US2173239A - Cathode-ray tube deflecting circuit - Google Patents

Description

N O S m T A. w

CATHODE-RAY TUBE DEFLECTING CICUIT INVENTOR VVz'lliam LTQlSon Sept. 19, 1939. w. A. ToLsoN 2,173,239

CATHODE-HAY TUBE DEFLECTING CIRCUIT Filed July 27, 1934 '2 Sheets-Sheet 2 Zit-V58 .213@ n-/ l 7j 'la 71 HV Patented Sept. i9, i939 UNITED STATES PATENT Aomi-ice mesne assignments, to Radi York,y

-America., New

laware o Corporation of N. Y., a. corporation of pplication July 27, 1934, Serial No. 737,163

11 Claims.

'I'he present invention relates to cathode-ray tube deflecting circuits and particularly to circuits for applying a deflecting voltage to electrostatic deecting plates in a television receiver tube.

In cathode-ray tubes in which the electron beam is to be deected at ahigh frequency and, especially, in which the electron beam must be v envelope of the cathode-ray tube. Even with this construction, the deflecting voltage must be rather high.

With the deflecting plates inside a cathode-ray tube of the type this diiiculty apparently being a result of the de:

fleeting plates '30 it is impossible to design a transformer which does not have a resonant point. Consequently, the transformer introduced transient voltages into 35 non-uniform speed.

It is, accordingly, an object of my invention to provide an improved electrostatic deilecting circuit for a cathode-ray tube.

More specifically, it is an object of my inven- 40 tion to provide an electrostatic deflecting circuit for a cathode-ray tube of the type utilizing electrostatic focusing which does not involve the above-mentioned disadvantages.

In a preferred embodiment of my invention, my 45 improved deecting circuit is utilized for impressing a voltage having a saw-tooth wave shape upon the deflecting plates in a cathode-ray tube of the above-mentioned type. An auto-transformer is employed for increasing the saw-tooth voltage 50 to the desired value, the auto-transformer being so designed that it does not resonate at any frequency which is a necessary component of the saw-tooth voltage wave. Transient voltages are prevented from appearing on the deecting plates 55 by means of a filter preceding the auto-,trans- (Cl. P18-7.7)

former which attenuates all frequency components having a frequency as high as the resonant point of the transformer.

In order to prevent defocusing of the electron beam, the voltage across the transformer is applied to the deflecting plates through a special potentiometer circuit.

Other objects, features, and advantages of my invention will appear from the following description taken in connection with the accompanying drawings in which,

Figure 1 is a circuit diagram of a television receiver embodying my invention;

Figure 2 is a group of curves which are referred to in explaining the operation of a portion of the circuit shown in Figure 1;

Figure 3 is a curve showing the frequency response characteristic of an amplifier in the horizontal defiectingcircuit shown in Figure 1;

Figure 4,is a diagram which is referred to in explaining the action of the auto-transformer shown in Figure 1; and

Figures 5 and 6 are diagrams which are referred to in explaining the operation of the horizontal deilecting circuit.

Referring to Figure 1, my invention is shown applied to a television receiver which includes a cathode-ray tube I comprising an evacuated envelope 3 having an electron gun therein. The electron gun consists of an indirectly heated cathode 5, a control grid l, a screen grid 9, and a first anode II. 'I'he electron beam is focused the desired amount by the electron gun and by a second anode I5 to obtain the desired small spot on the fluorescent screen I3 at the end of the envelope 3. The anode I5 may be in the form of a metallic coating on the inner surface of the envelope. Will be seen that the second anode I5 functions as an electrostatic focusing electrode as Well as means for accelerating the electrons to the necessary velocity for obtaining a bright spot on the uorescent screen I3.

Electrostatic deecting plates Il are located in'- vside the envelope 3 for dei'lecting the electron beam in a horizontal direction. The vertical deflection of the beam is preferably obtained by means of deecting coils I9. The cathode-ray tube described above is of the type described more in detail in the article by Taylor, Headrick, and Orth appearing inElectronics for December, 1933. In that article the manner in which the electron beam is focused is described. It may be noted that in some instances it is preferred to omit the screen or accelerating grid 9.

The receiving apparatus for applying picture impulses-as ing application ,Seriali No f 1934; thej transmitter iw v r signals dei; :with tneteievisiaa new is ef the@ einig reduit )il eig in i This separating circuit; is

zontall de v oscil-i lator or driver tube 39, an impulse tube Alban amplifier tube 43, and a power output tube 45. The blocking oscillator tube 39 may bev of the screen grid type including a cathode 41, a. control grid 49, a screen grid 5|, a suppressor grid 53 and an anode 55. The control grid 49 is connected through a. grid leak resistor 51 and through a bias battery l.39 to ground and through ground to the cathode 41. The grid circuit of the oscillator 33 also includes a grid condenser 6|, the secondary 63 of a transformer 65 and a coupling resistor E'l; the grid condenser, the secondary and the resistor being connected in series.

The anode 55 is connected through the primary 69 of the transformer 155 to a suitable source of positive potential. The screen grid 5I is supplied with positive potential in accordance with ordinary practice while the suppressor grid 53 is connected to the cathode 41.

The bias voltage applied to the control grid 49 by the biasing battery 59 is such that the oscillator will not oscillate unless a voltage impulse is applied to the circ 't from an external source and, when such an impulse is applied to the circuit, it'will oscillate through only one cycle and then stop.v In the usual sense, therefore, the device is not an oscillator since it will not oscillate continuously of its own accord.

The operation of the blocking oscillator tube 39 as a driver tube will be understood by referring to Fig. 2, which indicates wave shape and'phase relation but not relative magnitude. In this ngure, the horizontal synchronizing impulse which appears across the coupling resistor 61 is represented by the curve 1|, while the resulting volt- `pling circuit performs ,sl harglfillfolhzii i? tube.

The resulting awetic amplified by the amplifier tube 43 and impress upon the input circuit of the power tube through a coupling circuit which includes an inductance coil 8| and a blocking condenser 83.

The inductance coil 8| is of such value that it resonates with the grid-cathode capacity of the power tube 45 at the high frequency. end of the band of frequencies to be amplified. In some cases, additional capacity should be connected between the grid of the tube 45 and ground, as indicated at 85, in order to obtain a resonant point at the desired frequency. The tuned coutwo functions, one being to increase the response of the amplier'43-45 at the higher frequencies and the other being to cut off the highest frequency components of the same tooth wave for a purpose which Will be described later.

The effect of the inductance coil 8| resonating with the capacity of the input circuit of the tube 45 is shown by the curve 81 in Fig. 3. It will be seen that at the high frequency end of the curve 81 the gain of the amplifier is maintained at a high level and that beyond the point of resonance of the coil 8| and the tube capacity (indicated at 89) the gain drops off very rapidly.

After being amplified in the power tube 45, the saw-tooth voltage W'ave is impressed through a coupling condenser 9| upon the primary of an auto-transformer 93. In order to prevent defocusing of the electron beam in the cathode-ray tube l during deflection, as explained hereinafter, the midpoint of the transformer Winding 93 should be connected to ground as shown, this ieinem:szatieecnaitien hef;

l leakage inductances midpoint being one end of the primary section of the autoetransformer.

The saw-tooth voltage wave appears at a much higher voltage across the terminals of the transformer secondary and is impressed upon the deetisnlg plates i through blocking condensers an It has been found that de-focusing of the cathode beam during deection is prevented if the voltage on the deflecting plates ii is varied about the second anode potential. In order to obtain this result, a high resistance potentiometer 99 is connected across the deecting plates i'l'and the second anode I5 is connected through a conductor |0| to the midpoint of the potentiometer 99. It will be noted that the potentiometer 99 is also connected across the transformer secondary through the blocking condensers 95 and 91. By means of this circuit, upon the ap. plication of a deecting voltage'to the electrostatic deiiecting plates i1, when one plate is made positive a certain amount, the other plate is made negative an equal amount and the potential at a point half Way between the deecting plates remains unchanged. It is believed that because of this fact the electrostatic focusing eld is not distorted, with the result that there is no de-focusing during deflection of the electron beam.

In employing a transformer for obtaining the desired high voltage on the deecting plates, difficulty was encountered because of the leakage inductance of the transformer resonating with its distributed capacity at a certain high frequency, with the result that the resonance of the transformer introduced undesirable tran` sients into the deiiecting circuit. The effect of these transients is shown in Figure 6. It will be noted that at the beginning of each saw-tooth wave there are transients or irregularities in the wave shape indicated at |03 Whereas a voltage having the wave shape shown sired.

The reason for the occurrence of the transients on the deflecting plates will be better understood by referring to Figure 4 where the equivaient diagram for the auto-transformer 93 is shown. The mutual inductance of the transformer is indicated at |05 while the primary and secondary leakage inductances are indicated at |67 and |69, respectively. The output circuit of the power tube is represented by the alternating current generator IH and resistor H3. The distributed capacity of the transformer winding is represented by the condenser H5 while the dei'lecting plates il of the cathode ray tube are shown connected across the output terminals of the transformer. It will be seen that the distributed capacity i'i is in series with the two |07 and |09 whereby a series resonance circuit is formed which is resonant at a high frequency.

In accordance with one of the features of my invention, the transients |03 are eliminated by reducing the leakage inductance of the transformer 93 to a minimum whereby the resonant frequency is made higher than any frequency component which must be transmitted to obtain a satisfactory saw-tooth voltage wave and, since the resonant frequency is still Within the range of frequencies included in the saw-tooth wave being generated, shock excitation of the transformer resonant circuit is prevented by cutting off the high frequency components of the sawtooth defiecting wave at a frequency below the in Figure 5 is deeluded in the circuit in series resonant point of the transformer. This is ac complished, as shown in Figure 3, by means of the above-described tuned coupling circuit ill-83. In Figure 3, the leakage resonant point of the transformer 93 is indicated by the dotted line H1. It will b e seen that by resonating the inductance coil 8| with the tube capacity, the amplifier is in eiect given a sharp cut-olf at a frequency below the resonant point of the transformer 93.

It has been found that, in order to obtain satisfactory results, the transformer 93 must not be resonant at any point Withinthe range of frequencies which are impressed thereon. For this reason the transformer must be so designed that at the low end of the range of frequencies to be transmitted, the mutual inductance |05 of the transformer will not resonate with the distributed capacity H 5 at too highv a frequency. Therefore the transformer is so designed that its resonant point at the low frequency end is considerably below the fundamental frequency of the horizontal saw-tooth Waves. For example, if the horizontal deflecting frequency is 10,000 cycles per second the transformer may be so designed that its low frequency resonant point is at '7,000 cycles per second.

Vertical deiiection of the electron beam preferably is obtained by means of the deflecting coils I9 in View of the comparatively low frequency at which the vertical deflection occurs. The vertical deflecting circuit may include the blocking oscillator 31 comprising a vacuum tube l I9 which is biased by means of a biasing battery |2| beyond the cut-off point the same as the oscillator tube 39 in the horizontal deflecting circuit. The oscillator includes grid condenser |23, a grid leak resistor |25, and a feed-back transformer |21, all of which performed the functions described in connection with the horizontal blocking oscillator.

The vertical synchronizing impulses are impressed upon the grid circuit of the tube H9 through a coupling resistor |29 which is inwith the-secondary of the transformer |27. Preferably, a condenser |3| is provided for by-passing any horizontal synchronizing impulse component which may not be nltered out by the'inductance coil 35.

rThe positive voltage impulses which appear in the grid circuit of the driver tube i I9 in response to the reception of a vertical synchronizing impulse are impressed through a coupling condenser |33 -upon an impulse tube |35. The output circuit of the impulse tube |35 includes a condenser |37 having a variable resistor |39 connected in series therewith for supplying a voltage impulse wave containing a saw-tooth component. This voltage wave appears across the input circuit of a vpower tube Mii and is impressed across the deecting coils I9 to produce a saw-tooth wave of current therethrough. The

resistor |53, to which one terminal of the defleeting coils i9 is connected, is provided for the purpose of adjusting the direct current component through the deflecting coils to center the electron beam on the fluorescent screen i3.

Referring now to the voltage supplies for the deecting circuits and for the cathode-ray tube I, all the voltages for the vacuum tubes are supplied from a low voltage supply M5 across which a voltage divider mi is connected. All the plates of the vacuum tubes are connected to the positive terminal of the voltage divider |41, The screen grids of the screen grid tubes are connected to a point of lower potentialon the voltage divider |41 as indicated. The screen grid 8 of the cathode-ray tube is connected to a point of still lower potential on the voltage divider |41.

The cathode 5 of the cathode-ray tube I is connected to ground and to a point on the voltage divider |41 near its negative end, while the control electrode 1 of the cathode-ray tube is connected tothe negative end of the voltage divider |41 through a resistor |49 for maintaining it at the proper negative potential with respect to the cathode 5.

The higher voltages for the anodes and I5 of the cathode-ray tube are provided by a higher voltage supply |5| having a voltage dividerv |53 connected thereacross. The negative end of the voltage divider |53 is connected through ground to the cathode 5 of the cathode-ray tube. The second anode l5 is connected to the positive end of the voltage dividerl while the first anode is connected to a point of lower potential on the said voltage divider.

In either embodiment of my invention, the impulse tubes 4| and |35 are preferably biased be biased inserting a biasing battery (not shown) in the grid circuit. In the particular circuit illustrated, which is the preferred one, the tubes il and |35 are biased close to cut-olf by means of the ow of grid current in the coupling condenser-grid resistor combination.

Referring to the tube 4| as an example, a positive voltage impulse from the blocking oscillator 33 causes a iiow of grid current to charge the condenser 15, Between positive voltage impulses, the condenser discharges through the grid resistor 16 to maintain the grid of the tube 4| negatively biased. If the blocking oscillator is replaced by an amplifier (two resistance coupled vacuum tubes, for example) the biasing circuit shown is especially desirable as the bias on the impulse tube 3| increases with increase in signal strength whereby an automatic volume action is obtained.

The features of using a blocking oscillator 33 as a driver tube and of driving a deecing circuit directly and re-shaping a. synchronizing impulse into a saw-tooth voltage or current wave are described and claimed in my above-mentioned co-pending application Serial No. 732,415, which is assignedv to the same assignee as this application.

It will be seen from the foregoing description that I have provided a deecting circuit in which a comparatively small power or amplifier tube supplies sufficient voltage to the electrostatic deflecting plates of a cathode ray tube to deiiect the electron beam the desired amount without introducing transients during deflection. It will also be seen that I have provided a means for applying a deflecting voltage to internal deflecting plates in a cathode-ray tube without causing the electron beam to be de-focused.

It will be understood that various modifications may be made in my invention without departing from the spirit and scope thereof and I desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art and are set forth in the appended claims.

I claim as my invention: A

l. In combination, a cathode-ray tube comprising an evacuated envelope having means therein for producing a beam of electrons, a pair of deflecting plates therein for Adeflecting said beam, atransformer having a primary and a secondary, said transformer having leakage inductance and distributed capacity which resonate at a high resonant frequency to produce undesired effects, means for coupling said secondary across said deflecting plates, an amplifier having an output circuit and designed to pass a wide band of frequencies, said output circuit being connected to said primary, and means for preventing energy having a frequency as high as said resonant frequency from being impressed upon said primary.

2. Apparatus according to claim 1 characterized in that said amplifier includes an electric discharge tube comprising input electrodes having capacity effectively in shunt thereto, and further characterized in that said last means includes an inductance coil which is connected in series with said capacity and which has a value such that it resonates with said capacity at a frequency below the said resonant frequency of said transformer.

3. In a picture receiver, a cathode-ray tube comprlsing an evacuated envelope having means therein for producing a beam of electrons, a pair of deflecting plates therein for deflecting said beam, means for generating electrical deflecting impulses having a saw-tooth wave shape, means including a transformer for impressing said deecting impulses upon said deflecting plates, said transformer being resonant at a certain high frequency, and means for preventing components of said impulses having a frequency as high as said certain frequency from being impressed upon said transformer.

4. In combination, a cathode-ray tube comprising an evacuated envelope having means therein for producing a beam of electrons, electrostatic means for focusing said beam, said electrostatic means including a second anode, a pair of deecting plates in said envelope for deflecting said beam, a source of deiiecting voltage for said plates, a transformer having a primary and a secondary, said primary being connected to said source, and an impedance unit having one end connected to one end of said secondary through a condenser and having its other end connected to the other end of said secondary through another condenser, said deiiecting plates being connected across said impedance unit, and said second anode vbeing connected to a point on said impedance unit which isa mid-point with respect to the points thereon to which said deflecting plates are connected. l

5. In combination, a cathode-ray tube comprising an evacuated envelope having means therein for producing .a beam of electrons, an electrode positioned to focus said beam electrostatically, a pair of electrostatic deflecting plates in said envelope for deflecting said beam, a source of deiiecting voltage for said plates, a transformer having a primary and a secondary, said primary being connected to said source, and a resistor connected across said secondary through blocking condensers, said deflecting plates being connected across said resistor, and said focusing electrode being connected to a point on said resistor which is the mid-point with respect to the points thereon to which said defleeting plates are connected.

6. In combination, a cathode-ray tube comprising an evacuated envelope having an electron gun therein for producing a beam of electrons, said gun including a cathode, an electrostatic focusing electrode positioned to focus said beam, -a pair of electrostatic deecting plates in said envelope for deecting said beam, a source of deflecting voltage for said plates, a transformer having a primary and a secondary, said primary being connected to said source and said secondsaid source and to said y 2,173,289 f v 5 ary having its mid-point connected to said ponents all of which lie between said low i'recathode', a resistor connected across said secondquency resonant point and Isaid high frequency ary through blocking condensers. said deilectresonant point, and means' for impressing said ing plates being connected across said resistor. lsaw-tooth wave across said primary.

said focusing electrode being connected to the mid-point of s'aid resistor, .taining said focusing electrode at a positive potential with respect to said cathode.

7. In combination, a cathode-ray tube comprising an evacuated envelope having an electron 'gun therein for producing a beam of electrons.

a source of deecting voltage for said plates, a single winding transformer, the mid-point of said winding being connected to one terminal of cathode whereby Iit is maintained at the same alternating current potential as said cathode and another point on said winding being connected to the other terminal oi' said source, a resistor connected across said wind. ing through blocking condensers, said deecting plates being connected across said resistor, said focusing electrode being connected to the midpoint of said resistor. and means for maintaining said focusing electrode at a positive potential with respect to said cathode.

8. In combination, a cathode ray tube comprising an evacuated envelope having means therein for producing a beam of electrons, a pair of deiiecting platestherein for deilecting said beam, a transformer having a primary and a secondary, said transformer having a low fre.- quency resonant point and a high frequency resonant point and having no resonant point therebetween, means for coupling said deecting plates across said secondary, means for producing a saw-tooth wave having frequency comand means for main- A cathode ray device comprising means for producing aI moving beam oi electrons, an anode means for connecting substantially the midpoint of said resistance to said anode, means lfor generating saw-toothed sweep voltages, and transformer means for connecting said generating means to said deilecting plates.

10. A cathode ray device comprising means for producing a moving beam of electrons, for accelerating said beam, means for producing deflection of said beam comprising a pair o! electrostatic deiiecting plates, a high impedance unit connected between said plates, meansv for connecting substantially the midpoint of said high impedance unit to generating defiecting voltages, and transformer said deecting plates.

`11. In a sweep circuit, a condenser, means comprising a source of potential for charging said condenser substantially linearly with re-v spect to time, means comprising an electron dis- 'charge device for periodically discharging said` condenser, means for amplifying -the wave produced by the charging and discharging of said condenser, and a transformer the primary wind- WILLIAM A. TOLSON.

an anode said anode, means for

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