Abstract:
The present disclosure describes a technique that allows the amplitudes of vertical correction signal components to be adjusted independently. When the amplitude of each of the vertical correction signal components are set, they will not have to be readjusted when the amplitudes of the other vertical correction signal components are set. This greatly simplifies the process of setting the amplitudes of the vertical correction signal components, saving time and increasing the accuracy of the settings.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a raster display system and, more particularly, to a circuit and method that allows the amplitudes of vertical correction signal components to be adjusted independently. 
     2. Related Art 
     Raster display system are used in a variety of application such as televisions and computer displays. FIG. 1A shows a cross-sectional side view of a conventional raster display system  100 . Raster display system  100  includes an electron gun  110 , a deflection system  120 , and a screen  130 . Electron gun  110  generates and accelerates an electron beam  115  toward deflection system  120 . Deflection system  120  deflects electron beam  115  horizontally and/or vertically at screen  130 . Screen  130  includes a phosphor-coated faceplate that glows or phosphoresces when struck by electron beam  115 . 
     Deflection system  120  includes a horizontal deflection generator  122 , a horizontal deflection coil  124 , a vertical deflection generator  126 , and a vertical deflection coil  128 . Horizontal deflection coil  124  and vertical deflection coil  128  are collectively referred to as the yoke. Although not shown, horizontal deflection coil  124  and vertical deflection coil  128  are wound a ninety-degree angle relative to one another. Horizontal deflection generator  122  generates a horizontal deflection current signal I H . When horizontal deflection current signal I H  passes through horizontal deflection coil  124 , a magnetic field is created that deflects electron beam  115  horizontally. The horizontal angle of deflection (not shown) is proportional to the direction and the magnitude of horizontal deflection current signal I H . Similarly, vertical deflection generator  126  generates a vertical deflection current signal I V . When vertical deflection current signal I V  passes through vertical deflection coil  128 , a magnetic field is created that deflects electron beam  115  vertically. The vertical angle of deflection θ is proportional to the direction and the magnitude of vertical deflection current signal I V . 
     FIG. 1B is a front view of raster display system  100 . Deflection system  120  deflects electron beam  115  from a first side of screen  130  to a second side of screen  130  to draw a first line L 1 . Electron beam  115  is then briefly turned off, moved downward, and brought back to the first side of screen  130  by deflection system  120 . Electron beam  115  is then turned on and deflection system  120  deflects electron beam  115  from the first side of screen  120  to the second side of screen  130  to draw a second line L 2 . This process continues very rapidly so that lines L 3  through L N  (where N=1, 2, 3, . . . , N) are drawn thereby creating a raster on screen  130 . 
     To produce an accurate image, the distance d N  (where n=1, 2, 3, . . . , N) between each horizontal line L N  drawn on screen  130  must be equal as shown in FIG.  1 B. The distance between each horizontal line d N  is a function of two factors: the vertical angle of deflection θ and the shape of screen  130 . If the shape of the screen is spherical, a vertical deflection current signal I V  having a sawtooth shaped waveform can be used. A sawtooth shaped waveform can be used since the distance from the point of deflection  129  to the upper, center, and lower portions of the curved screen is constant. If the shape of the screen is non-spherical (e.g., a flat screen), a vertical deflection current signal I V  having a more complex S-shaped waveform must be used. An S-shaped waveform must be used since the distance from the point of deflection  129  to the upper and lower portions of a non-spherical screen is greater than the distance from the point of deflection  129  to the center portions of a non-spherical screen. Note that if the shape of the screen is non-spherical and a vertical deflection current signal I V  having a sawtooth shaped waveform is used, the distance d N  between horizontal lines L N  drawn on screen  130  will not be an equal from one another as shown in FIG.  1 C. This degrades the quality of the image drawn on screen  130  and thus is commercially undesirable. 
     As is well-known in the art, an S-shaped waveform can be produced by combining a sawtooth waveform with higher-order odd multiples of the sawtooth waveform. In particular, S-shaped waveforms be produced by combining the following components: a first-order signal component (i.e., a sawtooth signal), a third-order signal component, and a fifth-order signal component. Other higher-order odd signal components can also be combined with the sawtooth waveform to produce a more complex S-shaped waveform. FIG. 2 shows waveforms for a first-order signal component  210 , a third-order signal component  220 , and a fifth-order signal component  230 , respectively. 
     FIG. 3 shows a conventional horizontal deflection generator circuit  300  that can be used to generate a vertical deflection current signal I V  having an S-shaped waveform. Horizontal deflection generator circuit  300  includes a first-order signal generator  302 , a first-order amplitude signal generator  304 , a multiplier  306 , a third-order signal generator  308 , a third-order amplitude signal generator  310 , a multiplier  312 , a fifth-order signal generator  314 , a fifth-order amplitude signal generator  316 , a multiplier  318 , and a signal combiner  320 . 
     In operation, first-order signal generator  302  generates a first-order signal S 1  and first-order amplitude signal generator  304  generates a first-order amplitude signal A 1 . Multiplier  306  multiplies first-order signal S 1  with first-order amplitude signal A 1  to generate a first-order vertical correction signal component A 1 S 1 . Third-order signal generator  308  generates a third-order signal S 3  and third-order amplitude signal generator  310  generates a third-order amplitude signal A 3 . Multiplier  312  multiplies third-order signal S 3  with third-order amplitude signal A 3  to generate a third-order vertical correction signal component A 3 S 3 . Fifth-order signal generator  314  generates a fifth-order signal S 5  and fifth-order amplitude signal generator  316  generates a fifth-order amplitude signal A 5 . Multiplier  318  multiplies fifth-order signal S 5  with fifth-order amplitude signal A 5  to generate a fifth-order vertical correction signal component A 5 S 5 . 
     Signal combiner  320  combines the vertical correction signal components A 1 S 1 , A 3 S 3 , and A 5 S 5  to produce vertical correction signal A V S V . Vertical correction signal A V S V  can be equivalent to vertical deflection current signal I V , or vertical correction signal A V S V  can be further processed (e.g., amplified) prior to becoming vertical deflection current signal I V . 
     During the manufacturing process of a raster display system, a user must adjust amplitude signals A 1 , A 3 , and A 5  so that lines L 1  through line L N  (where N=1, 2, 3, . . . , N) are properly drawn on screen  130 . First, the user adjusts amplitude signal A 1  so that line L 1  is drawn at the proper position at the top of screen  130 . This is referred to as setting the vertical size (i.e., the maximum angle of vertical deflection θ MAX ). Next, the user adjusts amplitude signals A 3  and A 5  so that the distances d N  between each horizontal line L N  drawn on screen  130  are equal as shown in FIG.  1 B. Unfortunately, when the user adjusts amplitude signals A 3  and A 5 , the vertical size changes. As a result, the user must readjust amplitude signal A 1  to reposition line L 1  at the proper position at the top of screen  130 . However, the readjustment of amplitude signal A 1  causes the distances d N  between each horizontal line L N  drawn on screen  130  to become unequal again. Consequently, the user must readjust amplitude signals A 3  and A 5  so that the distances d N  between each horizontal line L N  drawn on screen  130  are equal. Unfortunately, the adjustment of amplitude signals A 3  and A 5  again causes the vertical size to change. As a result, the user must readjust amplitude signal A 1  to reposition line L 1  at the proper position at the top of screen  130 . This time-consuming, inexact, trial-and-error process must be performed numerous times before amplitude signals A 1 , A 3 , and A 5  are properly set. 
     Accordingly, what is needed is a circuit and method that allows the amplitudes of vertical correction signal components to be adjusted independently. 
     SUMMARY OF THE INVENTION 
     The present invention provides a technique that allows the amplitudes of vertical correction signal components to be adjusted independently. When the amplitude of each of the vertical correction signal components are set, they will not have to be readjusted when the amplitudes of the other vertical correction signal components are set. This greatly simplifies the process of setting the amplitudes of the vertical correction signal components, saving time and increasing the accuracy of the settings. 
     In one embodiment of the present invention, a circuit that allows the amplitudes of vertical correction signal components to be adjusted independently is provided. The circuit includes a first signal combiner having a first input coupled to 
     receive a first-order amplitude signal and a second input coupled to receive a third-order amplitude signal, a first multiplier having a first input coupled to receive a first-order signal and a second input coupled to receive an output signal of the first signal combiner, a second multiplier having a first input coupled to receive a third-order signal and a second input coupled to receive the third-order amplitude signal, and a second signal combiner having a first input coupled to receive an output signal of the first multiplier and a second input coupled to receive an output signal of the second multiplier. 
     In another embodiment of the present invention, a method that allows the amplitudes of vertical correction signal components to be adjusted independently is provided. The method includes combining a first-order amplitude signal with a third-order amplitude signal to generate a modified first-order amplitude signal, multiplying a first-order signal with the modified first-order amplitude signal to generate a first-order vertical correction signal component, multiplying a third-order signal with the third-order amplitude signal to generate a third-order vertical correction signal component, and combining the first-order vertical correction signal component with the third-order vertical correction signal component. 
     In another embodiment of the present invention, a method for generating a vertical deflection current signal including a first vertical correction signal component and a second vertical correction component is provided. The method includes setting an amplitude of the first vertical correction signal component, and setting an amplitude of the second vertical correction signal component, wherein the amplitude of the first vertical correction signal component will not have to be reset after the amplitude of the second vertical correction signal component has been set. 
     Other embodiments, aspects, and advantages of the present invention will become apparent from the following descriptions and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and for further embodiments, aspects, and advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which: 
     FIG. 1A shows a cross-sectional side view of a conventional raster display system. 
     FIG. 1B shows a front view of a raster display system. 
     FIG. 1C shows a front view of a raster display system. 
     FIG. 2 shows waveforms for a first-order signal, a third-order signal, and a fifth-order signal. 
     FIG. 3 shows a conventional vertical deflection generator circuit. 
     FIG. 4 shows a vertical deflection generator circuit, according to some embodiments of the present invention. 
     FIG. 5 shows a flowchart of an exemplary method of operation for the vertical deflection generator circuit of FIG. 4, according to some embodiments of the present invention. 
     FIG. 6 shows a vertical deflection generator circuit that allows for independent S corrections to the top half and the bottom half of a raster display, according to some embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The preferred embodiments of the present invention and their advantages are best understood by referring to FIGS. 4 through 6 of the drawings. Like reference numerals are used for like and corresponding parts of the various drawings. 
     Circuit that Allows the Amplitudes of Vertical Correction Signal Components to be Adjusted Independently 
     FIG. 4 shows a deflection generator circuit  400 , according to some embodiments of the present invention. Deflection generator circuit  400  allows the amplitudes of vertical correction signal components to be adjusted independently. Deflection generator circuit  400  can be implemented in hardware, firmware/microcode; software, or any combination thereof. Additionally, deflection generator circuit  400  can be implemented on a single integrated circuit device or integrated with other integrated circuits on a single integrated circuit device. 
     Deflection generator circuit  400  includes a first-order signal generator  402 , a first-order amplitude signal generator  404 , a multiplier  406 , a third-order signal generator  408 , a third-order amplitude signal generator  410 , a multiplier  412 , a fifth-order signal generator  414 , a fifth-order amplitude signal generator  416 , a multiplier  418 , a signal combiner  420 , and a signal combiner  422 . 
     First-order signal generator  402  generates a first-order signal S 1  and signal combiner  422  outputs a modified first-order amplitude signal A 1 ′. Multiplier  406  multiplies first-order signal S 1  with modified first-order amplitude signal A 1 ′ to generate a modified first-order vertical correction signal component A 1 ′S 1 . Third-order signal generator  408  generates a third-order signal S 3  and third-order amplitude signal generator  410  generates a third-order amplitude signal A 3 . Multiplier  412  multiplies third-order signal S 3  with third-order amplitude signal A 3  to generate a third-order vertical correction signal component A 3 S 3 . Fifth-order signal generator  414  generates a fifth-order signal S 5  and fifth-order amplitude signal generator  416  generates a fifth-order amplitude signal A 5 . Multiplier  418  multiplies fifth-order signal S 5  with fifth-order amplitude signal A 5  to generate a fifth-order vertical correction signal component A 5 S 5 . For clarity, a third-order signal generator  408  and a fifth-order signal generator  414  are shown. However, it should be recognized that an independent third-order signal generator  408  and a fifth-order signal generator  414  are not needed since first-order signal S 1  can be provided to multipliers that generate third-order signal S 3  and fifth-order signal S 5 . In some embodiments, first-order amplitude signal generator  404 , third-order amplitude signal generator  410 , and fifth-order amplitude signal generator  416  are N-bit registers (where N is a positive integer) that can be programmed by a user. 
     Signal combiner  420  combines the vertical correction signal components A 1 ′S 1 , A 3 S 3 , and A 5 S 5  to produce vertical correction signal A V S V . More specifically, signal combiner  420  subtracts vertical correction signal components A 3 S 3  and A 5 S 5  from vertical correction signal component A 1 ′S′ to produce vertical correction signal A V S V . Vertical correction signal A V S V  can be equivalent to vertical deflection current signal I V , or vertical correction signal A V S V  can be further processed (e.g., amplified) prior to becoming vertical deflection current signal I V . 
     Signal combiner  422  combines first-order amplitude signal A 1 , which is generated by first-order amplitude signal generator  404 , with third-order amplitude signal A 3 , and fifth-order amplitude signal A 5  to generate modified first-order amplitude signal A 1 ′. More specifically, signal combiner  422  adds third-order amplitude signal A 3  and fifth-order amplitude signal A 5  to first-order amplitude signal A 1  to produce modified first-order amplitude signal A 1 ′. As described above, modified first-order amplitude signal A 1 ′ is then multiplied with first-order signal S 1  to generate modified first-order vertical correction signal component A 1 ′S 1 . 
     The reason that third-order amplitude signal A 3  and fifth-order amplitude signal A 5  are added to first-order amplitude signal A 1  in signal combiner  422  is because third-order amplitude signal A 3  and fifth-order amplitude signal A 5  are subtracted from modified first-order amplitude signal A 1 ′ in signal combiner  420 . When third-order amplitude signal A 3  and fifth-order amplitude signal A 5  are subtracted from modified first-order amplitude signal A 1 ′ in signal combiner  420 , the amplitude A V  of vertical correction signal A V S V  decreases. However, as explained above, the amplitude A V  of vertical correction signal A V S V  should remain constant so that the vertical size remains constant. By adding third-order amplitude signal A 3  and fifth-order amplitude signal A 5  to first-order amplitude signal A 1  in signal combiner  422 , the amplitude of modified first-order amplitude signal A 1 ′ is increased and thus compensates for the decrease in the amplitude A V  of vertical correction signal A V S V . Consequently, first-order amplitude signal A 1  will not have to be readjusted after third-order amplitude signal A 3  and fifth-order amplitude signals A 5  have been set. As those of skill in the art will recognize, this greatly simplifies the process setting amplitude signals A 1 , A 3 , and A 5 . 
     It should be recognized that deflection generator circuit  400  can also include other circuitry. For example, deflection generator circuit  400  may include a second-order signal generator, a second-order amplitude signal generator, and a multiplier for multiplying the second-order signal with the second-order amplitude signal to produce a second-order vertical correction signal component. The second-order vertical correction signal component can then be combined with the other vertical correction signal components in signal combiner  420 . The second-order vertical correction signal provides what is commonly referred to as C correction. The second-order vertical correction signal or C correction signal is used to compensate for top/bottom asymmetry in the vertical deflection coil. 
     Method that Allows the Amplitudes of Vertical Correction Signal Components to be Adjusted Independently 
     FIG. 5 is a flowchart of an exemplary method  500  of operation for vertical deflection generator circuit  400 . Method  500  describes how the amplitudes of vertical correction signal components can be adjusted independently. Method  500  can be performed by a human operator, by automated devices, or by any combination thereof, and method  500  can be performed using hardware, firmware/microcode, software, or any combination thereof. Additionally, method  500  can be performed on a single integrated circuit device. 
     In step  502 , first-order amplitude signal A 1 , third-order amplitude signal A 3 , and fifth-order amplitude signal A 5  are set to predetermined values. The predetermined values can be optimal values that have been determined from testing. This step can be accomplished by programming first-order amplitude signal generator  404 , third-order amplitude signal generator  410 , and fifth-order amplitude signal generator  416  to output predetermined values. 
     In step  504 , the amplitude of first-order amplitude signal A 1  is set. More specifically, the amplitude of first-order amplitude signal A 1  is set such that vertical correction signal A V S V  causes the electron beam to be positioned at a desired position at the top of a screen. This is generally referred to as setting the vertical size. 
     In step  506 , the amplitude of third-order amplitude signal A 3  is set. Third-order amplitude signal A 3  introduces third-order non-linearities into vertical correction signal A V S V . The third-order non-linearities make vertical correction signal A V S V  non-linear or S-shaped and thus correct for the non-spherical shape of the screen. 
     In step  508 , third-order amplitude signal A 3  is added to first-order amplitude signal A 1 . In this step, third-order amplitude signal A 3  is fed into signal combiner  422  where it is added to first-order amplitude signal A 1  to generate modified first-order amplitude signal A 1 ′. The reason third-order amplitude signal A 3  is added to first-order amplitude signal A 1  is because third-order vertical correction signal component A 3 S 3  now exists and is subtracted from modified first-order vertical correction signal component A 1 ′S 1  in signal combiner  420 . When third-order vertical correction signal component A 3 S 3  is subtracted from modified first-order vertical correction signal component A 1 ′S 1 , the amplitude A V  of vertical correction signal A V S V  decreases. However, as explained above, the amplitude A V  of vertical correction signal A V S V  should remain constant so that the vertical size remains constant. By adding third-order amplitude signal A 3  to first-order amplitude signal A 1  in signal combiner  422 , the amplitude of modified first-order amplitude signal A 1 ′ is increased and thus compensates for the decrease in the amplitude A V  of vertical correction signal A V S V . Consequently, first-order amplitude signal A 1  will not have to be readjusted after third-order amplitude signal A 3  has been set. As those of skill in the art will recognize, this greatly simplifies the process setting amplitude signals A 1  and A 3 . 
     In step  510 , the amplitude of fifth-order amplitude signal A 5  is set. Fifth-order amplitude signal A 5  introduces fifth-order non-linearities into vertical correction signal A V S V . The fifth-order non-linearities make vertical correction signal A V S V  non-linear or S-shaped and thus correct for the flatness of the screen. Fifth-order non-linearities are typically introduced when the third-order non-linearities (introduced in step  506 ) do not adequately correct for the non-spherical shape of a screen. It should be recognized that higher-order amplitude signals can also be introduced into vertical correction signal A V S V . 
     In step  512 , fifth-order amplitude signal A 5  is added to first-order amplitude signal A 1 . In this step, fifth-order amplitude signal A 5  is fed into signal combiner  422  where it is added to first-order amplitude signal A 1  and third-order amplitude signal A 3  to generate modified first-order amplitude signal A 1 ′. The reason fifth-order amplitude signal A 5  is added to first-order amplitude signal A 1  and third-order amplitude signal A 3  is because fifth-order vertical correction signal component A 5 S 5  now exists and is subtracted from modified first-order vertical correction signal component A 1 ′S 1 . When fifth-order vertical correction signal component A 5 S 5  is subtracted from modified first-order vertical correction signal component A 1 ′S 1  the amplitude A V  of vertical correction signal A V S V  decreases. However, as explained above, the amplitude A V  of vertical correction signal A V S V  should remain constant so that the vertical size remains constant. By adding fifth-order amplitude signal A 5  to first-order amplitude signal A 1  and third-order amplitude signal A 3  in signal combiner  422 , the amplitude of modified first-order amplitude signal A 1 ′ is increased and thus compensates for the decrease in the amplitude A V  of vertical correction signal A V S V . Consequently, first-order amplitude signal A 1  will not have to be readjusted after third-order amplitude signal A 3  has been set. As those of skill in the art will recognize, this greatly simplifies the process setting amplitude signals A 1 , A 3 , and A 5 . 
     When compared with conventional techniques, method  500  is advantageous since a user will not have to make successive adjustments to amplitude signals A 1 , A 3 , and A 5 . Consequently, method  500  greatly simplifies the process setting amplitude signals A 1 , A 3 , and A 5 . 
     Circuit that Allows the Amplitudes of Vertical Correction Signal Components to be Adjusted Independently and that Allows for Independent Top and Bottom S Corrections 
     FIG. 6 shows a deflection generator circuit  600 , according to some embodiments of the present invention. Deflection generator circuit  600  is similar to deflection generator circuit  400 . However, in addition to allowing the amplitudes of vertical correction signal components to be adjusted independently, deflection generator circuit  600  also allows for independent S corrections to the top half and the bottom half of a raster display using independent top-bottom correction circuit  670 . Deflection generator circuit  600  can be implemented in hardware, firmware/microcode, software, or any combination thereof. Additionally, deflection generator circuit  600  can be implemented on a single integrated circuit device or integrated with other integrated circuits on a single integrated circuit device. 
     Deflection generator circuit  600  includes a first-order signal generator  602 , a first-order amplitude signal generator  604 , a multiplier  606 , a third-order signal generator  608 , a third-order top amplitude signal generator  610 T, a third-order bottom amplitude signal generator  610 B, a multiplexer  611 , a multiplier  612 , a fifth-order signal generator  614 , a fifth-order top amplitude signal generator  616 T, a fifth-order bottom amplitude signal generator  616 B, a multiplexer  617 , a multiplier  618 , a signal combiner  620 , a signal combiner  622 , a control signal generator  640 , signal combiners  642 ,  644 ,  646 , and  648 , divide-by-two elements  650  and  652 , a DC signal generator  658 , and signal combiners  660 , and  662 . 
     Independent top-bottom correction circuit  670  includes third-order top amplitude signal generator  610 T, third-order bottom amplitude signal generator  610 B, multiplexer  611 , fifth-order top amplitude signal generator  616 T, fifth-order bottom amplitude signal generator  616 B, multiplexer  617 , signal combiners  642 ,  644 ,  646 , and  648 , and divide-by-two elements  650  and  652 . 
     First-order signal generator  602  generates a first-order signal S 1  and signal combiner  622  outputs a modified first-order amplitude signal A 1 ′. Multiplier  606  multiplies first-order signal S 1  with modified first-order amplitude signal A 1 ′ to generate a modified first-order vertical correction signal component A 1 ′S 1 . 
     Third-order signal generator  608  generates a third-order signal S 3 . Third-order top amplitude signal generator  610 T generates a third-order top amplitude signal A 3T , and third-order bottom amplitude signal generator  610 B generates a third-order bottom amplitude signal A 3B . Multiplexer  611  outputs a third-order amplitude signal A 3 , which is either third-order top amplitude signal A 3T  or third-order bottom amplitude signal A 3B  depending on the value of control signal C. Multiplier  612  multiplies third-order signal S 3  with third-order amplitude signal A 3  to generate a third-order vertical correction signal component A 3 S 3 . 
     Fifth-order signal generator  614  generates a fifth-order signal S 5 . Fifth-order top amplitude signal generator  616 T generates a fifth-order top amplitude signal A 5T , and fifth-order bottom amplitude signal generator  616 B generates a fifth-order bottom amplitude signal A 5B . Multiplexer  617  outputs a fifth-order amplitude signal A 5 , which is either fifth-order top amplitude signal A 5T  or fifth-order bottom amplitude signal A 5B  depending on the value of control signal C. Multiplier  618  multiplies fifth-order signal S 5  with fifth-order amplitude signal A 5  to generate a fifth-order vertical correction signal component A 5 S 5 . 
     For clarity, a third-order signal generator  608  and a fifth-order signal generator  614  are shown. However, it should be recognized that an independent third-order signal generator  608  and a fifth-order signal generator  614  are not needed since first-order signal S 1  can be provided to multipliers that generate third-order signal S 3  and fifth-order signal S 5 . In some embodiments, first-order amplitude signal generator  604 , third-order top amplitude signal generator  610 T, third-order bottom amplitude signal generator  610 B, fifth-order top amplitude signal generator  616 T, and fifth-order bottom amplitude signal generator  616 B are N-bit registers (where N is a positive integer) that can be programmed by a user. 
     Control signal generator  640  generates control signal C. More specifically, control signal generator  640  receives first-order signal S 1  (i.e., a sawtooth signal) and determines whether the current value of first-order signal S 1  is positive or negative. When the current value of first-order signal S 1  is positive, the top half of the raster display is being drawn and control signal generator  640  outputs a logic low signal for control signal C. This causes third-order top amplitude signal A 3T  to be output from multiplexer  611  as third-order amplitude signal A 3 , and causes fifth-order top amplitude signal A 5T  to be output from multiplexer  617  as fifth-order amplitude signal A 5 . When the current value of first-order signal S 1  is negative, the bottom half of the raster display is being drawn and control signal generator  640  output a logic high signal for control signal C. This causes third-order bottom amplitude signal A 3B  to be output from multiplexer  611  as third-order amplitude signal A 3 , and causes fifth-order bottom amplitude signal A 5B  to be output from multiplexer  617  as fifth-order amplitude signal A 5 . Accordingly, the amplitudes of third-order vertical correction signal component A 3 S 3  and fifth-order vertical correction signal component A 5 S 5  can be independently controlled for the top and bottom halves of the raster display. 
     Signal combiner  620  combines the vertical correction signal components A 1 ′S 1 , A 3 S 3 , and A 5 S 5  to produce vertical correction signal A V S V . More specifically, signal combiner  620  subtracts vertical correction signal components A 3 S 3  and A 5 S 5  from vertical correction signal component A 1 ′S to produce vertical correction signal A V S V . 
     Signal combiner  622  combines first-order amplitude signal A 1  generated by first-order amplitude signal generator  604  with signal A 3,5  to generate modified first-order amplitude signal A 1 ′. More specifically, signal combiner  622  adds signal A 3,5  to first-order amplitude signal A 1  to produce modified first-order amplitude signal A 1 ′. As described above, modified first-order amplitude signal A 1 ′ is then multiplied with first-order signal S 1  to generate modified first-order vertical correction signal component A 1 ′S 1 . Signal A 3,5  is generated by independent top and bottom correction circuit  670  and can be described by the following equation: A 3,5 =(A 3T +A 5T )/2+(A 3B +A 5B )/2. 
     Signal combiner  660  combines signal A′ 3,5  and signal A DC  to generate a vertical position signal A VP . Signal A DC  is generated by DC signal generator  658  and is used to control the vertical position of the electron beam. Signal A′ 3,5  is generated by independent top and bottom correction circuit  670  and can be described by the following equation: A′ 3,5 =(A 3T +A 5T )/2−(A 3B-A   5B )/2. 
     Signal combiner  662  combines vertical correction signal A V S V  and vertical position signal A VP  to generate vertical correction signal A′ V S V ′. Vertical correction signal A′ V S V ′ can be equivalent to vertical deflection current signal I V , or vertical correction signal A′ V S V ′ can be further processed (e.g., amplified) prior to becoming vertical deflection current signal I V . 
     It should be recognized that deflection generator circuit  600  can also include other circuitry. For example, deflection generator circuit  600  may include a second-order signal generator, a second-order amplitude signal generator, and a multiplier for multiplying the second-order signal with the second-order amplitude signal to produce a second-order vertical correction signal component. The second-order vertical correction signal component can then be combined with the other vertical correction signal components in signal combiner  620 . The second-order vertical correction signal provides what is commonly referred to as C correction. The second-order vertical correction signal or C correction signal is used to compensate for asymmetry in the vertical deflection coil. 
     While particular embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspect and, therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the true spirit of this invention.