MXPA97003644A - Vertical deflexion circuit with tr correction - Google Patents

Abstract

An electron beam has to be tilted downward as it is deflected horizontally to form a screen in a video display apparatus. The inclination of the beam can cause geometric errors in the frame, for example, orthogonality and parallelogram errors. A frame correction circuit (100) substantially deviates the downward inclination of the electron beam by modulating a vertical deflection current (Iv) with an induced horizontal regime correction current (ICORR), substantially eliminating orthogonality errors, and parallelogram in the plot. In respective embodiments of an inventive arrangement taught herein, the horizontal rate frame correction current (ICORR) is induced in the vertical deflection coils (Lv1, Lv2) by magnetically coupling a waveform of filament pulses (11) , a horizontal deflection voltage waveform, a horizontal deflection current in the vertical deflection coils (Lv1, Lv

Description

VERTICAL DEFLECTION CIRCUIT WITH FRAME CORRECTION BACKGROUND This invention relates generally to the field of frame correction circuits, and in particular, to correction of orthogonality and parallelogram errors in a frame of a cathode ray tube of an apparatus of video display. In a cathode ray tube (CRT) of a video display apparatus, a screen was formed by deflection of at least one electron beam through a phosphor screen. Each electron beam is deflected in a horizontal direction by a magnetic field produced by the excitation of a horizontal deflection coil by a current in the form of a sawtooth of vertical regime. The result is a scanning line of negative or "downward" inclination, as the electron beam deviates from left to right to form the TRC frame. In a normal cathode ray tube, used in a television receiver and having a screen width of approximately 723 mm and a screen height of approximately 538 mm, a horizontal scanning line may fall a distance of approximately 2.4 mm from a perfectly horizontal position in a field. This descending scan effect introduces orthogonal and parallelogram errors in the frame, as shown in Figure 1. In a perfectly rectangular frame, the horizontal and vertical center lines are orthogonal, or perpendicular to each other. The downward 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 extent to which the horizontal and vertical center lines of a frame move away from the orthogonality. For a frame represented in terms of X and Y coordinates, as described in Figure 2, the orthogonality error can be calculated with the following trigonometric formula: X12-X6 Y3-Y9 tan'1 (-) + tan-1 ( ) Y12-Y6 X3-X9 A conventional descending scan can produce an orthogonality error in the order of approximately 0.2 °. A normal design tolerance for the orthogonality error in a CRT can be specified as ± 0.3 °.

This orthogonality error can be increased at the left and right edges of the frame because, as is well known, the deflection sensitivity of an electron beam increases as it approaches the edges of the frame. As a result, the edges of the weft can be tilted so that the weft has a generally parallelogram shape. The parallelogram error is a quantitative measurement, expressed in units of radians or degrees, of the degree to which a frame approaches a parallelogram. For a plot represented in terms of X and Y coordinates, as described in Figure 2, the vertical parallelogram error can be calculated with the following trigonometric formula: X10-X8 X2-X4 tan "1 () + tan" 1 ( - -) Y10-Y8 Y2-Y4 Y3-Y9 - + tan "1 (---). X3-X9 The horizontal parallelogram error can be calculated with the following trigonometric formula: Y2-Y10 Y4-Y8 tan" 1 ( -) + tan "1 () X2-X10 X4-X8 Y3-Y9 + tan" 1 (-). X3-X9 In a conventional descending scan, a normal orthogonality error can be translated into a parallelogram error that is in the order of approximately 1.5 times the orthogonality error. For example, a conventional descending scan that produces an orthogonality error of 0.2 ° can also produce a parallelogram error that is equal to approximately 0.3 °. A normal design tolerance for the parallelogram error in a CRT can be specified as ± 0.5 °.

If means are used to correct the distortion of lateral, or east-to-west, stippling, in one screen, the downward scanning effect may cause a misalignment of a dot correction current envelope with respect to the curvature of dashes in the frame. . Mitigating this misalignment can result in an increase in the parallelogram error by an amount that can be equal to approximately 80%. Thus, for a conventional downward scan that produces a parallelogram error equal to approximately 0.3 °, the use of lateral punch correction may increase the parallelogram error to approximately 0.6 °. It is convenient to completely eliminate both orthogonality and parallelogram errors in a frame so that a CRT can display the superior quality image. A possible solution requires rotation of the horizontal deflection coil in relation to the vertical deflection coil in order to align the inclined horizontal center line of the frame with the horizontal centerline of the CRT. The downward exploration effect is eliminated in this way, but, nevertheless, this approach can be problematic. First, this solution can affect the convergence in the video display apparatus. Second, as the central horizontal line inclined towards the center line of the CRT is rotated, the dotting curvature in the frame also rotates in order to maintain its original relationship with the inclined horizontal centerline. Therefore, while this solution can eliminate the orthogonality error, it is not directed to the parallelogram error component due to the misalignment of the dot correction current coverage with respect to the punching curvature in the frame.

COMPONENT A frame correction circuit according to an inventive arrangement taught herein, provides horizontal rate modulation of a vertical deflection current to substantially deviate a downward scanning effect caused by the vertical deflection of the electron beam. The orthogonality and parallelogram errors in the frame are therefore corrected. Said frame correction circuit comprises: a deflection bobbin to deflect an electron beam that responds to a sawtooth current waveform to form a frame; and, means for generating a corrective current coupled to the deflection coil to substantially eliminate a downward inclination imparted to the electron beam by the deflection coil as the electron beam is deflected between the first and second side edges of the frame. The generating means may establish a substantially orthogonal relationship between the left and right side edges of the frame, respectively, and a horizontal axis passing through a geometric center of the frame. The current waveform, which is substantially saw-shaped, can have a vertical scan rate. The corrective current may have a horizontal scanning regime and a substantially sawtooth shape. The corrective current can modulate the deflection current of vertical regime in the horizontal scanning regime. A deflection circuit for a video display apparatus, in accordance with an inventive arrangement described herein, comprises; a deflection coil having first and second windings for deflecting an electron beam responding to a substantially wave-shaped current waveform to form a frame; a waveform source of horizontal regime; and means for modulating the current waveform in the form of saw teeth with the horizontal regime waveform. In one embodiment of the vertical deflection circuit, the source may comprise a secondary winding of a high-voltage transformer that is coupled to a horizontal deflection circuit. The secondary winding of the high voltage transformer can provide a horizontal rate pulse waveform to a plurality of heaters of the video display apparatus. In a further embodiment of the vertical deflection circuit, the source may comprise a winding coupled in series with a horizontal deflection coil of a horizontal deflection circuit.

In a still further embodiment of the vertical deflection circuit, the source may comprise a horizontal waveform of pulses generated by a horizontal deflection circuit.

The vertical deflection circuit may further comprise a series arrangement of a plurality of resistors coupled in parallel with the first and second windings of the vertical deflection coil. One of the plurality of resistors may comprise an adjustable resistance. The secondary winding of the frame correction transformer may further comprise a central connection coupled to the adjustable resistor. A deflection system for a video display apparatus, according to an inventive arrangement described herein, comprises: a vertical deflection circuit for periodically deflecting an electron beam from an upper edge to a lower edge of a frame; a horizontal deflection circuit for periodically shifting an electron beam from a first lateral edge to a second lateral edge of the frame; and, a correction transformer for coupling horizontal regime energy of the horizontal deflection circuit to the vertical deflection circuit to substantially eliminate a downward inclination imparted by the vertical deflection circuit to the electron beam. The foregoing and other aspects and advantages of the present invention will be apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. BRIEF DESCRIPTION OF THE DIAMETERS Figure 1 is useful to explain orthogonality and parallelogram errors in a frame. Figure 2 is useful to explain a screen of a cathode ray tube in terms of X and Y coordinates.

Figure 3 is a schematic diagram of a vertical deflection system of the prior art for a video display apparatus. Figure 4 is a schematic diagram of a first embodiment of a deflection system for a video display apparatus according to an inventive arrangement described herein. Figure 5 shows a waveform of useful current to explain the operation of the deflection system shown in Figure 4. Figure 6 is a schematic diagram of a second embodiment of a deflection system for a video display apparatus according to an inventive arrangement described herein. Figure 7 shows waveforms of voltage and current useful to explain the operation of the deflection system shown in Figure 6. Figure 8 is a schematic diagram of a third embodiment of a deflection system for a display apparatus of video according to an inventive arrangement described herein. Figure 9 shows useful current waveforms to explain the operation of the deflection system shown in the Figure. Figure 10 is a schematic diagram of a fourth embodiment of a deflection system for a video display apparatus in accordance with an inventive arrangement described herein. Figure 11 shows a waveform of current useful for explaining the operation of the deflection system shown in Fig. 10. DESCRIPTION OF THE MODES LI DADES PR EFER I DAS In Figure 3, a vertical deflection circuit is shown of the prior art. A vertical-rate saw generator 61 provides a vertical-rate sawtooth waveform at a non-inverting input of a vertical output amplifier 62. The vertical output amplifier 62 is coupled to a positive supply voltage, for example +24 V and a negative supply voltage, for example a grounding potential and can comprise a complementary or almost complementary symmetrical transistor output stage. The vertical output amplifier 62 drives the first and second vertical deflection windings LV1 and LV2 of a vertical deflection coil with a vertical rated saw current lv, which may have a peak-to-peak amplitude of approximately 2 A. A current-sensitive resistor R4 generates a feedback voltage at a vertical output amplifier inverting input 62 that responds to the vertical deflection current lv. The capacitor C3 provides correction of S for the vertical deflection current lv.

The resistors R1 and R2 and the potentiometer P1 are selected during the design of a deflection anvil for the cathode ray tube and these resistors are included as part of the deflection anvil assembly. The three resistors are used to adjust the convergence of the electronic beams within the cathode ray tube. Potentiometer P1 is adjusted to achieve a desired correction. For example, a joint J 1 of first and second vertical deflection windings LV? and Lv2 is coupled to a wiper arm W of potentiometer P 1. The potentiometer P 1 can be adjusted to achieve a desired crossing of the electron beams of the external electron guns, normally red and blue, in a vertical center line of the cathode ray tube. A first embodiment of a deflection system 100 for a cathode ray tube of a video display apparatus, such as a television receiver of a video display terminal, is illustrated in block and schematic form in Figure 4. A voltage B + of approximately 140 V is coupled to a horizontal deflection circuit 20 through a primary winding LPR? of a TAVI integrated high voltage transformer. The horizontal deflection circuit 20 can be of a conventional design. For example, the particular implementation of the horizontal deflection circuit 20 shown in Figure 4, it is well known in the art. A current absorber lD flows through a damping diode D1 to deflect an electron beam from a left edge of a frame to a center of the frame. A horizontal output transistor Z1 conducts a current lHot to deflect the electron beam from the center of the frame to a right edge of the frame. A horizontal deflection current lH flowing through the horizontal deflection coil LH can have a peak-to-peak amplitude at about 7 A. The capacitor Cs provides correction S for the horizontal deflection current lH. The sum of resistors R1, R2 and P1 in vertical deflection circuit 60 is equal to approximately 200 O, with resistors R1 and R2 each being equal to approximately 47 O and the nominal value of potentiometer P1 equal to approximately 100 O. The values and particular resistance arrangement for convergence adjustment of the electron beam within the cathode ray tube can be varied only by one skilled in the art according to the requirements imposed by the design of a particular deflection anvil for a tube. particular cathode rays. The TAVI integrated high voltage transformer usually has several secondary windings, one of which can provide, for example, a filament pulse of horizontal regime 1 1, which can have a peak-to-peak voltage of approximately 28 V, for the respective heaters of the three electron guns of the cathode ray tube. The frame correction transformer 41 has a primary winding 42 with approximately 144 turns and a secondary winding 43 with approximately 64 turns. The number of primary and secondary turns of the frame correction transformer 41, and therefore their ratio of turns, can be varied by someone skilled in the art in accordance with the requirements imposed by the transformer 41 by a particular embodiment of the system. deflection 100. Both windings are wound around a ferrite rod matrix which may have a diameter of approximately 5 mm and a length of approximately 30 mm. Such a matrix, for example, can have an EOR29 industrial part number and can be manufactured by Nippon Co. Ltd. or by H itachi Co., Ltd. The use of a rod matrix is illustrative and is not intended to suggest that a matrix configuration having a closed loop magnetic path length, for example, can not be a toroid. The transformer 41 reduces the filament pulse of horizontal regime 1 1 according to its ratio of turns, which for the mode shown in Figure 4, is equal to 64/144. Therefore, the frame correction transformer 41 provides a reduced horizontal rate pulse waveform 12 with a peak-to-peak voltage of approximately 12.4 V through a secondary winding 43 and an ICOR frame correction current. R is induced in the secondary winding 43. The ICO RR frame correction current flows through both vertical deflection windings L? and L 2 to a horizontal regime and in such a direction that a magnetic field is created which opposes the downward scanning effect. In this manner, the vertical deflection current is modulated to a horizontal regime, as shown in Figure 5, and the downward scanning effect is substantially deviated for each horizontal scan line of the frame. A second embodiment of the deflection system 100 is illustrated in Figure 6. In this second embodiment, the secondary winding 43 of the frame correction transformer 41 has a central connection 47, which divides the secondary winding 43 into a first winding 43a and a second winding 43b. The central connection 47 is coupled to the cleaning arm W of the potentiometer P 1. The use of the central connection 47 in this way is advantageous since it allows the nullification of differences in voltage distribution and magnetic field between the first and second vertical deflection windings LV1 and LV2 by the adjustment of the wiper arm W, thus achieving the desired crossing of the electron beams of the red and blue electron guns of the cathode ray tube, as discussed in connection with the vertical deflection array of the prior art shown in Figure 3. Another advantage of connecting the central connection 47 to the cleaning arm W is a reduction of sound through the winding "Secondary 43. The pulse of filaments of horizontal regime 1 1 is decreased according to the ratio of turns of the frame correction transformer 41 and the waveform 12 of pulses of decreased horizontal regime, is divided substantially equal through the first and second windings 43a and 4b of the secondary winding 43. Therefore, the first and second windings 43a and 43b are provided with pulse waveforms of horizontal regime 13 and 14, respectively, each of which has a voltage peak-to-peak of approximately 6.2 V. The pulse-waveforms of decreased horizontal regime 13 and 14, through the first and second windings 543a and 43b, respectively, induces horizontal correction currents of horizontal regime lv? and kv2 for the first and second vertical deflection windings lLv? and kv2, respectively. The currents of correction of plot lLv? and k? they are not restricted to have equal amplitudes from peak to peak, as seen in Figure 7, by virtue of the connection of the central input 47 to the wiper arm W. The frame correction currents lLv? and I LV2 flow through the first and second vertical deflection windings LV? and L 2, respectively, in a horizontal regime and in one direction so that a magnetic field is created which opposes the downward scanning effect. In this route, the vertical deflection current is modulated to a horizontal regime and the downward scanning effect deviates substantially from each horizontal scanning line of the frame. The currents of correction of plot of horizontal regime lLv? and 2 are shown in Figure 7. In a third currently preferred mode of deflection system 100, which is shown in Figure 8, a frame correction transformer 44 has a primary winding 45 with approximately 1800 turns and a secondary winding. 46 with about 22 laps. A central connection 47 divides the secondary winding 46 into a first winding 46a and a second winding 46b. The particular number of primary and secondary turns of the frame correction transformer 44, and therefore its ratio of turns, depends on the requirements of a particular deflection system 100 and is left to the judgment of one skilled in the art. Both windings 45 and 46 are wound around the ferrite rod matrix of the same type which is used in the frame correction transformer 41 and, likewise, the use of a rod array with frame correction transformer 44 it is merely illustrative. The third embodiment differs from the first and second embodiments in that the primary winding of the frame correction transformer is coupled to the horizontal deflection circuit 20, rather than to a secondary winding of the integrated high voltage transformer TAVI. Specifically, in the third embodiment, the primary winding 45 of the frame correction transformer 44 is coupled between an ungrounded terminal of the capacitor Cs and a junction J2 of the horizontal deflection coil LH and a collector electrode of the output transistor horizontal Q 1. A horizontal deflection voltage Vc at junction J2 has a peak-to-peak amplitude of approximately 1000 V, and the voltage at capacitor Cs is equal to approximately voltage B + because both the primary winding LPR? and the horizontal deflection coil LH appear as essentially short circuits for voltage B. It is advantageous to couple the primary winding 45 to the horizontal deflection voltage Vc since the weft correction transformer 44 can then be mounted with the deflection anvil in a neck portion of the cathode ray tube of the video display apparatus. This simplifies the assembly of the video display apparatus since it obviates the need to bring wires from the structure of the video display apparatus to the frame correction transformer. The horizontal deflection voltage Vc is decreased according to the turn ratio of the frame correction transformer 44, which is equal to 22/1800. The decreased horizontal rate pulse waveform has a peak-to-peak voltage of approximately 12.2 V and is substantially evenly divided across the first and second windings 46a and 46b of the secondary winding 46. Therefore, the first and second windings 46a and 46b of the secondary winding 46. Therefore, the first and second windings 46a and 46b are each provided with a pulse waveform of horizontal regime which has a peak-to-peak voltage of approximately 6.1 V. Horizontal rate pulse waveforms decreased through first and second windings 46a and 46b induce horizontal rate frame correction currents LLV1 and I V2 for the first and second vertical deflection windings L i and L 2, respectively. The currents of correction of plot lLv? and IL 2 are not restricted to have equal peak-to-peak amplitudes, as seen in Figure 9, by virtue of the connection of the central branch 47 to the wiper arm W of the potentiometer P 1. The frame correction currents l v? and v2 flow through the first and second vertical deflection windings LV? and LV2, respectively, in one direction so that a magnetic field is created which opposes the downward scanning effect. In this form, the vertical deflection current is modulated to a horizontal regime and the downward scanning effect is deviated substantially for each scan line of the frame. The current lP R? through the primary winding 45 and the horizontal rate frame correction currents lLv? and v2 are shown in Figure 9. A fourth embodiment of the deflection system 100, which is shown in Figure 10, can be used more successfully when the downward scanning effect, and the orthogonality and parallelogram distortions produced by it. , they are relatively minor. A frame correction transformer 48 is used as a current transformer. The frame correction transformer 48 mainly has a winding 49 of about 3 turns coupled in series with the horizontal deflection coil LH of the horizontal deflection circuit 20 and a secondary winding 50 of about 288 turns coupled in series with the first and second windings L? and LV2 of the vertical deflection coil. The number of primary and secondary turns of the frame correction transformer 48, and therefore their ratio of turns, can be varied by someone skilled in the art according to the requirements of the particular mode of the deflection system 100. It is preferred keep the number of turns in primary winding 49 to a minimum in order to prevent vertical unwanted currents from coupling in the horizontal deflection coil LH. It is also preferred to keep the number of turns in the secondary winding 5 to a minimum in order to avoid saturation of the transformer matrix 48 by the vertical deflection current l. Both windings 49 and 50 are wound around the ferrite rod matrix of the same type as that used in the modalities previously described and similar to the modalities previously described, it is merely illustrative the use of a rod matrix with the transformer of frame correction 48. A horizontal deflection current lH flows through the primary winding 49 and is decreased according to the turn ratio of the frame correction transformer 48, which is equal to 288/3. Therefore, for a horizontal deflection current lH having a peak-to-peak amplitude of, for example, 7 A, an ICORR frame correction current having a peak-to-peak amplitude of approximately 73 mA is induced in the secondary winding 50. This horizontal speed correction current ICORR flows through the first and second vertical deflection windings LV? and LV2 to substantially deviate the downward scanning effect for each horizontal scan line of the frame. In this way, the vertical deflection current is modulated to a horizontal regime and the downward scanning effect is substantially deviated for each horizontal scanning line of the frame. The correction current of the horizontal regime frame ICO R R is shown in Figure 1 1. The implementation of the deflection system 100 using the frame correction transformer 48 is advantageous since a desired frame correction can be achieved while minimizing a voltage differential between the primary and secondary windings 49 and 50, respectively. The minimum voltage between the primary and secondary windings of a particular transformer is convenient since it significantly reduces the possibility of a voltage break in the transformer. For example, the primary winding 45 of the frame correction transformer 44 of Figure 8 is coupled to a peak voltage of approximately 100 V, while the secondary winding 46 is coupled to a vertical deflection circuit 60, which it normally uses a supply voltage that is equal to approximately 24 V. This produces a voltage differential of approximately 100 V from the primary to the secondary in the patch correction transformer 44. In the frame correction transformer 48 of Figure 10, however, the voltage appearing through the primary winding 49 is simply the voltage B * which is normally equal to about 140 V, while the secondary winding 5 again it is coupled to the vertical deflection circuit 60. Therefore, a differential voltage of sol approximately 140 V appears from the primary winding 49 to the secondary winding 50; this significantly reduces the possibility of a voltage break in the transformer.

Claims (17)

1. CLAIMS 1. A deflection circuit (100) for a video display apparatus, said circuit comprising: a deflection coil (LV1, L2) for deflecting an electron beam that responds to a current waveform in the form of saw substantially (l) to form a screen; and means (41; 44; 48) to generate a corrective current (ICORR) coupled with said deflection coil to substantially eliminate a downward inclination imparted to said electron beam by said deflection coil and such electron beam is deflected between the first and second side edges of such a frame.
2. 2. The deflection circuit of claim 1, wherein said generating means (41; 44; 48) establishes a substantially orthogonal relationship between the left and right lateral edges of said frame, respectively, and a horizontal axis passing through a geometric center. of said plot.
3. 3. The deflection circuit of claim 1, wherein said substantially saw-shaped current wave form (lv) has a vertical scan rate.
4. 4. The deflection circuit of claim 1, wherein said corrective current (ICORR) has a horizontal scanning regime.
5. The deflection circuit of claim 4, wherein said corrective current (ICORR) has a substantially sawtooth shape.
6. 6. The deflection circuit of claim 1, wherein said generating means (41; 44, 48) comprises a transformer.
7. 7. A vertical deflection circuit (100) for a video display apparatus, said circuit comprising: a deflection coil having at least one winding (LV1, LV2) to deflect an electron beam that responds to a current waveform substantially of sawtooth (lv) to form a frame; a source of a horizontal regime waveform (11; lH; Vc); and means (41; 44; 48) for modulating said sawtooth current waveform with said horizontal rate waveform.
8. 8. The vertical deflection circuit of claim 7, wherein; said source comprises a secondary winding of a first transformer (TAVI) which is coupled to a horizontal deflection circuit (20); and said horizontal rate waveform is a filament pulse waveform (11) for a heater of said video display apparatus.
9. The vertical deflection circuit of claim 8, wherein said modulation means comprises a second transformer (41) having a primary winding (42) coupled to said source (11) and a secondary winding (43) coupled in series with at least one winding (LV1, LV2) of said vertical deflection coil.
10. The vertical deflection circuit of claim 7, wherein: said source comprises a horizontal deflection coil (LH) of a horizontal deflection circuit (20).
11. The vertical deflection circuit of claim 10, wherein said horizontal rate waveform is a horizontal deflection voltage (Vc).
12. The vertical deflection circuit of claim 11, wherein said modulation means comprises a transformer (44) having a primary winding (45) coupled in parallel with said horizontal deflection coil (LH) and a secondary winding (46). ) coupled in series with at least one winding (LV ?, LV2) of said vertical deflection coil.
13. 13. The vertical deflection circuit of claim 10, wherein said horizontal rate waveform is a horizontal deflection current (lH).
14. The vertical deflection circuit of claim 13, wherein said modulation means comprises a transformer (48) having a primary winding (49) coupled in series with said horizontal deflection coil (LH) and a secondary winding (50). ) coupled in series with said at least one winding (LV1, LV2) of said vertical deflection coil.
15. 15. The deflection system of claim 7, further comprising a series arrangement of a plurality of resistors (R1, P1, R2) coupled in parallel with said at least one winding (LV ?, LV2) of said vertical deflection coil.
16. 16. The deflection system of claim 15, wherein one (P1) of said plurality of resistors comprises an adjustable resistor. The deflection system of claim 16, wherein: said secondary winding of said correction transformer further comprises a central connection (47); and said central connection (47) is coupled with said adjustable resistance (P1).