GB2030030A - Cathode ray tube apparatus - Google Patents

Abstract

In a convergence circuit for a shadow-mask colour cathode ray tube the square of a horizontal deflecting signal ex and that of a vertical deflecting signal ey are multiplied by respective coefficients. An ellipse centreing the display surface is defined by aex<2> + bey<2> = ec where a,b,ec designate constants. The degree of convergence follows aex<2> + bey<2> = e1 inside of the ellipse while following aex<2> + bey<2> + K(aex<2> + bey<2>- ec) outside of the ellipse where K is a variable constant. By changing the K for each of the quadrants, the degree of convergence may be different between them.

Description

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SPECIFICATION

Cathode ray tube apparatus

5 This invention relates to a shadow-mask colour cathode ray tube apparatus, and more particularly to means for improving the degree of convergence of electron beams generated in a shadow-mask colour cathode ray tube while following random deflections 10 thereof.

Heretofore, the desired convergence magnetic field has been established by integrating the horizontal or vertical deflecting current with respect to time to form a parabolic current and passing the 15 parabolic current through the horizontal or vertical convergence coil respectively. As this convergence magnetic field results from the time integral of the deflection signals, the history of the deflection effects the degree of convergence of electron beams. 20 Therefore the measure as above described has been applicable to limited scanning systems. For example, it has been only applicable to the raster scanning in which the convergence is uniformly corrected overthe entire area of the raster. Further, the meas-25 ure has been disadvantageous in that it is not applicable to the display of images according to random deflections and also it has been very difficult to correct the degree of convergence overthe entire area of images with a high accuracy.

30 Accordingly it is an object of the present invention to provide a shadow-mask colour cathode ray tube apparatus including a new and improved convergence circuit simple in circuit configuration and applicable to any of scanning systems and therefore 35 to the random scanning.

It is another object of the present invention to provide a shadow-mask colour cathode ray tube apparatus including a new and improved convergence circuit for correcting controllably the 40 degree of convergence of electron beams at least on the radially outer portion of a display surface of a shadow-mask colour cathode ray tube involved so that the correction of the convergence is separately adjustable in four quadrants of the display surface 45 referring to a Cartesian orthogonal coordinate system.

According to a first aspect of the present invention there is provided a cathode ray tube apparatus comprising a shadow-mask colour cathode ray tube 50 including a plurality of electron guns, and means for deflecting electron beams in directions of an X and a Y axis and constructed so as to display information in colour on a display surface, characterized in that there is provided a convergence correcting circuit - 55 including a first and a second square-law circuit for making an X axis deflecting signal ex and a Y axis deflecting signal ey signals with square-law waveforms ae\ and be% multiplied by predetermined coefficients a and b respectively, an adder cir-60 cuit for adding those output signals to each other, a reference signal generator circuit for generating a reference signal ec, a subtractor circuit for subtracting said reference signal e0 from the output signal e0 from said adder circuit, a polarity discriminator cir-65 cuit for discriminating the polarity of an output signal e2 from said circuit and delivering a signal e2 when e2 S 0, a coefficient circuit for multiplying the output signal e2 from said circuit by a predetermined coefficient/<", a second adder circuit for adding an output signal Ke2 from said circuit to the outpute, from said first adder circuit, and an output circuit driven with an output signal e3 from said second adder circuit to pass a convergence current corresponding to said output signal e3 through convergence means.

According to a second aspect of the present invention there is provided a cathode ray tube apparatus comprising a shadow-mask colour cathode ray tube including a plurality of electron guns, and means for deflecting electron beams within said cathode ray tube in directions of an X and a Y axis and constructed so as to display information in colour on a display surface, characterized in that there is provided a convergence correcting circuit including a first and a second square-law circuit for making an X axis deflecting signal ex and a Y axis deflecting signal ey signals with square-law waveforms ae\ and be\ multiplied by predetermined coefficientsa andb respectively, a first adder circuit for adding those output signals to each other, a reference signal generator circuit for generating a reference signal ec, a subtractor circuit for subtracting said reference signal ec from an output signal e, from said first adder circuit, a polarity discriminator circuit for discriminating the polarity of an output signal e2 from said circuit and delivering an output signal e2 when e2 ^ 0, a quadrant discriminator circuit for discriminating the polarity of said deflecting signalse* and ey and determining which quadrant of the display surface of said cathode ray tube the electron beams scanning said display surface belong to, by means of combinations of the positive and negative of said ex and ey and delivering a signal representing the quadrant being scanned with said electron beams, a coefficient circuit responsive to an output signal from said circuit to multiply said signal e2 by coefficients Ka to AW for respective quadrants, a second adder circuit for adding an output signal Ke2 from said circuitto the said signal e1( and an output circuit driven with an output signal e3 from said second adder circuitto pass a convergence current corresponding to said signal e3 through convergence means.

According to a third aspect of the present invention there is provided a cathode ray tube apparatus comprising a shadow-mask colour cathode ray tube including a plurality of electron guns, and means for deflecting electron beams within said cathode ray tube in directions of an X and Y axis and constructed so as to display information in colour on a display surface, characterized in that there is provided a convergence correcting circuit including a first and a second polarity discriminator circuits for discriminating the polarity of an X axis deflecting signal ex and a Y axis deflecting signal ey to deliver signals ex(+), ex(-), ey(+) and ey(-), a first to a fourth square-law circuit for delivering signals with square-law waveforms ae/(+), be/(-), cey2(+) and de/(~) which are respective output signals from said circuits multiplied by predetermined coefficients a, b,c and d

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respectively, a first adder circuit for adding said output signals to one another, a reference signal generator circuit for generating a reference signal ec, a subtracter circuit for subtracting said reference 5 signal ec from an output signal e1 from said first adder circuit, a polarity discriminator circuit for discriminating the polarity of an output signal e2 from said circuit and delivering a signal e2' when e2S 0, a quadrant discriminator circuit for discriminating the 10 polarity of said deflecting signals ex and ey and determining which quadrant of the display surface of said cathode ray tube the electron beams scanning said display surface belong to, by means of combinations of the positive and negative of said ex andey 15 and delivering a signal representing the quadrant being scanned with said electron beams, a coefficient circuit responsive to an output signal from said circuitto multiply said signaled by coefficients Ka, Kb, Kc and/fd for respective quadrants, a second 20 adder circuit for adding an output signal Kez' from said circuitto said signal e,, and an output circuit driven with the output signal e3 from said second adder circuitto pass a convergence current corresponding to said signal e0 through convergence 25 means.

The present invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which 30 Figure 1 is a block diagram of a general circuit configuration of a shadow-mask colour cathode ray tube apparatus to which the present invention is applicable;

Figure 2 is a block diagram of a convergence cir-35 cuit suitable for use with the arrangement shown in Figure 1;

Figure 3 is a circuit diagram of the details of the arrangement shown in Figure 2;

Figure 4 is a circuit diagram of a modification of 40 the square-law circuit shown in Figure 3;

Figure 5 is a block diagram of convergence circuit according to the present invention suitable for use with the arrangement shown in Figure 1;

Figure 6 is a circuit diagram of the details of the 45 polarity discriminator and coefficient circuits shown in Figure 5;

Figure7 isa block diagram of a modification of the present invention;

Figure 8 is a circuit diagram of the details of the 50 coefficient circuit shown in Figure 7; and

Figure 9 is a block diagram of another modification of the present invention.

Throughout the Figures like reference numerals designate the identical or corresponding compo-55 nents.

In a shadow-mask colour cathode ray tube apparatus shown in Figure 1, a shadow-mask colour cathode ray tube 1 includes a pair of horizontal and vertical deflecting coils schematically designated by 60 block 2 and a convergence element also schematically designated by block 3. The horizontal and vertical deflecting coils 2 are connected to a deflecting current generator circuit 4 and the convergence element 3 is connected to a convergence circuit 5 65 through electric leads labelled by R, G and B. Both circuits 4 and 5 are connected to a pair of inputs 6 and 7. An X and a Y axis deflecting voltage ex and ey are applied to the inputs 6 and 7 and the deflecting current generator circuit 4 supplies a horizontal and a vertical deflecting current/* and/y to the horizontal and vertical deflecting coils 2 which, in turn, deflects a plurality of electron beams emitted from respective electron guns (not shown) on a display surface of the tube 1 and the horizontal and vertical directions or along an X axis and a Y axis of a Cartesian orthogonal coordinate system having the origin lying at the centre of the display surface. This results in information being displayed in colour on the display surface of the colour cathode ray tube 1.

The convergence circuit 5 has been previously designed and constructed so that the X and Y axis or horizontal and vertical deflecting voltages ex and ey are integrated with respect to time to form signal waveforms proportional to the time integrals thereof and then a convergence current is generated are on the basis of those signal waveform after the waveforms have been properly modified in accordance with corrections required for the primary colours or the red R, green G and blue B. Under these circumstances, each of the deflecting voltages ex or ey forms saw-toothed waves each having a predetermined fixed time constant as long as the colour cathode ray tube 10 is scanned in accordance with the raster scanning system having a predetermined constant period. As a result, the time-integrals of the deflecting voltages ex and ey form parabolic waveforms repeatedly developed with predetermined constant periods respectively. This results in the generation of a convergence current proportional to ex2 or ey2 respectively. In other words, the convergence current is proportional to the square of a deflection distance and meets the requirements for effecting a first order approximation of the convergence correction.

However, the convergence circuit as above described has been only used with the raster scanning having the constant period and also it is apparent that the convergence circuit 5 is difficult to correct the degree of convergence overthe entire area of the display surface of colour cathode ray tubes with a high accuracy.

Figure 2 shows a convergence circuit substituted for the circuit 5 shown in Figure 1. The arrangement illustrated comprises a pair of first and second polarity discriminators 10 and 11, a first and a second square-law circuit 12 and 13 connected to the first polarity discriminator 10, a third and a fourth square-law circuits 14 and 15 connected to the second polarity discriminator 11, and an adder circuit 16 is connected to the four square-law circuits 12,13,14 and 15. The adder circuit 16 is connected to an output circuit 17. Subsequently, the adder circuit 16 is connected to a convergence coil 18 forming one part of the convergence element 3.

In operation, the polarity discriminator 10 receives the X axis or horizontal deflecting signal voltage ex to discriminate the polarity thereof so that a positive polarity signal voltage ex(+) is applied to the first square-law circuit 12 while a negative polarity signal voltage ex(-) is applied to the second square-law cir-

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cuit 13. The polarity discriminator 11 is similarly operated to apply a positive and a negative polarity signal voltage ey(+) andey(-) of the Y axis or vertical deflecting signal ey to the third and fourth square-5 law circuits 14 and 15 respectively.

More specifically, the deflecting signal voltages ex andey change from one to the other of the positive and negative polarities, dependent upon points of deflected electron beams on a display surface of a 10 colour cathode ray tube involved, while the X polarity discriminator 10 delivers to the square-law circuits 12 and 13, outputs ex(+) = ex and ex(-) =0 respectively for ex > 0 and outputs ex(+) = 0 and exH = ex respectively for ex < 0. Similarly, the polar-15 ity discriminator 19 delivers to the square-law circuits 14 and 15 outputs ey(+) = ey and ey(-) = 0 respectively for ey > 0 and outputs ey(+) = 0 and ey(—) = ey respectively for ey < 0.

Each of the square-law circuits 12,13,14and 15 is 20 operative to square approximately an input voltage applied thereto and multiply the square of the input voltage by a factor or a coefficient to produce an output voltage approximately proportional to the square of the input voltage. The square-law circuits 25 12,13,14 and 15 have their own coefficients a, b, c and d independently adjustable.

The adder circuit 16 receives output voltages from the square-law circuit 12,13,14 and 15 and delivers to the output circuit 17 an output voltage e0 expre-30 ssed by e0 = aex2 + bex2 + cey2 + dey2.

Dependent upon the polarity of the deflecting signal voltages ex and ey, the output voltage e0 may have the following four values:

for ex > 0 and ey > 0 for ex < 0 and ey > 0 forex < 0 and ev < 0

35 a) e0 = aex2 + cey2

b) e0 = bex2 + cey2

c) e0 = bex2 + dey2 and d) e0 = aex2 + dey2 for ex > 0 and ey < 0. 40 Four value of the output voltage e0 defined by different combinations of the polarity of the deflecting signal voltage ex with that of the voltage ey are developed in a first, a second, a third and a fourth quadrant of the display surface of colour cathode ray

45 tubes with reference to a Cartesian orthogonal coordinate system including an X and a Y axis running horizontally and vertically on the display surface and the origin lying at the centre thereof. The term "quadrant" used herein and in the appended claims 50 refers to that Cartesian orthogonal coordinate system. By adjusting the respective coefficients, b, c and d provided by the square-law circuits 12,13,14 and 15, convergence voltages can be generated with the characteristics different from one to another of 55 the quadrants.

The arrangement of Figure 2 may be of a circuit configuration shown in Figure 3. As shown in Figure 3, three semiconductor diodes 20 as series components and three variable resistors 21 as parallel 60 components are interconnected into a ladder network to form the square-law circuit 12 and similar semiconductor diodes 22 and variable resistors 23 are interconnected into a ladder network to form the square-law circuit 13. Similarly, three semiconductor 65 diodes 24 and three variable resistors 25 form the square-law circuit 14 in the form of a ladder network like three semiconductor diodes 26 and three variable resistors 27 forming the square-law circuit 16.

Further the diodes 20 and 24 are so poled as to 70 conduct with the positive polarity of the deflecting signal voltages ex and ey respectively while the diodes 22 and 26 are so poled as to conduct with the negative polarity of the voltages ex andey respectively. Therefore, those diodes perform the function 75 of discriminating the polarity of each deflecting signal voltage. Asa result, the arrangement of the diodes and variable resistors serves also as the polarity discriminators 10 and 11.

Also it will readily be understood that the variable 80 resistors are effective for adjusting the coefficients of the associated square-law circuits.

As shown in Figure 3, the variable resistors 21 and 25 are also connected to a base electrode of an NPN transistor 28 and the variable resistors 23 and 27 are 85 connected to a base electrode of a PNP transistor 29. The transistors 28 and 29 includes emitter electrodes interconnected through a series combination of resistors 30 and 31 with the junction of both resistors connected to ground. The transistor 28 also includes 90 a collector electrode connected to one half portion of the convergence coil 18 subsequently connected to a positive side of a DC source 32 having a negative side connected to ground. Similarly, the transistor 29 includes a collector electrode connected to a nega-95 tivesideof another DC source 33 having a grounded positive side through the other held portion of the convergence coil 18. Both half portions of the coil 18 are inductively coupled to a single magnetic core and induce instantaneous voltages thereacross as 100 denoted by the dot convention in Figure 3.

From the foregoing it is seen that the transistors 28 and 29 form a combination of the adder circuit 16 and the output circuit 17 with the resistors 30 and 31 and delivers to the convergence coil 18 a con-105 vergence current proportional to the output voltage e0 as a result of the addition effected by the adder circuit 16.

Figure 4 shows a modification of the square-law circuits 20-21 and 22-23 shown in Figure 3. Each of 110 the square-law circuits 20-21 or 22-23 is in a ladder network configuration formed of four resistors as series components and three series combinations of diode 20 or 22 and variable resistor 21 or 23. The last series resistor is connected to ground and the vari-115 able resistors 21 or 23 are connected to ground through a common resistor. As in the arrangement of Figure 3, the diodes 20 or 22 is so poled as to conduct the positive or negative signal voltage ex to the associated variable resistor 22 or 23 there-120 through.

Therefore, the square-law circuits 20-21 and 22-23 shown in Figure 4 serve also to discriminate the polarity of the deflection signal voltage ex.

It will readily be understood that the arrangement 125 is operative to provide at its output the square of its input voltage in accordance with a broken line approximation and that the variable resistors 21 or 23 variably adjust the square-law characteristics.

It is to be noted that the square-law circuits 24-25 130 and 26-27 as shown in Figure 3 may be arranged in

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the same manner as those 20-21 and 22-23 shown in Figure 4.

In the convergence circuit according to the present invention shown in Figure 5, the deflecting signal 5 voltages ex and ey are directly applied to two square-law circuits 12' and 14' respectively which, in turn, deliver respective outputs voltages approximately proportional toaex2 and bey2 to an adder circuit 40 where both voltages are added to each other to form 10 a signal voltageei approximately expressed byaex2 + 6ey2. This signal voltage e, is applied to both a subtracter circuit 41 and the adder circuit 16.

The subtracter circuit 41 has a reference voltage ec applied thereto and delivers to a polarity dis-15 criminator circuit 42 a signal voltage e2 representing a difference voltage between the e1 and ec and ec or e2 = e, -ec. The polarity discriminator 41 discriminates the polarity of this signal voltage e2 so that,

only when the signal voltage e2 has been determined 20 to be equal to or greater than zero, an output e2' is applied to a coefficient circuit 43. The coefficient circuit 43 is operative to multiple the outpute2' by a suitable adjustable coefficient K and then to supply a signal voltage Kez' to the adder circuit 16. 25 In other respects the arrangement is identical to that shown in Figure 2.

With the deflecting signal voltages ex and ey applied to the square-law circuits 12' and 14', electron beams generated in an associated colour 30 cathode ray tube land on the display surface of the tube at or close to a point as determined by the deflecting signal voltagesex and ey. Assuming that the landing point of the electron beam has its coor-' dinates proportional to the ex and ey referring to the 35 Cartesian orthoronal coordinate system and that the output voltageei from the adder circuit 40 is constant, each of the electron beams depicts an elliptical locus on the display surface defined by aex2 + bey2 = const. (1)

40 Therefore, by comparing the voltage e, with the reference voltage ec the display surface of the colour cathode ray tube can be divided into two regions or the inner and outer regions by an elliptical boundary expressed by 45 aex2 + bey2 = ec. (2)

Since the substracter circuit 41 delivers to the polarity discriminator circuit 42 its output voltage e2 expressed by

©2 = ©1 — 6C

50 = aex2 + bey2 —ec, (3)

the polarity discriminator circuit 42 can discriminates the polarity of the output voltage e2 so that the output voltage e2' therefrom is enabled to correct the degree of convergence only when e2 S 0 hold. This 55 results in the provision of a correcting magnitudes enabled only in the outer region of the ellipse as above described. In other words, the polarity discriminator circuit 42 can be operated to pass the intact input e2 therethrough only for e2§ 0 but to 60 produce a null output for e2 < 0 whereby the output e2' therefrom provides a signal enabled only outside the abovementioned ellipse.

The coefficient circuit 43 is operated to multiply the output e2' from the polarity discriminator circuit 65 42 by the coefficients and deliver its output voltage

Ke2' to the adder circuit 16 having the output voltage e-, from the adder circuit 40 applied thereto. As a result, the adder circuit 16 adds both output voltages to each other to produce selectively the following signal voltagee3:

e3 = ei + Ke2'

= aexz + beyz + K(aex2 + bey2- ec)

for aex2 + bey2 § ec (4)

and e3 = e,

= aex2 + bey2 for aex2 + bey2 < ec. (5)

Those signal voltages e3 are applied to convergence coil 18 through the output circuit 17 with the result that the degree of convergence is corrected in accordance with the expression (4) outside , of the ellipse and with the expression (5) inside thereof.

It is to be noted that, by changing the value of the reference voltage ec and the coefficient K and the sign of the latter, the degree of convergence can be independently corrected only on that portion of the display surface of the cathode ray tube located outside a predetermined ellipse on the display surface. Further no discontinuity appears in the transit of the corrected degree of convergence from the inside to the outside of the ellipse and vice versa because the corrected degree of convergence in the ellipse is equal to that within the ellipse that is determined only by the reference voltage ec in spite of the value of the AT.

The polarity discriminator circuit 42 and the coefficient circuit 43 shown in Figure 5 may be of a circuit configuration illustrated in Figure 6. As shown in Figure 6, a semiconductor diode 45 forms the polarity discriminator circuit 42 with a resistor 46 connected between the cathode electrode of the diode 45 and ground. The cathode electrode of the diode 45 is also connected to an input to an inverter 46 including an output connected to the input thereto through a potentiometer 47. The inverter 46 and the potentiometer 47 form the coefficient circuit 43 with a movable tap on the potentiometer connected to the adder circuit 16.

In operation, the signal voltage e2 from the substracter circuit 41 (see Figure 5) is half-wave rectified by the diode 45 and only the positive portion thereof e2' is applied to both the input to the inverter 46 and that end of the potentiometer 47 remote from the output of the inverter 46. That is, the diode 45 provides its output voltage e2' only for e2S 0. An inverted signal voltage e2' from the inverter 46 is also applied to the other end of the potentiometer 47. Accordingly an output voltage from at the tap on potentiometer 47 can have any desired magnitude ranging from the e2 to e2' as determined by the posi-. tion of the tap on the potentiometer 47. That is, the potentiometer 47 is effective for varying the coeffi-cient/f at will between-1 and +1 inclusive.

The arrangement illustrated in Figure 7 contemplates to extend a degree of freedom of the convergence correction. It is different from the arrangement shown in Figure 5 only in that in Figure 7 a quadrant discriminator circuit 50 is directly supplied with the deflecting signal voltages ex andey and connected to a coefficient circuit 43' that selec70

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tively multiplies the output voltage e2' from the polarity discriminator circuit 42 by four different coefficients Ka, Kb, Kc andKd.

More specifically, the quadrant discriminator cir-5 cuit 50 is operative to discriminate the polarity of each deflecting signal voltage ex or ey to determine which quadrant of the display surface of an associated cathode ray tube electron beams land at. Then the quadrant discriminator circuit 50 delivers an out-10 put to the coefficient circuit 43' through a first output lead 51 only for ex S 0 and ey > 0, that is, when the first quadrant is scanned, through a second output lead 52 only for ex < 0 and ey § 0, that is, when the second quadrant is scanned, through a third output 15 lead 53 only for ex<0 and ey<0, that is, when the third quadrant is scanned, and through a fourth output lead 54 only for etg0 and ey S 0, that is, when the fourth quadrant is scanned.

On the other hand, the coefficient circuit 43 is 20 responsive to the output developed in the first output lead 51 to multiply the signal ea' from the polarity discriminator circuit 42 by the coefficient/fa, to the output developed in the second output lead 52 to multiply the signal e2' by the coefficients, to the 25 output developed in the third output lead 53 to multiply the signal e2 by the coefficieritKc, and to the output developed in the fourth output lead 54 to multiply the signal ez' by the coefficient Kd.

As above described in conjunction with Figure 5, 30 the output voltage e, from the adder circuit 40 is expressed by e, = ae„2 + bey2 while the output voltage e2 from the polarity discriminator circuit 42 is expressed by e2' = aex2 + bey2- ec when the preceding subtracter circuit 41 gives the output voltage e2 35 expressed by e2 = aex2 + bey2- ec ^ 0 and become null when the e2 is expressed by e2 = ae/ 4- bey2 -ec < 0. The coefficient by which the voltage e2' is multiplied in the coefficient circuit 43' changes in value in accordance with the output voltage from the quad-40 rant discriminator circuit 50. That is, the coefficient AT may have a value of Ka, Kb, Kc orKd. Therefore, the output voltage Ke2' from the coefficient circuit 43' is changed in accordance with combination of the polarity of the deflecting signal voltage ex with that 45 of the deflecting signal voltage ey. More specifically, the output voltage Ke2' from the coefficient circuit 43' can have a value of a) Kae2 for ex§0 and ey > 0, b) Kbez for ex < 0 and ey > 0, c) Kce2 for xx < 0 and ey < 0 and d) Kde2 for ex§0 and ey<0.

50 For e2 = aex2 + bey2-ec s 0, therefore, the output voltage ec from the adder circuit 16 is expressed by 63 = 6, + Kae2'

= aex2 + bey2 + Ka(aex2 + bey2- ec) (6) when exS 0 and ey § 0 hold, by 55 63 = 6!+ Kbe2'

= aex2 + bey2 + Kb(aex2 + bey2- ec) (7) when ex < 0 and ey § 0 hold, by 63 = 6! + Kce2'

= aex2 + bey2 + Kc(aex2 + bey2 — ec) (8)

60 when ex < 0 and ey < 0 hold, and by e3 = e! + Kde2'

= aex2 + bey2 + Kd(aex2 + bey2- ec) (9) when e,g0 and ey < 0 hold.

Also for e2 = aex2 + bey2 - ec < 0, the output vol-65 tage e3 is expressed by e3 = aex2 + be y2 (10)

regardless of the polarity of the deflecting signal voltages ex and ey.

Accordingly, a current proportional to that output 70 voltage e3 from the adder circuit 16 flows through the convergence coil 18 via the output circuit 17 with the result that the degree of convergence is corrected in accordance with each of the expressions (6), (7), (8) and (9) in a different one of the quadrants 75 outside of the ellipse while in accordance with the expression (10) inside thereof.

From the foregoing it will readily be understood that, by changing the sign and value of the coefficients Ka, Kb, Kc and Kd in the expressions (7), (7), 80 (8) and (9), the degree of convergence can be independently corrected in the respective quadrants only outside of the predetermined ellipse.

It is to be noted in the arrangement of Figure 7 that no discontinuity appears in the ellipse between the 85 corrected degree of convergence approaching the ellipse from the outside thereof and that approaching the ellipse from the inside thereof for the same reasons as above described in conjunction with Figure 5.

90 The coefficient circuit 43' may be of a circuit configuration shown in Figure 8. In the arrangement illustrated, four parallel potentiometers 47a, 476,47c and 47d are substituted forthe single potentiometer 47 shown in Figure 6 and a movable tap on each 95 potentiometer is connected to the adder circuit 16 through an analog gate 55a, 55b, 55c or 55d. Then the output leads 51,52,53 and 54 from the quadrant discriminator circuit 50 are connected to the analog gates 55a, 556,55c and 55c/ respectively.

100 The potentiometers 47a, 476,47c and Aid serve to set four coefficients Ka, Kb, Kc and Kd respectively.

Each of the analog gates is responsive to the output developed in the associated output lead from the quadrant discriminator circuit 50 to pass the voltage 105 Ke2 at the tap on that potentiometer connected to the responding analog gate, to the adder circuit 16 therethrough. For example, the analog gate 47a is operative to pass the voltage Kae2 at the tap on the potentiometer 47a to the adder circuit 16 only in the 110 presence of the output in the first output lead 51.

The arrangement illustrated in Figure 9 is enabled to correct independently the degree of convergence not only outside of the ellipse as above described but also inside thereof in four quadrants of the dis-115 play surface. The arrangement illustrated is different from that shown in Figure 7 only in that in Figure 9, the two polarity discriminator circuits 10 and 11 and the four square-law circuits 12 to 15 inclusive as shown in Figure 2 are substituted forthe two 120 square-law circuits 12' and 13' as shown in Figure 7.

It will readily be understood that the adder circuit 40 produces the signal voltage e■, identical to that e0 produced by the adder circuit 16 shown in Figure 2, in each of four quadrants of a display surface of an 125 associated colour cathode ray tube. In other words, the display surface is first divided into four region, in this case, four quadrants corresponding to the expressions fore0 as above described in conjuction with Figure 2 and the signal voltage ei is produced to 130 be separately changed in the respective quadrants.

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Subsequently the signal voltage e, is applied to the substracter circuit 41 to be compared with the reference voltage ec thereby to divide the display surface into two regions located inside and outside 5 of an ellipse determined by the reference voltage ec and the degree of convergence is additionally corrected outside of the ellipse in the manner as above described in conjunction with Figure 7. It is, however, to be noted that a boundary between both reg-10 ions is defined by a curve consisting of four elliptic arcs expressed by the expression (1) having the righthand side equal to the e/s different between the four quadrants respectively and connected to one another, but not formed of the ellipse defined by the 15 expression (2).

In summary, the degree of convergence is first corrected on the inner portion of the display surface by changing properly the coefficients a, b, c and d of the four square-law circuits 12,13,14 and 15. Then, 20 by changing properly the coefficients Ka, Kb, Kc and Kd selectively given by the coefficient circuit 43, the degree of convergence is additionally corrected outside of a closed curve resulting from the connection of the four elliptical arcs dependent upon the degree 25 of convergence corrected inside of the closed curve while being separately corrected in the four quadrants of the display surface as above described in conjunction with Figure 7.

It is to be noted that the square-law circuit as 30 above described is required only to produce its output voltage approximately equal to the square of its input voltage but not to follow the square-law strictly. Also the term "ellipse" used therein means a curve approximating a true ellipse but no ellipse in 35 the strict sense.

The present invention is equally applicable to two regions into which the display surface of colour cathode ray tubes is equally devided transversely or longitudinally thereof. In this case, the square-law 40 circuit having the positive deflecting signal voltage ex(+) entered thereinto may have the same coefficient by which the square of its input is multiplied, as that applied with the negative deflection signal voltage ex(-). Under these circumstances, it is sufficient 45 to apply the X axis deflecting signal voltage ex to the single square-law circuit as by entering the negative voltage ex(-) into the square-law circuit after the inversion of the polarity thereof. This is applied to the Y axis deflecting signal voltage ey.

50 Where only the positive deflecting signal voltages are used, the signal voltage may be converted to a negative signal voltage as by slicing or clipping it at a voltage corresponding to the desired position on a display surface of an associated cathode ray tube. 55 There after the positive and negative signal voltages are processed in any of the manners as above described.

It will be apparent that, by partitioning each of the deflecting signal voltages ex and ey into more than 60 four regions, the fine correction can be effected as desired.

The present invention is advantageous in that the degree of convergence can be corrected as required, in each of a plurality of regions into which a display 65 surface of an associated colour cathode ray tube is divided and in spite of a scanning process involved. This perinuts random deflections. Therefore, the present invention is applicable to the display on radars, digital computers etc. requiring the random deflection resulting in the extremely large practical effect.

Claims (6)

1. A cathode ray tube apparatus comprising a shadow-mask colour cathode ray tube including a plurality of electron guns, and means for deflecting electron beams in directions of an X and a Y axis and constructed so as to display information in colour on a display surface, characterized in that there is provided a convergence correcting circuit including a first and a second square-law circuit for making an X axis deflecting signal ex and a Y axis deflecting signal ey signals with square-law waveforms aex2 and be y2 multiplied by predetermined coefficientsa and b respectively, an adder circuit for adding those output signals to each other, a reference signal generator circuit for generating a reference signal ec, a subtractor circuit for subtracting said reference signal ec from the output signal e0 from said adder circuit, a polarity discriminator circuit for discriminating the polarity of an output signal e2 from said circuit and delivering a signal e2' when e2§ 0, a coefficient circuit for multiplying the output signal e2' from said circuit by a predetermined coefficients, a second adder circuit for adding an output signal Ke2' from said circuitto the output en from said first adder circuit, and an output circuit driven with an output signal e3 from said second adder circuit to pass a convergence current corresponding to said output signal e3 through convergence means.

2. A cathode ray tube apparatus comprising a shadow-mask colour cathode ray tube including a plurality of electron guns, and means for deflecting electron beams within said cathode ray tube in directions of an X and a Y axis and constructed so as to display information in colour on a display surface, characterized in that there is provided a convergence correcting circuit including a first and a second square-law circuit for making an X axis deflecting signal ex and a Y axis deflecting signal ey signals with square-law waveforms aex2 and bey2 multiplied by predetermined coefficientsa andb respectively, a first adder circuit for adding those output signals to each other, a reference signal generator circuit for generating a reference signal ec, a subtractor circuit for subtracting said reference signal ec from an output signal et from said first adder circuit, a polarity discriminator circuit for discriminating the polarity of an output signal e2 from said circuit and delivering an output signal e2' when e2 ^ 0, a quadrant discriminator circuit for discriminating the polarity of said deflecting signals ex and ey and determining which quadrant of the display surface of said cathode ray tube the electron beams scanning said display surface belong to, by means of combinations of the positive and negative of said ex andey and delivering a signal representing the quadrant being scanned with said electron beams, a coefficient circuit responsive to an output signal from said circuit to multiply said signal e2' by coefficients Ka to Kd for respective quadrants, a second adder circuit for

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adding an output signal Ke2' from said circuitto the said signal e1( and an output circuit driven with an output signal e3 from said second adder circuit to pass a convergence current corresponding to said 5 signal e3 through convergence means.

3. A cathode ray tube apparatus comprising a shadow-mask colour cathode ray tube including a plurality of electron guns, and means for deflecting electron beams within said cathode ray tube in direc-

10 tions of an X and Y axis and constructed so as to display information in colour on a display surface, characterized in that there is provided a convergence correcting circuit including a first and a second polarity discriminator circuits for discriminating the polar-15 ity of an X axis deflecting signal ex and a Y axis deflecting signal ey to deliver signals ex(+), ex(~), ey(+) and ey(-), a first to a fourth square-law circuit for delivering signals with square-law waveforms aex2(+),bexH-),cef(+) and cfey2(—) which are respec-20 tive output signals from said circuits multiplied by predetermined coefficients a, b, c and d respectively, a first adder circuit for adding said output signals to one another, a reference signal generator circuit for generating a reference signal ec, 25 a subtractor circuit for subtracting said reference signal e0 from an output signal e1 from said first adder circuit, a polarity discriminator circuit for discriminating the polarity of an output signal e2 from said circuit and delivering a signal e2' when e, § 0, a 30 quadrant discriminator circuit for discriminating the polarity of said deflecting signals e„ and ey and determining which quadrant of the display surface of said cathode ray tube the electron beams scanning said display surface belong to, by means of combi-35 nations of the positive and negative of said ex andey and delivering a signal representing the quadrant being scanned with said electron beams, a coefficient circuit responsive to an output signal from said circuitto multiply said signal e2' by coefficients Ka, 40 Kb, Kc and Kd for respective quadrants, a second adder circuit for adding an output signal Ke2' from said circuit to said signal eu and an output circuit driven with the output signal e3 from said second adder circuitto pass a convergence current corres-45 ponding to said signal e0 through convergence means.

4. A cathode ray tube apparatus substantially as described herein and with respectto Figure

5 of the accompanying drawings.

50 5. A cathode ray tube apparatus substantially as described herein and with respectto Figure 7 of the accompanying drawings.

6. A cathode ray tube apparatus substantially as described herein and with respectto Figure 9 of the 55 accompanying drawings.

Printed for Her Majesty's Stationery Office by The Tweeddale Press Ltd., Berwick-upon-Tweed, 1980.

Published at the Patent Office, 25 Southampton Buildings, London, WC2A1 AY, from which copies may be obtained.