GULLWING DISTORTION CORRECTION CIRCUIT

Abstract: In a televison picture tube deflection apparatus a gullwing distortion correction signal (V gc ) and a north-south pincushion distortion correction signal (V pc ) are generated and then summed to form a sum signal (V gp ). The sum signal is coupled to a primary winding (W₁) of a transformer (T). A secondary winding (W₂) of the transformer (T) is coupled in a current path of a vertical rate deflection current (i V ) for modulating the deflection current in a manner that reduces the gullwing and north-south pincushion distortions. The secondary winding (W₂) is included in a resonant circuit (63) that is tuned to resonate at the horizontal frequency.

Description: This invention relates to gullwing distortion corrected deflection circuits for television picture tubes, particularly new, flatter faceplate picture tubes, such as the RCA Corporation square-planar picture tubes, which have aspherical faceplate curvatures. In one form of flatter faceplate picture tube, as typified by the RCA 110° COTY-SP, square-planar, 27V, color television picture tube A68ACC10X, the formula for the tube faceplate sagittal height, z, in millimeters, with reference to the center of the faceplate is given by: where X and Y are the distance coordinates, in millimeters, from the faceplate center along the major and minor axes, respectively, and where: A₁ = -0.236424229 x 10⁻⁴ A₂ = -0.363538575 x 10⁻⁸ A₃ = -0.422441063 x 10⁻³ A₄ = -0.213537355 x 10⁻⁸ A₅ = +0.883912220 x 10⁻¹³ A₆ = -0.100020398 x 10⁻⁹ A₇ = +0.117915353 x 10⁻¹⁴ A₈ = +0.527722295 x10⁻²¹ The picture tube faceplate defined by this formula has a relatively shallow curvature near the center of the faceplate, which increases near the edges along paths parallel to both the major and minor axes of the tube. The overall result is a faceplate of relatively flat appearance and with planar edges, namely, with points along the top, bottom, right and left edges located substantially in a common plane. Such picture tubes may require modulation of the field deflection current for correcting a geometrical distortion defined as gullwing distortion, illustrated by the raster lines of FIGURE 1. A cause of this distortion is the difference between the beam scanning radius of curvature and the tube faceplate radius of curvature, as the electron beams scan a raster pattern. In FIGURE 1, as is also discussed in WO 86/00170, a raster area R is schematically represented by a rectangular box that encompasses the viewing area of a faceplate 30 of a square-planar picture tube SP of FIGURE 2. Horizontal and vertical deflection circuits 20 and 40 of FIGURE 2 generate horizontal and vertical deflection currents in horizontal and vertical deflection windings L H and L V , respectively. The horizontal and vertical deflection currents produce a pattern of scanned raster lines on faceplate 30. Assuming that horizontal and vertical deflection circuits 20 and 40 correct for distortions such as east-west, north-south and S-distortion (as disclosed in US-A-4563618), the display of a pattern of horizontal raster scan lines on faceplate 30 is illustrated in FIGURE 1. The raster scan lines of FIGURE 1 exhibit a residual distortion identified as gullwing distortion. In gullwing distortion, the vertical deviation of the electron beams scanning a given raster line, such as line L₁+, undergoes approximately two cycles of oscillation about its straight, dashed-line position in FIGURE 1. During the first half of the vertical trace interval, between time T V1 and time T V0 , the vertical deviation of each raster line scan produces an upward excursion at intermediate points of a given line scan, near times t H2 and t H3 of the line trace interval, T Ht . Maximum downward excursion of each raster line scan during the top half of vertical trace occurs at the beginning, center and end of each line scan, corresponding to times t H1 , t H0 and t H4 , respectively. Additionally, in gullwing distortion, the phase of the deviations of a given raster line switches by 180° when scanning from the top half of the raster to the bottom half of the raster. Thus the phase of the deviations of raster line L₁₋, scanned at vertical instant T V3 , is inverted in phase relative to the excursions of the corresponding raster line L₁+, scanned at vertical instant T V2 . When horizontal and vertical deflection circuits 20 and 40 are used in conjunction with raster scanning on faceplate 30 of square-planar picture tube SP of FIGURE 2, the effects of gullwing distortion on raster R of FIGURE 1 varies during the vertical trace interval T Vt . Gullwing distortion is at a maximum for raster lines scanned at times intermediate the center of vertical trace and the beginning or end of vertical trace. Thus, maximum gullwing distortion or maximum deviation of a raster line occurs when scanning raster lines L₁+ and L₁₋ during vertical scan instants T V2 and T V3 . Minimum or no gullwing distortion of the raster scan lines is associated with line scanning at the top, center and bottom of the raster, when scanning raster lines L₂+, L₀ and L₂₋, during vertical scan instants T V1 , T V0 and T V4 , respectively. As disclosed in WO-A-86/00170, gullwing distortion that tends to occur in conjunction with raster scanning of an aspherical faceplate picture tube is compensated by a correction circuit that modulates the field deflection current. The gullwing correction circuit is responsive to a first signal that repeats at a line rate and to a second signal that repeats at a field rate, for modulating the field deflection current during a line deflection period within the field deflection trace interval. The modulation is properly phased to correct the gullwing distortion. Another well-known form of raster distortion with which the present invention is concerned is pincushion distortion, and particularly, the top and bottom or N-S aspect of such distortion. This type of distortion is discussed in EP-A-201336 and is characterized by a central bowing of the raster scanning lines, the character of the bowing varying from a maximum downward bowing at the raster top through a minimum near the raster middle to a maximum upward bowing at the raster bottom. The bowing is approximately hyperbolically or parabolically shaped. FIGURE 3 illustrates the effect of both top and bottom pincushion distortion and side or E-W pincushion distortion, when left uncorrected, on the shape of stripes of a crosshatch pattern. This distortion results from the physical geometry of the deflection system as determined by such factors as the size and configuration of the target area and the relative position of an electron beam deflection center with respect to the target. A well known solution to the top-bottom pincushion distortion problem is to modulate the vertical scanning current, at the frequency f v , with a horizontal rate f H correction current. Thus, during the scanning of a horizontal scan line at the top of the screen of the CRT, for example, the horizontal rate correction current causes a varying change in the vertical scanning current. The varying change is such that at the center of such horizontal line, the vertical scanning current is larger than at the edges. Thus, the center portion of such horizontal scan line is displayed further from the horizontal center of the screen of the CRT. Consequently, the bow-shaped horizontal scan line is modified to appear closer to a horizontal straight line. EP-A-201336 discloses a combined top and bottom pincushion and gullwing distortion correction circuit which uses a nonlinear reactor to introduce an appropriately modulated horizontal frequency and second harmonic of the horizontal frequency component into the vertical scanning current path. The nonlinear reactor is preferably a transformer with a secondary that provides a correction voltage in series with the vertical scanning current path. The transformer effectively has two series opposing primary windings magnetically coupled to the secondary. These primaries, energized by waves at the horizontal frequency and the second harmonic frequency, alternately predominate over each other to a variable degree, and in a manner determined by the vertical scanning current, for inducing corresponding voltage at the secondary winding. In accordance with the present invention, there is provided a television deflection apparatus with gullwing and N-S pincushion raster distortion corrections, comprising: a first source of an input signal at a horizontal deflection frequency; a second source of an input signal at a vertical deflection frequency; means responsive to said signals that are produced by said first and second sources for generating, in accordance with said gullwing raster distortion, a gullwing raster distortion correction signal at a third frequency that is a multiple of said horizontal deflection frequency that is modulated in accordance with said signal that is produced by said second source; means responsive to said signals that are produced by said first and second sources for generating, in accordance with said pincushion raster distortion, a pincushion raster distortion correction signal at said horizontal deflection frequency that is modulated in accordance with said signal that is produced by said second source; a deflection circuit output stage responsive to said signal at said vertical deflection frequency that includes a deflection winding for generating a deflection current in said deflection winding at said vertical deflection frequency; characterized by a winding of a transformer coupled to said deflection winding; and means responsive to said gullwing and pincushion raster distortion correction signals for applying each substantially by means of a transformer action of said transformer to said first winding to generate in said first winding, in accordance with said gullwing and pincushion raster distortion correction signals, a modulation voltage that modulates said deflection current in a manner that provides correction of said gullwing and pincushion raster distortions such that a given winding turn of said first winding develops a voltage thereacross that is representative of both said gullwing and pincushion raster distortion correction signals. In the Drawing: FIGURE 1 illustrates the raster pattern of gullwing distortion appearing on an aspherical faceplate of a square-planar picture tube; FIGURE 2 illustrates in block diagram form raster scanning circuitry used in conjunction with raster scanning on an aspherical faceplate of a square-planar picture tube; FIGURE 3 illustrates pincushion distortion of a raster; FIGURE 4 illustrates a detailed embodiment of the vertical deflection circuit of FIGURE 2, including circuitry, embodying the invention, that corrects gullwing distortion; FIGURES 5a-5j illustrate waveforms at the vertical frequency that are useful for explaining the operation of the circuit of FIGURE 4; and FIGURES 6a-6j illustrates waveforms at the horizontal frequency and at twice the horizontal frequency that are useful for explaining the operation of the circuit of FIGURE 4. In a deflection circuitry illustrated in FIGURE 4, a vertical deflection circuit 40 includes a vertical deflection amplifier 41 that generates vertical deflection current i v in a vertical deflection winding L V . A combined pincushion and gullwing distortion correction circuit 70, embodying the invention, modulates vertical deflection current i v by applying a gullwing modulation voltage component V1 g , of a gullwing and pincushion modulation voltage V1 that is developed across a capacitor C₁₇, to vertical deflection winding L V . To provide north-south pincushion raster distortion correction, correction circuit 70 modulates vertical deflection current i V by applying to vertical deflection winding L V a north-south correction voltage component V1 p of voltage V1. Vertical deflection current i V flows to ground via a coupling capacitor C V and a current sampling resistor R s . FIGURES 5a-5j and 6a-6j illustrate waveforms useful in explaining the operation of correction circuit 70 of FIGURE 4. Similar numbers and symbols in FIGURES 4, 5a-5j and 6a-6j illustrate similar items or functions. North-south pincushion correction of vertical deflection current i V of FIGURE 4 is provided by a raster distortion correction circuit 70 that generates a north-south modulation voltage component V1 p across capacitor C₁₇ that together with gullwing modulation voltage component V1 g is applied to vertical deflection winding L V . North-south modulation voltage component V1 p is a line frequency, sinusoidal voltage, phased by LC resonant circuit 63 to have a zero crossing near the center of the horizontal trace interval. The amplitude envelope of line frequency voltage component V1 p is made to vary at a vertical rate in a generally sawtooth manner, having maximum envelope height near the top and bottom of the raster and zero height near the center. To generate modulation voltage component V1 p , raster distortion correction circuit 70 includes a pincushion modulation control circuit 60 that generates a north-south pincushion modulation voltage V pc at a terminal 151, as described below. A sawtooth signal V RS of FIGURE 5a that is developed across resistor R s of FIGURE 4 is AC coupled via a capacitor C100 to a junction terminal 100 that is coupled to a cosine amplitude control resistor R100 Resistor R100, that is coupled to an inverting input terminal of an operational amplifier U1 A , forms with amplifier U1 A an inverting amplifier that generates a vertical rate inverted sawtooth signal V t of FIGURE 5b. The peak-to-peak amplitude of signal V t is adjustable by adjusting variable resistor R100 of FIGURE 4 that controls the input level of the amplifier. The noninverting input terminal of amplifier U1 A is coupled to a DC reference voltage REF that is developed across a zener diode Z8.2. Sawtooth signal V RS is AC coupled through capacitor C100 and DC reference voltage REF is added via resistor R100′ to the inverting input terminal of amplifier U 1A . Therefore, signal V t that is developed at an output terminal of amplifier U1 A is also a sawtooth signal having a portion that is more positive than voltage REF and a second, substantially symmetrical portion, that is less positive than reference voltage REF. In this way, sawtooth signal V t has an average value that is equal to voltage REF as shown in Figure 5b. Signal V t of FIGURE 4 is coupled through resistor R101 to a junction terminal 101 of pincushion modulation control circuit 60. Terminal 101 is coupled to an output terminal of a comparator U2 B . As described below, comparator U2 B , operating as a switch, is responsive to horizontal retrace pulses F H . Horizontal retrace pulses F H of FIGURE 6a, that are generated in, for example, a flyback transformer of a horizontal deflection circuit 20 of FIGURE 2, are coupled to an integrating network that is formed by a resistor R9 and a capacitor C7 of FIGURE 4. Similar numbers and symbols in FIGURES 2 and 4 indicate similar items or functions. Consequently, a sawtooth signal F HS of FIGURE 6b at a horizontal rate f H is developed across capacitor C7 of FIGURE 4 having an average value that is equal to zero. Signal F HS is coupled to an inverting input terminal of comparator U2 B and to a noninverting input terminal of a comparator U2 A The other corresponding input terminals of comparators U2 A and U2 B are coupled to ground and therefore are at zero volts. Consequently, terminal 101 is grounded by the output terminal of comparator U2 B , that operates as a conductive switch during a first half, and as a nonconductive switch during a second half, of each horizontal period H of FIGURE 6a. During the second half of each horizontal period H, when comparator U2 B of FIGURE 4 operates as a nonconductive switch, signal V t is coupled through a diode D1 to terminal 151 to form, in each period H, a first portion of a north-south pincushion modulation signal V pc of FIGURE 6f, that was mentioned before. During the first half of period H, grounded terminal 101 is decoupled from terminal 151 by back biased diode D1. A fixed resistor R112 of FIGURE 4 and a variable resistor R111 form a voltage divider that develops at terminal 102 a signal V₁₀₂ at a level that is adjustable. Terminal 102 is coupled to an output terminal of a comparator U2 A . Comparator U2 A , operating as a switch that is coupled between ground and terminal 102, causes terminal 102 to be at, approximately, ground potential during the second half of each horizontal period H of FIGURE 6c. Consequently, terminal 102 is decoupled from terminal 151 by back biased diode. Thus, during the first half of each horizontal period H, that occurs during vertical trace, signal V₁₀₂ at terminal 102 that is close in value to that of reference voltage REF is coupled through diode D2 to terminal 151 to form a second portion of pincushion modulation signal V pc , as shown in FIGURE 6f. As described before, during the second half of each horizontal period H, signal V t is coupled to terminal 151 instead of signal V₁₀₂ to form the first portion of signal V pc . North-south pincushion modulation signal V pc of FIGURE 4 is coupled via a resistor R124 to an inverting input terminal of an amplifier U1 D . Amplifier U1 D , that is coupled in a configuration of a linear inverting amplifier, generates an output signal V gp having a corresponding signal component that is linearly proportional to signal V pc . Signal V gp is AC coupled through capacitor C110 and resistor R110 to the base of a power transistor Q₄ that operates in the class A mode. Transistor Q₄ is coupled to the primary winding W₁ of a transformer T. The secondary winding W₂ of transformer T is coupled in series with vertical deflection winding L V . Secondary winding W₂ of transformer T forms with capacitor C₁₇ an LC resonant circuit 63 that is tuned to the line frequency f H . In response to line rate, square-wave component voltage of signal V pc , shown in Fig. 6f, power transistor Q₄ generates a collector current i c that excites resonant circuit 63 into oscillation at the line rate to generate north-south modulation voltage component V1 p having a sinewave waveform at the frequency f H that is applied to vertical deflection winding L V . The amplitude envelope variation at the vertical rate of voltage component V1 p is accomplished in accordance with the vertical rate variation of the amplitude of signal V pc . Phase variation of voltage component V1 p is adjustable by varying the inductance of winding W₂. Sinewave, north-south modulation voltage component V1 p , when applied to vertical deflection winding L V , generates a cosine north-south correction modulation current component in field deflection current i V that is phase shifted by 90° from voltage V1 p . Thus, with respect to line scanning instants t H1 through t H4 of FIGURE 1, the north-south correction current component of vertical deflection current i V reaches maximum magnitude at the center of horizontal trace at time t H0 . During the first half of each horizontal period H of FIGURE 6f, that occurs during vertical trace, signal V pc is substantially equal to voltage REF, as described before. During the second half of those horizontal periods H that occur during the first half of vertical trace, the level of signal V pc is less positive than its level in the first half of such period H; whereas, during the second half of those horizontal periods H that occur during the second half of vertical trace, the level of signal V pc is more positive then its level in the first half of such period H. Thus, the horizontal rate phase of signal V pc reverses by 180° at a corresponding crossover point that occurs when signal V t of FIGURE 5b becomes equal to voltage REF. A second such crossover point occurs during vertical retrace. Adjusting resistor R111 varies signal V₁₀₂, and thus varies the time within vertical trace when the first crossover point occurs. In this way, adjusting resistor R111, advantageously, provides north-south pincushion or cosine centering. The horizontal rate peak-to-peak amplitude of signal V pc of FIGURE 4 in a given period H is equal to the difference between the level of signal V pc of FIGURE 6f, that occurs during the first half of the given horizontal period H that, as described before, is approximately equal to constant voltage REF, and its level during the second half of such horizontal period H. During the second half, the level of signal V pc is proportional to signal V t of FIGURE 5b. As described before, signal V t is a sawtooth signal having an average value that is approximately equal to voltage REF. It follows that the vertical rate envelope of the peak-to-peak magnitude of signal V pc of FIGURE 5d decreases gradually in a vertical rate ramping manner from the beginning of vertical trace toward its center where the first phase crossover point occurs. Similarly, it increases gradually in the vertical rate ramping manner from the center of vertical trace toward the end of vertical trace. North-South modulation voltage component V1 p changes by 180° approximately at the center of the raster. The time when the phase reversal occurs is controlled by adjusting resistor R111, as described before. Also, the phase has to change back again by 180° immediately prior to the beginning of the following vertical scanning. Hence, it has to change by 180° during, for example, vertical retrace. The response of voltage component V1 p to the abrupt change by 180° of the phase of voltage V pc that occurs during vertical retrace may not be sufficiently fast. Because the amplitude of voltage component V1 p is at its maximum prior to vertical retrace, a slow response to such change in phase, if not speeded-up, disadvantageously, might introduce raster distortions at the top of the raster. Therefore, it may be desirable to advance the time when such phase reversal begins, to allow a longer response time for reversing such phase during vertical retrace. During vertical retrace the phase reversal in voltage component V1 p begins to occur when downramping signal V t of FIGURE 5b becomes equal to the voltage at terminal 102. In accordance with an aspect of the invention, a series arrangement of a zener diode Z20, a diode D20 and a resistor R103 is coupled between terminal 102 and an output terminal of vertical deflection amplifier 41 where a vertical rate signal V v of FIGURE 5h is developed. A portion of a corresponding retrace pulse of signal V v that causes zener diode Z20 to conduct is coupled to terminal 102 that makes the voltage at terminal 102 more positive during vertical retrace than during vertical trace. It follows that signal V t of FIGURE 5b becomes equal to the voltage at terminal 102 earlier within vertical retrace than if the vertical retrace pulse of signal V v were not coupled to terminal 102. It follows that the time, during vertical retrace, when the phase reversal, or the second crossover point occurs in both signal V pc of FIGURE 4 and in voltage component V1 p across capacitor C₁₇ is, advantageously, advanced. Thus, the phase reversal is, advantageously, speeded-up. To correct gullwing raster distortion, combined pincushion and gullwing correction circuit 70 modulates vertical deflection current i V , during each line deflection period within the field deflection trace interval in the manner illustrated by the current i Vc , illustrated in FIGURE 1 by the two current waveforms ±i Vc . Current i Vc represents a line repetitive modulation component of the vertical deflection current wherein approximately two cycles of oscillation of modulation current i Vc is developed during the line trace interval T Ht . To correct gullwing distortion of the raster lines, the modulation current component i Vc is 180° out-of-phase with the oscillatory vertical deviations of the corresponding raster lines. Thus, for the lines scanned in the top half of the raster, such as raster line L₁+, modulation current component +i Vc reaches its negative minima AC-wise near the line trace instants t H2 and t H3 , and reaches its positive maxima near times t H1 , t H0 and t H4 . For lines scanned in the bottom half of raster R, the modulation current component is the phase inverted current -i Vc , reaching maxima near times t H2 and t H3 and minima near times t H1 , t H0 and t H4 . In addition, to provide gullwing distortion correction of a raster displayed on the aspherical faceplate of a square-planar picture tube, the amplitude envelope m V of modulation current component i Vc is varied in envelope height during the vertical trace interval T Vt in the manner illustrated in FIGURE 1. The height of the modulation envelope undergoes approximately two cycles of oscillation, achieving maximum height near times T V2 and T V3 , corresponding to the scanning of raster lines L₁+ and L₁₋. The modulation envelope reaches zero or near zero height near the center of vertical trace, time T V0 , when scanning raster line L₀ and near the top and bottom of the raster, near times T V1 and T V4 , when scanning raster lines L₂+ and L₂₋. Other modulation envelopes may be generated to correct gullwing distortion for television systems that require different envelop vertical variations. To generate modulation current component i Vc , having a modulation envelope m V , distortion correction circuit 70 includes a gullwing modulation control circuit 50 that generates at a terminal 51 a gullwing modulation signal V gc . Gullwing modulation control circuit 50 includes a sinewave generator 80 that generates a sinewave signal V SW at an output terminal of an amplifier U1 B having a sinewave waveform that is shown in FIGURE 5c. The sawtooth waveform of signal V RS that is developed across resistor R s is AC coupled through capacitor C100 to terminal 100 of generator 80. Generator 80 forms sinewave signal V SW by double integrating sawtooth signal V RS . Sinewave signal V SW is coupled via a resistor R1 and a capacitor C1 to the inverting input terminal of amplifier U1 A . In accordance with a feature of the invention, signal V SW is added in amplifier U1 A to the vertical sawtooth that, as described before, is coupled to terminal 100, thus, advantageously, providing S- correction. Consequently, as shown in FIGURE 5b, the trace portion of signal V t is not a straight line; rather, it includes a sinewave voltage component. Horizontal rate signal V₁₀₂ of FIGURE 6c having approximately 50% duty cycle is coupled via a transistor Q1 of FIGURE 4 operating as an emitter follower to a differentiation network that includes a capacitor C82 and a resistor R82. The differentiation network produces a signal V DIF having a positive going narrow pulse when a positive going transition occurs in signal V₁₀₂ and a negative going narrow pulse when a negative going transition occurs in signal V₁₀₂. Signal V DIF of FIGURE 6d is coupled via a comparators U2 C and U2 D of FIGURE 4, having corresponding output terminals that are coupled together, to the base electrode of a transistor Q2. In carrying out a yet further aspect of the invention, comparators U2 C and U2 D operate as a frequency doubler to produce a signal V 2H of FIGURE 6e at the frequency 2×f H that is used for gullwing distortion correction and that is developed at the collector electrode of transistor Q2 of FIGURE 4. Signal V 2H of FIGURE 6e contains a positive narrow pulse when each signal transition occurs in signal V₁₀₂ of FIGURE 6c. The narrow pulses of signal V 2H that occur at the frequency 2×f H are coupled to a gullwing modulator 81. A resistor R2 of gullwing modulator 81, embodying an additional aspect of the invention, has a terminal that is driven by sinewave signal V SW , that was described before, and a second terminal 81a, that is coupled to a plate of an integrating capacitor C2. The other plate of capacitor C2 is grounded. Consequently, during each one-half of period H, capacitor C2 is charged in an upramping manner when sinewave signal V SW is more positive than voltage REF, and in a downramping manner when it is less positive than voltage REF, to develop at terminal 81a a first portion of a sawtooth signal V gmod . A switching transistor Q3 has an emitter that is grounded and a collector that is coupled through a zener diode Z7.5 to terminal 81a. The base of transistor Q3 is coupled through a resistor R81 to signal V 2H . Transistor Q3 and diode Z7.5 clamp or establish signal V gmod at terminal 81a of capacitor C2 to be approximately at the same level as reference voltage REF each time the corresponding narrow pulse of signal V 2H of FIGURE 6e occurs. Consequently, a second portion of sawtooth signal V gmod is formed that changes in the opposite direction to that of the first portion. For example, when sinewave signal V SW of FIGURE 5c is less positive than voltage REF, the positive pulse of signal V 2H of FIGURE 6e is coupled through a diode D81c of FIGURE 4 to terminal 81a to charge capacitor C2 to the clamping level that is approximately equal to voltage REF and that is established by zener diode Z7.5. During the corresponding portion of each half of period H, when the corresponding positive pulse of signal V 2H does not occur, signal V gmod at terminal 81a is upramping if sinewave signal V SW is then positive relative to voltage REF, and is downramping signal if signal V SW is then negative relative to voltage REF. The magnitude or peak of signal V gmod of FIGURE 6g that occurs immediately prior to the occurrence of the clamping operation of transistor Q3 of FIGURE 4 during each half of period H of FIGURE 6g is determined by the level of vertical rate sinewave signal V SW of FIGURE 5c at that time. When the polarity of signal V SW of FIGURE 4 reverses, the phase of signal V gmod also reverses by 180°. Consequently, sawtooth signal V gmod that occurs at twice the horizontal rate is amplitude modulated in accordance with the current value of signal V SW . Phase reversal in signal V gmod occurs approximately at the center of vertical trace. Modulated signal V gmod is coupled through a resistor R83 to an active bandpass filter 83 having a center passing frequency at 2×f H that, in, for example, the PAL standard, is 31.25 KHZ. Filter 83 produces, from signal V gmod , gullwing correction signal V gc at terminal 51. In signal V gc , vertical rate and quadruple horizontal rate signal components and their respective harmonics are, advantageously, substantially removed or highly attenuated. Fine adjustment of the phase of signal V gc relative to horizontal deflection current in deflection winding L H of FIGURE 2 is accomplished by varying a resistor R114 of bandpass filter 83 of FIGURE 4. In accordance with an aspect of the invention, gullwing modulation signal V gc is coupled to the inverting input terminal of amplifier U1 D where it is summed with north-south pincushion modulation signal V pc to develop, at the output terminal of amplifier U1 D , signal V gp that contains the sum of both and that provides both gullwing and pincushion distortion correction. As described before, signal V gp is coupled to the base of transistor Q4. Because transistor Q4 operates as a linear amplifier, the corresponding collector current component of collector current i c of transistor Q4 that is at the frequency 2×f H and that is coupled to winding W₁ is, advantageously, amplified without distortion. Gullwing modulation voltage component V1 g is developed across winding W₂ of transformer T by a transformer action, as a result of the corresponding current component of collector current i c in transistor Q4 that is modulated by signal V gc at terminal 51. Gullwing correction voltage component V1 g that is applied to vertical deflection winding L V modulates vertical deflection current i V . The vertical rate amplitude modulation of voltage component V1 g enables distortion correction circuit 70 to produce a vertical rate modulation envelope of the gullwing correction current i Vc of FIGURE 1. In carrying out another aspect of the invention, voltage component V1 g that provides gullwing distortion correction, and voltage component V1 p , that provides pincushion distortion correction, are formed by the transformer action of transformer T. Each of voltage components V1 g and V1 p includes a corresponding portion that is developed across each winding turn of the same winding such as, for example, winding W₂ of transformer T. Thus, advantageously, only one transformer such as, for example, transformer T is required for generating both voltage components V1 g and V1 p that form the combined modulation voltage V1 that is coupled to deflection winding L V . Modulator 81 of FIGURE 4 functions as a suppressed carrier modulator. Therefore, the phase of gullwing correction voltage component V1 g switches 180° near the center of vertical trace at an instant that is controlled by adjusting resistor R117 that is coupled to terminal 81a. This phase change enables correction circuit 70 to change the phase of gullwing correction current i Vc at the center of vertical trace, from +i Vc to -i Vc , as is required for proper gullwing distortion correction. Signal V pc that provides pincushion distortion correction contains, advantageously, substantially no signal components at the frequency 2×f H , or at other even harmonics, that may adversely affect gullwing distortion correction because it is substantially a square-wave waveform having a 50% duty cycle. Advantageously, gullwing modulating signal V gc contains substantially no signal components at the horizontal frequency f H because signal V₁₀₂, that is coupled to frequency doubler 82, has a 50% duty cycle. Because signals V gc and V pc are coupled to winding W₂ through linear stages, advantageously, no cross modulation occurs that could adversely affect raster distortion correction. The signal component at the frequency f H , but not that at the frequency 2×f H , of signal V gp that is developed at the output terminal of amplifier U1 D is, advantageously, amplified by the resonance action of circuit 63 that forms a high impedance at the collector of transistor Q4 at the frequency f H . The signal component at the frequency 2×f H need not be amplified, since only a small gullwing signal amplitude is required for gullwing distortion correction. Additionally, because circuit 63 is tuned to the frequency f H that is substantially lower than that of voltage component V1 g , the phase of voltage component V1 g is, advantageously, unaffected by adjusting the inductance of winding W₂. As indicated before, the phase of voltage component V1 p is adjusted by varying the inductance of winding W₂ to provide properly phased pincushion distortion correction. As a result of the double integration operation of sinewave generator 80, sinewave signal V SW of FIGURE 5c causes the peak-to-peak amplitude of gullwing modulation signal V gc of FIGURE 5f to be at a corresponding maximum when the gullwing distortion in the aspherical faceplate picture tube 30 of FIGURE 2 is at a maximum. Thus, signal V gc and voltage component V1 g of FIGURE 1 are, advantageously, at a corresponding maximum when vertical scanning is approximately one-third down from the top edge of the raster and also when it is one third up from the bottom edge of the raster. Signal V gc of FIGURE 5f and voltage component V1 g of FIGURE 1 have advantageously, minimum peak-to-peak amplitude during vertical scanning of each of the top, bottom and center of the raster where no gullwing correction is required.

Claims: A television deflection apparatus with gullwing and N-S pincushion raster distortion corrections, comprising: a first source (R9,C7) of an input signal (F HS ) at a horizontal deflection frequency; a second source (R S ) of an input signal (V RS ) at a vertical deflection frequency; means (U2 C,D ) responsive to said signals that are produced by said first and second sources for generating, in accordance with said gullwing raster distortion, a gullwing raster distortion correction signal at a third frequency (2f H ) that is a multiple of said horizontal deflection frequency (f H ) that is modulated in accordance with said signal (V RS ) that is produced by said second source (R S ); means (U2 A,B ) responsive to said signals that are produced by said first and second sources for generating, in accordance with said pincushion raster distortion, a pincushion raster distortion correction signal (V PC ) at said horizontal deflection frequency that is modulated in accordance with said signal (V RS ) that is produced by said second source (R S ); a deflection circuit output stage (40) responsive to said signal (V RS ) at said vertical deflection frequency that includes a deflection winding (L V ) for generating a deflection current in said deflection winding at said vertical deflection frequency; characterized by a winding (W₂) of a transformer (T) coupled to said deflection winding (L V ); and means (63) responsive to said gullwing and pincushion raster distortion correction signals for applying each substantially by means of a transformer action of said transformer (T) to said first winding (W₂) to generate in said first winding, in accordance with said gullwing and pincushion raster distortion correction signals, a modulation voltage (V₁) that modulates said deflection current (i V ) in a manner that provides correction of said gullwing and pincushion raster distortions such that a given winding turn of said first winding (W₂) develops a voltage thereacross that is representative of both said gullwing and pincushion raster distortion correction signals. An apparatus according to claim 1 characterized in that said deflection winding (L V ) provides vertical deflection for a square-planar picture tube (SP). An apparatus according to claim 1 characterized by combining means (V1 D ) for combining said gullwing (V gc ) and pincushion (V PC ) distortion correction signals to generate a combined signal (V gp ) that is coupled to said first winding (W2) such that a signal path, that is formed between each of said gullwing and pincushion distortion correction signals and said first winding, is linear, so as to prevent said modulation voltage from being distorted in said signal path. An apparatus according to claim 1, characterized by a capacitance (C₁₇) coupled to said first winding (W₂) to form a resonant circuit (63) that is tuned to a horizontal deflection frequency (f H ) for amplifying by a resonance action of said resonant circuit an amplitude of a voltage component (V1 p ) of said modulation voltage (V1) that provides said north-south pincushion distortion correction. An apparatus according to claim 4 characterized in that said first winding (W₂) and said capacitance (C₁₇) are coupled in parallel to form said resonant circuit (63). An apparatus according to claim 4 characterized in that a voltage component (V1 g ) of said modulation voltage (V1) that provides gullwing distortion correction is at a harmonic of said horizontal frequency (f H ) and has an amplitude that is modulated at a vertical rate. An apparatus according to claim 1 characterized by a summing amplifier (V1 D ) responsive to said correction signals (V PC ,V gc ) for generating a sum signal (V gp ) thereof that is coupled to a second winding (W1) of said transformer (T). An apparatus according to claim 7 characterized by a transistor (Q4) having a control electrode (base) that is coupled to said sum signal (V gp ) and a main current conducting electrode (collector) that is coupled to said second winding (W₁) of said transformer (T) to generate in said second winding (W₁) a first current component at a horizontal frequency that corresponds with said pincushion distortion correction signal (V1 p ) and a second current component at a higher harmonic of said horizontal frequency that corresponds with said gullwing distortion correction signal (V1 g ). An apparatus according to claim 8 characterized by a capacitance (C₁₇) coupled to said first winding (W₂) to form a resonant circuit (63) that is tuned to said horizontal frequency such that a ratio between an amplitude of a voltage component of said modulation voltage (V1) that correspond with said pincushion distortion correction signal (V1 p ) and that of said first current component is, as a result of said resonant circuit (63) being in resonance, substantially higher than a corresponding ratio between an amplitude of a voltage component of said modulation voltage (V1) that corresponds with said gullwing distortion correction signal (V1 g ) and that of said second current component. An apparatus according to claim 1 characterized in that said deflection circuit output stage (40) generates said deflection current (i V ) at a vertical rate. An apparatus according to claim 10 characterized in that said gullwing distortion correction signal generating means comprises a sinewave generator (80) responsive to said deflection current for generating a sinewave signal (V SW ) at a frequency that is related to said vertical rate, a frequency doubler (U2 C,D ) responsive to said input signal at said frequency that is related to said horizontal frequency for generating a signal at a harmonic of said horizontal frequency, and a modulator (81) responsive to said sinewave signal (V SW ) and to said signal (V 2H ) at said harmonic for generating said gullwing distortion correction signal (V gmod ) by amplitude modulating said harmonic signal in accordance with said sinewave signal (V SW ). An apparatus according to claim 11 characterized by said frequency doubler comprises means (U2 A ) responsive to a signal at said horizontal frequency for generating a square-wave signal (V₁₀₂) at said horizontal frequency having approximately a 50% duty cycle, and means (Q1,U2 C,D Q2) responsive to said square-wave signal (V₁₀₂) for generating an output pulse (V 2H ) of said signal at said harmonic when each transition edge occurs in said square-wave signal (V₁₀₂). An apparatus according to claim 12 characterized in that said modulator (81) comprises a capacitance (C2) coupled to said sinewave signal (V SW ) for generating a second sawtooth signal (V gmod ) in said capacitance (C2) at double the horizontal frequency having a portion that ramps in a first direction at a rate that is determined by said sinewave signal (V SW ), said modulator being responsive to said output pulse of said harmonic signal that causes said second sawtooth signal (V gmod ) to ramp in an opposite direction when said pulse of said harmonic signal that is generated by said frequency doubler occurs. An apparatus according to claim 13 characterized in that said modulator (81) further comprises, level clamping means (Z7.5) responsive to said pulse of said frequency doubler for clamping a level of said second sawtooth signal (V gmod ) to be at a predetermined level prior to a beginning time of said portion of said sawtooth signal that ramps in said first direction, and adjustable means (R117) for adjusting said predetermined level of said sawtooth signal to provide gullwing distortion correction centering. An apparatus according to claim 11 characterized by a bandpass filter (83) coupled to said modulator (81) having a bandpass frequency range that is centered around a frequency (2f H ) that is equal to twice the horizontal frequency for filtering out component signals outside said bandpass frequency range from said gullwing distortion correction signal, and means (R114) coupled to said modulator (81) for adjusting a phase of said gullwing distortion correction signal relative to that of said input signal that is at said horizontal frequency. An apparatus according to claim 11 characterized in that said sinewave generator (80) is responsive to a sawtooth signal (V RS ) that is proportional to said deflection current (i v ) and that is developed in said output stage (40) to generate said sinewave signal by double integrating said sawtooth signal. An apparatus according to claim 11 characterized by means (R S ) responsive to said deflection current (i v ) for generating a sawtooth signal (V RS ) that is coupled to said modulator (81) to provide S- distortion correction. An apparatus according to claim 10 characterized in that said pincushion distortion correction signal generating means comprises means (U2 A,B ) responsive to said input signal (F HS ) at said frequency that is related to said horizontal frequency for generating a square-wave signal (V₁₀₂) having 50% duty cycle at said horizontal frequency, and a modulator (60) responsive to a sawtooth signal (V RS ) at said vertical rate, that is generated in said output state (40) and to said square-wave signal (V₁₀₂) for generating said pincushion distortion correction signal (V pc ) by amplitude modulating said square-wave signal (V₁₀₂) in accordance with said sawtooth signal (V RS ). An apparatus according to claim 18 characterized in that said modulator (60) of said pincushion distortion correction signal generating means comprises first switching means (D2) responsive to said square-wave signal (V₁₀₂) at said horizontal frequency for generating, during a first portion of a given horizontal period, a corresponding portion of said square-wave signal (V₁₀₂) at a level that is determined by a level of said sawtooth signal, and during a second portion of said given horizontal period, a corresponding portion of said square-wave signal at a level that, during each vertical trace interval of said deflection current, is substantially constant. An apparatus according to claim 19 characterized by means (41) coupled to said output stage (40) for generating a signal (V V ) that is representative of a vertical retrace pulse in said output stage, said retrace pulse representative signal (V V ) being coupled to said first switching means (D2) to control said level of said square-wave signal during said second portion of said given horizontal period that advances, during said vertical retrace, a time when phase reversal occurs in a component current of said deflection current that provides pincushion distortion correction.

Inventors: LEONARDI, GIOVANNI MICHELE
Applicants: RCA THOMSON LICENSING CORPORATION
Application year: 1988
Main classification: H04N3
IPC codes: H04N3