also due to the deflection yoke.In this case, the spot shape of the beam is almost not a circle. In the peripheral portion, it is distorted in an elliptical shape.

However, if the voltage of the second grid G2 is increased and the spot diameter of the beam is reduced as in the present invention, the resolution is visually improved, and as a result, the image quality is improved as in the correction of the spot diameter of the round beam. Has already been confirmed by experiments.

In the above-described embodiment, the output of the dynamic focus circuit is divided and supplied to the second grid G2. However, this configuration can be shared to simplify the configuration and further improve the image quality. For this reason, it goes without saying that the dynamic focus circuit is not always necessary.

〔The invention's effect〕

As described above, the present invention provides a first voltage generating circuit that generates a parabolic waveform voltage that increases in voltage toward the periphery of a screen in synchronization with horizontal deflection, and a peripheral portion of a screen in synchronization with vertical deflection. A second voltage generation circuit that generates a parabolic waveform voltage that increases in voltage as one goes, an addition circuit that adds the voltages output from the first and second voltage generation circuits, and an output of the addition circuit. And a driving circuit for supplying the second grid to the second grid, so that a simple circuit can be added to correct the deterioration of the spot diameter and the correction of the reduction in brightness to correct the image quality unevenness. The effect is that uniform image quality can be obtained, and the effect is particularly great in FS tube CRTs.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a circuit for correcting image quality unevenness of a CRT according to the present invention, and FIG. 2 is a configuration diagram showing an example of a dynamic focus circuit. In the figure, reference numerals 1 and 2 denote first and second voltage generation circuits, 3 denotes an addition circuit, 4 denotes an amplification circuit, and 6 denotes a drive circuit.

Claims (1)

(57) [Claims] 1. A first grid (G) mainly controlling luminance.
1), a second grid (G2) for controlling the spot diameter or the spot diameter and brightness, and a third grid for controlling the focus.
A first voltage generation circuit (1) for generating a parabola-waveform voltage that increases in voltage toward the periphery of a screen in synchronism with horizontal deflection and is a circuit for correcting image quality unevenness of a CRT having a grid (G3) A second voltage generating circuit (2) for generating a parabolic waveform voltage that increases in voltage toward the periphery of the screen in synchronization with the vertical deflection, and output from the first and second voltage generating circuits. (3) Adder circuit for adding voltage
And a driving circuit (6) for dividing the output of the adding circuit and supplying the divided voltage to the second grid.
T image quality unevenness correction circuit.