MXPA95005253A - Dynamic focus coupling - Google Patents

Abstract

A dynamic focus voltage generating circuit comprises a source of DC voltage coupled to a focus electrode of a cathode ray tube. A source of varying is coupled to the focus electrode outer conductor of said coaxial pair is coupled to said source of varying voltage, and the inner conducto of said coaxial pair is coupled to said source of DC voltage.

Description

COUPLING DYNAMIC APPROACH The present invention relates to the field of display of video image, and in particular, to the electrostatic modulation of focusing voltage in a cathode ray tube. The scanning electron beam in a cathode ray visual display tube may be subject to out of focus due to the variation in distance from the electron gun to the screen as the beam scans horizontally and vertically. These blur effects can be corrected by the use of dynamic focus or DF, where an alternating current signal voltage that varies with the deviation is superimposed on a static focusing potential. This dynamic focusing configuration is shown in U.S. Patent No. 5,043,638 to Ya ashita. The alternating current signal voltage may comprise a sum of a parabolic shape signal of horizontal frequency and a parabolic shape signal of vertical frequency. In a typical dynamic focusing system, the static focusing potential of direct current applied to a focusing electrode is adjustable, and may be approximately 9 ilovolts (KV). The AC signal voltage can be coupled with a focusing electrode via a capacitor. This dynamic focus coupling capacitor must have sufficient capacitance to couple the low frequency parabolic components of the alternating current signal voltage with the focusing electrode. In addition, the capacitor requires an interruption voltage evaluation of, for example, 15 KV. A dynamic focus coupling capacitor can be encapsulated or reunited with a resistive potential splitter, which generates the direct current focusing potential. The direct current focusing potential can be derived from either the ultor supply voltage (EHT) of, for example, approximately 30 KV, or from a 1/3 shunt on an integrated high-voltage transformer (IHVT). ), which produces a voltage of, for example, approximately 10 KV. However, in any case, a large-value series resistor, eg, 50 MO, may be required to limit the current flow during the EHT arc to the focusing electrode inside the tube. Figure 1 illustrates, in a simplified form, a typical dynamic focus configuration, wherein a dynamic focus signal, resulting from the sum of the signals of horizontal and vertical parabolic shape in a transformer TI, is coupled, by means of a capacitor C3, with a FG focusing grid of a cathode ray tube (CRT). The wire harness between the dynamic focusing coupling capacitor C3, the focusing potential splitter 100, and the focusing grid FG in the cathode ray tube, may exhibit a parasitic capacitance, for example, of the order of 50 pF, shown as capacitor C4. The internal structure of the tube can introduce another parasitic bypass capacitance of, for example, 20 pF, shown as capacitor C5. Accordingly, the dynamic focus signal coupled to alternating current is subject to attenuation by a capacitive voltage divider formed by the coupling capacitor C3 and the shunt capacitance of the capacitors C4 and C5. It is desirable that this parasitic capacitance be minimized and well controlled, and for this purpose, the conductor coating can control the parasitic or distributed capacitance, by separating the conductors from other conductors. However, this technique is inconvenient and can be impractical in a mass production. In addition, it may not be completely effective, to require the value of the dynamic focus coupling capacitor C3 to be increased, in order to reduce the action of the spurious capacitor potential divider. However, the requirement for a high evaluation of the interruption voltage rating of the dynamic focus coupling capacitor C3 imposes a significant increase in the size and cost of the capacitance if its value is increased.

In order to compensate for the attenuation of the dynamic focus signal by the capacitive voltage division, the dynamic focus signal can be increased to compensate the attenuation. However, this may require dynamic focus signal amplifiers that have a higher power capacity, and a higher interruption voltage. In addition, the CT transformer may require a higher evaluated value of core saturation or crown interruption level. It is also desirable that a focus splitter be used, which operates coupled with a 1/3 shunt on the integrated high voltage transformer (IHVT, not shown), since this splitter is widely used and does not require clustering, and therefore, it is of a lower cost than an encapsulated unit. In accordance with the present invention, a dynamic focusing voltage generating circuit comprises a direct current voltage source coupled to a focusing electrode. A variable voltage source is coupled to the focusing electrode through a capacitance, formed as a pair of coaxial conductors. The external conductor of the coaxial pair can be coupled with the variable voltage source, and the internal conductor of the coaxial pair can be coupled with the direct current voltage source.

Figure 1 illustrates, in a simplified form, a typical dynamic focus configuration. Figure 2 illustrates, in a simplified form, a dynamic focusing configuration of the present invention. Figure 3 illustrates a hybrid dynamic focusing configuration, which utilizes the principles of the present invention. An approach to provide a dynamic focusing voltage is shown in Figure 1. The divider 100, which comprises the variable resistor R3 and the resistor R4, produces a direct current focusing voltage which is fed through the resistor R5 to the focusing electrode FG. An alternating current dynamic focusing voltage DF is derived from the horizontal pulse amplifier 10 and the vertical pulse amplifier 20. The horizontal pulse signal is fed through the inductance HY and the resistor Rl to the transformer TI, and it comes out through capacitor C2 and resistor R2. The vertical pulse voltage exits through the capacitor Cl, and is added with the horizontal pulse voltage to produce a dynamic focus voltage DF. The dynamic focusing voltage DF is added with the direct current focusing voltage through capacitor C3. In the event that an arc is present inside the cathode ray tube (CRT), which can apply a high voltage to the focusing electrode, either or both of the SG spark gaps will become conductors to dissipate the energy applied to the electrode. approach, in order to protect the circuits. In the configuration shown in Figure 1, there is the inevitable parasitic capacitance, shown as capacitor C4, and the capacitance inside the cathode ray tube of the focusing electrode, shown as capacitor C5. Capacitors C4 and C5 form a voltage divider with capacitor C3, which reduces the level of alternating current voltage that is applied to the focus electrode FG. This problem of a reduced AC voltage can be overcome either by increasing the value of the capacitor C3, or by increasing the value of the dynamic focus voltage DF. The increase in the value of capacitor C3 is undesirable, since this capacitor must be evaluated at or above the value of the focusing voltage, nominally approximately 10 KV. This large capacitor tends to be large and expensive. The increase in AC dynamic voltage focus voltage value requires larger amplifiers, which are bulky and consume more power. Figure 2 shows a preferred embodiment of the present invention. Figure 2 is similar to Figure 1, except that the C3 capacitor has been replaced by the DC capacitor, formed as two coaxial conductors 200. The internal conductor is coupled with the direct current from the divider 110 through the resistor R5, to the focusing electrode FG of the cathode ray tube, while the external conductor is coupled to the source dynamic focus voltage DF. With this configuration, the coaxial pair takes the place of the coupling capacitor C3. The parasitic capacitance C4 appears in parallel with the output capacitance of the alternating current source, rather than in parallel with the capacitance of the focus electrode C5. In this way, the parasitic capacitance C4 does not form a capacitive voltage divider with the coaxial pair capacitance, so that the only capacitance acting to reduce the value of the dynamic focus portion of the focusing voltage is the capacitance of the capacitor. focus electrode itself, shown as capacitor C5. Since the capacitor C5 has a relatively low value, on the order of 20 pF, the value of the dynamic focusing voltage at the focusing electrode FG is maintained at its appropriate value without the need for an increased value of the dynamic focusing voltage, or an increased value of the coupling capacitance C3. The DC capacitor is constructed as a coaxial conductor around the direct current focusing wire, to form a shield. This protector can take the form of a metallized insulating tape, such as Mylar, with a drainage wire, a spunbond, a spiral spring, or some other structure that uses the dielectric of the focusing wire insulation as the dielectric of a capacitor distributed. The length of this coaxial structure is typically about 18"(46 cm), and has a capacitance of about 150 pF.If the length of the coaxial structure is increased, the capacitance increases correspondingly, which further reduces the loss in the dynamic focus signal Figure 3 shows another embodiment of the present invention, which uses the principles shown in Figure 2. In certain applications that require a very high dynamic focus voltage level, such as in the applications using multiple cathode ray tubes, the value of the coupling capacitance provided by the coaxial pair 200 may be insufficient.In such a case, a hybrid configuration consisting of a coaxial pair of conductors 200 coupled in parallel with the coupling capacitor C33. Due to the use of the coaxial pair of conductors 200, a smaller capacitance value can be used coupling agent C33 than would otherwise be required in order to provide a sufficient value of dynamic focusing voltage, and the effect of the capacitive voltage divider is substantially reduced.

Claims (13)

1. A dynamic focus voltage generating circuit, comprising: a) a source (++ V) of direct current voltage coupled to a focusing electrode (FG), and b) a variable voltage source (10, 20) coupled to the focusing electrode through a capacitance (200), characterized in that the capacitance is in the form of a pair of coaxial conductors.

2. A circuit according to claim 1, characterized in that the external conductor of the coaxial pair (200) is coupled to the variable voltage source (10, 20).

3. A circuit according to claim 1, characterized in that the internal conductor of the coaxial pair (200) is coupled to the source (++ V) of direct current voltage.

4. A circuit according to claim 1, characterized in that the external conductor of the coaxial pair (200) is coupled to the variable voltage source (10, 20), and the internal conductor of the coaxial pair is coupled with the source (++ V) of direct current voltage.

5. A circuit according to claim 1, characterized in that it comprises a second capacitance coupled in parallel with the coaxial pair.

6. A circuit according to claim 5, characterized in that the second capacitance (C33) is coupled with the output of the variable voltage source (10, 20) and with the internal conductor.

7. A circuit according to claim 1, characterized in that the source (10) of variable voltage varies in a horizontal deviation index.

8. A circuit according to claim 1, characterized in that the variable voltage source (20) varies in a vertical deviation index.

9. A circuit according to claim 1, characterized in that the variable voltage source (10, 20) varies both in a horizontal deviation index and in a vertical deviation index.

10. A circuit according to claim 1, characterized in that it comprises a resistor (R5) coupled in series with the focusing electrode.

11. A circuit according to claim 10, characterized in that the resistance (R5) is coupled between the capacitance (200) and the focusing electrode (FG).

12. A circuit according to claim 1, characterized in that the capacitance (200) comprises an insulated wire surrounded by a protector.

13. A circuit according to claim 12, characterized in that the protector is a metallized insulating tape.