US3708715A

US3708715A - Convergence apparatus utilizing independently adjustable half-period triangular waveforms

Info

Publication number: US3708715A
Application number: US00135991A
Authority: US
Inventors: D Rhee
Original assignee: GTE Sylvania Inc
Current assignee: GTE Sylvania Inc
Priority date: 1971-04-21
Filing date: 1971-04-21
Publication date: 1973-01-02
Anticipated expiration: 1990-01-02

Abstract

A convergence system with minimized control interaction is disclosed. A signal with a parabolic waveform is generated and summed with a signal with a triangular waveform to provide a convergence signal. The triangular waveform has independently adjustable half-periods so that independent top and bottom or right and left adjustment is obtained.

Description

United States Patent 1191 Rhee 1 51 Jan. 2, 1973 s41 CONVERGENCE APPARATUS 3,543,080 11/1970 Wuensch .315/21 on UTILIZING INDEPENDENTLY 3,155,873 ll/l964 Paschal 315/21 TD ADJUSTABLE HALF-PERIOD TRIANGULAR WAVEFORMS Inventor:

Assignee:

Filed:

Appl. No.:

U.S.Cl

Int.Cl.

Dong Woo Rhee, Williamsville, NY.

GTE Sylvania Incorporated, Seneca Falls, NY.

April 21, 1971 Field of Search ..3l5/l3 C, 24, 30

References Cited UNITED STATES PATENTS Primary Examiner-Carl D. Quarforth Assistant Examiner-P. A. Nelson Attorney-Norman .l. O'Malley, Robert E. Walrath and Thomas H. Buffton 57] ABSTRACT A convergence system with minimized control interaction is disclosed. A signal with a parabolic waveform is generated and summed with a signal with a triangular waveform to provide a convergence signal. The triangular waveform has independently adjustable halfperiods so that independent top and bottom or right and left adjustment is obtained.

18 Claims, 10 Drawing Figures PATENTED A 2 7 3. 7 08,715

sum 1 ur 3 G G 132 R i l 7% f 54' H RF, IF Au D10, LUMINANCE cuzomm ANCE,

AND CON TROL SECTIONS HORIZONTAL 'DEFLECTION APPARATUS CONVERGENCE,

CIRCUImY l31 VERTICAL V INVENTOR. OSCILLATOR m'pu'r 0N6- w. RHEE.

BY P 1 9. l I.

ATTORN E.Y

PATENTEDJAH 2 I975 SHEET 2 [IF 3 iizuuut 3.

luhkjan 2: ZmdUmEH ATTORNE Y PATENTEDJAN 21975 SHEET 3 [IF 3 ATTORNEY CONVERGENCE APPARATUS UTILIZING INDEPENDENTLY ADJUSTABLE HALF-PERIOD TRIANGULAR WAVEFORMS CROSS-REFERENCE TO RELATED APPLICATION Dong W. Rhee, Current Drive Deflection Apparatus," Ser. No. 44,476, filed June 8, 1970, and assigned to the same assignee as the present invention.

BACKGROUND OF THE INVENTION This invention relates to convergence apparatus of the type used to converge the electron beams in a color cathode ray tube. In a typical color CRT the electron beams are statically converged at the center of the display screen. Away from the center of the screen, however, the beams converge at a point before they reach the screen. The non-linearity of the beam deflection with respect to the screen is generally spherical requiring a parabolic correction toward the edges. This parabolic correction is obtained by applying parabolic currents of the form i=kt to windings of a deflection yoke which operate to correct the deflection of the various beams to converge them at the screen.

Since the amount of correction required varies, the amplitudes of the parabolic currents must be variable. In prior art convergence systems the variable amplitudes are obtained by summing sawtooth signals with parabolic signals. Typically, two sawtooth signals with opposite slopes and variable amplitudes are summed with a parabolic signal. One of the sawtooth signals has the greatest effect on one area of the screen, e.g., top or right, while the other sawtooth signal has the greatest effect on another area of the screen, e.g., bottom or left. The effects of the two sawtooth signals, however, are not independent. For example, the signal that has the most effect on convergence at the top of the screen also interacts with or affects the convergence at the bottom of the screen and vice versa. Similar interaction occurs between the left and right convergence signals. Thus, converging the electron beams in a color CRT in accordance with the prior art is a laborious and time consuming procedure because the various controls must be adjusted and readjusted many times.

Furthermore, distortion of the parabolic signals by the sawtooth signals may also disturb or affect the areas of the screen that are statically converted. The distortion may also make it extremely difficult to obtain acceptable convergence on all areas of the screen. This problem often results in a best compromise convergence. The above noted problems are especially severe in color CRTs with wide'angle deflection because misconvergence becomes inherently greater with increasing deflection angle of the electron beams.

OBJECTS AND SUMMARY OF THE INVENTION It is a primary object of this invention to obviate the above noted disadvantages of the prior art.

It is a further object of this invention to provide improved convergence apparatus for color CRTs.

It is a further object of this invention to provide a convergence apparatus with minimized interaction between the signals and controls applicable to convergence on different portions of the screen.

The above objects and advantages are achieved in one aspect of this invention in a color television receiver having a cathode ray display tube with a plurality of electron beams therein, a deflection yoke for deflecting the plurality of electron beams, and convergence apparatus for converging the electron beams. The convergence apparatus includes a convergence yoke adapted for mounting in operable relationship with the cathode ray display tube and has a plurality of windings for deflecting corresponding ones of the plurality of electron beams. A periodic signal with a parabolic waveform having first and second halfperiods is summed with one or two periodic signals having triangular waveforms in time coincidence with the first and second half-periods of the first periodic signal. The amplitudes of the triangular waveforms are variable. The summed signal is a control signal utilized to control a current through one of the windings of the convergence yoke.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a block diagram of a color television receiver illustrating the relationship of convergence apparatus thereto;

FIG. 2 is a waveform diagram illustrating typical prior art convergence waveforms;

FIG. 3 is a block diagram of one embodiment of the invention;

FIG. 4 is a waveform diagram illustrating typical waveforms used in the invention;

FIGS. 5A, 5B, 5C, 5D, and 5E are schematic diagrams illustrating electron beam movement for convergence; and

FIG. 6 is a schematic diagram of one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings.

A typical color television receiver is illustrated in FIG. 1. An antenna 10 intercepts transmitted signals and conducts them to a block 11 which contains the usual RF, IF, audio, luminance, chrominance, and control sections of a color television receiver. Outputs from the luminance and chrominance sections are applied to a cathode ray display tube 12. Outputs from the control section are applied to a vertical oscillator 13 and to a horizontal deflection apparatus 14 which has an output connected to a horizontal deflection winding of a deflection yoke 15 positioned about the neck of tube 12. Vertical oscillator 13 has an output connected to a vertical output stage 16 which has an output connected to a vertical deflection winding of deflection yoke I5. Outputs from horizontal deflection apparatus 14 and vertical output stage 16 are connected to convergence circuitry 17 which has outputs connected to a convergence yoke 20 positioned or mounted about the neck of tube 12.

Vertical oscillator 13 and vertical output stage 16 are preferably in accordance with the above-referenced copending application. Horizontal deflection apparatus 14 can also be in accordance with the referenced application.

In a typical prior art convergence system a signal with a parabolic waveform such as waveform 21 of FIG. 2, is used for convergence. Since the magnitude of the error of the electron beams varies, the magnitude of the correction signal applied to the windings of the convergence yoke should be variable. The usual prior art technique for varying the amplitude of the signal is to add variable amplitude signals with sawtooth waveforms to the parabolic signal.

Assume a signal with waveform 21 is used to converge the electron beams at the top and bottom of the screen. A signal with a sawtooth waveform such as waveform 22 is added to the parabolic signal to effect convergence at the bottom of the screen. Another signal with a sawtooth waveform but having a slope opposite to the slope of waveform 22, is used to effect convergence at the top of the screen. Both sawtooth waveforms have variable amplitudes so that the correct amount of convergence can be obtained.

Waveform 23 is the sum of

waveforms

21 and 22. During the vertical scans of the top portion of the screen, the control signal is represented by half-periods 24 of waveform 23. After the vertical scans pass the central portion of the screen the control signal is represented by half-periods 25 of waveform 23.

Ideally, the sawtooth signal represented by waveform 22 should affect the control signal only during halfperiods 25 since the sawtooth signal is intended for convergence at the bottom of the screen. However, the control signal is also affected or distorted during halfperiods 24 by the sawtooth signal, thereby affecting or distorting the convergence at the top of the screen. The second sawtooth signal (not shown) is added to the signal represented by waveform 23 to form a control signal for application to one of the convergence windings. The second sawtooth signal has its major effect on half-periods 24, however, it also affects halfperiods 25. Thus, there is control interaction since varying either of the sawtooth signals affects the convergence at both the top and bottom of the screen although the effect is greater on one than the other. Similarly, there is control interaction between the controls for left and right convergence.

In FIG. 3 a block diagram of the invention is shown.

Signal generators

26 and 27 for generating periodic signals with sawtooth or triangular waveforms have first outputs connected to

variable attenuators

30 and 32, respectively, and second outputs connected to

variable attenuators

31 and 33, respectively.

Attenuators

32 and 33 each have an output connected to a summing means 34. A signal generator 35 for generating a periodic signal with a parabolic waveform has an output connected to summing means 34 which provides a control signal to a convergence winding 36 of a convergence yoke.

An output of variable attenuator 30 is connected to a differential splitter 37 which has a first output connected to a summing means 40 anda second output connected to a summing means 41. An output of variable attenuator 31 is connected to a differential splitter 42 which has first and second outputs connected to summing

means

40 and 41, respectively. The output of parabolic signal generator 35 is connected to summing

means

40 and 41. Summing means 40 has an output connected to a convergence winding 43, and summing means 41 has an output connected to a convergence winding 44. Preferably,

convergence windings

36, 43, and 44 are all part of the same convergence yoke.

Parabolic signal generator 35 generates a periodic signal with a parabolic waveform represented by waveform 45 of FIG. 4. Waveform 45 has first-half periods 46 and second half-periods 47.

Sawtooth signal generators

26 and 27 generate periodic signals with sawtooth or triangular waveforms represented by

waveforms

50 and 51, respectively. Waveform 50 is in time coincidence with the first half-periods 46 of parabolic waveform 45 while waveform 51 is in time coincidence with the second half-periods 47 of parabolic waveform 45.

In typical prior art convergence systems the red and green electron beams are converged and the blue electron beam is then superimposed. Accordingly, the invention will be explained using this convergence procedure, but those skilled in the art will realize that other procedures can be used as well.

To converge the beams at the top and bottom of the screen parabolic and sawtooth signals at the vertical deflection frequency are used. To converge the beams at the right and left of the screen parabolic and sawtooth signals at the horizontal deflection frequency are used. The circuits utilizing vertical and horizontal frequency signals are preferably independent. Accordingly, to explain convergence at the top and bottom of the screen, assume the frequency of the signals provided by

signal generators

26, 27, and 35 are at the vertical frequency.

Assume that the position of the red, green, and blue electron beams at the top of the screen is that represented by the dots labeled R, G, and B respectively, in FIG. 5A. Sawtooth generator 26 provides a signal with triangular waveform 50 which is coupled through variable attenuator 30 and differential splitter 37 to summing

means

40 and 41. In summing

means

40 and 41 the parabolic and sawtooth signals are summed or added and applied to

convergence windings

43 and 44 which, for example, deflect the red and green electron beams, respectively. The amplitude of the sawtooth signal is varied by attenuator 30 to control the amount of deflection of the red and green electron beams. The amount of deflection of each bearn will be equal, assuming that differential splitter 37 is set to provide equal signals to summing

means

40 and 41 as is illustrated in FIG. 5A where the R and G beams converge at point 52.

The signal from sawtooth generator 26 is also coupled through variable attenuator 32 to summing means 34 where it is summed with the parabolic signal from generator 35 and is applied to convergence winding 36 which deflects the blue electron beam. Attenuator 32 varies the amplitude of the signal therethrough to con verge the blue electron beam of B beam in FIG. 5A to point 52. The blue electron beam can be moved to the left or right, if necessary, by the usual blue lateral magnet.

In FIG. 5B the R and G beams are illustrated oflset in the horizontal plane as well as the vertical plane. Variable attenuator 30 varies the amplitude of the signal therethrough to converge the R and G beams to a vertical line 53, however, the beams still are not converged. Differential splitter 37 is varied to decrease the signal to summing means 40 while simultaneously increasing the signal to summing means 41. Thus, the R beam is deflected less by winding 43 while the G beam is deflected more by winding 44, as is shown in FIG. SC, to converge the R and G beams at point 54. The B beam is converged as was explained above. Thus, variable attenuator 30 causes the R and G beams to converge on a vertical line while differential splitter 37 causes the R and G beams to converge on a horizontal line.

As the electron beams are deflected toward the center of the screen by the vertical winding of the deflection yoke, the parabolic signal from generator 35 and the sawtooth signal from generator 26 decrease toward zero. After the beams pass the center of the screen, triangular waveform 50 remains at zero and the sawtooth signal from generator 27 starts to increase as shown by triangular waveform 51.

Variable attenuators

31 and 33 and differential splitter 42 operate on the sawtooth signal to converge the R, G, and B beams at the bottom of the screen in a manner similar to that described above. Variable attenuator 31 converges the R and G beams on a vertical line while differential splitter 42 converges them on a horizontal line. Variable attenuator 33 converges the B beam to the R and G beams.

The convergence of the R, G, and B beams at the right and left of the screen is similar to that described above and similar circuitry can be used. Assume that

generators

26, 27, and 35 provide signals with

waveforms

50, 51, and 45 respectively, at the horizontal scan frequency. The sawtooth signal from generator 26 (triangular waveform 50) is coupled through variable attenuator 30 and differential splitter 37 to summing means .40 and 41 where it is summed with the parabolic signal from generator 35 and applied to

windings

43 and 44. By adjusting attenuator 30 the R and G beams are converged on a horizontal line as is illustrated in FIG. 5D. Adjusting splitter 37 converges the R and G beams on a vertical line as is illustrated in FIG. 5E. The signal from generator 36 is also coupled through attenuator 32 to converge the B beam. Thus, the signal from generator 36 is used to converge the R, G, and B beams at one side of the screen. Similarly, the signal from generator 27 is used to converge the beams at the other side of the screen.

From the above description it is clear that similar circuits (but operating at different frequencies) can be used for top-bottom convergence and for right-left convergence. However, the circuit of FIG. 3 can be used for one convergence circuit (e.g., top-bottom convergence) while a prior art circuit is used for the other circuit (e.g., right-left convergence), if desired.

In FIG. 6 a specific example of a circuit in accordance with the invention is illustrated. A source of positive potential illustrated as a terminal 60 is connected to a collector of an NPN transistor 61 which has an emitter connected to an emitter of a PNP transistor 62. The collector of transistor 62 is connected by a resistor 63 to a common conductor illustrated as ground. Source 60 is further connected to a constant current generator 68. A variable current generator 64 is connected between the base of transistor 62 and ground. The base of tranSistor 61 is connected to the base of transistor 62 by series connected diodes 65 and 66. The

current through variable current generator 64 is varied by a signal applied at a terminal 67 such as can be provided by vertical oscillator 13 of FIG. 1. Components -68 comprise vertical output stage 16. A description of the operation and of various alternative forms of vertical output stage 16 can be found in the abovereferenced copending application.

The junction of the emitters of

transistors

61 and 62 is connected to one end of a vertical deflection winding 70 of the deflection yoke, the other end of which is connected by a coupling capacitor 71 in series with a resistor 72 to ground. The junction between resistor 72 and capacitor 71 is connected by a resistor 73 in series with a resistor 74 to the junction between the collector of transistor 62 and resistor 63.

Resistors

63 and 72 are preferably very small. The junction between

resistors

73 and 74. is connected by a diode 75 to one end of the resistance element of each of

potentiometers

76 and 77, the other ends of which are connected to ground. The wiper of potentiometer 77 is connected to the wiper of a potentiometer 80.

The junction between the collector of transistor 62 and resistor 63 is connected by a resistor 81 in series with a diode 82 to one end of the resistance element of each of

potentiometers

83 and 84, the other ends of which are connected to ground. The wiper of potentiometer 84 is connected to the wiper of a potentiometer 85.

One end of the resistance element of potentiometer 85 is connected by a resistor 86 in series with a resistor 87 to one end of the resistance element of potentiometer 80. The junction between

resistors

86 and 87 is connected to ground by a resistor 90 and is further connected by a resistor 91 to a control electrode ofa control means illustrated as the base of a transistor 92. The emitter of transistor 92 is connected to ground by a resistor 93. An output electrode or collector of transistor 92 is connected by a convergence winding 94, such as the convergence winding for the red electron beam, to a source of positive potential illustrated as a terminal 95. A damping resistor 96 can be connected in parallel with winding 94 if necessary, and winding 94 can be a split winding as illustrated.

The other end of the resistance element of potentiometer 85 is connected by a resistor 100 in series with a resistor 10] to the other end of the resistance element of potentiometer 80. The junction between

resistors

100 and 101 is connected to ground by a resistor 102 and by a resistor 103 to a control electrode of a control means illustrated as the base of a transistor 104. The emitter of transistor 104 is connected to ground by a resistor 105. An output electrode or collector of transistor 104 is connected by a convergence winding 106, such as the convergence winding for the green electron beam, to source 95. A damping resistor 107 can be connected in parallel with winding 106 if necessary, and winding 106 can be a split winding as illustrated.

The wiper of potentiometer 83 is connected by a resistor 110 in series with a resistor 111 to the wiper of potentiometer 76. The junction between resistors 110 and 111 is connected to ground by a resistor 112 and by a resistor 113 to a control electrode of a control meanS illustrated as the base of a transistor 114. The emitter of transistor 114 is connected to ground by a resistor 115. An output electrode or collector of transistor 114 is connected by a convergence winding 116, such as the convergence winding for the blue electron beam, to source 95. A damping resistor 117 can be connected in parallel with winding 116 if necessary, and winding 116 can be a split winding as illustrated.

The junction between deflection winding 70 and the emitters of

transistor

61 and 62 is connected to an input of an integrator 120 illustrated as a resistor and capacitor connected in an RC circuit. The output of integrator 120 is connected by a coupling capacitor 121 in series with a resistor 122 to the base of transistor 92 which is further connected to ground by a resistor 123. The junction between capacitor 121 and resistor 122 is connected by a reverse poled diode 124 to a source of positive potential illustrated as a terminal 125. Source 125 and diode 124 act as a clamping circuit. The junction of capacitor 121 and resistor 122 is further connected by a resistor 126 to the base of transistor 104 and by a resistor 127 to the base of transistor 114. The base of transistor 104 is further connected to ground by a resistor 130. The base of transistor 114 is further connected to ground by a resistor 131.

In operation,

transistors

61 and 62 provide a sawtooth current through deflection winding 70. A large portion of the voltage developed across the winding 70 due to this sawtooth current is integrated by integrator 120 to provide a periodic signal with a parabolic waveform illustrated by waveform 45 of FIG. 4. The sawtooth deflection current also flows through resistor 72 to provide a sawtooth voltage thereacross illustrated as waveform 132 of FIG. 4. As was explained in the above-referenced copending application, transistor 62 conducts current only during one-half of the cycle of the sawtooth deflection current. Thus, the voltage across resistor 63 is represented by waveform 50 of FIG. 4. This signal is coupled through resistor 81 and diode 82 to the resistance elements of

potentiometers

83 and 84. The voltages across

resistors

63 and 72 are summed by

resistors

73 and 74. The summed voltage, represented by waveform 51 of FIG. 4 which is the sum of

waveforms

50 and 132, is coupled by diode 75 to the resistance elements of

potentiometers

76 and 77. Thus, the vertical output stage, deflection winding 70, integrator 120, and the various resistors correspond to

generators

26, 27, and 35 of FIG. 3.

Potentiometer 84 varies the amplitude of the sawtooth signal represented by waveform 50 and cor responds to variable attenuator 30 of FIG. 3. Potentiometer 85 splits the signal at its wiper into two signals with amplitudes relatively or differentially variable by the wiper of potentiometer 85. Thus, potentiometer 85 corresponds to differential splitter 37. Potentiometers 77 and 80 operate similar to

potentiometers

84 and 85 to split the sawtooth signal represented by waveform 51 into two variable amplitude signals. Thus, potentiometers 77 and 80 correspond to variable attenuator 31 and differential splitter 42, respectively.

One signal from potentiometer 80 is summed with one signal from potentiometer 85 by

resistors

86, 87, and 90 to provide a periodic signal with a waveform illustrated as waveform 133 of FIG. 4. This signal has first and second half-periods each with a triangular waveform in time coincidence with the first and second half-periods of the parabolic signal as is illustrated in FIG. 4. This periodic signal is summed with the parabolic signal by

resistors

91, 122, and 123. Thus,

resistors

86, 87, 90, 91, 122, and 123 correspond to summing means 40 of FIG. 3. The control signal formed at the base of transistor 92 controls the current through transistor 92 and hence the current through winding 94 to deflect the red electron beam.

The other signals provided by potentiometers and are similarly summed by

resistors

100, 101, and 102. The resultant signal is summed with the parabolic signal by

resistors

103, 126, and to provide a control signal to control the current through transistor I04 and winding 106 to deflect the green electron beam. Thus,

resistors

100, 101, 102, 103, 126, and 130 correspond to summing means 41.

Potentiometers

76 and 83 provide signals with

waveforms

51 and 50, respectively, which have variable amplitudes depending upon the position of the potentiometer wipers. These signals are summed by

resistors

110, 111, and 112 to provide a periodic signal with a waveform represented ,by waveform 133. This signal is summed with the parabolic signal by

resistors

113, 127, and 131 to provide a control signal for controlling the current through transistor 114 and winding 116 to deflect the blue electron beam. Thus,

potentiometers

83 and 76 correspond to

variable attenuators

32 and 33, respectively, while the various summing resistors correspond to summing means 34.

While the circuit of FIG. 6 has been described with reference to the vertical deflection apparatus, it is clear that a similar circuit can be used with the horizontal deflection apparatus to generate suitable convergence signals. Alternatively, the horizontal retrace pulse (flyback pulse) can be singly integrated to provide a sawtooth signal and doubly integrated to provide a parabolic signal with suitable summing circuits used to provide signals in accordance with

waveforms

50 and 51.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

I claim:

1. In a color television receiver having a cathode ray display tube for generating a plurality of electron beams therein and a deflection yoke for deflecting said plurality of electron beams, convergence apparatus for converging the electron beams comprising:

a convergence yoke mounted in operable relationship with said cathode ray display tube and having a plurality of windings for deflecting corresponding ones of said plurality of electron beams;

first means for generating a first periodic signal with a parabolic waveform having first and second halfperiods;

second means for generating second and third periodic signals, said second periodic signal having a triangular waveform during said first half-periods and said third periodic signal having a triangular waveform during said second half-periods, said second and third periodic signals further having independently variable amplitudes;

summing means connected to said first and second means for summing said first, second, and third periodic signals to provide a control signal with independently variable amplitudes during said first and second half-periods; and

means connecting said summing means to one of said windings of said convergence yoke for controlling the current through said one of said windings with said control signal.

2. Convergence apparatus as defined in claim 1 including:

third means for generating fourth and fifth periodic signals, said fourth periodic signal having a triangular waveform during said first half-periods and said fifth periodic signal having a triangular waveform during said second half-periods, said fourth and fifth periodic signals further having independently variable amplitudes;

second summing means connected to said first and third means for summing said first, fourth, and fifth periodic signals to provide a second control signal with independently variable amplitudes during said first and second half-periods; and

means connecting said second summing means to a second one of said windings of said convergence yoke for controlling the current through said second one of said windings in accordance with said second control signal.

3. Convergence apparatus as defined in claim 2 wherein said second and third means include:

a first signal generator for generating a periodic signal having a triangular waveform during said first half-periods of said first periodic signal;

a second signal generator for generating a periodic signal having a triangular waveform during said second half-periods of said first periodic signal;

first and second variable resistance means connected to said first and second signal generators, respectively, for varying the amplitudes of the periodic signals generated by said first and second signal generators; and

third and fourth variable resistance means connected to said first and second variable resistance means, respectively, said third variable resistance means for providing said second and fourth periodic signals with relatively variable amplitudes, and said fourth variable resistance means for providing said third and fifth periodic signals with relatively variable amplitudes.

4. Convergence apparatus as defined in claim 2 wherein said means connecting said first-named summing means to one of said windings includes a first transistor, and said means connecting said second summing means to a second one of said windings includes a second transistor.

5. Convergence apparatus as defined in claim 2 including:

fourth means for generating sixth and seventh periodic signals, said sixth periodic signal having a triangular waveform during said first half-periods and said seventh periodic signal having a triangular waveform during said second half-periods, said sixth and seventh periodic signals further having independently variable amplitudes;

third summing means connected to said first and fourth means for summing said first, sixth, and seventh periodic signals to provide a third control signal with independently variable amplitudes during said first and second half-periods; and

means connecting said third summing means to a third one of said windings of said convergence yoke for controlling the current through said third one of said windings in accordance with said third control signal.

6. Convergence apparatus as defined in claim 2 wherein said first means includes an integrator for integrating a signal representative of a current flowing through a winding of said deflection yoke for generating said first periodic signal, and said second and third means generate said second and third periodic signals from said current flowing through said winding of said deflection yoke.

7. In a color television receiver having a cathode ray display tube with a plurality of electron beams therein, a deflection yoke for deflecting said plurality of electron beams, and a convergence yoke adapted for mounting in operable relationship with said cathode ray display tube and having a plurality of windings for deflecting corresponding ones of said plurality of electron beams, a convergence circuit comprising:

first signal generating means for generating a first periodic signal with a parabolic waveform having first and second half-periods;

second signal generating means for generating second and third periodic signals each having first and second half-periods in time coincidence with said first and second half-periods, respectively, of said first periodic signal and each further having a first triangular waveform with a variable amplitude during said first half-periods and a second triangular waveform with a variable amplitude during said second half-periods;

first summing and control means connected to said first and second signal generating means and to a first winding of said convergence yoke for summing said first and second periodic signals to provide a first control signal for controlling the current through said first winding; and

second summing and control means connected to said first and second signal generating means and to a second winding of said convergence yoke for summing said first and third periodic signals to provide a second control signal for controlling the current through said second winding.

8. A convergence circuit as defined in claim 7 wherein said second signal generating means includes first and second signal generators for generating signals with said first and second triangular waveforms, respectively, and first and second summing means each connected to said first and second signal generators for summing the signals from said first and second signal generators to provide said second and third periodic signals, respectively.

9. A convergence circuit as defined in claim 8 wherein said first signal generator includes a first variable attenuator for varying the amplitude of the signals generated by said first signal generator and a first differential splitter connected to said first variable attenuator for providing first and second signals with differentially variable amplitudes to said first and second summing means, respectively, and said second signal generator includes a second variable attenuator for varying the amplitude of the signals generated by said second signal generator and a second differential splitter connected to said second variable attenuator for providing third and fourth signals with differentially variable amplitudes to said first and second summing means, respectively.

10. A convergence circuit as defined in claim 9 wherein said first and second variable attenuators and said first and second differential splitters are each potentiometers.

11. A convergence circuit as defined in claim 7 wherein said first and second summing and control means include first and second summing means, respectively, for summing said first and second periodic signals and said first and third periodic signals to provide said first and second control signals, respectively, and first and second transistors, respectively, each havin g a control electrode connected to the respective one of said first and second summing means and an output electrode connected to the respective one of said first and second windings.

12. A convergence circuit as defined in claim 7 wherein said first signal generating means includes an integrator connected to said deflection yoke for integrating a voltage across a winding of said deflection yoke.

13. A convergence circuit as defined in claim 8 wherein said first and second signal generators include means for deriving first and second voltages, respectively, from a current flowing through a winding of said deflection yoke.

14. A convergence circuit as defined in claim 7 including a third signal generating means for generating a fourth periodic signal having first and second halfperiods in time coincidence with said first and second half-periods, respectively, of said first periodic signal and further having a first triangular waveform with a variable amplitude during said first half-periods and a second triangular waveform with a variable amplitude during said second half-periods; and third summing and control means connected to said first and third signal generating meansand to a third winding of said convergence yoke for summing said first and fourth periodic signals to provide a third control signal and for controlling the current through said third winding. I

15. A convergence circuit as defined in claim 14 wherein said third signal generating means includes a first variable attenuator for varying the amplitude of said fourth periodic signal during said first half-periods and a second variable attenuator for varying the amplitude of said fourth periodic signal during said second half-periods.

16. A convergence circuit as defined in claim 15 wherein said third summing and control means includes summing means for summing said first and fourth periodic signals to provide said third control signal and a transistor having a control electrode connected to said summing means and an output electrode connected to said third winding.

17. A convergence circuit as defined in claim 7 wherein the frequency of said first, second, and third periodic signals is at the vertical deflection frequency of the television receiver.

l A convergence circuit as defined in claim 7 wherein the frequency of said first, second, and third periodic signals is at the horizontal deflection frequency of the television receiver.

Claims

1. In a color television receiver having a cathode ray display tube for generating a plurality of electron beams therein and a deflection yoke for deflecting said plurality of electron beams, convergence apparatus for converging the electron beams comprising: a convergence yoke mounted in operable relationship with said cathode ray display tube and having a plurality of windings for deflecting corresponding ones of said plurality of electron beams; first means for generating a first periodic signal with a parabolic waveform having first and second half-periods; second means for generating second and third periodic signals, said second periodic signal having a triangular waveform during said first half-periods and said third periodic signal having a triangular waveform during said second half-periods, said second and third periodic signals further having independently variable amplitudes; summing means connected to said first and second means for summing said first, second, and third periodic signals to provide a control signal with independently variable amplitudes during said first and second half-periods; and means connecting said summing means to one of said windings of said convergence yoke for controlling the current through said one of said windings with said control signal.

2. Convergence apparatus as defined in claim 1 including: third means for generating fourth and fifth periodic signals, said fourth periodic signal having a triangular waveform during said first half-periods and said fifth periodic signal having a triangular waveform during said second half-periods, said fourth and fifth periodic signals further having independentLy variable amplitudes; second summing means connected to said first and third means for summing said first, fourth, and fifth periodic signals to provide a second control signal with independently variable amplitudes during said first and second half-periods; and means connecting said second summing means to a second one of said windings of said convergence yoke for controlling the current through said second one of said windings in accordance with said second control signal.

3. Convergence apparatus as defined in claim 2 wherein said second and third means include: a first signal generator for generating a periodic signal having a triangular waveform during said first half-periods of said first periodic signal; a second signal generator for generating a periodic signal having a triangular waveform during said second half-periods of said first periodic signal; first and second variable resistance means connected to said first and second signal generators, respectively, for varying the amplitudes of the periodic signals generated by said first and second signal generators; and third and fourth variable resistance means connected to said first and second variable resistance means, respectively, said third variable resistance means for providing said second and fourth periodic signals with relatively variable amplitudes, and said fourth variable resistance means for providing said third and fifth periodic signals with relatively variable amplitudes.

5. Convergence apparatus as defined in claim 2 including: fourth means for generating sixth and seventh periodic signals, said sixth periodic signal having a triangular waveform during said first half-periods and said seventh periodic signal having a triangular waveform during said second half-periods, said sixth and seventh periodic signals further having independently variable amplitudes; third summing means connected to said first and fourth means for summing said first, sixth, and seventh periodic signals to provide a third control signal with independently variable amplitudes during said first and second half-periods; and means connecting said third summing means to a third one of said windings of said convergence yoke for controlling the current through said third one of said windings in accordance with said third control signal. 6. Convergence apparatus as defined in claim 2 wherein said first means includes an integrator for integrating a signal representative of a current flowing through a winding of said deflection yoke for generating said first periodic signal, and said second and third means generate said second and third periodic signals from said current flowing through said winding of said deflection yoke.

7. In a color television receiver having a cathode ray display tube with a plurality of electron beams therein, a deflection yoke for deflecting said plurality of electron beams, and a convergence yoke adapted for mounting in operable relationship with said cathode ray display tube and having a plurality of windings for deflecting corresponding ones of said plurality of electron beams, a convergence circuit comprising: first signal generating means for generating a first periodic signal with a parabolic waveform having first and second half-periods; second signal generating means for generating second and third periodic signals each having first and second half-periods in time coincidence with said first and second half-periods, respectively, of said first periodic signal and each further having a first triangular waveform with a variable amplitude during said first half-periods and a second triangular waveform with a variable amplitude during said second half-periods; FIRST summing and control means connected to said first and second signal generating means and to a first winding of said convergence yoke for summing said first and second periodic signals to provide a first control signal for controlling the current through said first winding; and second summing and control means connected to said first and second signal generating means and to a second winding of said convergence yoke for summing said first and third periodic signals to provide a second control signal for controlling the current through said second winding.

11. A convergence circuit as defined in claim 7 wherein said first and second summing and control means include first and second summing means, respectively, for summing said first and second periodic signals and said first and third periodic signals to provide said first and second control signals, respectively, and first and second transistors, respectively, each having a control electrode connected to the respective one of said first and second summing means and an output electrode connected to the respective one of said first and second windings.

14. A convergence circuit as defined in claim 7 including a third signal generating means for generating a fourth periodic signal having first and second half-periods in time coincidence with said first and second half-periods, respectively, of said first periodic signal and further having a first triangular waveform with a variable amplitude during said first half-periods and a second triangular waveform with a variable amplitude during said second half-periods; and third summing and control means connected to said first and third signal generating means and to a third winding of said convergence yoke for summing said first and fourth periodic signals to provide a third control signal and for controlling the current through said third winding.

18. A convergence circuit as defined in claim 7 wherein the frequency of said first, second, and third periodic signals is at the horizontal deflection frequency of the television receiver.