JPH04321092A - Right and left pincushion distortion correcting circuit - Google Patents

Abstract

PURPOSE:To shift a raster in the vertical direction and to prevent the generation of keystone distortion by providing this right and left pincushion distortion correcting circuit with a control circuit and a circuit for adding a vertical saw tooth wave having two kinds of polarity to a vertical parabolic waveform. CONSTITUTION:The pincushion distortion correcting circuit having a keystone distortion correcting function is provided with an inversional amplifier 8 for inversely amplifying a vertical saw tooth wave of minus polarity, a DC voltage low pass filter(LPF) 16 corresponding to a vertical centering position, a bias adjuster 17, and an amplifier 18 for controlling the gain of the polarity-inverted vertical saw tooth wave by DC voltage. Thus the amplitude of the vertical saw tooth wave having single polarity is controlled by the DC voltage corresponding to the vertical centering position, the vertical saw tooth wave, the polarity-inverted vertical saw tooth wave and the vertical parabolic waveform are added and the waves are corrected so as not to generate keystone distortion correspondingly to the vertical position of the raster. Even when the raster displayed on the surface of a CRT is shifted in the vertical direction, the generation of keystone distortion can be prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to pincushion distortion correction in horizontal deflection circuits.

0002

2. Description of the Related Art In a conventional horizontal deflection circuit, a voltage parabolically modulated with a vertical period is supplied as a power supply voltage to correct left and right pincushion distortion. As shown in Figure 3, when the vertical center position of the raster is at the center of the cathode ray tube surface, the corrected left and right vertical lines are vertical, but the vertical center position of the raster is shifted upward or downward. In this case, keystone distortion occurs. The cause of this keystone distortion will be explained below with reference to FIG. In Figure 4, focus on the vertical line at the left end of the raster, divide it into 10 equal parts, and mark the equal dividing points from the bottom as A.
, B, C, ...K. For example, if we consider a case in which the raster is moved upward by a length L0 divided into 10 equal parts, point A is first moved to point A'. Focusing on the vertical line AB section, the horizontal size at point B is L compared to point A.
An extra correction of 1 was added to maintain the vertical line. Therefore, when point A moves up by L0, the horizontal correction amount of point A with respect to point B is insufficient by L1, so point A does not move directly to point B, but A moves to the right by L1. ’Move to point. Similarly, point B is B of point C.
It moves to point B', which is moved to the right by the horizontal correction amount shortage L2 with respect to the point. After point F, moving upward will result in excessive correction in the horizontal direction, resulting in the line protruding beyond the original vertical line. What shape will the left end of the raster be when moved upward by L0? Points A', B', and C.
Point '...If you connect point J' and point K', you will get a straight line with a certain slope. This means that the vertical parabolic waveform is y=ax2
Since it is a parabola, Δy/Δx, that is, the rate of change of the parabola correction amount is differentiated to become dy/dx=2ax. In this way, the rate of change is a linear function of x, so it is a straight line.

Therefore, in order to correct this keystone distortion, a sawtooth wave having an opposite phase to the raster slope is superimposed on the vertical parabolic waveform, and the amplitude of this sawtooth wave is adjusted to keep the vertical line vertical. was. FIG. 2 shows a left and right pincushion distortion correction circuit with conventional keystone correction. In FIG. 2, the vertical parabolic waveform is input to the inverting input terminal of the inverting amplifier 8 via the coupling capacitor 1. The vertical sawtooth wave is also input to the inverting input terminal via the coupling capacitor 3 and the amplitude adjustment resistor 4. The inverting amplifier 8 outputs a waveform obtained by inverting and adding a vertical parabolic waveform and a vertical sawtooth waveform.

To adjust the keystone correction amount, the adjustment resistor 4 is adjusted to vary only the sawtooth wave component of the output waveform.

[0005]

[Problems to be Solved by the Invention] However, in the conventional keystone correction circuit, only a vertical sawtooth wave having a slope in one direction is superimposed on a vertical parabolic waveform. If it were moved sufficiently downward, it would be necessary to add correction for the inclination in the opposite direction, which was not possible. The normal display image is that the vertical back porch is sufficiently larger than the front porch.
In order to center the displayed image on the cathode ray tube surface, the raster is positioned slightly upward. Therefore, for display devices that handle only a single polarization frequency, you only need to perform keystone adjustment once, but for multi-scan type display devices that handle multiple polarization frequencies,
Because images with different sizes of vertical back porches were displayed, keystone distortion could become noticeable in certain frequency modes. Furthermore, in multi-scan type display devices, the size and centering adjusters are often left open to the user, so there is a problem in that keystone distortion becomes noticeable at the user's preferred display position.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a correction circuit that prevents keystone distortion from occurring even when a raster is shifted in the vertical direction.

[0007]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides an inversion method for inverting and amplifying a unipolar vertical sawtooth wave in a conventional pincushion distortion correction circuit having keystone distortion correction. The configuration includes an amplifier, a low-pass filter for a DC voltage corresponding to the vertical centering position, a bias adjuster, and an amplifier that controls the gain of the vertical sawtooth wave of reversed polarity using the DC voltage.

[0008]

[Operation] The amplitude of the unipolar vertical sawtooth wave is controlled by the DC voltage corresponding to the vertical centering position, and this vertical sawtooth wave is added to the vertical sawtooth wave whose polarity is reversed and the vertical parabolic waveform, and the raster is created. Corresponding to the vertical position, compensation is added to prevent keystone distortion from occurring.

[0009]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. In Figure 1, DC indicates the vertical centering position.
The voltage is divided by resistors 14 and 15 and passed through a low pass filter 1.
6 to the gain control terminal of the amplifier 18. A bias adjuster 17 for gain offset adjustment is also connected to the gain control terminal. The vertical sawtooth wave is inverted by an inverting amplifier 13 and input to the amplifier 18 . After outputting the amplifier 18, the sawtooth wave whose amplitude varies depending on the vertical centering position is input to the inverting input terminal of the inverting amplifier 8 via the coupling capacitor 11 and the amplitude adjustment resistor 12.

On the other hand, the vertical sawtooth wave and the vertical parabolic wave are also input to the inverting input terminal of the inverting amplifier 8 via the coupling capacitors 3, 1 and the amplitude adjusting resistors 5, 2. Then, a waveform obtained by inverting and adding the three waveforms applied to the inverting input terminal is output to the output terminal of the inverting amplifier 8. Next, the DC voltage corresponding to vertical centering and the amplifier 8
The relationship between the output voltages will be explained based on FIG. When the vertical center of the raster is at the center of the cathode ray tube, the DC voltage indicating the vertical center position is Vc, and the raster is Δ from the center.
Assume that when moving x, the DC voltage changes by Vc/2. The amplitude of the sawtooth wave voltage output from the amplifier 18 is set to V1 when the vertical center of the raster is at the center of the cathode ray tube, and the amplitude of the sawtooth wave is set to change in proportion to Vd, which is the gain control voltage. The output sawtooth wave of the amplifier 18 and the vertical sawtooth wave of constant amplitude V1 are output to the amplifier 8.
Since they are added at the inverting input terminal of , when Vd=Vc, the polarity is inverted and the amplitude becomes a sawtooth wave, so when they are added, they cancel each other out and the sawtooth wave component disappears. However, V
If d≠Vc, that is, if the center position of the raster deviates from the center of the cathode ray tube, two sawtooth waves with different amplitudes and reversed polarities will be added, so the amplitude will change according to the amount of movement of the raster. There are sawtooth wave components. This sawtooth wave component and the vertical parabolic wave component are further inverted and added to become the output of the amplifier 8, so that the sawtooth wave component can be superimposed on the parabolic wave in a direction that compensates for keystone distortion.

[0011]

As described above, the present invention can provide a raster, that is, a display image that does not cause keystone distortion no matter how the displayed raster is shifted in the vertical direction with respect to the cathode ray tube surface. It functions effectively for scan type display devices to maintain image quality.

[Brief explanation of the drawing]

FIG. 1 is a diagram of a pincushion distortion correction circuit having keystone distortion correction according to the present invention.

FIG. 2 is a pincushion distortion correction circuit diagram with conventional keystone distortion correction.

FIG. 3 is a diagram showing how keystone distortion occurs depending on the vertical center position of a raster.

FIG. 4 is a diagram illustrating the principle of generation of keystone distortion.

FIG. 5 is an operational waveform diagram of each part of the pincushion distortion correction circuit having keystone distortion correction according to the present invention.

[Explanation of symbols]

1, 3, 11 Coupling capacitor 2, 4, 5, 6, 12 Amplitude adjustment resistor 7 Phase compensation capacitor 8, 13 Inverting amplifier 16 Low-pass filter 17 Bias adjuster

Claims (1)

[Claims] 1. A vertical parabolic waveform generation circuit, a vertical sawtooth wave generation circuit having two polarities, and control for varying the amplitude of the vertical sawtooth wave of one polarity in accordance with a voltage corresponding to a vertical raster center position. A left and right pincushion distortion correction circuit consisting of a circuit that adds a vertical sawtooth waveform and a vertical parabolic waveform having these two polarities.