US3094645A - Deflecting circuit - Google Patents

Description

ATTORNEYS R. O 2 3 4 6 7 a 9 mm m m m .a. m m m w m F F F H F F F m m r 4. J uu fi 1.1---- J J. DI PAOLO l I 22 F l g as I I I 4| l I I 45 June 18, 1963 DEF'LECTING CIRCUIT Filed Nov. 24, 1959 United States Patent Office 3,094,645 Patented June 18, 1963 3,094,645 DEFLECTING CIRCUIT Jolrn Di Paolo, Cedar Grove, N .J., assignor, by mesne assiguments, to Fairchild Camera and Instrument Corporation, Syosset, Long Island, N.Y., a corporation of Delaware Filed Nov. 24, 1959, Ser. No. 855,193 7 Claims. (Cl. 3l527) This invention relates to a deflecting circuit for a cathode ray tube, and more particularly to one that provides an undistorted display.

Cathode ray tubes draw visual displays by moving a spot of light across the tubes faceplate. The spot of light, proper, is produced by impingement of a beam of electrons on a fluorescent screen, the movement being caused by deflecting the electron beam so that its changing trajectory produces different successive points of impingement. To prevent the display from being either compressed or stretched at various parts thereof, a given deflection signal should produce the same spot movement, regardless of which part of the display is being drawn. An undistorted deflection of this type is called linear.

Two types of deflection systems are widely used. The first is known as electrostatic." In one type of electrostatic deflection system a capactance is charged, and the resultant voltage thereacross is applied to deflection plates which thereupon form an electrostatic field of varying strength. This varying strength field causes the beam of electrons passing therethrough to be deflected. The second type of deflection system known as electromagnetic is one in which current is caused to flow through deflection coils. This produces a varying strength magnetic field that deflects the electron beam.

Inherently, however, these two types of deflection systems, instead of producing linear deflection, produce a deflection that progressively departs from linearity. Further increasing the nonlinearity, are the inherent system resistances, or those intentionally introduced into the circuitry for various reasons, which cause the resultant deflection to depart even further from linearity. As a result, the prior art abounds in compensatory circuitry that seeks to correct this nonlinearity.

It is therefore the principal object of my invention to provide an improved deflection circuit.

It is another object of my invention to provide an improved deflection circuit having extremely good linearity.

The attainment of these and other objects will be realized from the following specification, taken in conjunction with the drawings, in which,

FIGS. 1-4 and 6-9 show various waveforms associated with electron beam deflection; and

FIG. shows one form of my invention.

Broadly speaking, my invention produces a novel energizing signal for a deflection system, said signal comprising a composite waveform that includes a sinusoidal component and a pedestal component.

The following background information will aid in the understanding of my invention. In FIG. 1, the desired variation of the deflecting signal with respect to time is shown by the solid line waveform 10. This waveform, generally known as a sawtoot waveform, comprises a ramp portion 12 and a retrace portion 14. During ramp portion 12, the deflecting signal is increasing, and therefore deflects the electron beam progressively further from its starting point. The slope of ramp portion 12 is a measure of how fast the electron beam is deflected, while the straightness, linearity, therefore is an indication of the absence of compression or stretching. Retrace portion 14 repositions the electron beam to its starting position. Since no display is drawn during retrace, linearity is unimportant during this interval.

As previously discussed, prior art deflecting signals inherently depart from linearity. This departure from linearity produces a curved shape deflection signal known as an exponential, one form of which is shown by dotted line 16. As may be readily realized, the departure from linearity shown in FIG. 2 causes the final portions of the beam trace and therefore the cathode ray tube display to be compressed. Prior art compensating circuitry was designed to correct waveform 16 to the desired waveform 12.

It was previously explained that an electrostatic deflection system depends on variations in voltage, whereas an electromagnetic deflection system depends upon variations in current. Thus, in an electrostatic deflection system, waveform represents the variation of the deflecting voltage; whereas if the deflection system were of the electromagnetic type, waveform 10 would represent variations of the deflecting current.

In order to obtain the deflecting signal, an energizing waveform must be used. FIG. 2 shows a pedestal-type energizing waveform 18 which, when impressed across the deflection coils or the aforementioned capacitance, produces the nonlinear dotted line waveform 16 of FIG. 1. In the case of electrostatic deflection, waveform l8 represents a constant current that flows through the capacitance, and produces a deflecting voltage; whereas in the case of an electromagnetic deflection system, waveform 18 represents a constant voltage applied across the deflection coils, and produces a deflecting current.

One way of obtaining the desired solid line deflecting signal 10 of FIG. 1 with the linear ramp portion 12, is to use energizing waveform 20 of FIG. 3, wherein the ramp portion 22 compensates for the undesirable dropping off characteristic 16 shown in FIG. 1. Unfortunately, production of the ramp portion of FIG. 3 is subject to the same nonlinearity problems as waveform 12 of FIG. 1. The waveform of FIG. 3 therefore tends to be diflicult to produce.

I have found that a very close approximation of the desired waveform 10 of FIG. 1 can be provided by using the energizing waveform 24 of FIG. 4. Waveform 24 comprises a sinusoidal component 25 superposed upon a pedestal waveform component 27. Both of these components may be easily produced.

I produce composite waveform 24 by means of a sinusoidal Waveform generator, a pedestal waveform generator, and a circuit combining the outputs of these two generators. While electron tubes may be used, I have found it most convenient to use the transistorized waveform generator shown in FIG. 5. In this circuit, the sinusoidal component 25 is produced by the primary winding 26 of transformer 28 coacting with capacitance 30 to form a resonant circuit. Transistor 32, which is shown as a PNP type, acts like a switch which supplies pulses of energy to the resonant circuit. When transistor 32 is nonconductive, as controlled by the positive-going pulses of an input waveform 34, such as the one shown in FIG. 6, the resonant circuit oscillates and produces a series of sine waves. The control waveform 34 may be produced by any suitable generator, for example, a suitably connected multivibrator (not shown). The duration of the positive pulses 35' is equal to the duration of one horizontal line scan. However, the negative-going pulses 35" of control waveform 34 cause transistor 32 to conduct so that it shorts out capacitance 30. This stops the oscillations, and the circuits output appears as waveform 36 of FIG. 8. The ratio of turns between primary winding 26 and secondary Winding 38 determines the amplitude of the sinusoidal component.

The pedestal waveform 27 of FIG. 4 is produced by a circuit comprising a second transistor 40, whose state of conductivity is controlled by a second input waveform 42 of FIG. 7, which is an inverted replica of waveform 34. The waveform 42 may be produced by the same generator which produces the waveform 34, it being only necessary to invert the waveform 34. When transistor 40 is conductive, as controlled by the negative-going pulses 43' of waveform 42, power source 47 produces a constant potential across deflection coil 46, this corresponding to the desired pedestal 27. This pedestal is also produced across the secondary winding 38 of the transformer 28. The positive-going pulses 43" of the waveform 42, corresponding to the retrace interval, keep transistor 40 nonconducting.

Transformer 28 superposes the sinusoidal component 25, produced in winding 26, onto the pedestal 27, produced in deflection coil 46 to produce the composite volt age waveform 24; the short duration intervals of waveforms 34 and 42 producing the retrace portion.

Deflection coil 46 inherently contains some resistance, and pedestal 27 therefore produces an exponential current flow therethrough as shown by waveform 41 of FIG. 9. Meanwhile, the sinusoidal component 25 causes the deflection coil to experience the current flow shown by waveform 45 of FIG. 9. This result can be shown mathematically, by considering sinusoidal component 36 to be the portion of a sine wave between 270 and 90, and therefore varying its unit value from --1 to +1. Since this is a voltage, the resultant current through the coil is the mathematical derivative, and this is a cosine waveform varying between 27 and 90; its unit value therefore changes from 0 to l, to 0. The resultant currents therefore flow simultaneously through winding 38 dur ing the long interval portions 35' and 43' of input waveforms 34 and 42. Proper selection of the transformer turns ratio assures that the amplitude of the two components combine to form the straight ramp portion 44 of FIG. 9.

The foregoing inventive concept has been explained in connection with an electromagnetic deflection system where the energizing waveforms represent voltages, and the deflection signals represent current. The same inventive concept may be applied to electrostatic deflection, wherein the energizing and deflection Waveforms would represent current and voltage respectively. Whereas FIG. 5 shows the use of PNP transistors, it may at times be desirable to use NPN transistors. This is readily accomplished by reversing the polarity of the input signals and the batteries.

It may thus be seen that my invention provides easily produced waveforms that may be used to produce extremely linear deflection.

While I have described a preferred embodiment of the invention, it will be understood that I wish to be limited not by the foregoing description, but solely by the claims granted to me.

What is claimed is:

1. A voltage deflection waveform generator for producing a deflection waveform having a scansion interval and a retrace interval for application to a deflection system comprising: means producing a pedestal waveform; means energizing said pedestal waveform producing means for a duration equal to one scansion interval; means deenergizing said pedestal waveform producing means for a duration equal to said retrace interval; means producing a sinusoidal waveform; means energizing said sinusoidal waveform producing means for a duration equal to one scansion interval; means deenergizing said sinusoidal waveform producing means for a duration equal to one retrace interval; and means combining said waveforms, said combining means comprising a deflection coil.

2. A voltage deflection waveform generator for producing a deflection waveform for application to a deflection system, said deflection waveform having a scansion interval and a retrace interval, comprising: means producing a pedestal waveform; means energizing said pedestal waveform producing means for a duration equal to one scansion interval; means deenergizing said pedestal waveform producing means for a duration equal to said retrace interval; means producing that portion of a sinusoidal waveform between 270 electrical degrees and electrical degrees on the normal sine wave curve; means energizing said sinusoidal waveform producing means for a duration equal to one scansion interval; means deenergizing said sinusoidal waveform producing means for a duration equal to the retrace interval; and means combining said waveforms for the duration of said scansion interval.

3. A voltage deflection waveform generator for producing a deflection waveform for application to an electromagnetic deflection system, said deflection waveform having a scansion interval and a retrace interval, comprising; means producing a pedestal voltage waveform; means energizing said pedestal waveform producing means for a duration equal to one scansion interval; means deenergizing said pedestal waveform producing means for a duration equal to the retrace interval; means producing the portion of a sinusoidal voltage waveform between 270 electrical degrees and 90 electrical degrees on the normal sine wave curve; means energizing said sinusoidal waveform producing means for a duration equal to one scansion interval; means deenergizing said sinusoidal waveform producing means for a duration equal to the retrace interval; means combining said waveforms, said combining means comprising a deflection coil; and means applying said composite voltage waveform to said electromagnetic deflection system, whereby the resultant current in said system produces linear deflection.

4. In a deflection system having a scansion interval and a retrace interval the combination comprising: a resonant circuit comprising an inductance and a capacitance, said resonant circuit having a resonant frequency corresponding approximately to one half said interval, whereby said resonant circuit produces one half of a sinusoidal waveform during a scansion interval; means shorting out said capacitance to render said resonant circuit inoperative during said retrace interval, said shorting means comprising an electron conduction device; means producing a pedestal waveform, a deflection means; means energizing said pedestal waveform producing means for a duration equal to said interval, said energizing means comprising an electron conduction device, and means for combining said Waveforms for application to said deflection means.

5. The combination comprising: a transformer having two windings; a capacitance connected in series with one of said windings whereby a series resonant circuit is formed; a source of potential connected to said resonant circuit; a control device connected to said resonant circuit whereby, according to the state of said device, said resonant circuit is capable of producing a sinusoidal waveform of a predetermined frequency; a second circuit comprising the other winding of said transformer and a deflection coil; a source of potential connected to said second circuit; a second control device connected to said second circuit, whereby, according to the state of said second device, a pedestal waveform having a duration equal approximately to one-half the inverse of said predetermined frequency is produced at said deflection coil; means controlling the states of said devices so that said sinusoidal and pedestal waveforms are produced at the same time, whereby the action of said transformer causes said Waveforms to be combined and impressed on said deflection coil.

6. In a deflection system having a scansion interval of a predetermined time duration, the combination comprising: resonant circuit means, means for energizing said resonant circuit means to produce a substantially sinusoidal waveform signal, the parameters of the elements of said resonant circuit means being such that substantially only one half of a complete sinusoidal waveform signal is produced during the predetermined time duration of each scansion interval, means for producing during said scansion interval a pedestal waveform signal of a duration substantially equal to said scansion interval, and means for combining said pedestal and sinusoidal waveform si gnals produced during said scansion interval.

7. In a deflection system having a scansion interval of a predetermined time duration the combination comprising: a resonant circuit comprising an inductance and a capacitance, means for energizing said resonant circuit to produce a substantially sinusoidal waveform signal, the elements of said resonant circuit having parameters such so that the frequency of said sinusoidal waveform signal corresponds substantially to one half the said predetermined time duration of said scansion interval, means for producing a pedestal waveform signal of substantially rectangular shape during said scansion interval, a deflection means, and means for combining a predetermined selected portion of said sinusoidal waveform signal with each said pedestal waveform signal for application to said deflection means.

References Cited in the file of this patent UNITED STATES PATENTS 2,332,253 Peterson Oct. 19, 1943 2,479,081 Poch Aug. 16, 1949 2,496,283 Gall Feb. 7, 1950 2,513,722 Harris July 4, 1950 2,562,305 Ellsworth et al July 31, 1951 2,659,837 Murdock Nov. 17, 1953 2,739,308 Lee Mar. 20, 1956 2,911,566 Taylor Nov. 3, 1959 2,923,888 Buesing Feb. 2, 1960 2,933,641 Goodrich Apr. 19, 1960 2,962,664 Stryker et al Nov. 29, 1960

Claims (1)

1. A VOLTAGE DEFLECTION WAVEFORM GENERATOR FOR PRODUCING A DEFLECTION WAVEFORM HAVING A SCANSION INTERVAL AND A RETRACE INTERVAL FOR APPLICATION TO A DEFLECTION SYSTEM COMPRISING: MEANS PRODUCING A PEDESTAL WAVEFORM; MEANS ENERGIZING SAID PEDESTAL WAVEFORM PRODUCING MEANS FOR A DURATION EQUAL TO ONE SCANSION INTERVAL; MEANS DEENERGIZING SAID PEDESTAL WAVEFORM PRODUCING MEANS FOR A DURATION EQUAL TO SAID RETRACE INTERVAL; MEANS PRODUCING A SINUSOIDAL WAVEFORM; MEANS ENERGIZING SAID SINUSOIDAL WAVEFORM PRODUCING MEANS FOR A DURATION EQUAL TO ONE SCANSION INTERVAL; MEANS DEENERGIZING SAID SINUSOIDAL WAVEFORM PRODUCING MEANS FOR A DURATION EQUAL TO ONE RETRACE INTERVAL; AND MEANS COMBINING SAID WAVEFORMS, SAID COMBINING MEANS COMPRISING A DEFLECTION COIL.

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