Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
  • H01J29/56—Arrangements for controlling cross-section of ray or beam; Arrangements for correcting aberration of beam, e.g. due to lenses
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
  • H01J29/70—Arrangements for deflecting ray or beam

Definitions

• the invention relates to a deflection system for a cathode ray tube (CRT).
• CRT cathode ray tube
• Some prior art arrangements produce a quadrupole magnetic field in a beam path of an electron beam of a CRT.
• such quadrupole field has been utilized to control the shape or size of a beam spot formed by an electron beam landing on a display screen of the CRT for reducing spot enlargement and distortions.
• Spot enlargement and distortions are due to, for example, the obliquity of the screen and space-charge repulsion.
• a variation in the beam landing location that is caused by a corresponding change of a fundamental Fourier component of a winding-current product distribution, alone, of a horizontal deflection winding and/or of a vertical deflection winding tends to produce an elongation in the beam spot.
• a length of a major axis of the spot produced at, for example, the 3 o'clock hour point tends to be elongated in the horizontal direction by approximately 1.5 times the spot major axis at the screen center, as shown in FIGURE 1.
• a pair of quadrupole arrangements are disposed around a neck portion of a CRT to form a pair of quadrupole magnetic fields in a beam path of the electron beam at different distances from the display screen.
• Such pair of quadrupole arrangements may provide advantages that are not available when only one quadrupole arrangement is utilized such as in some prior art arrangements.
• such pair of quadrupole arrangements may be utilized for improving three beam convergence and/or controlling the spot size on the display screen of the CRT.
• a deflection apparatus in accordance with another aspect of the invention, includes a cathode ray tube having an evacuated glass envelope.
• a display screen is disposed at one end of the envelope.
• An electron gun assembly is disposed at a second end in the envelope. The electron gun assembly produce an electron beam that forms a beam spot at electron beam landing locations on the screen.
• a plurality of deflection windings produce a main deflection field in a main deflection region of a deflection yoke that deflects the electron beam to the beam landing location.
• a first quadrupole arrangement produce in a first region of a beam path of the electron beam a first quadrupole magnetic field that varies in accordance with the beam landing locations.
• a second quadrupole arrangement produce in a second region of the beam path a second quadrupole magnetic field that varies in accordance with the beam landing locations, such that the first and second regions are at different distances from the display screen.
• FIGURE 1 illustrates a shape of a beam spot at corresponding beam landing locations obtained in a prior art deflection apparatus that utilizes a uniform, main deflection field;
• FIGURE 2 illustrates a block diagram of a deflection apparatus embodying an aspect of the invention, that includes a quadrupole coil arrangement;
• FIGURE 3 illustrates a diagram of a quadrupole field that is produced in the arrangement of FIGURE 2 and its effect on a cross section of an electron beam;
• FIGURE 4 is a diagram showing a winding-current product distribution in one quadrant of a quadrupole coil of FIGURE 2;
• FIGURES 5a-5d illustrate waveforms useful for explaining the operation of the arrangement of FIGURE 2;
• FIGURES 6a and 6b illustrate a double quadrupole arrangement having eight magnetic poles that is included in the arrangement of FIGURE 2;
• FIGURES 7a-7e illustrate additional waveforms useful for explaining the operation of the arrangement of FIGURE 2;
• FIGURE 8 illustrates the shape of a beam spot at corresponding beam landing locations when a main deflection field is of the type produced in the arrangement of FIGURE 2;
• FIGURE 9 illustrates a. block diagram of a deflection system embodying a further aspect of the invention.
• FIGURE 10 illustrates a diagram useful for explaining the operation of each double quadrupole arrangement of the arrangement of FIGURE 9
• FIGURE 11 illustrates a diagram illustrating the operation of a quadrupole doublet formed by a pair of double quadrupoles of the arrangement of FIGURE 9
• FIGURE 12 illustrates a shape of a beam spot at corresponding beam landing locations in a main deflection field that is similar to that produced in a prior art, static self-converged deflection yoke.
• FIGURE 2 illustrates a deflection system 100, embodying an aspect of the invention, in which an electron beam lensing action that tends to converge the beam spot in the direction of the deflection is produced in a main deflection region of a yoke 55.
• Deflection system 100 of FIGURE 2 may be used in, for example, a television receiver.
• Deflection system 100 includes a CRT 110 of the 25V110 type having, for example, 110 degree maximum deflection angle.
• CRT 110 has a longitudinal axis Z that is perpendicular to a display screen 22.
• Display screen 22 is of, for example, the 25-inch viewing screen type having, for example, a 4:3 aspect ratio.
• a neck end 33 of CRT 110 contains an electron gun 44 that produces three electron beams.
• the electron beams produced by gun 44 are modulated in accordance with video signals R, B, and G, respectively, for producing an image on display screen 22.
• a given one of the beams produces a spot 999 that, when scanned, forms a raster on display screen 22 at a corresponding color.
• Deflection yoke 55 is, for example, of a saddle-saddle-saddle type and is mounted on CRT 110.
• Deflection yoke 55 shown in a partial cross sectional view, includes a line or horizontal deflection yoke assembly 77 formed by a pair of saddle coils 10 that surround a portion of neck 33 and a portion of a conical or flared part of CRT 110.
• Deflection yoke 55 further includes a vertical or field deflection coil assembly 88 formed by a pair of saddle coils 99 that surround coils 10.
• Deflection yoke 55 further includes a quadrupole coil assembly 28 formed by a pair of saddle coils 11 that surround coils 99.
• Deflection yoke 55 further includes a core 66 having a conically shaped body that is made of a ferrite magnetic material and that surrounds coils 11.
• the main deflection region of yoke 55 is formed between a beam entrance end and a beam exit end of core 66.
• Horizontal axis X and vertical axis Y of screen 22 are such that when coils 99 are not energized, the spot is positioned along axis X and when coils 10 are not energized the spot is positioned along axis Y.
• a vertical deflection circuit 177 that may be conventional produces a vertical sawtooth current i v that is coupled to field deflection coil assembly 88 and also produces a vertical rate parabolic signal V pv .
• Current i v and signal V pv are synchronized to a vertical synchronization signal Vy , produced in a well known manner.
• a horizontal deflection circuit 178 that may be conventional produces a horizontal sawtooth current i y that is coupled to line deflection coil assembly 77 and also produces a horizontal rate parabolic signal V ph .
• Current i y and signal V pf - are synchronized to a horizontal synchronization signal F ⁇ -r , produced in a well known manner.
• yoke 55 operates as an electron beam lens, as well as a beam deflector.
• the electron beam lensing action of yoke 55 that is similar to each of the three beams, is explained herein with respect to only one of the electron beams.
• the electron beam lensing action reduces spot elongation.
• the electron beam lensing action is obtained by producing a deflection field having a field nonuniformity.
• the nonuniformity of the deflection field causes different portions of the beam at a given cross section or profile in the electron beam path in deflection yoke 55 to be deflected by slightly different amounts in a manner that tends to reduce spot elongation, thus providing lensing action.
• a more detailed explanation of how a nonuniformity in the deflection fields reduces the ellipticity in the spot is provided later on.
• a stigmator 24, described in more detail later on, is positioned to surround neck 33 behind yoke 55.
• Stigmator 24 is interposed between gun 44 and yoke 55.
• Stigmator 24 produces a magnetic field having a field nonuniformity in neck 33 outside yoke 55 for eliminating an astigmatism produced by the lensing action of yoke 55 so as to make spot 999 anastigmatic.
• Spot 999 is considered anastigmatic if the entire area of the electron beam spot can be focused at a single level of a focus voltage F applied to a focus electrode 333 of CRT 110.
• Coils 11 are driven by a current iq that produces a negligible magnetic field when spot 999 is positioned at the corners at, for example, the 2 o'clock hour point and substantially anywhere on the diagonals of display screen 22, as described later on. Therefore, the electron beam lensing action of yoke 55, when spot 999 is at the corners of display screen 22, is substantially unaffected by quadrupole coil assembly 28.
• a predetermined winding distribution of each of horizontal deflection coils 10 and vertical coils 99 is established.
• the n-th harmonic may refer to the Fourier component of the n-th order of the winding distribution, or winding-current product distribution.
• Such winding distribution, or winding-current product distribution is periodic as a function of an angle measured from, for example, the horizontal axis of the yoke.
• the term winding-current product typically depicted by the notation, N • I, refers to a value obtained when multiplying the number of winding turns by the current in a given winding turn. Such term is measured by the units ampere-turns.
• the term winding-current product or winding-current product distribution may be associated with a current component that flows in such winding turns at, for example, the horizontal rate or at the vertical rate.
• Winding distribution parameters may be established empirically for obtaining a round spot at each of the corners of display screen 22, such as, for example, at the 2 o'clock hour point.
• the winding distribution of coils 10 in such plane is selected to obtain a positive, first ratio of about +10% between a positive third harmonic component and a fundamental haimonic component.
• Such positive first ratio indicates a pincushion shaped horizontal deflection field.
• a positive sign of the third harmonic indicates a pincushion field and a negative sign indicates a barrel field.
• a negative sign indicates a pincushion field and a positive sign indicates a barrel field.
• the aforementioned values of the first and second ratios are selected primarily for obtaining spot 999 that is, for example, round. Convergence and geometry errors may be corrected by other arrangements, not in yoke 55, as described later on.
• the sign of each ratio is selected to obtain the desired type of field nonuniformity, namely pincushion shaped horizontal deflection field and pincushion shaped vertical deflection field at the corner.
• spot 999 When focused by the operation of focus electrode voltage F of CRT 110 and made anastigmatic by the operation of stigmator 24, spot 999, at a given corner of screen 22, will obtain a shape with optimal ellipticity. For a typical CRT, optimal ellipticity is obtained when spot 999 has, for example, a round shape.
• the first and second ratios establish a desired first electron beam lensing action of yoke 55 for obtaining, for example, a round spot at the corners of display screen 22.
• yoke 55 significantly reduces a ratio between a length of a major axis of spot 999 at the corner of display screen 22 and a major axis of spot 999 at the center of display screen 999 relative to such ratio of FIGURE 1.
• Gun 44 and stigmator 24 form an additional electron beam lensing action that makes spot 999 anastigmatic.
• a barrel shaped horizontal deflection field alone, can produce the required field gradient in the beam path for reducing spot elongation, thus establishing the first electron beam lensing action.
• a barrel shaped vertical deflection field alone, can produce the required field gradient in the beam path for reducing spot elongation.
• the flux density along axis Y generally decreases as the distance from the screen center increases when the spot is located on axis Y; in a pincushion shaped vertical deflection field, the field gradient is generally opposite.
• the field or flux density gradient in yoke 55 that is required for reducing spot elongation on axes X and Y is established mainly by quadrupole coil assembly 28 formed by saddle coils 11 having quadrupole symmetry.
• the quadrupole deflection field component produced by coils 11 corrects the elliptical distortion of the spot when the spot lies on each of axis X or Y of display screen 22 and reduces the elongation of the major axis of spot 999 relative to such length at the center of screen 22.
• Coils 11 do not significantly affect the nonuniformity of the magnetic fields when spot 999 is at each of the corners, as explained later on.
• FIGURE 3 illustrates, schematically, the flux or field produced by coils 11 of quadrupole 28 having a winding-current product distribution that contains mainly a second harmonic component.
• Arrow H q in FIGURE 3 represents the direction of flux density of the field or flux component produced only by coils 11 in yoke 55 when spot 999 is at the 3 o'clock hour point at the end of axis.
• the field represented by arrow H q of FIGURE 3, produced by coils 11 of FIGURE 2 has a direction that is generally opposite to the direction of the pincushion shaped horizontal deflection field component, not shown, produced by horizontal deflection coils 10.
• the strength of the field produced by coils 11 increases in the direction of the deflection.
• the combined effect of the two fields produces a net or total deflection field that is obtained by a vectorial summation of the field components.
• the magnitude of current iq of FIGURE 2 that energizes coils 11 is made sufficiently large to change the deflection field nonuniformity in the beam path at each end of the horizontal axis X of rectangle 112 of FIGURE 3, when spot 999 is at the corresponding 3 and 9 o'clock hour points.
• the deflection field nonuniformity is changed by current iq from being pincushion shaped to a deflection field that can be produced in the beam path by a barrel shaped horizontal deflection field, alone.
• a net deflection field H ⁇ ( j ) closer to a center point C of rectangle 112, is stronger than a net deflection field H ⁇ ( 2 ) , that is further from the center C.
• coils 11 of FIGURE 2 produce a net field in the beam path at each end of the vertical axis Y of rectangle 112 when spot 999 is at the 6 and 12 o'clock hour points, respectively, of FIGURE 3 having a deflection field nonuniformity that can be produced in the beam path by a barrel shaped vertical deflection field, alone.
• a highly elliptic beam profile or cross section 999a of FIGURE 3 shows how the cross section of the beam, in rectangle 112 of yoke 55 of FIGURE 3, might have looked like when spot 999 of FIGURE 2 is at the 3 o'clock hour point of screen 22 of FIGURE 2 had the horizontal deflection field been entirely a uniform field.
• the particular ellipticity of cross section 999a has been selected for explanation purposes, only. Also, for explanation purposes, the field nonuniformity caused by coils 10 and 99 has been neglected since the field nonuniformity produced there by coils 11 dominates.
• the field nonuniformity or flux density gradient produced by coils 11 together with the field nonuniformity produced by stigmator 24 tends to make spot 999 of FIGURE 2 anastigmatic and close to being round such that the ratio between the major axis of spot 999 at the end of the horizontal axis and that at the center of screen 22 is substantially smaller than if the electron beam were to travel entirely in a uniform horizontal deflection field.
• the nonuniformity in the flux density, or flux density gradient produced by, for example, the resulting barrel shaped horizontal deflection field causes, for example, an end portion 108 of cross section 999a of the electron beam of FIGURE 3 that is closer to center point C of rectangle 112 to be deflected away from center point C in the direction of the deflection X a longer distance, or more strongly than a second end portion 109 that is further away from center point C.
• This situation that is depicted schematically by straight arrows 108a and 109a is equivalent to having magnetic forces applied at opposite directions to end portions 108 and 109, respectively, as a result of the field nonuniformity or flux density gradient.
• yoke 55 of FIGURE 2 in addition to performing scanning or deflection action, operates as an electron beam lens that converges spot 999 in the direction of its elongation.
• the direction of elongation is also the direction of the deflection, X.
• Such pair of flare portions make spot 999 astigmatic-
• the flares in spot 999 produced by the deflection field in yoke 55 can be eliminated such that spot 999 becomes again anastigmatic by the use of stigmator 24 of FIGURE 2 and/or gun 44.
• Stigmator 24 that is located further from screen 22 than yoke 55, produces a field nonuniformity that tends to diverge cross section 999a of FIGURE 3 in the direction of axis X. This is in contrast with the beam converging operation of yoke 55 in the direction of axis X. The result is that spot 999 is maintained anastigmatic. By performing the beam converging operation closer to screen 22 and the beam diverging operation further from screen 22, the length of the major axis of spot 999 is reduced, as shown by the circle in broken lines of FIGURE 3. Similar electron beam lensing action that converges spot 999 in the direction of the deflection or elongation occurs, by the operation of coils 11, when spot 999 is at each of the 12, 9 and 6 o'clock hour points.
• the net deflection field in the electron beam path has an azimuthal field component H ⁇ such as shown in FIGURE 3 in a direction that is generally perpendicular to the direction of the deflection.
• H ⁇ in yoke 55 in the vicinity of the electron beam decreases as the distance from the center point C in the direction of the deflection increases.
• such field gradient requires a field nonuniformity that can be formed by a horizontal or a vertical, respectively, barrel-shaped deflection field producing positive isotropic astigmatism.
• field component H ⁇ of FIGURE 3 decreases as the distance from the center point C increases in the direction of the deflection along axis X.
• field gradient when spot 999 is located at the corner of a display screen, having a 4:3 aspect ratio, such field nonuniformity is formed by a combination of the pincushion-shaped horizontal deflection field and the pincushion-shaped vertical deflection field. It should be understood that an aspect ratio different from 4:3 may require a different type of field shape to achieve such field nonuniformity at the corners. .
• FIGURE 4 The required winding-current product distribution in the first quadrant of coils 11 of FIGURE 2 is shown in FIGURE 4 as a function of an angle ⁇ . Angle ⁇ is measured from axis X. Similar symbols and numerals in FIGURES 1, 2, 3 and 4 indicate similar items or functions.
• Each vertical bar in FIGURE 4 represents a winding slot of the first quadrant of coils 11 having a gross angular width of 6 degrees. In each slot, a bundle of conductor windings of the respective coil portion are placed. Thus, fifteen slots span a total of 90 degrees of the first quadrant.
• the bar height and position relative to the axis represents the magnitude and sign of the winding-current product, N • I, that is produced by the respective bundle in the slot.
• the winding-current product distribution of coils 11 of FIGURE 2 contains substantially only a second harmonic component, defined by the Fourier series expansion.
• current iq of FIGURE 2 that energizes coils 11 is arranged to flow in a predetermined direction in a corresponding bundle of conductor windings of coils 11 between the entrance region and the exit region of the yoke.
• current iq is arranged to flow simultaneously in the opposite direction, in a second bundle of conductor windings of coils 11.
• controlling the spot size at the corners is obtained by the winding distribution selected for coils 10 and for coils 99 and not by the winding distribution selected for coils 11 ; whereas, the spot size is controlled when the spot is at axis X or Y by the selected winding distribution of coils 11 and not of coils 10 and 99.
• the dynamic variation is used for obtaining the required magnetic field nonuniformity as a function of the beam landings of spot 999 location on screen 22.
• a waveform generator 101 produces a signal vIOl.
• Signal vlOl is coupled to current driver 104 that may operate as a linear amplifier for producing current iq that may be linearly proportional to signal 101.
• Signal vlOl is represented by the sum of product terms stated in an equation form, (kl • vpv)+(k2 • vph).
• the terms vpv and vph represent the instantaneous values of signals V pv and V pn , respectively, and kl and k2 are predetermined constants selected for obtaining the desired waveform, as explained later on.
• Signal V pv that is produced in deflection circuit 177 is zero when spot 999 is positioned at the center of vertical trace and has a positive peak when spot 999 is positioned at the top or bottom.
• Signal V p j- that is produced in deflection circuit 178 is zero when spot 999 is positioned at the center of horizontal trace and has a negative peak when spot 999 is positioned at the left or right side of screen 22, as shown by the waveforms in FIGURE 2.
• current iq contains the sum of a parabola-shaped current component in accordance with signal V pf - and a parabola-shaped current component in accordance with signal V pv .
• a waveform generator that is capable of producing such waveform is described in detail in United States Patent No. 4,683,405, entitled PARABOLIC VOLTAGE GENERATING APPARATUS FOR TELEVISION, in the names of Truskalo et al., (the Truskalo patent) that is incorporated by reference herein.
• FIGURES 5a-5d illustrate waveforms useful for explaining the operation of the arrangement of FIGURE 2. Similar symbols and numerals in FIGURES 1, 2, 3, 4 and 5a-5d indicate similar items or functions.
• Constants kl and k2 of generator 101 of FIGURE 2 are selected at values that, for example, are substantially equal, such that the sum of the parabola shaped current components produces a magnitude of current iq that is small or substantially zero, as shown in FIGURE 5c, when spot 999 is positioned in the vicinity of the corners of screen 22 of FIGURE 2. Therefore, the quadrupole field produced by coils 11 will be, for example, negligible so as not to affect the shape of spot 999 when spot 999 is in the vicinity of the corners or of the diagonals of screen 22, as indicated before.
• the shape of spot 999 at the corners of screen 22 is mainly determined by the harmonic components at the negative third harmonic produced by the vertical deflection coils and by the positive third harmonic produced by the horizontal deflection coils.
• the values of constants kl and k2 of generator 101 that determine the peak magnitude of current iq of FIGURE 5c are selected to produce the required magnitude and polarity of the quadrupole field of coils 11 when spot 999 is located at the 3 and 9 o'clock hour points.
• the magnitude of the quadrupole field when spot 999 is at the 6 or 12 o'clock hour point is also fixed.
• a different waveform generator may be used, instead of generator 101, for varying the nonuniformity of the field produced by quadrupole coils 11, in a manner not shown in the figures, such that the strength of the field produced by coils 11 at, for example, the 12 o'clock hour point may be established independently of the strength of the field at the 3 o'clock hour point.
• a spot on axis Y at a given distance from the screen center is less elliptic or more round than a spot produced at the same distance on axis X. This is so because, in the self-converged yoke, the field nonuniformity of the vertical deflection field is already barrel shaped for obtaining convergence. However, in the self-converged yoke, the degree of field nonuniformity, unlike in the arrangement of FIGURE 2, is, disadvantageously, not optimized for obtaining round spot. In the arrangement of FIGURE 2, a corresponding winding-current product distribution at a given beam landing location can be selected with respect to each one of the three coils, 10, 99 and 11.
• the ability to select it with respect to each of the three deflection coils provides a high degree of freedom for establishing the required field nonuniformity.
• the high degree of freedom enables an overall improvement in reducing spot elongation than, for example, if the winding-current product distribution could be selected with respect to only one of the coils.
• the net effect of the magnetic field in the beam path in yoke 55 that is determined mainly by coils 11 is similar to that produced by a barrel shaped horizontal deflection field, alone.
• the horizontal deflection coils of a self-converged yoke produce field nonuniformity that results in an undesirable electron beam lensing action. This is so because, in the self-converged yoke, such field nonuniformity, unlike that of the arrangement of FIGURE 2, is pincushion shaped.
• the pincushion shape vertical deflection field tends to produce a significant positive trap convergence and positive anisotropic astigmatism error that may be corrected by another arrangement and not in yoke 55, as explained later on.
• the trap error is minimized in the yoke.
• spot coma is the difference in distance, as the beam is deflected, between a center portion of the beam and a point located at a : unt midway between two extreme end portions of the bram. Spot coma occurs because of factors analogous to those responsible for convergence coma of three beams. For example, spot coma may occur due to the nonuniformity of the magnetic field at, for example, the intermediate region. The entrance region has the greatest effect on spot coma.
• the winding distribution is made in such a way that the resulting sign of the third harmonic component of the winding distribution at the entrance region of each of coils 10 and 99 of yoke 55 is opposite to the sign of the third harmonic component of the winding distribution associated with the intermediate deflection region of yoke 55.
• each of the fields produced by coils 10 and 99 is generally pincushion shaped for producing round corner spots.
• a pincushion shaped deflection field may be undesirable because it causes the spot to be elongated in the direction of the deflection to an unacceptable degree.
• stigmator 24 of FIGURE 2 in cooperation with yoke 55, produces an anastigmatic spot.
• Stigmator 24 includes a double-quadrupole coil arrangement forming an electromagnet having eight poles.
• the double-quadrupole coil arrangement of stigmator 24 of FIGURE 2 is shown schematically in each of FIGURES 6a and 6b. Similar symbols and numerals in FIGURES 1, 2, 3, 4, 5a-5d and 6a-6b indicate similar items or functions.
• a quadrupole coil 24a of FIGURE 6b that forms four magnetic poles 224 is energized by a current ia.
• a quadrupole coil 24b of FIGURE 6a that forms the alternate magnetic poles 124 is energized by a current ib.
• Quadrupole coil 24a of FIGURE 6b corrects astigmatism generally in the direction of axes X and Y.
• Quadrupole coil 24b is rotated by 45 degrees relative to quadrupole coil 24a.
• Coil 24b corrects astigmatism generally in a direction that forms, for example, an angle of +45 degrees with axis X by applying a magnetic force generally in a direction that forms an angle, in such example, of +45 degrees with axis X or Y.
• the magnitudes and waveforms of currents ia and ib in stigmator 24 and of current iq in coils 1 1 of yoke 55 are selected for obtaining a beam spot that is anastigmatic when located at the corners and along the axes of screen 22.
• the use of the double quadrupole coil arrangement of stigmator 24 provides a way to electrically rotate a total quadrupole field produced by stigmator 24 by a predetermined angle relative to axis X in a dynamic manner as a function of the spot landing location.
• a waveform generator 102 that may be similar to that shown in the Truskalo patent produces a signal vl02 that is coupled to a current driver 105.
• Current driver 105 may operate as a linear amplifier.
• Signal vl02 may be represented, for example, by the equation,
• Constant k3 is selected for producing current ia at a level shown in FIGURE 5d for reducing the astigmatism in the spot when the spot is positioned at the 12 o'clock hour point of display screen 22 of FIGURE 2.
• Constant k4 is selected for producing current ia of FIGURE 5d at a level that reduces the astigmatism in the spot at the 3 o'clock hour point.
• Constant k5 is selected for producing current ia at a level that reduces the astigmatism in the spot at the 2 o'clock hour point.
• Constant k6, indicating a DC current is selected for producing current ia at a level that reduces the astigmatism in the spot at the center of display screen 22.
• a waveform generator 114 produces a signal VI 14.
• Signal VI 14 is represented by the equation, (k7 • vpv • vph)+k8.
• the terms k7 and k8 are predetermined constants selected for obtaining the desired waveform for correcting the astigmatism of spot 999 at the corners of display screen 22.
• Generator 114 may be similar to that described in United States Patent No. 4,318,032 in the name of Kureha, entitled, CONVERGENCE CIRCUIT INCLUDING A QUADRANT SEPARATOR.
• FIGURES 7a-7e illustrate waveforms useful for explaining the operation of the generator 114 of FIGURE 2. Similar symbols and numerals in FIGURES 1, 2, 3, 4, 5a-5d ,6a-6b and 7a-7e indicate similar items or functions.
• Current ib of FIGURE 7a has a peak value each time spot 999 of FIGURE 2 is in the vicinity of the corners of display screen 22.
• Current ib of FIGURE 7a is zero when spot 999 is at the center of display screen 22, as shown in FIGURES 7a, 7b and 7c, and is also zero at the vicinity of axes X and Y of display screen 22, as shown in FIGURE 7a.
• the phase of current ib changes polarity each time spot 999 of FIGURE 2 crosses horizontal axis X at the vertical center of screen 22.
• a waveform generator 103 that may be similar to that described in the Truskalo patent produces a signal vl03 that is equal to (k9 • vpv)+(kl0 • vph)+(kll «vpv • vph). Constants k9, klO and kll are selected for obtaining the required focusing action.
• Signal vl03 is coupled to a focus voltage generator and modulator circuit 106 for producing focus voltage F.
• Voltage F is dynamically modulated in proportion to signal vl03.
• the round spot associated with the given electron beam can be produced in CRT 110 of FIGURE 2 with a very large beam current of, for example, 3 milliamperes.
• the beam spot becomes focused, anastigmatic, and close to being round, as shown in FIGURE 8.
• Such beneficial electron beam lensing action may be utilized also in conjunction with a monochrome CRT.
• the type of field nonuniformity of the horizontal or vertical deflection field that can make a round spot at each corresponding hour point is also shown there.
• FIGURES 1, 2, 3, 4, 5a-5d, 6a-6b and 7a-7e and 8 indicate similar items or functions.
• variations in the size of the spot produced by the arrangement of FIGURE 2, as a function of the spot position, as shown in FIGURE 8, are substantially smaller from those shown in FIGURE 1.
• the spots shown in FIGURE 1 are produced by a yoke that produces uniform fields.
• the length of the major axis of the elliptical spot is 1.48 times the diameter of the spot at the center of the display screen that is approximately round at the center.
• the maximum increase is only 1.18 times.
• a video signal processor 222 produces signals R, G and B.
• signals R, G and B in a given picture frame may be divided into pixel signals that are stored separately in a memory.
• the time when each individual pixel signal of each of signals R, G and B is read out and applied to the respective cathode of CRT 110 may vary as a function of the spot position in such a manner to eliminate the aforementioned convergence or geometry distortion.
• FIGURE 9 illustrates a deflection system 100", embodying yet another aspect of the invention. Similar symbols and numerals in FIGURE 9 and in FIGURES 1-4, 5a-5d, 6a-6b, 7a-7e and 8 indicate similar items or functions.
• Deflection system 100" of FIGURE 9 includes a deflection yoke 55" that, unlike, for example, deflection yoke 55 of FIGURE 2, may produce uniform horizontal and vertical deflection fields.
• An electron beam lensing action is produced in the arrangement of FIGURE 9 by a pair of quadrupole arrangements 424 and 324 operating in an analogous manner to that of a quadrupole doublet. Each of quadrupole arrangements 424 and 324 may be constructed as a double quadrupole in a similar manner to that of stigmator 24 of FIGURE 2.
• Arrangement 324 of FIGURE 9 is placed coaxial ly with arrangement 424 along axis Z such that anangement 324 is closer to display screen 22" than arrangement 424.
• Arrangement 324 may be placed closer to display screen 22" than deflection yoke 55"; alternatively, instead of arrangement 324, an arrangement 324a that is similar to arrangement 324 may be placed between arrangement 424 and yoke 55", as shown in broken lines.
• double quadrupole arrangement 324 may be included in yoke 55".
• each quadrupole of the double quadrupole may be constructed in a similar way that was discussed before with respect to the quadrupole windings in coils 11 of FIGURE 2.
• the axes of the pair of quadrupoles that form the double quadrupole form an angle of +45°.
• each of the pair of double quadrupole arrangements 424 and 324 produces a pair of quadrupole deflection fields.
• One of the pair of quadrupole fields of each of double quadrupole arrangements 424 and 324 can be represented as formed by four magnetic poles, qa, shown in FIGURE 10. Similar symbols and numerals In FIGURE 10 and in each of the preceding FIGURES indicate similar items or functions. Poles qa of FIGURE 10 are similar to. magnetic poles 124 of FIGURE 6a.
• the other one of the pair of quadrupole fields can be represented as formed by four magnetic poles qb of FIGURE 10 that are similar to magnetic poles 224 of FIGURE 6a.
• One pair of magnetic poles qa of FIGURE 10 lies on axis X.
• the other pair of magnetic poles qa lies on axis Y.
• One pair of magnetic poles qb lies on an axis V that forms an angle of +45 degrees with axis X.
• the other pair of magnetic poles qb lies on an axis W that is perpendicular to axis V.
• the quadrupole field produced by magnetic poles qa of double quadrupole arrangement 424 of FIGURE 9 is dynamically controlled by a current i ⁇ that is analogous to current ib of FIGURE 6a.
• the quadrupole field produced by magnetic poles qb of FIGURE 10 of double quadrupole arrangement 424 of FIGURE 9 is dynamically controlled by a current 12 that is analogous to current ia of FIGURE 6b.
• Currents i ⁇ and 12 that control double quadrupole arrangement 424 of FIGURE 9 determine a total quadrupole field that is produced by arrangement 424.
• Such total quadrupole field is the superposition of the pair of quadrupole fields produced by poles qa and qb.
• the total quadrupole field of each of arrangements 424 and 324 of FIGURE 9 can be represented as formed by four magnetic poles Q of FIGURE 10 that define axes M and N.
• the strength, polarity and orientation of the total quadrupole field that is produced by, for example, arrangement 424 are determined by the magnitudes and polarities of currents i ⁇ and ⁇ .
• an angle ⁇ between axis M of poles Q and axis X and also the polarity and strength of the total quadrupole field vary as a function of currents ij and 12 that, in turn, vary as a function of the beam spot landing location.
• Currents 13 and . 4 dynamically control double quadrupole arrangement 324 in an analogous manner to currents i ⁇ and , respectively.
• the total quadrupole field of each of arrangements 424 and 324 can be represented by corresponding four magnetic poles Q of FIGURE 10 having a corresponding diverging axis D at 45 degrees relative to axis N and a corresponding converging axis 0 that is perpendicular to axis D.
• Axis 0 of FIGURE 10 represents the direction in which the corresponding total quadrupole field tends to converge a cross section or profile of the electron beam.
• axis X for example, represents such beam converging direction when the beam spot lies on axis X that is analogous to axis 0 of FIGURE 10.
• Axis D of FIGURE 10 represents the direction in which the total quadrupole field produced by arrangement 424 of FIGURE 9 tends to diverge a profile of the electron beam.
• FIGURE 11 illustrates, schematically, the orientation of converging axis 0(1) and of diverging axis D(l) of double quadrupole arrangement 424 relative to the direction of spot elongation.
• the direction of spot elongation and the direction of the deflection are the same.
• the orientation of converging axis 0(2) and of diverging axis D(2) of double quadrupole arrangement 324 is also shown.
• FIGURE 1 1 1 represents the fields produced by the doublet that is formed by arrangements 424 and 324 of FIGURE 9. Similar symbols and numerals in FIGURE 11 and in each of the preceding FIGURES indicate similar items or functions.
• Axes D(l) and 0(1) of FIGURE 11 of double quadrupole arrangement 424 of FIGURE 9 may be rotated dynamically as a function of the beam spot landing location by varying currents ⁇ ⁇ and i 2 .
• axes D(2) and 0(2) of FIGURE 11 of double quadrupole arrangement 324 of FIGURE 9 may be rotated dynamically as a function of the beam spot, landing location by varying currents 13 and i 4 .
• currents i3 and 14. of FIGURE 9 are controlled in such a manner so as to dynamically rotate the total quadrupole deflection field relative to axis Z of arrangement 324 of FIGURE 9 such that converging axis 0(2) of FIGURE 11 is maintained dynamically aligned in parallel with the direction of the spot elongation as the direction of the deflection varies.
• arrangement 324 of FIGURE 9 causes a reduction in spot elongation.
• the way a profile of the beam spot is converged in the direction of its elongation so as to reduce the spot elongation is similar to that explained before with respect to FIGURE 3.
• double quadrupole arrangement 324 of FIGURE 9 also diverges the beam spot in the direction D(2) of FIGURE 1 1 that is perpendicular to axis 0(2).
• the converging-diverging effects of the total quadrupole deflection field produced by arrangement 324 of FIGURE 9, advantageously, tends to change beam spot 999 from being significantly elliptic to being substantially less elliptic or closer to being round.
• the convergence lensing action of arrangement 324 produces spot astigmatism as a result of overconvergence in the direction of spot elongation.
• currents ii and i 2 of FIGURE 9 are controlled in such a manner so as to dynamically align diverging axis D(l) of FIGURE 11 of arrangement 424 of FIGURE 9 in parallel with the direction of spot elongation such that the spot astigmatism caused by, for example, arrangement 324 is reduced.
• arrangement 424 produces an increase in the beam aperture angle in the region between arrangements 424 and 324 relative to the beam aperture angle in the region between arrangement 324 and the screen.
• the spot diverging operation produced by arrangement 424 of FIGURE 9 further from the display screen, in cooperation with the spot converging operation produced by arrangement 324 closer to the display screen, both occurring in the direction of spot elongation, are capable of reducing the spot elongation.
• This can be explained by a well known theorem derived from the Helmholtz Lagrange law stating that the product of beam aperture angle and spot size is constant.
• the beam spot diverging action of arrangement 424 produces an increase in the beam aperture angle that results in a reduction of the spot size on screen 22".
• Quadrupole coil assembly 28 of FIGURE 2 may include an additional pair of saddle coils, not specifically identified in FIGURE 2, having an axis that forms a corresponding angle of, for example, 90° with the analogous axis of coils 11 such that assembly 28 forms, for example, a double quadrupole having eight magnetic poles.
• Such assembly 28 operates similarly to arrangement 324 of FIGURE 9.
• each of arrangements 324 and 424 may be constructed as a single quadrupole. Converging axis 0(2) of such single quadrupole arrangement 324 is in the direction of horizontal axis X.
• diverging axis D(l) of single quadrupole arrangement 424 is also in the direction of axis X.
• the magnetic poles of each such single quadrupole 324 and 424 are oriented relative to axes X and Y in a similar manner to the magnetic poles 224 of FIGURE 6b.
• Arrangements 324 and 424 have opposite effects on convergence of the beams. Therefore, advantageously, reduction in spot elongation is obtained without significant degradation in 3-beam convergence. The result is that a compromise can be stricken among 3-beam convergence, spot elongation and astigmatism such that spot elongation is reduced relative to the spot elongation obtained in prior art self-converged yoke without significantly sacrificing the self convergence property of the deflection system.
• Another advantage is that since arrangement 324 and 424 operate in opposite directions on a given electron beam, similar waveform generators may be used for energizing quadrupole arrangements 324 and 424.

Landscapes

• Video Image Reproduction Devices For Color Tv Systems (AREA)
• Details Of Television Scanning (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=24213610

Family Applications (1)

Country Status (5)

Cited By (5)

Families Citing this family (9)

Citations (1)

Family Cites Families (21)

• 1990
  • 1990-07-19 US US07/554,503 patent/US5327051A/en not_active Expired - Lifetime
• 1991
  • 1991-07-19 DE DE19914191630 patent/DE4191630T/de active Pending
  • 1991-07-19 KR KR1019930700153A patent/KR100228325B1/ko not_active IP Right Cessation
  • 1991-07-19 JP JP03513362A patent/JP3097862B2/ja not_active Expired - Fee Related
  • 1991-07-19 WO PCT/US1991/005113 patent/WO1992002033A1/en active Application Filing
  • 1991-07-19 DE DE4191630A patent/DE4191630B4/de not_active Expired - Fee Related

Patent Citations (1)

Non-Patent Citations (3)

Also Published As

Similar Documents

Legal Events