JPH0265567A - Image distortion correction circuit - Google Patents

Abstract

PURPOSE:To suppress picture distortion by connecting a saturable reactor causing an inductance change in response to the detection of video output current fluctuation in parallel or series with a horizontal deflection coil through the detection of the fluctuation in an anode voltage in terms of the fluctuation of the video output current. CONSTITUTION:A secondary coil L2 of a saturable reactor transformer is connected in series with a horizontal deflection coil Ly, a deflection output of a horizontal output transistor(TR) Q4 is divided by the horizontal deflection coil Ly and the said secondary coil L2 and the load impedance of the horizontal output TR Q4 is increased by the impedance of the secondary coil L2 simultaneously. Thus, the primary current 1l flowing to the primary coil is decreased to increase the inductance of the secondary coil L2, the deflection current Ly flowing to the horizontal deflection coil Ly is decreased to weaken the deflection magnetic field and to reduce the deflection amplitude thereby making the deflection amplitude on the screen unchanged substantially.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention relates to a circuit for correcting image distortion due to dynamic fluctuations in anode voltage in an image display device using a CRT.

[Prior Art] In an image display device using a CRT, when the contrast of the image changes, the anode current of the CRT changes, causing the anode voltage to fluctuate, and therefore the deflection amplitude to fluctuate, causing distortion in the image. Conventionally, as a preventive measure, a capacitor was added to the anode to suppress fluctuations in the anode voltage, thereby suppressing fluctuations in deflection amplitude and suppressing image distortion.

[Problem to be solved by the invention] However, when a capacitor is added to the anode, the anode voltage is directly applied to the capacitor, so the capacitor needs to have an ultra-high withstand voltage, and is also required to have high reliability, so it must be large. It is an expensive special part, and since it is used in such places, it must be handled with care.

The present invention aims to achieve the above-mentioned purpose without using special parts, and instead of suppressing the fluctuations in the anode voltage, the present invention aims to deflect the effect of canceling the influence of the fluctuations in the anode voltage on the deflection amplitude of the image. This is intended to be included in the circuit to suppress image distortion.

[Means for Solving the Problem] Therefore, the present invention detects fluctuations in the anode voltage by detecting fluctuations in the video output current, and installs a saturable reactor in the horizontal deflection coil that changes the inductance in accordance with the detected fluctuations. connected in series or in parallel.

[When the working core node voltage changes, the current in the primary coil of the saturable reactor transformer changes and the inductance of the secondary coil changes.

Therefore, if the same secondary coil is connected in series or parallel to the horizontal deflection coil, the deflection voltage or deflection current that would have been applied entirely to the horizontal deflection coil will be divided or shunted to the secondary coil, resulting in the deflection amplitude. can be increased or decreased, and image distortion can be corrected.

[Example 1] First, the relationship between the deflection amplitude, the anode voltage, and the strength of the deflection magnetic field will be explained.

The relationship among the deflection amplitude (d), the anode voltage (Va), and the strength of the deflection magnetic field (H) is expressed by the following equation.

That is, the deflection amplitude d is inversely proportional to the square root of the anode voltage Va and proportional to the strength H of the magnetic field created by the deflection coil.

Therefore, when the anode voltage fluctuates, the present invention changes the inductance of a saturable reactor connected in series or parallel to the deflection coil, thereby changing the deflection power applied to the deflection coil approximately in proportion to the square root of the anode voltage, This suppresses fluctuations in deflection amplitude and prevents image distortion.

Examples of the present invention will be described in detail below.

First, image distortion will be explained using FIGS. 3 to 5 and FIG. 7.

Figure 3 shows the video output transistors Q1 and Q2 shown in Figure 1.
, Q3 are input to the respective bases 6.7 and θ, and the waveform diagram of the video signal pattern is shown in 4 in FIG.

Further, FIG. 4 shows an example of an image displayed on a CRT without the correction according to the present invention, and FIG. 5 shows an example of an image displayed on a CRT when the correction according to the invention is performed.

Now, when horizontal scanning starts from the top of the screen, ie, from 21 in FIG. 3, the screen is black between 21 and 22, so almost no anode current flows and the anode voltage does not drop.

Therefore, although it cannot be visually observed due to the black screen, the deflection amplitude is constant.

Next, from 22 to 23 in Figure 3, most of the horizontal scanning period is a white screen, so the anode current flows during most of the horizontal scanning period, and the white screen is displayed for a period that cannot be covered by the anode capacity of the CRT. If the screen continues, the anode voltage will gradually drop.

Due to the drop in the anode voltage, the deflection amplitude gradually increases from 22 to 23 in FIG. 4, and the CRT screen becomes an image extending to the left and right at 23 compared to <22, as shown in FIG.

Furthermore, since the screen becomes black from 23 to 24 in Figure 3, almost no anode current flows, and the anode voltage returns to the same voltage as from 2 to 22, so the deflection amplitude also decreases from 2 to 2.
Returning to the same state as up to 2, the deflection amplitude at 24 in FIG. 4 is approximately the same as the deflection amplitude at 22.

From 24 to 25 in FIG. 3, most of the horizontal scanning period becomes a white screen again, so the anode current flows during most of the horizontal scanning period, the anode voltage gradually decreases, and the deflection amplitude gradually increases. As shown in FIG. 4, the image becomes an image in which 25 extends to the left and right compared to 24.

No. 2 in FIG. 7 shows how the anode voltage changes.

If distortion correction is not performed, the CRT screen displays the image shown in FIG. The purpose is to correct the image so that it becomes a distortion-free image as shown in Figure 5.

FIG. 1 is a circuit diagram showing the main parts of the embodiment.

In the figure, Q7, Q2, and Q3 are R, G, and B video output transistors, and a video output current according to the video signal input to each base flows through each transistor, and the load resistances R/ and R2 are respectively connected to the transistors. , outputs a video signal to R3, and the output is C
It is connected to the cathode of RT77.

Since each video output current flows from the power supply Vcc through the equivalent power supply impedance Rr, a ripple voltage Vr is generated at point 4 in the figure in accordance with a change in the video output current.

Furthermore, since the ripple voltage Vr is a combination of ripples caused by changes in the output currents of the three video output transistors g and GSB, it closely matches the strength of the video brightness on the CR7 screen.

On the other hand, the high voltage boosted by the high voltage generator 13 is applied to the CRT.
The anode voltage is applied to the anode 12 of II.
The anode voltage changes as a result of integrating the change in anode current by the anode capacitance.

Since the anode voltage current changes in accordance with the video output current, the variation in the anode voltage is similar to the integration of the ripple voltage Vr.

Therefore, the LJ pull voltage Vr at the point 4 can be treated as a detection signal indicating fluctuations in the anode voltage.

In the figure, I is an active filter for removing the horizontal component included in the detection signal and amplifying the detection signal, which manually inputs the waveform 4 in Figure 7 and outputs the voltage waveform 5 in the same figure. .

2 is a driver for driving the saturable reactor transformer 3, and since the load is a saturable reactor transformer, that is, an inductive load, the current I driving the transformer is
N has a form obtained by integrating the detection signal voltage Vr (shown in FIG. 7 I!), and is similar to the anode voltage fluctuation (shown in FIG. 7 12).

The inductance characteristics of a saturable reactor are generally expressed as shown in FIG.

That is, as the primary current I2 flowing through the primary coil Ll of the saturable reactor transformer increases, the inductance of the secondary coil L2 of the saturable reactor transformer decreases.

Therefore, the same primary current! By changing l within an appropriate range, the inductance of the secondary coil L2 can be changed to a required value.

Therefore, if the secondary coil L2 of the saturable reactor transformer is connected in series with the horizontal deflection coil Ly, the deflection output of the horizontal output transistor Q4 can be connected to the horizontal deflection coil ty and the above two.
The voltage is divided by the secondary coil L2, and at the same time, the load impedance of the horizontal output transistor Q4 is increased by the impedance of the secondary coil L2, so that the 1-forming 1Jt1!2 flowing through the primary coil is reduced, and the secondary coil L2
By increasing the inductance of the horizontal deflection coil Ly and decreasing the deflection current ry flowing through the horizontal deflection coil Ly (shown as 1y in Fig. 7), the deflection magnetic field is weakened, the deflection amplitude is reduced, and the change in the deflection amplitude on the screen is substantially reduced. It is possible to avoid this.

The image shown in FIG. 4 is thus corrected as shown in FIG.

Ls and CS connected in series to the other end of the secondary coil L2 are a coil and a capacitor for correcting horizontal linearity.

Note that if the ripple voltage is reduced by adding a capacitor to the point 4 of the power supply VCC in Figure 1, etc., the ripple voltage Vr will be detected as a waveform integrated by the capacitor. However, by adjusting the constants of the circuits such as the active filter I and the driver 2, it is possible to obtain the current 11 required for the primary coil Ll and perform the necessary correction.

Figure 2 shows the secondary coil L of the saturable reactor transformer 3'.
2' is connected in parallel to the horizontal deflection coil Ly'', and a small portion 1y'' of the horizontal deflection current /y is shunted to the secondary coil L2''. The saturation reactor transformer 3'' and the driver 2' for the reactor transformer gradually increase the current in the primary coil L1'' of the reactor transformer 3'' during the period from 22 to 23 in FIG. The inductance of ' is gradually decreased, the shunt current ty' to the secondary coil L2' is gradually increased, and the deflection current to the horizontal deflection coil Lp' is decreased by the same amount of increase, weakening the deflection magnetic field, and deflecting The structure is such that the amplitude is reduced to correct distortion.

[Effects of the Invention] As described above, the present invention is capable of correcting image distortion caused by fluctuations in anode voltage without using expensive special parts, thereby saving costs and achieving satisfactory results. It provides excellent performance and is extremely effective.

[Brief explanation of the drawing]

FIGS. 1 and 2 show an embodiment of the present invention; the circuit shown in FIG.
4 and 5 are diagrams for explaining image distortion, FIG. 6 is a diagram for explaining characteristics of the saturable reactor, and FIG. 7 is a waveform diagram of each part. Patent applicant: Fujitsu General Ltd.

Claims (1)

[Claims] An image distortion correction circuit consisting of a saturable reactor connected in series or parallel to a horizontal deflection coil, which detects fluctuations in video output current and changes the inductance in response to the detected fluctuations.