CORRECTION OF CONVERGENCE OF DIFFERENTIAL ERROR OF THE RIGHT SHORE
This invention relates, in general terms, to the field of convergence correction. The television projection receivers are subject to numerous image distortions because the three cathode ray tubes (CRT) used in those receivers are off-axis one with respect to the other and two of the three cathode ray tubes projections are off-axis with respect to a flat screen, as shown in diagram form, for example, in the lower right corner of FIGURE 4. Dynamic convergence correction requires that numerous convergence correction signals are generated and apply to a set of auxiliary convergence correction coils in the horizontal and vertical deflection yokes of each cathode ray tube. In television projection receivers using curved cathode ray tubes, which have a concave bottom curvature, a distortion in the form of a differential sin has been identified in relation to the trapezoidal distortion of the red and blue images. With reference to FIGURE 1, this distortion causes the blue horizontal lines (punctuated in FIGURE 1) of an image that converges differently to be on the green and red lines in the upper left (UL) and lower right quadrants ( LR) of the image and be below the green and red lines in the upper right (UR) and lower left (LL) quadrants of the image. Similarly, the horizontal red lines (dashed lines in FIGURE 1) of an otherwise converging image are above the green and blue lines in the upper right (UR) and lower left (LL) quadrants of the image and they are below the green and blue lines in the lower right (LR) and upper left (UL) quadrants of the image. This distortion is of a zero amplitude in the horizontal centerline (HCL) and increases in amplitude towards the top and bottom of the image. It can be seen that this distortion is generally sinusoidal. A second distortion causes the horizontal red and blue lines to differentially wave up and down on the left edge of the image, as shown in FIGURE 2. It has been seen that this distortion is due to the slow response time in the amplifiers of convergence energy. A third common distortion in all television projection receivers is trapezoidal distortion, as shown in FIGURE 3. Since the optical axis of the green cathode ray tube is orthogonal to the surface of the screen in the center of the screen , there is very little trapezoidal distortion in the green image. Similarly, since the optical axes of the red and blue cathode ray tubes are in the plane that includes the horizontal midline of the screen and is perpendicular to the surface of the screen there is very little vertical trapezoidal distortion of red and blue. blue. However, the red and blue cathode ray tubes are deflected from the horizontal center of the screen and tilted inward. The red and blue cathode ray tubes are located on either side of the green cathode ray tube. This arrangement produces horizontal and equal horizontal trapezoidal distortions of red and blue. The red and blue images have parallel left and right edges and opposingly divergent upper and lower edges. The trapezoidal distortion has been corrected by means of a signal that represents the product of a sawtooth of horizontal regime and a serrated tooth of vertical regime. A signal of this type is also known under the nomenclature "horizontal saw X vertical saw". Other convergence correction waveforms are also referred to with a similar nomenclature as the product of other signals. The product is an exit sign in the form of a "bow tie" of vertical regime, as shown in FIGURE 6, where the sawtooth of horizontal regime has a maximum amplitude in the upper and lower part of the image and zero amplitude in the horizontal midline. The horizontal phase is reversed in the horizontal midline. Consequently, the trapezoidal distortion correction waveforms for red and blue must be of opposite polarity and apply mainly to red and blue vertical convergence correction coils. The correction of particular convergence errors, or distortions, can often interfere with the correction of other convergence errors due to the many convergence correction signals that are applied to the horizontal and vertical deflection yokes convergence correction coils . The problems caused by the differential sinus and the ripple distortions on the left and right edges are, first, the correction of such distortions, and second, the correction of those distortions without interfering with other convergence corrections. The red and blue differential sinus distortion in the horizontal lines is sine-shaped. As a result, a horizontal regime sine correction multiplied by a vertical saw can be used to correct it. The red and blue differential sinus distortion can be corrected by adding a horizontal sine signal to the same horizontal sawtooth signal used to generate the trapezoidal distortion correction signal before the horizontal sawtooth signal is multiplied by the vertical sawtooth signal to produce the trapezoidal distortion correction signal. The sine phase is chosen so that the upper and lower peaks of the horizontal saw appear limited and the zero crossing has an increased slope. The differential ripple of the left bank can be corrected by developing an overloaded pulse during the horizontal retrace, and adding that overloaded pulse to the horizontal sine signal and the horizontal sawtooth signal, also before multiplication with the tooth signal vertical saw, to accelerate the response of the amplifier. As a result of a subsequent and successful effort to reduce interference, which is the presence of horizontal regime currents in the vertical yoke buffers, by applying equal damping to each of the vertical yoke coils, it was discovered that an equal damping also corrects the differential ripple distortion on the left edge of the image. In addition to, and in conjunction with, the application of equal damping for each of the vertical yoke coils, the horizontal sawtooth signal was previously changed to center the pivot point of the vertical skew control. However, it was discovered that this phase change produces a fourth distortion, which causes the red and blue horizontal lines to differentially wave up and down, respectively, on the right edge of the image, as shown in FIGURE 11 It has been determined that the differential ripple of the right bank can be corrected by developing a negative pulse from a horizontal right linearity signal and adding that negative impulse to the horizontal signal, generally sinusoidal and to the horizontal sawtooth signal before multiplying it by the vertical sawtooth signal. A correction circuit for a cathode ray tube that displays images subject to distortion comprises: an element for generating a sawtooth waveform of horizontal regime; an element to generate a generally sinusoidal waveform, of horizontal regime; an element for generating a pulse waveform of horizontal regime; an element to add the sawtooth waveforms, generally sinusoidal and impulse, of horizontal regime, to define a composite waveform of horizontal regime; an element for generating as output signal a product of the composite waveform of horizontal regime and a waveform of vertical regime, the composite waveform of horizontal regime being coupled by direct current to the generating element of the product; an element to amplify the output signal; and a correction coil for the cathode ray tube coupled to receive the amplified output signal and generate a dynamic magnetic field that in response to the output signal, the output signal having a first component to correct a trapezoidal distortion, a second component to correct a red / blue differential sinusoidal distortion and a third component to correct a ripple distortion of the red / blue differential right edge. According to a feature of one embodiment of the invention presented herein, a correction circuit for a cathode ray tube that displays images subject to distortion comprises: an element for generating a sawtooth waveform of horizontal regime; an element for generating a pulse waveform of horizontal regime; an element to generate a generally sinusoidal waveform, of horizontal regime; an element for summing the waveforms of sawtooth, impulse and generally sinusoidal, of horizontal regime, to define a composite waveform of horizontal regime; an element for generating as output signal a product of the composite waveform of horizontal regime and a waveform of vertical regime, the composite waveform of horizontal regime being coupled by direct current to the element that generates the product; an element to amplify the output signal; and, a correction coil for the cathode ray tube coupled to receive the amplified output signal and generate a dynamic magnetic field that in response to the output signal, the output signal having a first component to correct a trapezoidal distortion, a second component to correct a red / blue sine distortion and a third component to correct a ripple distortion of the right red / blue edge. A television projection receiver comprises: a plurality of cathode ray tubes, each of the cathode rays having a vertical yoke coil and each vertical yoke coil coupled to the other in series; a plurality of equal damping resistors, each of the same damping resistors coupled in parallel through one of the vertical yoke coils; an element for adding three waveforms of horizontal regime for each of the cathode ray tubes to define a composite waveform of horizontal regime for each of the cathode ray tubes; an element to generate as output signal for each of the cathode ray tubes a product of the composite waveform of horizontal regime for each of the cathode ray tubes and a waveform of vertical regime for each of the cathode ray tubes; an element for amplifying the output signal for each of the cathode ray tubes; and a plurality of correction coils, each of the correction coils coupled to one of the cathode ray tubes to receive the amplified output signal from the cathode ray tube and generate a dynamic magnetic field for the cathode ray tube in response to the output signal, the output signal having a first component to correct a trapezoidal distortion, a second component to correct a red / blue sine distortion and a third component to correct a ripple distortion of the right red / blue edge. According to a feature of one embodiment of the invention shown herein, a television projection receiver comprises: a plurality of cathode ray tubes, each of the cathode ray tubes having a vertical yoke coil and each of the vertical yoke coils coupled with one another in series; a plurality of damping resistors, each of the damping resistors coupled in parallel with the associated one of the vertical yoke coils; an element for generating a sawtooth waveform of horizontal regime; an element for generating a pulse waveform of horizontal regime; an element for generating a generally sinusoidal waveform of horizontal regime; an element to add the waveforms of sawtooth, impulse and generally sinusoidal horizontal regime, to define a composite waveform of horizontal regime; an element for generating as output signal a product of the composite waveform of horizontal regime and a waveform of vertical regime, the composite waveform of horizontal regime being coupled by direct current to the element that generates the product; an element to amplify the output signal; and, a correction coil for one of the cathode ray tubes coupled to receive the amplified output signal and generate a dynamic magnetic field in response to the output signal, the output signal having a first component for correcting a trapezoidal distortion, a second component to correct a red / blue sine distortion and a third component to correct a ripple distortion of the right red / blue edge. The damping resistors can be the same. The trapezoidal distortion is due to the off-axis orientation of the cathode ray tube; the red / blue differential sinusoidal distortion is due to the geometry of the bottom of the cathode ray tube; and the ripple of the right edge is influenced by a change of the reset pulse of the horizontal sawtooth waveform at a previous time with respect to the horizontal retrace to the center of the pivot point of the vertical and key bias settings . The foregoing, and other features and advantages of the present invention, will become apparent from the following description along with the accompanying drawings, in which like reference numerals designate the same elements. FIGURE 1 is a useful diagram to explain the distortion of differential sine of red and blue in horizontal lines. FIGURE 2 is a useful diagram to explain the ripple distortion of the differential left edge of the horizontal lines. FIGURE 3 is a useful diagram to explain trapezoidal distortion. FIGURE 4 is a diagram, in blocks and schematically, of a television projection receiver, which includes a circuit for correcting trapezoidal distortion, the distortion of differential sine of red and blue in horizontal lines and the distortion of ripple of the left bank differential of the horizontal lines. FIGURE 5 is a schematic diagram of the parabola generator shown in FIGURE 4. FIGURE 6 is a useful diagram for explaining waveforms used for the correction of trapezoidal distortion. FIGURE 7 is a schematic diagram of the sine wave generator shown in FIGURE 4. FIGURE 8 is a schematic diagram of the horizontal sawtooth generator and the blocker, each shown in FIGURE 4. FIGURE 9 is a schematic diagram of the output circuit of the convergence correction waveform shown in block form in FIGURE 4. FIGURE 10 is a schematic diagram of the integrated circuit AN614, shown in block form in FIGURE 4. FIGURE 11 is a useful diagram to explain the ripple distortion of the right edge differential of the horizontal lines. FIGURE 12 is a diagram, in blocks and schematically, of a television projection receiver, including a circuit for correcting trapezoidal distortion, differential distortion of red and blue in horizontal lines and distortion of ripple the right edge differential of the horizontal lines. FIGURES 13 and 14 are schematic diagrams useful for explaining the damping of vertical yoke coils in a television projection receiver. FIGURE 15 is a schematic diagram of the parabola generator shown in FIGURE 12. FIGURE 16 is a schematic diagram of the horizontal sawtooth generator shown in FIGURE 12. A television projection receiver is shown in block and form schematic in FIGURE 4 and is generally designated with the reference numeral 1. The receiver comprises a synchronization signal separator 2 and a chrominance processor 3, each responding to a visual display signal input. The horizontal synchronization components H and the vertical synchronization components V are supplied to the horizontal and vertical deflection circuits 4 and 5, respectively. Three projection cathode ray tubes 80, 81 and 82 are provided for the red R, green G and blue B signals, respectively, such as those generated by the chrominance processor 3. Each cathode ray tube displays a monochrome image corresponding to its color on the screen 83, using a lens 84. Only the green cathode ray tube 81 is orthogonal to the screen 83. The red and blue cathode ray tubes are located on each side of the green cathode ray tube, horizontally deflected from the center of the screen and tilted inwards. This arrangement produces opposite and equal horizontal trapezoidal distortions of red and blue as described above. The red and blue images have parallel left and right edges that diverge in opposite ways on the upper and lower edges. Each cathode ray tube is provided with deflection yokes. Each horizontal deflection yoke includes a main vertical deflection coil 86, a horizontal main deflection coil 87, an auxiliary vertical deflection coil 88 for vertical convergence correction and an auxiliary horizontal deflection coil 89 for horizontal convergence correction. The various coils of the respective cathode ray tubes are distinguished as necessary with the suffixes R, G, and B for red, green and blue, respectively. A system for generating a plurality of waveforms for convergence correction is generally designated by the reference numeral 6. The convergence correction system 6 receives and / or generates a plurality of different waveforms that are scaled, added and / or multiplied in a wide variety of combinations to provide six composite convergence correction waveforms, which represent the corrections for horizontal red (SRH), vertical red (SRV), horizontal green (SGH), vertical green (SGV) , horizontal blue (SBH), and vertical blue (SBV). The output signal SRV is coupled to the convergence correction coil 88R through the output amplifier 71. The output signals SGV and SBV are coupled to their respective convergence correction coils by the output amplifiers 72 and 73, respectively . A circuit for generating only one such convergence correction waveform, designated as the waveform I, is shown in detail in FIGURE 4. The waveform I is a first CCW1 convergence correction waveform introduced. to a convergence correction waveform combination circuit 70. The waveform CCW1 (I) is the product of a waveform multiplication. The multiplier output signal is damped by transistor Q70 and is coupled by alternating current to the convergence correction waveform combination circuit 70 via capacitor C70. Other convergence correction waveforms are the CCW2 inputs through CCWn. Forty or more of those convergence correction waveforms may be required. The waveform I represents the product of two signals. A signal is generally a vertical rate saw, shown as the F waveform. The vertical saw F has a peak-to-peak voltage of 4.25 volts and a direct current level of 5.3 volts. A small amount of size correction is made in the vertical direction by adding a small vertical range sine, shown as the G waveform, to the vertical saw F. The vertical sine G has a peak-to-peak voltage of. 2 volts and a direct current level of .1 volts. The vertical saw F and the vertical sine G are added in a resistive sum network formed by the R60 resistors, R61 and R62. This corrects the gain of the correction of the horizontal lines at the top and bottom of the image. The other signal is a waveform H, which is the sum of the waveforms C, D and E. The generation of the H waveform begins with a parabola of horizontal regime, designated as the waveform A, which it is supplied to a sine wave generator 10, which develops the generally sinusoidal wave designated C wave form. The horizontal regime parabola has a positive peak voltage of +5.6 volts and a negative peak voltage of -1 volts. In addition, the parabola of horizontal regime directs the main exploration by the delay in the convergence energy amplifier, which is around 5 microseconds. It is also necessary to configure the parabola to achieve straight horizontal lines in the image. That parabola of horizontal regime can be generated by the circuit 90 shown in FIGURE 5, or by the circuit 190 shown in FIGURES 12 and 15. With reference to FIGURE 5, a constant current IDC is generated by the source 91. A variable feedback current IAC is added to the IDC current at junction 95. The composite current charges capacitor C91. The capacitor C91 is periodically discharged by the reset circuit 94, by means of the horizontal retrace pulses of the horizontal deflection circuit 4, which "turn on" the transistor Q93 in the horizontal regime. The result is a horizontal-rate sawtooth signal as shown, which is coupled by alternating current to the integrator 92. The integrator 92 includes an operating amplifier Ul having an integration capacitor C90 and a direct current polarizing circuit that includes R90. The output parabola waveform A is coupled by alternating current to junction 95 as the variable current IAC. A blocking circuit 93 coupled to the output of the integrator 92 includes the transistors Q90 and Q91 and the resistor R91. The horizontal reset pulses are coupled by alternating current so that only its projecting edge restores the horizontal parabola. This allows the integration to start around 5 microseconds before the end of the horizontal reset impulses. The direct current polarization supplied by resistor R90 to the reversing input of Ul is used at the input to the integrator to tilt the horizontal parabola so that the peak occurs about 5 microseconds before the center of the horizontal scan . Normally, after the peak, the parabola continues in a negative direction until the retrace pulse occurs and resets the output back to zero. However, it results in an overshoot that goes to negative when the direct current polarization tilts the horizontal parabola and the useful part of the horizontal parabola ends around 5 microseconds before the horizontal reset pulse begins. This causes the horizontal lines to be arranged on the right edge of the image. Lock 93 turns on the parabola that goes to negative to around -100 V. This was determined as the best level to reach straight horizontal lines on the right edge of the image. This level can be critical and is maintained by blocking 93 even when temperature changes occur. Transistor Q91 receives an almost constant current in its collector of approximately 1 mA. A small fraction of this current, determined by the direct current beta of the transistor Q91, flows into the base of the transistor 90 and determines the voltage of the base to the emitter that is forced by feedback to also be the voltage of the collector to the emitter. The current flowing in transistor Q90 during blocking is approximately 10 mA. Transistors Q90 and Q91 are of the same type that operate at a similar ambient temperature. The higher collector current in transistor Q90 produces a higher voltage from the base to the emitter than in transistor Q91, so that the difference, of around 100 mV, tends to remain constant with temperature changes. The integration of the horizontal parabola is restored by the discharge of the integration capacitor C90 by transistor Q92 during the first half of the horizontal reset pulses and it is allowed to start during the second half of the horizontal reset pulses. The function that is integrated during this time is a capacitance discharge that goes to negative due to the effect of the resistor R92 and the transistor Q93 on the capacitor C91 voltage. This produces a positive increasing slope in the horizontal parabola during the first 5 microseconds of integration instead of the decreasing positive slope that is characteristic of a parabola. This glow from the horizontal parabola helps to straighten the horizontal lines on the left edge of the image. Referring again to FIGURE 4, the horizontal parabola waveform A is filtered at a low pass and phase shifted in a sine wave generator 10 to produce the C waveform, shown as a horizontal sine with a zero crossing that goes to positive approximately 5 microseconds before the horizontal average exploration, an average direct current value of 1.35 volts and a peak-to-peak amplitude of 1.6 volts. A schematic circuit for the sine wave generator 10 is shown in FIGURE 7. The horizontal parabola is filtered at a low pass through a network that includes the RIO, Rll and R12 resistors and the CIO and Cll capacitors. The filtered signal is damped by transistor Q10, which is a transmitter deflected by a resistor R13. Returning to FIGURE 4, a horizontal sawtooth generator 20 produces the horizontal sawtooth signal as shown in waveform D. The horizontal sawtooth generator 20 is shown in greater detail in FIGURE 8. A current source charges a C20 capacitor. Capacitor C20 is rapidly discharged at the start of horizontal retrace pulses of 10 microseconds by driving transistor Q20. The horizontal retrace pulses are 22 volts peak-to-peak, having a positive peak of +18 volts and a negative peak of -4 volts, as shown by the wave form B. The resulting waveform D is 0 volts for 10 microseconds during the horizontal retrace and increases to a peak amplitude of 3.6 volts during the trace. The average direct current is approximately 1.5 volts. A voltage divider is formed by resistors R43 and R42, coupled in series between +12 volts and ground. The union of the resistors R43 and R42 forms a resistive sum joint 45 for the horizontal sine C and the horizontal sawtooth D, which are coupled to the sum joint 45 by the resistors R40 and R41, respectively. The sum joint 45 is coupled by direct current to the differential input terminal 5 of a signal multiplier 60, for example a Panasonic AN614 multiplier. The opposite differential input, terminal 1, is biased by a voltage divider formed by resistors R50 and R51 coupled in series between +12 volts and ground. The resulting polarization level is approximately 3.4 volts, which is equal to the direct current value of the sum of the horizontal saw and the horizontal sine approximately 5 microseconds before the horizontal average scan. Since on both sides of the differential input reference is also made to the +12 V supply, any variation of this supply is canceled. This coupling to direct current is an unconventional polarization arrangement for multipliers like AN614, which are usually coupled by alternating current to the signal sources that are multiplying. For example, the summed signal representing the combination of the waveforms F and G is coupled by alternating current to the terminal 3 of the multiplier 60 via the capacitor C61. Coupling to direct current is used to solve another problem, namely, the ripple of the differential left bank. The solution causes the addition of an impulse signal during the horizontal retrace that accelerates the response time of the convergence output amplifier and straightens the red and blue differential ripple on the left edge of the image. If the coupling to alternating current is used, this addition of the retrace pulse distorts the response during the trace time. This occurs because the composite waveform has a new direct current average and a change occurs that moves the equilibrium point of the differential amplifier out of the desired time during the trace. The coupling to direct current allows the addition of the impulse during retrace without disturbing the balance of the amplifier during the trace. Additionally, it was discovered that with direct current coupling a very large pulse could be used during the retrace, and that the output peak would be controlled by the internal design of the amplifier. This means that the response of the power amplifier can be adjusted with the duration of the pulse instead of the amplitude. The adjustment of the power amplifier by the duration of the pulse can be achieved with the transistor Q30. The horizontal retrace pulses, according to waveform B, at 22 volts peak-to-peak, are also an input for blocking circuit 30. As shown in FIGURE 8, blocking circuit 30 comprises resistor R30 and the Zener CR30 diode. The Zener CR30 diode graduates at 6.8 volts. The output of the blocking circuit 30 is a limited horizontal retrace pulse having a positive peak of 6.8 volts and a negative peak of -6 volts. The retrace pulses blocked at a 7.4-volt peak-to-peak level are coupled by alternating current to the base of transistor Q30 via capacitor C30, and through a voltage divider formed by resistors R31 and R32. The transistor Q30 is lit on the projecting edge of this locked horizontal retrace pulse and is turned off at a time determined by the capacitor C30 and the resistor R31. The collector of the transistor Q30 is also coupled to the sum joint 45, and is added to the horizontal sine and the horizontal saw. The net result of the sum is shown in the H wave form. It has been discovered that the distortion that causes the red and blue horizontal lines to differentially wave up and down on the left edge of the image, as shown in FIGURE 2 can be corrected without resorting to the addition of the locked horizontal retrace waveform E at the sum joint 45, as described hereinabove. The correction of the differential ripple on the left edge of the image can also be effected by applying a damping equal to each of the vertical yoke coils to suppress the horizontal regime currents in the vertical yoke. Referring to FIGURE 13, the vertical deflection circuit 5 drives the main vertical deflection coils 86. The vertical deflection circuit 5 requires a specific load resistance to ensure proper operation; in this case a load resistance of 270 O is required. A series that couples the main vertical deflection coils 86 is coupled in parallel with the resistance of 270 O. In this configuration, at a high frequency the central deflection coils vertical main 86 behaves like a voltage generator charged by the other two main vertical deflection coils 86. Large circulating currents at horizontal regime can be introduced into the center of the main vertical deflection coils 86 by corresponding coils of the coils horizontal deflection coils 87 and auxiliary deflection coils 89. Circulating current of induced horizontal regime is passed to the other two of the main vertical deflection coils 86 due to the series interconnection of the coils. The circulating currents can be suppressed by the damping of each of the main vertical deflection coils 86 with an equal parallel resistance, as shown in FIGURE 14. The values for the damping resistors are chosen so that the damping resistances are equal and the sum of the damping resistors equal the load resistance required by the vertical deflection circuit 5. However, the application of that damping in combination with an earlier phase for the horizontal sawtooth signal M introduces a distortion of convergence on the right edge of the image, as shown in FIGURE 11. Specifically, the red lines ripple toward the horizontal midline and the blue lines ripple away from the horizontal midline. If the ripple of the differential left edge is corrected by equally damping each of the vertical yoke coils, the transistor Q30 can be used to rectify the ripple of the differential right edge. Referring to FIGS. 12 and 16, a forward horizontal pulse signal J taken from the parabola generator 190 is used to generate the horizontal sawtooth signal M. Referring to FIGURE 15, the parabola generator 190 is similar to the parabola generator 90, shown in FIGURE 5, except that the parabola generator 190 has two added feedback loops that produce the parabola of horizontal regime A more stable and less susceptible to component tolerances. The peak amplitude control cycle 191 compares the peak amplitude of the parabola A of horizontal regime with a voltage apparatus by means of a low tolerance Zener diode CR190, and adjusts the amplitude of the horizontal-regime sawtooth signal that it is coupled by alternating current to the integrator 92 to maintain a peak amplitude of +5.6 volts for the parabola A of horizontal regime. The control cycle of the length of the previous horizontal pulse 192 compares the average direct current value of a pulse going to negative, which is derived from the horizontal pulse signal J above and has an amplitude equal to the total voltage across the resistors R190 and R191, with the voltage present at the junction of resistors R190 and R191, and adjust a current flowing to the operating amplifier Ul by resistor R90 so as to maintain a ratio between the impulse amplitude of the impulse going to negative and the horizontal scan period that is determined by the ratio of the resistor R190 to the sum of the resistors R190 and R191. In the parabola generator 190 of FIGURE 15, the pulse amplitude of the pulse going to negative is set to be (10/57) (63.5 μsec), or approximately 11 microseconds. Referring to FIGURE 16, the horizontal sawtooth generator 120 is similar to the horizontal sawtooth generator 20, shown in FIGURE 8, except that the horizontal sawtooth generator 120 is restored by the horizontal pulse signal Previous J, which has the effect of advancing the horizontal sawtooth signal M in phase with respect to the horizontal reset pulses. A horizontal right linearity signal K is derived from the horizontal sawtooth signal M and is used to "turn on" the transistor Q30. The resulting negative pulse in the collector of the transistor Q30 is added via the gain determining resistor R106 for the horizontal sine signal C and the horizontal sawtooth signal M. The composite signal is then multiplied by the vertical sawtooth signal F to produce waveform H. The horizontal right linearity signal K is a triangular pulse that follows a few of the last microseconds of the horizontal sawtooth signal M; it has a peak of 0.8 volts and otherwise it is zero. The voltage at the output of the horizontal saw generator 120 is coupled to the base of the transistor Q100 by the ClOO capacitor. Once the horizontal sawtooth signal M reaches a level of approximately 2.7 volts, the transistor Q100 is sufficiently "turned on" so that the emitter of the transistor Q100 tracks the horizontal sawtooth signal M. The output of the transistor Q100 of this mode tracks the last few microseconds of the horizontal sawtooth signal M to produce the right horizontal linearity signal K. The CR100 diode compensates for the drop in voltage at the junction of the emitter-base of transistor Q100. The horizontal right linearity signal K is then coupled to the base of transistor Q30 by resistor R105. Transistor Q30"turns on" when the horizontal right linearity signal K exceeds the threshold voltage of the base to the emitter of Q30. The resulting negative pulse in the collector of the transistor Q30 is coupled by the resistor R106 to the horizontal input terminal 5 of the multiplier 60, where the negative pulse is added to the horizontal sine signal C and to the sawtooth signal M in the sum joint 45 to produce the horizontal composite waveform L. The effect of the pulses of the transistor Q30 is to produce a slight extra flattening of the right peak of the horizontal composite waveform L. When this effect is multiplied by the signal of vertical saw tooth F, and later fed the red and blue amplifiers 74 and 75, shown in FIGURE 9, which amplify them oppositely, the differential ripple of the right bank is corrected. Referring to FIGURE 9, the resistors
R72 and R73 are central range resistors for the trapezoidal distortion controls R75 and R76, respectively. Their values are chosen to roughly correct the trapezoidal distortion when the controls are centered. Resistors R71 and R74 adjust the range and sensitivity of the control. The waveforms I and II of FIGURES 4 and 12 illustrate the trapezoidal distortion correction waveforms in both the horizontal and vertical regime. In each case, the peak-to-peak voltage is 2.4 volts and the direct-current level is 8.37 volts. The waveform I solves the problems caused by the distortions of the differential sinus and the ripple of the left bank, and the waveform II solves the problems caused by the distortions of the differential sinus and the ripple of the right bank. First, the distortions of the differential sinus and the ripple of both edges are corrected; and, secondly, the correction of the distortions of the differential sinus and of the undulation of both edges does not interfere with other convergence corrections. In addition, the differential sinus and ripple distortions of both edges can be corrected very efficiently by modifying existing trapezoidal distortion convergence waveforms.