JPH0377709B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a raster distortion correction circuit for correcting raster distortion of horizontal lines at the top and bottom of a screen that occurs in a display device such as a television receiver using a cathode ray tube.

[Conventional technology]

The raster on the phosphor screen, which is the image display part of the cathode ray tube, is created by the 3D pattern due to the curvature of its face plate and the magnetic field distribution of the raster forming means, that is, the electromagnetic deflection yoke.
An inverted W-shaped distortion occurs as shown in the example shown in the figure. Third
The raster distortion in the example shown in the figure is, for example,
As shown in Japanese Patent No. 57014, the raster distortion is generally corrected by a raster distortion correction circuit surrounded by a broken line in FIG.

In Fig. 4, 1a and 1b are vertical output transistors, 2 is a coupling capacitor, 3 is a vertical deflection coil, 4 is a vertical feedback resistor, 5 is a raster distortion correction transformer, and 5a is a transformer horizontal winding of the raster distortion correction transformer. , 5b is a transformer vertical winding of a raster distortion correction transformer, 6 is a phase adjustment converter, 7 is a resonant capacitor, and 8 and 9 are capacitors and resistors forming a bypass circuit for the correction current. Since the raster distortion shown in FIG. 3 has a high frequency distortion twice as high as the horizontal deflection frequency _fH , the horizontal frequency is approximately A resonant circuit tuned twice is formed, and a raster correction current generated by this resonant circuit is passed through a capacitor 8 and a resistor 9 to the vertical deflection coil 3 to perform correction. The waveform of the raster correction current is superimposed on the vertical deflection current, and if the waveform of the vertical deflection current is observed at a vertical period, it will be as shown in FIG. 5a. The waveform of the raster correction current in the horizontal period is ideally as shown in FIG. 5b, and the second-order distortion shown in FIG. 3 is corrected. In addition, if we observe the waveform of the correction current in a vertical cycle, as shown in Figure 5c, the amplitude is almost at its maximum at the beginning and end of the scan of the vertical cycle, and the amplitude is at the center of the vertical cycle (corresponding to the center of the screen). The correction becomes 0, and the envelope from the maximum to 0 has an almost straight line or a slightly convex shape as shown by the broken line in FIG. 5c, although it depends on the characteristics of the raster distortion correction transformer and the like.

Note that a horizontal pulse is applied to the transformer horizontal winding 5a of the raster distortion correction transformer 5 from a flyback transformer (not shown) or the like, and horizontal energy is supplied to the resonance circuit as a horizontal timing pulse.

[Problem that the invention seeks to solve]

In recent years, the face of cathode ray tubes has become increasingly flat and larger. In this case, if the curvature of the face surface is flattened by simply increasing the radius R of the spherical surface, problems such as doming of the shadow mask will occur. It is often chosen for its aspherical structure. FIG. 6 is an example of a contour diagram of a face plate having an aspherical structure. When a cathode ray tube with such a face surface is raster scanned by a deflection yoke, as shown by the broken line in Figure 6, there is a large second-order distortion and inverted W-shaped distortion at the upper and lower edges of the screen, but as it approaches the center a little. When the second-order distortion tendency suddenly decreases, nonlinear raster distortion occurs in the vertical period. Therefore, if the correction current of the conventional raster distortion correction circuit is used to correct the distortion in the upper and lower parts of the screen, as shown in Figure 2, the middle part of the screen will be overcorrected and the distortion will increase. There were some drawbacks.

The present invention has been made to solve the above-mentioned problems, and provides means for correcting nonlinear raster distortion in the vertical period caused by an aspherical structure face plate, etc., using a simple structure.

[Means for solving problems]

Therefore, the raster distortion correction circuit according to the present invention has a minimum amplitude when scanning the center of the screen,
A vertical modulation circuit that amplitude-modulates the horizontal timing pulse with vertical synchronization so that the amplitude is maximum when scanning the top and bottom of the screen, and applies this amplitude-modulated horizontal timing pulse to the transformer horizontal winding of the raster distortion correction transformer. It is characterized by having the following.

[Effect]

The vertical modulation circuit modulates the amplitude of the horizontal timing pulse in a vertical period so that the amplitude is minimum when scanning the center of the screen, and maximum when scanning the top and bottom of the screen.

Thus, a horizontal timing pulse amplitude modulated with a vertical period is applied to the horizontal winding of the raster correction transformer.

As a result, the current generated in the resonant circuit consisting of the coil and capacitor including the vertical winding of the raster distortion correction transformer has an envelope of As the screen becomes U-shaped as shown in the figure, the amount of correction decreases sharply as it goes inward from the top and bottom edges of the screen. Therefore, the distortion shown in FIG. 6 is ideally corrected.

〔Example〕

An embodiment of the present invention will be described below based on the drawings.

Note that the same components as in the prior art are given the same numbers and their explanations are omitted.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In FIG. 1, 10 is a vertical modulation circuit. This vertical modulation circuit 10 is of a saturable reactor type, and 10a is a modulation circuit horizontal winding;
0b is the vertical winding of the modulation circuit, and 10c is the saturable core. In this saturable reactor method, since a sawtooth vertical deflection current flows through the vertical winding 10b of the modulation circuit, the inductance of the horizontal winding 10a of the modulation circuit changes at the beginning and end of scanning of the vertical period due to the well-known characteristics of the saturable reactor. The inductance shows the minimum value when the current is maximum, and the maximum inductance value is shown in the middle of scanning, that is, when the vertical deflection current is 0. Therefore, the voltage across the transformer horizontal winding 5a of the raster distortion correction transformer 5 becomes a pulse modulated with a vertical period in a parabolic manner.

Transformer horizontal winding 5 of raster distortion correction transformer 5
When the voltage applied to a is modulated concavely in a parabolic manner with a vertical period as described above, the voltage generated in the resonant circuit including the transformer vertical winding 5b of the raster distortion correction transformer 5 no longer has an envelope curve as shown in FIG. 5c. Instead, it becomes a U-shaped envelope as shown in FIG. Such resonant voltages result in large distortion corrections at the beginning (or end) of the vertical scan, but
Thereafter, as the middle portion approaches, the correction effect decreases rapidly, and the nonlinear raster distortion as shown in FIG. 6 is successfully corrected.

In the embodiment shown in FIG. 1, a saturable reactor is used as the vertical modulation circuit. For the vertical bias in this case, a vertical deflection current is passed through the modulation circuit vertical winding 10b, but for example, the modulation circuit vertical winding 10b is not provided and the core is of an open magnetic path type, and the core of the deflection yoke 3 (not shown) is used.
It is also possible to install an open magnetic path type saturable core nearby and use the leakage flux of the deflection yoke as a magnetic bias.

Furthermore, it is also possible to realize a vertical modulation circuit using an electronic circuit combining ordinary semiconductor elements without using a saturable reactor. Furthermore, the voltage applied to the transformer horizontal winding 5a of the raster distortion correction transformer 5 before vertical modulation has been explained with reference to the flyback pulse.
The present invention can be applied to a method in which the repetition frequency is the horizontal deflection frequency or an n-th harmonic is applied.

〔Effect of the invention〕

As explained above, the raster distortion correction circuit according to the present invention adjusts the horizontal timing pulse so that the amplitude is minimum when scanning the center of the screen, and maximum when scanning the top and bottom of the screen. A vertical modulation circuit is provided that performs amplitude modulation with vertical synchronization and applies this amplitude-modulated horizontal timing pulse to the horizontal winding of the raster distortion correction transformer. It is possible to easily and accurately correct vertical raster distortion.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure shows the distortion when the raster distortion in Figure 6 is corrected using the conventional method, Figure 3 is a waveform diagram showing the raster distortion waveform on the screen, and Figure 4 is the circuit of a conventional raster distortion correction circuit. 5a to 5c are waveform diagrams showing the waveforms of the vertical deflection current and the raster correction current, and FIG. 6 is a line diagram showing the contour lines and raster distortion of the screen having an aspherical structure. 5...Raster distortion correction transformer, 5a...Transformer horizontal winding, 5b...Transformer vertical winding, 10...
...Vertical modulation circuit, 10a...Modulation circuit horizontal winding,
10b...Modulation circuit vertical winding.

Claims (1)

[Claims] 1 By applying a horizontal timing pulse to the transformer horizontal winding of the raster distortion correction transformer, a resonant circuit consisting of a coil including the transformer vertical winding of the raster distortion correction transformer and a coil capacitor is driven. In the raster distortion correction circuit, which corrects raster distortion on the screen by passing a correction current through the vertical deflection coil, the amplitude is minimum when scanning the center of the screen, and maximum when scanning the top and bottom of the screen. A raster distortion characterized in that a vertical modulation circuit is provided which amplitude-modulates the horizontal timing pulse in a vertical period so that the amplitude-modulated horizontal timing pulse is applied to the transformer horizontal winding of the raster distortion correction transformer. correction circuit.