JPH087536B2 - CRT brightness unevenness correction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a CRT for computer terminals and the like, which has a relatively high resolution and requires good image quality, and its peripheral portion is compared with the central portion. The present invention relates to a brightness unevenness correction circuit for a CRT, which can correct uneven brightness of a screen and thereby obtain a uniform brightness on the entire screen.

[Conventional technology]

Currently, CRTs that are generally used have an electron gun structure called a cathode modulation type for both color and monochrome. The brightness of the cathode modulation type CRT is
Since it is almost determined by the voltage between the first grids, a video signal is applied to the cathode, a DC voltage is applied to the first grid, and normally, the DC voltage of the first grid is changed to adjust the brightness. ing.

However, normally, due to the structure of the CRT, the brightness is high in the central part of the screen and low in the peripheral parts.

In recent years, the number of display dots has increased in computer terminal displays and the like, and the use of multi-windows is becoming more common.However, if the CRT has uneven brightness, the brightness changes depending on the position where the window is displayed. The screen becomes very difficult to see.

A method for solving this problem is disclosed in Japanese Patent Laid-Open No. 50-11073.
As shown in Japanese Patent Publication No. 61-166668,
There has been a method of generating a signal having a parabolic waveform of a deflection cycle, and providing a correction circuit for increasing the brightness of an image on a CRT toward the peripheral portion of the screen according to this signal to correct the brightness unevenness.

[Problems to be solved by the invention]

In the conventional brightness unevenness correction circuit as described above, the period of the signal of the parabolic waveform for correcting the brightness unevenness is set by the time constant of the circuit, so that it has been recently developed, for example, 15.75 to 32 kHz, 48. When used in a multi-scan CRT that can change the operating frequency in the range of up to 64 kHz, there was a problem that the time constant had to be set according to the operating frequency each time.

Moreover, since the signal is generated by the integrating circuit, there is a problem that a time delay occurs and the screen position of the beam and the phase of the voltage of the parabolic waveform do not match.

The present invention has been made to solve such a problem, and can be used for a multi-scan CRT, and it also corrects the luminance unevenness of the CRT in which the screen position of the beam and the phase of the voltage of the parabolic waveform do not shift. Aim to get the circuit.

[Means for solving problems]

A luminance unevenness correction circuit for a CRT according to the present invention generates a voltage of a parabolic waveform in which the voltage increases toward the peripheral portion of the screen in synchronization with horizontal deflection based on the current supplied to the horizontal deflection coil. A second voltage generating circuit for generating a voltage of a parabolic waveform in which the voltage increases toward the peripheral portion of the screen in synchronization with the vertical deflection based on the voltage generating circuit of No. 1 and the current supplied to the vertical deflection coil. And an adder circuit for adding the voltages of the parabolic waveforms output from the first and second voltage generating circuits and supplying the added voltage to the first grid.

[Action]

According to the present invention, the first and the second are based on the current supplied to the horizontal deflection coil and the vertical deflection coil.
The luminance is corrected by the voltage of the parabolic waveform generated by the voltage generation circuit of.

〔Example〕

Normally, in the case of a monochrome CRT, pincushion distortion is often corrected at the deflection yoke using a magnet etc., but in the case of a color CRT, the left and right pincushion distortion is corrected in a circuit. Generally, a method is adopted in which a parabolic waveform synchronized with vertical deflection is generated and horizontal deflection is modulated.

In the present invention, a vertical parabolic waveform generating circuit system for pincushion distortion correction for a color CRT is applied to generate a vertical parabolic waveform voltage, and a horizontal parabolic waveform voltage is also generated by the same system. By adding the waveforms with an analog adder such as an operational amplifier and applying a DC bias voltage with horizontal and vertical parabola modulation to the first grid of the CRT, the voltages at the center and peripheral parts of the screen are changed, The correction is performed to increase the brightness of the peripheral area.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a luminance unevenness correction circuit of a CRT according to the present invention.

In this figure, 1 and 2 are first and second voltage generation circuits, 3 is an adder circuit, 4 is a CRT, L1 and L2 are CRT horizontal deflection coils and vertical deflection coils, and C1 is a horizontal linearity correction circuit. S-shaped correction capacitor, C2 is a vertical output capacitor, AMP1 is a differential amplifier that picks up a parabolic waveform voltage generated at both ends of the S-shaped correction capacitor C1, and AMP2 is a parabolic waveform generated at both ends of the output capacitor C2. Amplifier, VR1 that picks up the voltage of
Is a variable resistor for adjusting the brightness unevenness correction amount in the center and left / right direction of the screen, VR2 is a variable resistor for adjusting the brightness unevenness correction amount in the center of the screen and up / down direction, and AMP3 is the sum of the voltage of the parabolic waveform in both horizontal and vertical directions Differential amplifier for driving the first grid G1, E1 is a reference voltage source for DC bias of the first grid G1,
VR3 is a variable resistor for brightness adjustment of the CRT4.

In this embodiment, the differential amplifiers AMP1 and AMP2 are constructed as shown in FIGS. 2 and 3, respectively. That is, the input end of the inverting amplifier is one input end, the output end of this inverting amplifier is the other input end, and the resistance values of the resistors R10, R20 and the resistance values of the resistors R30, R40, R50. The ratio is set appropriately. This adds between the input ends
The voltage of 200-300V will be inverted after being converted to about 15v.

The differential amplifier AMP3 is constructed as shown in FIG.

That is, according to the present invention, based on the current supplied to the horizontal deflection coil L1 and the vertical deflection coil L2, the peripheral portions of the screen are synchronized with the horizontal deflection and the vertical deflection by the first and second voltage generation circuits 1 and 2. The voltage of the parabolic waveform that becomes higher as the voltage goes to is generated, and these voltages are added by the adder circuit 3 and then supplied to the first grid G1 to correct the brightness. Even if it is used, it is not necessary to reset the time constant according to the used frequency, and the phase difference between the screen position of the beam and the voltage of the parabolic waveform is also eliminated.

〔The invention's effect〕

As described above, according to the present invention, based on the current supplied to the horizontal deflection coil, the first voltage generation for generating the voltage of the parabolic waveform in which the voltage increases toward the peripheral portion of the screen in synchronization with the horizontal deflection. A second voltage generating circuit that generates a voltage of a parabolic waveform that increases in voltage toward a peripheral portion of the screen in synchronization with the vertical deflection, based on a current supplied to the circuit and the vertical deflection coil; And an adder circuit for adding the voltages of the parabolic waveforms output from the second voltage generating circuit and supplying the same to the first grid. There is no need to reset the CRT, and there is no phase shift between the beam screen position and the parabola waveform voltage.
Has the effect of being able to correct the brightness unevenness of the screen and making the brightness uniform on the entire screen, and this effect is particularly great in the FS tube CRT.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a luminance nonuniformity correction circuit for a CRT according to the present invention, and FIGS. 2, 3, and 4 are diagrams showing the configuration of a differential amplifier. In the figure, 1 and 2 are first and second voltage generating circuits, 3 is an adding circuit, and L1 and L2 are horizontal deflection coils and vertical deflection coils.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04N 5/57

Claims (1)

[Claims] 1. A brightness unevenness correction circuit for a CRT having at least a first grid for controlling brightness, wherein a circuit for going to a peripheral portion of a screen is synchronized with horizontal deflection based on a current supplied to a horizontal deflection coil. Based on the current supplied to the first voltage generating circuit (1) that generates a parabolic waveform voltage that becomes higher and the vertical deflection coil, the voltage is increased toward the peripheral portion of the screen in synchronization with the vertical deflection. And a second voltage generating circuit (2) for generating a voltage of a parabolic waveform with a high parabolic waveform, and the voltages of the parabolic waveforms output from the first and second voltage generating circuits are added and supplied to the first grid. A brightness unevenness correction circuit for a CRT, which is provided with an adder circuit (3).