US3537098A - Circuit - Google Patents

Description

Oct. 27,1970 A. v1'. 'NIELSEN ETAL 3,537,058

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Oct. 27, 1970 A.1.N|El.sEN ETAL 3,537,098

4 CIRCUIT Filed sept. 2v. 196e s sheets-sheet 2 INVENT ORS ASGE? /WE'LSEN R/CHARD R. WHEELOCI( ATTO EYS Oct. 27,1970 A. T. NIELSYEN ETAI- 3,537,098

v 3H CIRCIT Filed sepnxzv, 196e s sheets-sheet a F76. 30 FIG. 3E

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U.S. Cl. 340-324 8 Claims ABSTRACT 0F THE DISCLOSURE Symbol generators including a cathode ray tube, a system for applying successive pairs of signals to the deflection coils of the tube to cause the electron beam to trace a character on the face of the tube as a series of interconnected strokes, and a beam intensity control for maintaining the intensity of successive strokes generally uniform.

This invention pertains basically to a system of character generation for graphically reproducing and visually displaying selected characters in response to electric signals representing such characters lbut in its broader aspects is applicable more generally to curve plotting and line generation from data indicative of the coordinates of successive points on the curve to be plotted.

More specifically the invention pertains to a system for displaying alphabetic, numeric and other predetermined characters on a cathode ray tube in accordance with signals indicative of the character to be displayed received thereby.

A number of prior art devices exist by the use of which it is possible to generate alphanumeric characters on the phosphor screen of a cathode ray tube. Three principal types of cathode ray tube character display units are known. A Iirst type includes units in which a shaped electron beam is generated by the electronic illumination of a mask inside the tube. The mask is provided with a plurality of apertures each having the shape of a different letter or number, and by directing an electron beam onto the mask from the electron gun a shaped beam is provided. By the use of a deflection system the shaped beam is positioned on the screen as required. A second type is that in which a scanning raster is formed at a desired position on the screen; and the tube is `unblanked to form a character composed of line segments in a manner similar to the composition of a television picture. Still a third type of unit is that in which an electron beam is rst positioned to a reference point and then is caused to trace out the character through the application of the X and Y component `functions to the deflection system.

This invention relates to cathode ray tube character display systems of this last type.

In accordance with the present invention input data to be displayed is transmitted in coded form, and is decoded by suitable means to select the corresponding characters in a character programming device. The programming device comprises a plurality of units (corresponding in number to the number of characters to be selectively displayed), each of which is adapted, in conjunction with a sequential timing device, to generate unique sequence signals of varying amplitudes for a given character to control the generation of a visual display of such character upon a cathode ray tube or other display device.

A display generating unit generates selected horizontal nited States aten and vertical sweep voltage wave forms, and beam intensity control signals, which are applied to the vertical and horizontal deflection systems and intensity control systems of the display tube cause the electron beam to trace the selected character on the face thereof.

In prior patents such as exemplified by Palrniter, No. 3,047,851, dated July 3l, 1962 and entitled Electronic Character Generating and Displaying Apparatus, it is old to displace a cathode ray beam through a predetermined number of locations on the face of the tube, in accordance with the character being generated, so that phosphor retentvity will produce a continuous display. Customarily, the locations through which the beam is directed are determined by a matrix uniqe to the character to 'be generated, and is effected under control of a timing circuit which triggers the matrix for sequential control of the beam, from a predetermined starting point, over the face of the tube. The beam control pulses are emitted in units of fixed amplitude and time duration, as X and Y coordinate increments, and are integrated to form a continuous signal to the horizontal and vertical deflection control elements of the cathode ray tube.

In other patents of the prior art, such as Dell, No. 3,090,041, issued May 14, 1943 for Character Generation and Display, the beam control pulses are of variable amplitude and are applied to the deflection plates without integration to trace a distinctly dotted pattern, in which the dots in the character outlines are Imore or less pronounced depending on the closeness of their location.

As distinct from the above prior art, the present invention utilizes individual character matrixes which control the generation of pulse trains of variable amplitudes which are determinative of sequential beam locations in terms of X and Y coordinates, and these are processed for each successive beam location to determine the algebraic difference between each successive pair of X and Y values respectively, and the differences obtained are integrated to control beam displacement.

The system has definite advantages over the prior art in that the resultant characters displayed are generatedv in continuous lines the segments of which while varying in length are maintained at substantially constant inten; sity. In addition, the present invention provides high speed and better character definition independently of character size and location. To provide a display device control system which will achieve these results is the basic object of this invention.

These and other objects of the present invention will become Imore fully apparent by reference to the appended claims and as the following detailed description proceeds in reference to the accompanying drawings wherein:

FIG. l is a diagram illustrating the present invention;

FIG. 2 is a diagram illustrating the details of the intensity control of the circuit of FIG. l; and

FIG. 3 is a series of coordinate diagrams illustrating the display of a typical character and the several signals generated in the circuit of FIG. l for the display of that character upon a cathode ray tube.

Referring now to FIG. l, the circuit of the present invention responds to a coded data indicative input identified by the simultaneous selective application of input signals to certain of the six input lines L, to Ls in a pattern indicative of the character to be displayed. The pattern of input signals in lines L1 to L6 is sensed and decoded by the decoding and selection network 10 to energize a single one of its sixty-four output lines S1 to S64 in accord with 3 the pattern of the input signals appearing in lines L1-L6.

The thus selected output lines S1 to S64 activates the one of the character generator matrixes C-l to C-74 to which it is connected.

Each of the matrixes C-1 to C-64 has sixteen X coordinate output lines X1 to X16, sixteen Y coordinate output lines Y1 to Y16, and sixteen Z coordinate output lines Z1 t0 216.

The lines X1 to X16 are each connected to one of the input terminals of sixteen distinct two-input AND gates 16. The other inputs to these AND gates are connected respectively to the input terminals T1 to T16 from the timing circuits 14. Input terminals T1 to T16 are successively activated in sixteen successive time intervals so that a time sequential signal appears at the common output of the X AND gates the magnitude of which, in each of its sixteen successive time intervals, is proportional to the magnitude of the signal appearing at the input terminals connected to X1 and X16 respectively. Such a signal is shown at X in full lines in FIG. 3E. The magnitude of the signal at the input terminals connected to X1 to X16 depends on the character to be displayed. For example, for the numeral 2, shown in FIG. 3C, these inputs will be:

Terminal connected to Voltage (units) These same voltages are simultaneously applied from leads X1 to X16 to the inputs of the X AND gates 18 each lead being individually connected to one of the two input terminals of one of the sixteen X AND gates 18. The other terminals of the X' AND gates 18 are successively activated from the timing circuit 14 through the input terminals T1' to T16. There is a one time interval time delay between the activation of the input terminals T1 to T16 and the input terminals T1' to T16. That is, for example, T2 and T1' are activated simultaneously as are T6 and T2', T4 and T6', etc.

As a result a signal X appears at the common output of the X AND gates 18 which is identical with that appearing at the output of the X AND gates but delayed by one time interval. This is indicated for the numeral 2 at X in FIG. 3E in dash lines.

The signal X is fed through an X inverter 20 to produce a signal -X. The output of the X AND gates 16 and of the X inverter 20 are connected to the inputs of the X integrator 22, the resultant input signal being X-X which for the numeral 2 is shown in FIG. 3D. The output of the X integrator 22 is a continuous signal AX substantially of the form indicated in dot-dash lines in FIG. 3E at AX.

Since the rate of change of the output of the X integrator 22 is proportional to the amplitude of the input signal, (X-X), one can by proper selection of the integrator time constant cause the output Voltage to describe a curve A X that connects the corner of the staircase voltage X as indicated in FIG. 3E.

The sixteen Y AND gates 24 and sixteen Y AND gates 26 are similarly connected to sixteen input terminals Y1 to Y16 from the character matrixes C-1 to C-64 and to the input terminals T1 to T16 and T1' to T16' from the timing 4 circuit 14 to produce signals Y and Y as shown for the numeral 2 in FIG. 3B. When the Y signal is inverted in the Y inverter 28 to produce a -Y signal and combined with the Y signal, the resultant input (Y-Y) to the Y integrator 30 is as shown in FIG. 3A and the output is as indicated in dot-dash lines in FIG. 3B as AY for the numeral 2. The input voltages at Y1 to Y16 for the numeral 2 are:

Terminal: Voltage (units) Y1 1 Y-7 1l Y-S 16 Y-9 19 Y-l() 24 Y-11 29 Y-12 32 Y-13 33 Y-14 32 Y-15 .28

When AX and AY signals that are generated in this manner are impressed in the horizontal and vertical deflection system of a cathode ray tube 31, the outline of an alphanumeric character or other programmed symbol can be drawn as indicated by the display of the number 2 in FIG. 3C.

As is apparent in FIG. 3, the several sub-figures have been plotted on the common coordinates so that the X and Y voltages and beam positions can be readily compared for the successive time intervals as can the X, X', (X-X), Y, Y and (Y-Y) values.

From an analysis of FIGS. 3B, 3C and 3E, it is apparent that certain strokes must be blank and others must be visible. For the numeral 2 as displayed in FIG. 3C, these are strokes 1, 2 and 16. For control of the blanking and unblanking the character matrixes C-l to C-64 are each connected to one of the inputs Z1 to Z16 of the sixteen Z AND gates 32. The other inputs of these Z AND gates 32 being connected respectively to the timing circuit input lines T1 to T16 respectively. The inputs Z1 to Z16 from the selected character matrixes C-1 to C-64 are such that, when a blank stroke is required within a character, there is a positive output on the line Z from the Z AND gates 32 synchronized with the X, X', Y and Y' signals. The Z signal through a ip-op (not shown) is transmitted to the intensity control 34 and the Z amplier 36 to the control grid of the cathode ray tube 31.

The intensity control 34 contains two independent circuits for blanking and unblanking, and a ip-flop is set and reset by the leading and trailing edges of the time pulses if a Z-diode is programmed in the character matrix for a given line segment.

This applies in almost all cases where the electronic beam is to be moved from the character reference point (lower left corner of character rectangle FIG. 3C), to the beginning of the character. Either one or two strokes are used depending on the distance and both must be blanked. One or two Z-diodes in time 1 and/or 2 causes the Hip-op in the intensity control 34 to set at the beginning of time pulse 1 and reset at the end of time pulse 1 or 2. This way the electronic beam is blanked as it moves from reference position to beginning of character.

As is apparent from FIG. 3C, the time intervals are constant but the distance through which the beam is deflected in different time intervals varies. Unless compensated for, there would be variations in light intensity of the diierent segments of the character traced due to variations in beam velocity. In the present invention the beam intensity is controlled as will now be explained.

The magnitude of the signal X-X is directly proportional to the horizontal component of the stroke and is therefore also proportional to the horizontal velocity component. If dx/dt and dy/dt Were added directly, an error of 2-l.4/ 1.4 would result. This is approximately 43%. By selecting the larger component and adding this to one-half of the smaller component, the error can be reduced to 16%. A small analog computer is used to accomplish this. This computer is the circuit denominated intensity control in FIG. 1 and shown in detail in FIG. 2.

The circuit on FIG. 2 generates a signal that is proportional to S L-r where L is the length of the longest component AX or AY for a given stroke and S is the length of the shortest component. This Way controls the intensity with an error of only i6%.

Since the lines carrying the X and the inverted X' signals and Y and the inverted Y signals in the other case are the inputs to the intensity control 34, the resultant input is X-X and Y-Y'.

The operation of the circuit in FIG. 2 is as follows.

The two differential amplifiers 38 and 40 generate two outputs each. In amplifier 38 they are (X-X) and -(X-X'); for amplifier 40 they are (Y-Y) and (Y-Y').

Therefore independent of the sign of X and X and Y and Y at the input, one of the two outputs of each of the amplifiers 38 and 4f) will be negative, and one will be positive.

Diodes 42 and 44 form an OR gate. Only the diode that has its anode connected to the positive output will conduct, thus back biasing the other diode. The same is true for diodes 46 and 48.

Diodes 50 and 52 complete the OR functions in such a Way that the most positive of all four amplifier outputs will cause a current to ow through resistor 54 to the summing junction of amplifier 36.

This current is proportioned to L. Diodes 58, 60; 62 and 64 form tWo other OR gates selecting the negative outputs of each amplifier 38 and 40.

Diodes 66 and 68 and the resistor 70, to -V selects the least negative of the two negative outputs and thus function -S is generated. It supplies current through resistor 72 (the value of which is twice that of the resistor 54) to the summing junction. The output of amplifier 36 is thus This signal is applied to the control grid of the cathode ray tube during the strokes of the character during which the tube is not blanked by the Z signal to maintain the intensity of the strokes uniform Within i6% regardless of the variations in their lengths.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present invention is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. A symbol generator comprising:

(a) a cathode ray tube having a pair of beam defiection control inputs, display means on which a character can be generated by so defiecting an electron beam impinging on said display means by the application of varying voltage signals to the beam deflection control inputs as to cause said beam to trace out the character, and a beam intensity control input responsive to the application of a signal thereto to vary the intensity of the electron beam;

(b) means for generating and applying pairs of beam defiecting signals to said control inputs in each of successive periods of equal duration, whereby the character is traced as a series of strokes which are of equal duration but of varying length, position and direction, said signal generating means comprising, for each beam deflection control input, means for producing a first pulse train, means for producing a second pulse train identical to the first pulse train but with each pulse thereof following the identical pulse of the first train by a period equal to the duration of one stroke, means for inverting the pulses in the second pulse train, means for summing the inverted pulses and the pulses of the first pulse train and for integrating the summed pulses to produce an unbroken beam deflecting signal for application to the associated beam deflection control input; and

(c) means for generating and applying to the intensity control input simultaneously with the application of said pairs of signals to the beam deflection control inputs signals which will cause said beam intensity control to so vary the beam intensity as to maintain the intensity of successive strokes generally uniform.

2. The symbol generator of claim 1, wherein each means for generating first and second pulse trains comprises first and second AND gates each having a plurality of coded pulse inputs equal to the number of pulse train pulses and a like number of timing pulse inputs, said gates being capable of transmitting pulses when corresponding code pulse inputs and timing pulse inputs are energized, means for supplying coded pulses equal to the number of pulses in the train simultaneously to the coded pulse inputs of the first and second AND gates, and timing means for successively energizing the timing pulse inputs of the first and second AND gates with a delay between energization of corresponding timing pulse inputs of the first and second AND gates equal to the duration of one stroke, whereby said pulses are transmitted through the first and second AND gates in the same predetermined sequence with the pulses being transmitted first through the first AND gate and then through the second AND gate.

3. The symbol generator of claim 2', wherein the inverter of each signal generating means is operatively connected to the output of the second AND gate thereof and the integrating means of each signal generating means has one input connected to the output of the first AND gate thereof, a second input connected to the output of the inverter thereof, and an output connected to the associated beam deflection control input.

4. The symbol generator of claim 2, wherein the means for applying signals to said beam intensity control input comprises blanking means operatively connected to said beam intensity control for causing the latter to prevent the generation of a trace on said display means during those of the equal duration periods when a positive pulse is applied to said control, said last-mentioned means including a third AND gate capable of transmitting only positive pulses, said third AND gate having coded pulse inputs connected to the coded pulse supplying means and timing pulse inputs connected to said timing means, and means connecting said third AND gate to said beam intensity control.

5. A symbol generator comprising:

(a) a cathode ray tube having a pair of beam deflection control inputs, display means on which a character can be generated by so deflecting an electron beam impinging on said display means by the application of varying voltage signals to said beam deflection control inputs as to cause said beam to trace out the character, and a beam intensity control input responsive to the application of a signal thereto to vary the intensity of the electron beam;

(b) means for generating and applying to said control inputs in each of successive periods of equal duration pairs of signals which so deflect the electron beam that the character is traced as a series of strokes which are of equal duration but of varying length, position, and direction and which are comprised of components determined by the signals applied to the control inputs; and

(c) means for generating and applying to the intensity control input simultaneously with the application of said pairs of signals to the beam deflection control inputs signals which will cause said beam intensity control to so vary the beam intensity as to maintain the intensity of the successive strokes generally the same, said last-mentioned means comprising means for generating in each period in which a stroke is traced a signal which is proportional to the difference between the length of the longer component of the stroke and one-half the length of the shorter component of the stroke and means for applying the signals thus generated to the intensity control input in said successive periods.

6. The symbol generator of claim 5, together with blanking means operatively connected to said signal generating means and said beam intensity control for causing the latter to prevent the generation of a trace on said display means during at least one of said equal duration periods.

7. A symbol generator comprising a cathode ray tube having a pair of beam deflection control inputs, display means on which a character can be generated by so deliecting an electron beam impinging on said display means by the application of varying voltage signals to the beam deflection control inputs as to cause said beam to trace out the character, and a beam intensity control input responsive to the application of a signal thereto to vary the intensity of the electron beam, means for generating and applying pairs of beam deflecting signals to said control inputs in each of successive periods of equal duration whereby the character is traced as a series of strokes which are of equal duration but of varying length, position and direction and which are comprised of components determined by the signals applied to the control inputs, said signal generating means comprising, for each beam deflection control input, means for producing a first pulse train, means for producing a second pulse train identical to the first pulse train but with each pulse thereof following the identical pulse of the lirst train by a period equal to the duration of one stroke, means for inverting the pulses in said second pulse train, and means for summing the inverted pulses and the pulses of the first pulse train and for integrating the summed pulses to produce an unbroken beam deliecting signal for application to the associated beam deflection control input, and means for generating and applying to the intensity control input simultaneously with the application of the pair of signals to the beam deflection control inputs in each period in which a stroke is generated a signal which will cause the beam intensity control to so vary the beam intensity as to maintain the intensity of successive strokes generally uniform, said last-mentioned means comprising a first differential amplifier for generating two signals of equal magnitude and opposite polarity which are proportional to the magnitude of one of the components of the stroke and a second differential amplilier for generating two signals of equal magnitude and opposite polarity which are proportional to the magnitude of the other of the components of the stroke, a third amplifier, means for passing to the summing junction of the third amplifier the most positive of the four signals generated by the differential amplifiers, means for reducing the magnitude by one-half and transmitting to the summing junction, of the third amplifier the least negative of said four signals, and means connecting the output of said third amplifier to the intensity control input of the cathode ray tube.

8. The symbol generator of claim 7, wherein:

(a) the means for selecting the most positive of the four signals generated by the differential amplifiers comprises an OR gate connected to each of the differential amplifiers, said OR gates being connected to outputs of the differential amplifiers which are capable of transmitting only signals of positive polarity, and a diode connected between each of said OR gates and the summing junction of the third amplifier, said diodes being connected in parallel and in opposed relationship, whereby only the diode to which the more positive signal is applied will conduct;

(b) the means for selecting the least negative of said four signals comprises a further OR gate connected to each of said differential amplifiers, the further OR gates being connected to the outputs of said differential amplifiers which are capable of transmitting only signals of negative polarity, and a further diode connected between each of the further OR gates and the summing junction of the third ampliers, the further diodes being connected in parallel and in opposed relationship, whereby only the further diode to which the least negative signal is applied will conduct; and

(c) the means for reducing by one-half the magnitude of the least negative of said signals comprises a resistance connected in series with and between the further diodes and said summing junction.

References Cited UNITED STATES PATENTS 3,047,851 7/l962 Palmiter 340-3241 3,205,488 9/1965 Lumpkin 340-3241 3,234,534 2/1966 Todman 340-324-l 3,333,147 7/1967 Henderson 340324.1 3,382,487 5/1968 Sharon et al. 340-324.1

ALVIN H. WARING, Primary Examiner M. M. CURTIS, Assistant Examiner U.S. Cl. X.R.

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