DE2724552A1 - Circuit for east-west cushion correction in TV set - includes capacitor whose variable capacitance depends on correction voltage frequency - Google Patents

Abstract

The line deflection current in the deflecting coils (8) is modulated in amplitude at vertical frequency by the correction circuit (10) in such manner that the current amplitude at the upper and lower edges of the picture is reduced and vertical lines at the left and right edges of the picture are straight lines. However, vertical lines adjacent the picture centre still exhibit cusion error, and in order to overcome this defect the condenser (11) is one in which with increasing voltage across it its capacity decreases with the frequency of the east-west cushion correction voltage. In a modification, the correction circuit (10) is replaced by a capacitor which serves as a short-circuit for the line frequency, land a parabolic correcting voltage of vertical frequency is applied to the capacitor (11), whereby to correct the whole of the east-west cushion error.

Description

Circuit for east-west pillow correction of the deflection in a color television receiver In the case of a color television receiver, it is known that this occurs without any special corrective measures a so-called east-west pillow error, i.e. the image width is at the top and bottom The edge of the picture is too large compared to the center of the picture. To eliminate this error it is known to modulate the amplitude of the line deflection current with vertical frequency in such a way that that it is reduced at the top and bottom of the picture.

For this purpose it is known (DT-OS 19 38 158), in series or in parallel to switch the working winding of a transductor to the line deflection coils, whose Control winding is fed with a vertical frequency voltage.

If in this way the real east-west pillow bug is eliminated becomes, so the vertical lines on the left and right side of the picture are straight again, Another pillow flaw can arise, which is known as the interlining flaw will.

This error consists of that vertical lines near the Center of the picture, i.e. left and right of a vertical line in the center of the picture, a K @@ se @ experience hmful award, so up and down to the edge of the picture are curved. There are additional circuits to eliminate this interpad error required for additional modulation of the line deflection current.

In a known circuit for eliminating the inter-cushion error (DT-AS 20 08 767) is the one in series with the line deflection coils for tangent equalization serving tangent capacitor, the working winding of a transductor is connected in parallel, whose control winding is fed with a vertical-frequency current. Through this controlled inductance, the effective capacitance of the tangent capacitor becomes vertical frequency modulated to reduce the inter-cushion error.

This circuit also requires additional components, namely the transducer and the associated control circuit.

The known circuits for eliminating the pillow errors, be it the margin pad defect at the left and right edge of the image or the inter-pad defect in the center of the picture, so require additional active or passive components for the Modulation of the line deflection current.

The invention is based on the object of a circuit for elimination to create the cushion defect, which works largely without additional components.

This object is achieved by the invention described in claim 1 solved. Advantageous further developments of the invention are described in the subclaims.

The invention is based on the following consideration. There are capacitors whose capacity depends on the applied voltage. This is the case, for example for ceramic capacitors with a certain ceramic material as dielectric. This dependence of the capacitance on the applied voltage is usually undesirable. because in general the capacitance of a capacitor from the adjacent DC voltage should be independent and a dependency on undesired signal distortion or cause other disadvantages. In the invention, however, this per se undesired dependency is advantageously used to create an automatic Change in capacity and thus achieve the desired correction of the cushion defect.

Due to this automatic change in capacity by the anyway available modulation voltage for the line deflection current for east-west pincushion equalization there are practically no additional components for the correction of the cushion error needed.

The desired dependence of the capacitance on the applied voltage can be achieved by a suitable choice of material for the dielectric of the capacitor reach. For this, e.g. one known under the term DK 2000, DK 4000 to DK 10000 can be used Material to be used.

The voltage dependence of such capacitors is also sufficient inertia-free, so that in the desired way the capacitance with the equalization frequency, e.g. 50 Hz can change. On the other hand, there is indolence in the ability of The change in voltage is not so great that the capacity increases with speed, for example the line frequency can change. This is even more beneficial for the pillow rectification, because a change in capacitance depending on the addition on the capacitor effective line-frequency voltage would even be undesirable and the voltage across the capacitor would distort. This would be particularly disadvantageous if the voltage-dependent capacitor is a tangent capacitor.

The invention is basically applicable to both the correction of the edge cushion error as well as for the correction of the interpad error. Depending on the type of Deflection system can the solution according to the invention in a different ratio more for the edge cushion defect and less for the inter-cushion defect or else more for the inter-cushion error and less for the edge cushion bug can be used. With certain deflection systems, it is also possible with the inventive Circuit both the edge cushion defect and the inter-cushion defect are sufficient to eliminate.

Preferably, the voltage-dependent capacitor is anyway usually used in line deflection circuits existing tangent capacitor, the serves to give the line deflection current an S-shaped curve. The invention but is not limited to the tangent capacitor. It can also be in addition to the Tangent capacitor a voltage-dependent capacitor for pincushion equalization be provided. Such a voltage-dependent capacitor for pincushion equalization can also be used if the circuit does not contain a tangent capacitor.

The invention is based on the drawing of an exemplary embodiment explained. FIG. 1 shows an embodiment of the invention for the elimination the inter-cushion defect, Figure 2 in principle the mentioned inter-cushion defect, FIG. 3 shows the dependence of the capacitance on the voltage across the capacitor, FIG 4 voltage curves for explaining the mode of operation and FIG. 5 for another exemplary embodiment the invention.

FIG. 1 shows that controlled by the line-frequency voltage 1 Line output stage transistor 2, the working winding 3 of the line transformer, the Filter resistor 4, the filter capacitor 5, the flyback capacitor 7, the line deflection coils 8, the differential transformer 9, the tangent capacitor 11 and the circuit 10 for east-west pillow rectification. Through the circuit 10, the line deflection current iH vertical frequency modulated in amplitude so that its amplitude at the top and lower edge of the picture is reduced and vertical lines on the left and right Can be shown as straight lines.

FIG. 2 shows the result achieved with this circuit. The vertical Lines 12 on the left and right edges of the image are due to the vertical frequency Modulation of the line deflection current shown as straight lines, d. H. the east-west marginal pillow flaw is eliminated. The vertical line 13 in the center of the picture is also straight. The lines 14 left and right close to line 13, however, still have the inter-cushion defect, i.e. they are curved outwards at the top and bottom of the picture.

To eliminate this remaining inter-cushion defect, now as the capacitor 11, no capacitor with a fixed capacitance is used, but rather a capacitor, the capacity of which with increasing voltage at least increases with speed the Ost-est equalization voltage, e.g. 50 Hz, decreases. This change can now dimensioned so that the inter-cushion defect shown in FIG. 2 is thereby eliminated becomes, so the lines 14 are straight.

Figure 3 shows the capacitance C of the capacitor 11 as a function from the applied voltage U2.

FIG. 4 shows the envelope of the line-frequency voltages at the both electrodes 11a and 11b of the capacitor 11 during a vertical deflection period, than 20 ms. The parabolic modulated line frequency is at the electrode 11a Voltage 15, whose mean value (curve 20) represents the effective modulation voltage. The voltage 15 is shown on an enlarged time scale. At the electrode 11 is the mean value of the operating voltage U1, the value of the resistance 4 can be neglected. At the top and bottom of the picture is the one on the capacitor 11 standing mean voltage, i.e. the difference between lib and U1la, through the Circuit 10 reduced in the sense of an East Wcst pillow correction. A smaller tension at the capacitor 11, however, according to FIG. 3, means a greater capacitance. The capacity C of the capacitor 11 thus becomes vertical frequency according to FIG. 3, 4 modulated so that they are larger at the top and bottom of the picture and in the middle of the picture is smaller. This modulation of the capacitance C results in the desired correction of the interpad defect of Figure 2, i.e. lines 14 in the vicinity of the vertical line 13 become straight vertical lines. So while in this Switching of the edge cushion defects essentially by modulating the amplitude of the line deflection current is eliminated by the circuit 10, that in FIG 2 essentially due to the change in capacitance of the capacitor 11 according to FIG. 3 eliminated.

Figure 5 shows a circuit in which the total east-west pillow error, thus both the edge cushion defect and the inter-cushion defect, due to change the capacitance C is eliminated. The vertical deflection circuit 16 becomes the tangent capacitor 11 a parabolic vertical frequency correction voltage 17 is supplied. The condenser 18 represents a short circuit for the line frequency. In this circuit So only the voltage drop at the tangent capacitor becomes for the entire pillow correction 11 changed parabolic by changing its capacitance value. It is then for the entire east-west pillow correction no further switching means such as a East-west modulator or transducer required.

The invention is independent of the presence of a tangent capacitor. For example, there could be such a large capacitor in the path of the line deflection current, that this is no longer effective for the tangent equalization. The capacity of this Tangent capacitor could, however, by a vertical frequency correction voltage be changed so that an east-west pillow correction in the manner described he follows.

L e r s e i t e

Claims (10)

Claims 1, circuit for east-west pillow correction of the deflection in a color television receiver where the effective reactance is one in a circle of the line deflection current lying capacitor by a vertical frequency voltage is modulated with vertical frequency, characterized in that the capacitor (11) a capacitor is used whose capacitance (C) increases with the applied voltage (U2) at least with the speed of the correction frequencies: (50 Hz) decreases. 2. Circuit according to claim 1, characterized in that the capacitor (11) is a ceramic capacitor. 3. A circuit according to claim 2, characterized in that de capacitor (11) contains a material of type DK 2,000 to 10,000 as the dielectric. 4. A circuit according to claim 1, characterized in that the change in capacitance with a voltage change of 40 V is in the range of 0.39 - 0.56 µF. 5. A circuit according to claim 1, characterized in that the capacitor (11) is dimensioned so that its capacitance (C) increases with the speed of the line frequency (16 KHz) does not change. 6. A circuit according to claim 1, characterized in that the capacitor is the tangent capacitor (11). 7. A circuit according to claim 1, characterized in that the capacitor one separated from the tangent capacitor, coupled to the deflection circuit, with a vertical frequency correction voltage is applied to the capacitor. 8. A circuit according to claim 1, characterized in that it is used for Elimination of the so-called inter-cushion defect in the form of cushion-shaped distortions vertical lines (14) in the vicinity of the image fllitte is used (Fig. 1-4). 9. A circuit according to claim 1, characterized in that it is used for Elimination of the so-called edge cushion defect in the form of cushion-shaped distortions vertical lines at the 1 left and right edge of the picture is used. 10. Circuit according to claim 8 and 9, characterized in that it both for correcting the inter-cushion error and for correcting the edge-cushion error is exploited.