US2739264A

US2739264A - Cathode ray tube intensity compensation

Info

Publication number: US2739264A
Application number: US302172A
Authority: US
Inventors: Warren T Shreve; Robert J Mccurdy
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-08-01
Filing date: 1952-08-01
Publication date: 1956-03-20
Anticipated expiration: 1973-03-20

Description

March 20, 1956 w. T. SHREVE ET AL 2,739,264

CATHODE RAY TUBE INTENSITY COMPENSATION Filed Aug. 1, 1952 VOLTAGE IN VEN TOR.

-WARRE/V 7.' SHREl E BY ROBE/FT J McCURD) I AHOIQya CATHODE RAY TUBE INTENSITY COIVHENSATION Warren '1. Shreve, Oreland, Pa., and Robert J. McCurdy, Bridgeboro, N. 5., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application August 1, 1952, Serial No. 302,172

6 Claims. (Cl. 315-22) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates generally to cathode ray tube brightness control and more particularly to means for controlling the trace brightness in accordance with average signal or beam deflection rate.

It has previously been proposed that the grid of the cathode ray tube be modulated in accordance with the voltage applied for deflection of the beam, this arrangement being particularly applicable to radar and other similar applications of the cathode ray tube. By this means the base line is substantially eliminated and only the desired pips are shown on the tube. It has also been proposed that the beam be intensified during the interval of deflection by an amount proportional to the average of the deflecting voltage in order that additional beam intensity be provided to maintain trace brightness during the more rapid movement of the beam when it is being deflected. Various other modifications have been employed in an eifort to secure special effects or other features related to trace intensity.

In certain information display circuits employing a cathode ray tube it has been the practice to employ a cathode voltage control for the purpose of adjusting cathode ray beam intensity to provide appropriate visibility. In such circuits the beam intensity may be selfregulating in that a higher average beam intensity causes an increased cathode current in the cathode ray tube and this increased current automatically elevates the cathode potential, as for example, when the cathode is controlled by a voltage drop across series-connected resistors between a positive voltage supply and ground, the cathode being connected to a point in the series resistance array. The cathode ray tube control grid is then normally controlled by a separate voltage dropping device either between the positive supply and ground or between the positive supply and a negative supply, such that the average grid potential can be held at a desired potential either slightly above or slightly below ground in accordance with cathode potential and required bias. In a circuit of this type the beam intensity is controlled in accordance with the beam intensity desired and may be adjusted by adjusting the potential at which the cathode is connected. This arrangement providesa means for limiting brightness of beam trace but does not fully compensate for changes in frequency of sweep or in duty cycle for a given sweep frequency.

It is accordingly an object of the present invention to provide means for further controlling the beam intensity in accordance with the averaged signal applied to the deflecting plates of the cathode ray tubes.

A further object of the invention is to provide simple and efficient means for amplifying a fixed portion of the deflecting signal and applying the amplified signal at a changed potential for control of beam brightness.

A still further object of the invention is to provide means for decreasing average grid potential of a cathode ray tube as the sweep frequency or sweep duration is increased.

A still further object is to provide simple means in a cathode ray grid control circuit for transferring a beam intensity regulating voltage to a lower potential level.

Other objects and features of the invention will become apparent to those skilled in the art as the disclosure is made in the following detailed description of a preferred embodiment of the invention as illustrated in the accompanying sheet of drawing in which:

Fig. 1 is a diagrammatic view of an electrical circuit in accordance with present invention;

Fig. 2 illustrates a sweep voltage signal of two different frequencies and two duty cycles, each with an averaged sweep voltage indicated thereon.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts, there is shown in Fig. 1 a circuit for applying a portion of the sweep voltage, after averaging the same, to an amplifying device and thence through voltage transferring means to a cathode follower tube from which an output signal is applied in control of the grid potential of a cathode ray tube. This circuit comprises 4 tubes of which 101 is preferably a triode connected as an amplifier, 102 and 103 are gaseous discharge tubes such as normally used for voltage regulators and 104 is preferably a triode arranged as a cathode follower. The input for triode 101 is taken across resistor 11, one end of which is grounded and the input voltage thereacross is averaged by an averaging circuit comprising series resistor 12 and parallel capacitor 21. The junction of 12 and 21 is connected to the grid 31 of tube 101. Tube 101 may be self-biased by means of cathode resistor 14 in any conventional manner or by a biasing battery 23 between resistor 11 and ground, or by both means. Tube 101 is supplied from a suitable direct current voltage source B+ of suitable value such as 180 volts, the current supply being through resistor 13, the resistance of 13 being large with respect to the resistance of 14 in order to provide appropriate amplification within the tube circuit.

Triode 104 is preferably connected at the plate thereof to the same power source, the cathode being connected to ground through a load resistor 16 in conventional cathode follower relationship. The grid 32 of triode 104 is preferably controlled at a potential below the cathode potential in accordance with the amplified signal from triode 101, the circuit being provided by connection of two constant

voltage discharge tubes

102 and 103 in series between the anode of 101 and the grid 32, connection therefrom being made through resistor 15 to a negative voltage terminal, for example, volts negative. By this means it may be seen that voltage variations occurring at the relatively high positive potential existing at the anode of amplifier 101 are transferred substantially without change through

tubes

102 and 103 to the grid 32 at an appropriate lower potential. It is seen that

tubes

102 and 103 are thus a potential dropping device interposed between

series resistors

13 and 15 connected between the positive and negative power terminals.

Since the averaging circuit comprising resistor 12 and condenser 21 is imperfect and the imperfections thereof become amplified in effect. in tube 101 and resistor 13 a further condenser 22 is connected between the anode of tube 101 and ground in order to further stabilize the'positive voltage at the anode of

tubes

101 and 102.

The cathode ray tube 105 is shown schematically hav ing therein deflecting

electrodes

106 and 107, of which 107 is taken as the pair of sweep producing electrodes energized by a suitable sweep generator which producw a sweep signal of variable duration and frequency, such Patented Mar. 20, 1956.

as 26. The accelerating electrode is conveniently connected to the positive voltage supply employed for energization of

tubes

101 and 104. The series resistors 17, 18 and 19 are also connected between the same positive voltage supply and ground, connection being provided from resistor 18 through a variablecontact arm to the cathode of tube 105. The accelerating voltage of the cathode ray tube accordingly is the voltage between the positive voltage supply and the contact arm of resistor 18 and remains fixed for any particular adjustment of beam intensity. if the grid 36 of tube 105 were connected to a fixed point in the series resistor array 17, '18 and 19, the beam intensity would remain constant.

When the grid is connected to a separate voltage source generator 26 and ground, and has an adjustable arm 25 thereon which is connected to resistors 11 and 12 and supplies the input voltage for amplifier 101- through the averaging circuit- Potential divider 24 is employed to select any desired portion of the sweep voltage and apply the same as an input to the brightness control circuit.

In Fig. 2 there is shown in a voltage against time diagram a typical sweep voltage pattern a as employed in radar or other electronic distance measuring apparatus. At b is shown a similar pattern at increased frequency and at ca similar pattern except that the duration of the sweep has been increased to effect a longer duty cycle. The

dashed lines

33, 34 and 35 indicate average signal level for the patterns at a, I) and c respectively. It is seen that the average signal level in b and c is higher than in a. Therefore there is a rise in voltage at grid 31 corresponding to the higher average sweep voltage whenever the sweep freqeuncy or duty cycle is increased for a given tube persistence and energization. Since either of these circumstances would result in a brightened trace, by more frequent repetition and by longer dwell in each sweep of a given sweep velocity, an undesirable brightening or fluctuation is encountered, even though some degeneration is inherent in the circuit whenever the cathode of tube 105 is resistively coupled to ground.

By the circuit means hereinbefore described an automatic compensation is provided for screen brightness fluctuations due to causes such as change of sweep frequency and change of duty cycle. The average signal to the sweep electrodes is taken in whole or in part, applied to the grid of an amplifier, the potential level of the amplified resultant change of average sweep signal is transformed to a lower potential level, applied to the coupling device, such as a follower triode circuit and then applied to the current control grid of the cathode ray tube in opposite polarity to the change in average sweep voltage, thereby compensating the tendency of the trace to fluctuate. It is found that amplification of the changes of averaged sweep voltage is generally necessary to effect complete compensation. It is further desirable that the degree of compensation be readily adjustable and potential divider 24 provides this adjustment while effectively coupling the sweep voltage to the averaging circuit input.

Various modifications are contemplated and may obviously be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as

hereinafter defined by the appended claims, as only a preferred embodiment thereof has beendisclosed.

\Vhat is claimed is:

1. In an information display system including a cathode ray tube having therein a cathode, control grid and deflecting electrodes, the combination of, a sweep generator adapted to produce a sweep signal of variable duration and frequency, said generator being connected to energize the deflecting electrodes of the cathode ray tube, means selecting a portion of the voltage energizing said electrodes, means averaging said selected voltage, means amplifying and inverting changes in said averaged selected voltage, non-linear means transferring said amplified voltage from a higher to a lowerpotential level without change of magnitude thereof, means coupling said transferred voltage to said control grid of the cathode ray tube, whereby changes in average voltage applied to the electrodes are amplified, inverted and applied to prevent cathode ray tube trace brightness changes.

2. In the system of claim 1 the transferring means comprising a gaseous discharge means of the voltage regulator type connected between the output of the amplifying means and a potential point below the potential of said cathode. i

3. In the system of claim 1 said coupling means comprising a cathode follower circuit having a grid thereof at said lower potential level and controlled by said amplified voltage and having the output thereof connected to said cathode ray tube grid.

4. In combination, a cathode ray tube having a cathode, a controltgrid and deflecting means; a sweep generator adapted to producea sweep signal of variable sweep duration and sweep freqeuncy; an averaging circuit; means for applying the output of the sweep generator to the deflecting means of the cathode ray tube and for applying a portion of the output of the generator to the averaging circuit; a'D. C. amplifying circuit having an odd number of stages of amplification; a cathode follower circuit; a coupling circuit, said coupling circuit connecting the output of the amplifying circuit to the input of the cathode follower circuit; the output of the cathode follower circuit being connected to the control grid of the cathode ray tube; whereby, the light intensity of the cathode ray tube is of subsantially constant value irrespective of the length of each sweep or the magnitude of the sweep frequency of the signal produced by the sweep generator.

5. In the combination defined in claim 4 in which the number of stages of the D. C. amplification is one. 6. In the combination defined in claim 5 in which the coupling circuit comprises a voltage regulating tube and a resistor connected in series.

References Cited in the file of this patent UNITED STATES PATENTS 2,313,967 Read Mar. 16, 1943 2,363,810 Schrader et al 'Nov. 28, 1944 2,399,754 Miller May 7, 1946 2,438,717 Puckette Mar. 30, 1948 2,448,299 Dorne Aug. 31, 1948 2,453,711 Isbister Nov. 16, 1948 2,455,373 Lester Dec. 7, 1948 2,465,364 Ferrar Mar. 29, 1949 2,569,240 King et al. Sept. 25, 1951 2,620,455 Fockler Dec. 2, 1952 2,648,027 Geohegan Aug. 4, 1953