MXPA01006992A - Deflection circuits coupled via a filter - Google Patents

Abstract

A secondary winding (LSEC) of a horizontal flyback transformer (IHVT) of a horizontal deflection circuit (20) develops a horizontal retrace pulse voltage (12). A secondary winding (43) of a second transformer (41) is coupled in series with a vertical deflection coil (LV) of a vertical deflection circuit (60). An R-C filter (40) is coupled between the secondary winding (LSEC) of a flyback transformer (IHVT) and a primary winding (42) of the second transformer (41). Horizontal parallelogram errors are corrected by a horizontal rate current (Icorr) injected in a current path of the vertical deflection coil (LV). The R-C filter (40) prevents the vertical deflection current from being parasitically coupled to the horizontal deflection circuit (20).

Description

DEFLECTION CIRCUITS COUPLED THROUGH A FILTER FIELD OF THE INVENTION The invention relates to frame correction circuits of a video presentation.

BACKGROUND In a cathode ray tube (CRT) of a video presentation, a frame is formed by flexing an electron beam through a phosphor screen. Each electron beam is flexed in a horizontal direction through a magnetic field produced by a horizontal deflection coil through a sawtooth current of horizontal regime. Likewise, the electron beam is simultaneously flexed in a vertical direction by a magnetic field produced by a vertical deflection coil through a sawtooth current of vertical regime. The result is a negatively tilted or "sloping" scan line as the electron beam is flexed from left to right to form the CRT frame. In a typical cathode ray tube used in a color television receiver, and having, for example, a screen width of approximately 723 mm and a screen height of approximately 538 mm, a horizontal scanning line may fall at a distance of approximately 2.4 mm from a perfectly horizontal position in a field. This slope exploration effect introduces both orthogonality and parallelogram errors in the frame. In a perfectly rectangular pattern, the horizontal and vertical center lines are orthogonal, or perpendicular, to each other. The slope scan does not produce a perfectly rectangular frame, and therefore, results in a non-orthogonal relationship between the horizontal and vertical center lines of the frame. The orthogonality error is a quantitative measure, expressed in units of radians or degrees, of the degree to which the horizontal and vertical center lines of a frame are separated from the orthogonality. The orthogonality error can be increased in the left and right edges of the frame because the deflection sensitivity increases near the edges of the frame. As a result, the edges of the frame can be tilted, so that the frame has a generally parallelogram shape. The elimination of orthogonality and parallelogram errors in a frame can be obtained by providing a horizontal rate modulation of a vertical deflection current to substantially deviate the slope scanning effect caused by the vertical deflection of the electron beam. A winding of a horizontal sweep transformer can be used to apply a horizontal return pulse voltage to a primary winding of a transformer. A secondary winding of a transformer can be coupled to a vertical deflection winding providing a saw-tooth current of small horizontal regime that will be super-imposed in a vertical deflection current. The coupling of the vertical current to the horizontal deflection circuit is reduced by the relatively large leakage of the transformer. However, the vertical residual current, during the vertical return, can continue to produce a disorder in the upper part of the screen, immediately after the vertical return. It may be desirable to further reduce the return coupling to the vertical current to the horizontal deflection circuit. To carry out an aspect of the invention, an R-C filter is interposed in a current path between the transformers. The filter R-C attenuates the vertical deflection current back coupled. In this way, the addition of the coupling filter R-C prevents the vertical deflection current from affecting the horizontal deflection circuit.

COMPENDIUM OF THE INVENTION A video presentation deflection apparatus, modeling an aspect of the invention, includes a first circuit of deflection to generate a first deflection current at a first deflection frequency in a first deflection winding to vary a position of an electron beam in a first direction. A second deflection circuit is used to generate a second deflection current in a second deflection winding at a second deflection frequency to vary the position of the electron beam in a second direction. A filter couples the second deflection circuit to the first deflection winding to generate a correction current in a current path formed by the first deflection winding at a frequency related to the second deflection frequency to provide the frame error correction. The filter significantly attenuates the parasitic signal coupling in an opposite direction, from the first deflection circuit to the second deflection circuit.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates an array for correcting orthogonality and parallelogram errors in a frame, including a filter, according to one aspect of the invention. Figures 2a and 2b illustrate waveforms useful to explain the operation of the deflection system shown in Figure 1, when the filter is employed; and Figures 3a and 3b illustrate waveforms useful in explaining the operation of the deflection system shown in Figure 1, when the filter is removed.

DETAILED DESCRIPTION A deflection system 100 of Figure 1 provides the deflection for a cathode ray tube, not shown, of a television receiver or a video display terminal. A voltage B + is coupled to a conventional horizontal deflection circuit 20 through a primary winding LPR (of the horizontal sweep transformer IHVT.) A damping current lD flows through a damping diode D1 to deflect an electron beam from an edge A horizontal output transistor Q1 conducts a current lHot to divert the electron beam from the center of the network to a right edge of the network A horizontal deflection current lH flowing through the network. A horizontal deflection winding LH can have a peak-to-peak amplitude of several amperes A tracking capacitor Cs, coupled in series with the deflection winding LH provides the correction S for the horizontal deflection current lH- A secondary winding LSEC horizontal sweep transformer IHVT is coupled through an RC filter 40, modeling an aspect of the invention, to a primary winding 42 of a frame correction transformer 41. Transformer 41 has a secondary winding 43. Transformer 41 is wound on a ferrite slag core with a length of 2.54 cm by a diameter of 10.13 mm. The winding 43 has a wire of Ns = 60 turns, of 5 strands Litz AWG # 30 (0.2546 mm), and a winding 42 has a wire of NP = 180 turns, AWG # 29 (0.2859 mm). A return pulse of horizontal regime, not shown, produced in a conventional manner in the deflection circuit 20, is coupled by the transformer to the secondary winding LSEC of the IHVT transformer to develop a return pulse of horizontal regime 12. The pulse in return 12 is coupled through the RC filter 40, modeling an aspect of the invention, to the winding 42 of the transformer 41. The transformer 41 scales an important portion of the horizontal rate pulse 12 coupled through the RC filter 40 and developed in the winding 42 according to the transformer 41 with its ratio of turns or turns. The frame correction transformer 41 develops a stepped horizontal rate pulse waveform 11 with a peak-to-peak voltage of approximately 40V pp through the secondary winding 43. Similarly, a horizontal frame correction circuit lcorr is induced in the secondary winding 43. A vertical deflection circuit coupled to direct current (DC) 60 includes a conventional vertical-rate sawtooth generator 61 that provides a sawtooth waveform of vertical regime at an input without inverting a conventional vertical output amplifier 62. The vertical output amplifier 62 may include a push-pull transistor output stage, not shown. The vertical output amplifier 62 drives the vertical deflection windings L? and LV2, coupled in series, together with a current in serrated teeth of vertical regime lV- The vertical deflection windings L? and LV2 are also coupled in series with the winding 43 of the transformer 41 and with the resistor R4. The current sense resistor R4 generates a feedback voltage at an inverting input of the vertical output amplifier 62 sensitive to the vertical deflection current l - Except for the modulation provided by the ICORR induced frame correction current in the secondary winding 43, the vertical deflection circuit 60 generates the current lv in a conventional manner. The ICORR horizontal rate frame correction current flows through both the vertical deflection windings LV1 and LV2 to produce a magnetic field that opposes the aforementioned slope exploration effect. In order to explain, assume that the filter 40 is not used. Rather, assume that the LSEC winding of the high-voltage transformer IHVT is coupled directly in parallel with the winding 42 of the transformer 41, as shown through a connector bridge conductor 40a. The vertical deflection current lv flows through the secondary winding 43 of the transformer 41. During the vertical return, a vertical pulse voltage Vv of Figure 3b, developed through the windings LV1 and LV of Figure 1, produces a component of vertical rate current in a current I42 of the winding 42 of the transformer 41. The vertical rate modulation of the current 142 of Figure 3a, during the return portion of the vertical pulse voltage Vv of Figure 3b, shifts the average value of stream 142 in a vertical regime. Similar symbols and numbers in Figure 1, 3a and 3b indicate similar items or functions. The current vertical current component I42 of Figure 1 can be coupled to the horizontal deflection circuit 20 through the transformer IHVT and, disadvantageously, can initiate oscillation in the horizontal deflection winding LH. A resulting width error may be visible on the display screen, not shown. To carry out an aspect of the invention, the coupling from vertical to horizontal is reduced or eliminated through the addition of the RC filter 40 between the LSEC winding of the IHVT transformer and the winding 42 of the transformer 41. This situation is demonstrated, when the connector bridge conductor 40a in Figure 1 is removed, and the filter 40 is interposed. The capacitor C of the filter 40 forms a low impedance for the horizontal current component of the current I42. Therefore, the capacitor C of the filter 40 does not attenuate the horizontal rate current component of the current I42. On the other hand, for the vertical regime current component of current I42, capacitor C forms a high impedance and acts as an attenuator. In this way, the return coupling is advantageously significantly attenuated.

The waveform of the primary current 142 when the filter R-C 40 is in circuit is shown in Figure 2a. In contrast to the waveform in Figure 3a, the vertical deflection current lv of Figure 2b, during vertical return, advantageously produces no significant vertical current component in current 142 of Figure 2a. Similar symbols and numbers in Figures 1, 3a, 3b, 2a and 2b indicate similar items or functions. The elimination of the return coupling effect, parasitic on the current I42 of Figure 2a of the stream lv of Figure 2b, advantageously eliminates the width artifact at the beginning of the vertical scan. A damping circuit 60 is formed through a resistor R1 and a capacitor C1, coupled in series. The circuit 60 is coupled between the central connection 21, approximately at the midpoint of the vertical deflection windings LV ?, and a central connection 21, approximately at the midpoint of the vertical deflection windings L 2. The effectiveness of the injection of parallelogram / orthogonality error correction current lCOrr through the winding 43 at an end terminal 43a of the vertical deflection windings Lvi and LV2, ie away from the amplifier 62, is facilitated by installing the damping circuit 60 formed by the resistor R1 and the capacitor C1. The damping circuit 60 increases the sensitivity of the windings LV1 and LV2 to the correction current Icorr- Consequently, a single driven impeller is sufficient.

Claims (6)

1. - A video display deflection apparatus, comprising: a vertical deflection circuit (60) for generating a vertical deflection current (lv) at a vertical deflection frequency in a vertical deflection winding (Lv) to vary a position of an electron beam in a vertical direction; a horizontal deflection circuit (20) for generating a horizontal deflection current (lH) in a horizontal deflection winding (LH) at a horizontal deflection frequency to vary the position of the electron beam in a horizontal direction, wherein a filter (40) for coupling the horizontal deflection circuit (20) to the vertical deflection winding (L) generates a correction current in a current path formed by the vertical deflection winding at a frequency related to the horizontal deflection frequency to provide the correction of the frame error, said filter (40) significantly attenuating the stray signal coupling in an opposite direction, from the vertical deflection circuit (60) to the horizontal deflection circuit (20).

2. A deflection device according to the claim 1, wherein the correction current (lCOrr) substantially reduces a downward inclination imparted to the electron beam as the electron beam is flexed between the first and second side edges of a generated frame.

3. A deflection apparatus according to claim 1, wherein the correction current (lCOrr) corrects at least one of the parallelogram and orthogonality errors.

4. A deflection circuit according to claim 1, wherein the correction current (lCorr) has a horizontal scanning regime.

5. A deflection circuit according to claim 1, wherein the vertical deflection circuit (60) includes a winding (43) of the first transformer (41) and the horizontal deflection circuit (20) includes a winding (LPR) |) of a horizontal sweep transformer (IHVT) and wherein the filter (40) is coupled in a current path between the transformers.

6. A deflection apparatus according to claim 1, wherein the filter comprises a capacitor (C) having a low impedance at a horizontal deflection frequency for coupling a horizontal rate signal of the horizontal deflection circuit (20) to the vertical deflection circuit (60) without significant attenuation and high impedance at a vertical deflection frequency to attenuate a vertical rate signal of the vertical deflection circuit (60).