US2144351A - Deflecting circuit - Google Patents

Description

Patented Jan. 17, 1939 v I I UNITED "STATES PATENT 'oFFi DEFLECTING' omoorr Arthur W. Vance, Philadelphia, Pa., assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application October 31, 1934, Serial No. 750,908

7 Claims. (01. 250-36) My invention relates to deflecting circuits for circuit I! through a coupling capacitor l9. The cathode-ray tubes and particularly to television synchronizing signals consist of horizontal syndeflecting circuits which are operated in synchronizing impulses which occur at the end of chronism with controlling or synchronizing imeach scanning line and of framing impulses pulses. which occur at the end of each picture frame.

An object of my invention is to provide an The separating circuit I'I separates the picture improved deflecting circuit which is comparativesignals from synchronizing signals, and the horily low in cost. zontal synchronizing impulses from the vertical A further object of my invention is to provide framing impulses. 10 a simplified deflecting circuit which will produce The vertical framing impulses are impressed 10 a voltage of the desired waveform and which through a coupling capacitor 2| upon a vertical may be synchronized readily with a controlling deflecting circuit 23 which produces a flow of signal. saw-tooth current through the deflecting coils A still further object of my invention is to H in synchronism with the framing impulses. provide an improved deflecting circuit which will The horizontal synchronizing impulses are im- 15 produce a voltage wave containing a saw-tooth pressed through a coupling capacitor 25 upon a component and a large impulse component. horizontal deflecting circuit designed in accord- In the preferred embodiment of my invention, ance with a preferred embodiment of my invenan electric discharge tube is so connected with tion. One unit of the horizontal deflecting circuit associated circuit elements that it oscillates to is an oscillator 27 of the type described and 20 produce substantially square-top voltage imclaimed in my copending application, Serial No. pulses periodically. These impulses are im- 718,353, filed March 31, 1934, and assigned to the pressed upon a resistor and a-capacitor which Radio Corporation of America. This oscillator are connected in series, the resistor having a comprises an electric discharge tube 29 such as comparatively high resistance value. Voltage a vacuum tube having a cathode 3!, a control 25 appearing across a portion of the resistor-capacigrid 33 and a plate 35. The plate 35 is supplied tor combination is applied to a second electric with positive potential from a suitable source discharge tube which supplies either a saw-tooth such as a battery 31 through the primary windcurrent or a saw-tooth voltage to a cathode-ray ing 39 of a transformer 41. The control grid 33 p tube deflecting device. is connected through the secondary winding 43 30 Other objects, features and advantages of my of the transformer Alto the cathode 3| whereby invention will appear from the following descripthe plate and grid circuits of the vacuum tube tion taken in connection with the accompanying 29 are inductively coupled.

drawing, in which- As explained, in the above mentioned copend- 35 Figure 1 is a circuit diagram of a television ing application, the plate and grid circuits of the 35 receiver embodying my invention, and tube 29 are coupled in such phase that as the Fig. 2 is a circuit diagram illustrating another flow of plate current through the primary windembodiment of my invention. ing 39 increases, a positive voltage is applied to In Fig. 1, my improved deflecting circuit is the control grid 33 through the transformer 4|.

40 shown applied to a television receiver which in- The plate current increases until saturation is 40 cludes a radio receiver I, a picture amplifier 3 reached, at which time a negative voltage is imand acathode-ray receiver tube 5. The cathodepressed upon the control grid 33 through the ray tube 5 comprises an evacuated envelope havtransformer 4! whereby the tube 29 is rapidly ing a fluorescent screen I at one end and an driven beyond the cut-off point. As a result of 4,5 electron gun 9 at the other end for producing this action, negative voltage impulses of the charan electron beam. acter indicated by the curve 45 are produced Suitable deflecting devices, such as deflecting across the secondary winding 43. coils II and i3, are provided for deflecting the In practice it has been found that in order electron beam vertically and horizontally, reto produce a substantially perfect saw-tooth ourspectively, for scanning the fluorescent screen 1. rent flow through a deflecting coil, the voltage 50 The output of the picture amplifier 3 includes impressed upon the deflecting coil circuit must both picture signals and synchronizing signals, contain a saw-tooth component in addition to all these signals being impressed upon the con the square-top impulse component, this being trol grid of the cathode-ray tube 5 through a necessary since the deflecting coil circuit is not coupling capacitor [5 and upon a separating purely inductive. In order to produce such a 55 composite voltage wave, I provide a resistor 41 having a comparatively high resistance value and a capacitor 49 connected in series. The secondary winding 43 of the transformer is connected across this resistor-capacitor combination, the connection to the resistor 4'! being through a slidable contact point 5|. By varying the position of the contact point 5| the magnitude of the electron beam deflection may be varied as will be apparent from the following description.

The impedance of the resistor 41 is so high that the flow of current through the capacitor 49 produced by the square top voltage impulses 45 is substantially independent of the voltage built up across the capacitor 49 as it becomes charged. Therefore, the flow of current through the capacitor 49 and resistor 41 has substantially the same wave form as the voltage as indicated by the curve 0. The voltage appearing across the capacitor 49 will have a saw-tooth wave form as indicated by the curve e'e. The voltage appearing across the resistor 41 will have the form indicated by the curve ir, er. It will 'be apparent that the desired composite wave form for producing a flow of saw-tooth current through a deflecting coil may be obtained by adding the saw-tooth voltage appearing across the capacitor 49 to the square-top voltage impulse appearlng across a portion 01' the resistor 41.

The composite voltage wave is impressed upon the input terminals of an electric discharge tube 53 which preferably is a vacuum tube having a low plate impedance, As illustrated, the tube is a vacuum tube comprising a cathode 55 a control gride 51 and a plate 59. The control grid 51 is connected through a slidable contact point 6| to the resistor 41. The cathode 55 is con nected through a self-biasing resistor 63 to the lower end of the capacitor 49, the self-biasing resistor being provided with the usual by-pass capacitor 65. r

The plate 59 of the vacuum tube 53 is supplied with a positive potential from a suitable source, such as a battery 61, through an inductance coil 69. One terminal of the deflecting coils I3 is connected to the plate 59 through a conductor H and a blocking capacitor 13, while the other terminal of the coils I3 is connected tothe cathode 55 through a conductor 15. A resistor TI is provided which may be connected across the deflecting coils l3 by means of a switch 19 for a purpose which will be described hereinafter.

An important characteristic of my improved deflecting circuit is that the impulse component of the voltage wave applied to the deflecting coils may be much larger than the voltage of any battery or another power supply. For this reason my circuit is especially valuable where it is desired to employ a low plate impedance output tube such as the one illustrated. It will be understood that because of its low plate impedance, such a tube requires only a small saw-tooth component in the voltage impressed upon its input electrodes.

It may be noted that there are several advantages in employing an output tube having a low plate impedance, One advantage is that because of the small saw-tooth voltage component required, any imperfection in this saw-tooth component has comparatively little effect on the shape of the deflecting current wave form. Therefore, with a low impedance tube it is easier to obtain a good saw-tooth current in the deflecting coils.

A further advantage in the use of a low impedance output tube is pointed out in my copending application, Serial No. 741,230, filed August 24, 1934, and assigned to RCA Victor Company, Inc. In the said application it is shown how a resistor, such as the resistor Tl, may be connected across the deflecting coils whereby energy stored in these coils will be discharged through the resistor instead of through the Vacuum tube during the return line period. This makes it possible to obtain a greater deflection with a given size vacuum tube by increasing the plate voltage and, at the same time, increasing the number of turns on the deflecting coils. With the circuit operated in this manner, the plate voltage is raised considerably above the rated plate voltage with a corresponding increase in plate current, providing a low plate impedance type of tube is employed. In the case of a screen grid tube, which has a high plate impedance, an increase in the plate voltage above the rated value will not materiallyincrease the plate current output.

If the circuit is adjusted to operate with the deflecting coils discharging through a resistor, instead of through the vacuum tube, the preferred adjustment is such that the impulse component of the voltage impressed upon the grid of the output tube is great enough to drive the tube beyond the cut-off point.

My deflecting circuit is easily synchronized with the incoming synchronizing impulses in the manner described in my above mentioned application, Serial No. 718,353. As stated in that application, the oscillator readily oscillates in synchronism with negative synchronizing impulses applied to the control grid.

In Fig. 2, an embodiment of my invention is shown applied to a vertical deflecting circuit. In this circuit a generator of square-top voltage impulses is indicated at 8|. The squaretop impulses, similar to the impulses 45, are impressed across a resistor 83 and a capacitor 85 connected in series whereby a voltage wave having a sawtooth component and an impulse component is produced which may be impressed upon a vacuum tube indicated at 81. In this embodiment, the output tube 81 is shown as a pentode although it will be understood that a different type of tube may be utilized if desired. Positive potential is applied to the plate of the tube 87 through a plate resistor 89 instead of through an inductance coil because of the difflculty in obtaining an inductance coil having the desired high impedance at the low vertical deflecting frequency.

The output circuit of the tube is coupled to the vertical deflecting coils H. It may be noted that deflecting coils always have a certain amount of distributed capacity as indicated in dotted lines at 9|. This causes certain undesired resonant efiects which are minimized by damping the resonant circuit. If a low impedance tube, such as illustrated in Fig. 1, is employed as the output tube, its plate impedance may be low enough to provide the necessary damping. In Fig. 2 the necessary damping is provided by the plate resistor 89 which is efiectively shunted across the deflecting coils Hand the distributed capacity.

While certain types of tubes and certain circuit values have been indicated in Figs. 1 and 2, it Will be understood that these are merely given by way of example. The circuit values are indicated in ohms, micro-farads, henrys, and number of turns. Also, although only one form of impulse generator has been illustrated, it should be understood that other forms may be substituted. For example, in a television transmitter deflecting circuit, the vacuum tube oscillator 21 may be replaced by a rotatable disc having openings therein through which a light beam passes to strike a photoelectric cell for the production of voltage impulses in a manner well known.

It will be apparent that various other 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 imposed thereon as are necessitated by the prior art and set forth in the appended claims.

I claim as my invention:

1. In combination, means for producing substantially square-top voltage impulses periodically, a resistor and a capacitor connected in series, means for impressing said impulses across said resistor-capacitor combination, an electric discharge tube having an input circuit and an output circuit, means for appying the voltage drop appearing across said capacitor tosaid input circuit, and a utilization device coupled to said output circuit, said resistor having such high impedance that the flow of current produced through said capacitor by said voltage impulses is substantially independent of the voltage built up across said capacitor.

2. Apparatus according to claim 1 characterized in that said utilization device is an inductance coil and further characterized in that, in addition to the voltage drop across said capacitor, the voltage appearing across a portion of said resistor is applied to said input circuit.

3. Apparatus according to claim 1 characterized in that said tube is a low plate impedance tube of the three element type.

4. Apparatus according to claim 1 characterized in that said first means comprises an electric discharge tube having plate and grid circuits which are inductively coupled and which are non-resonant at the frequency of occurrence of said impulses.

5. In combination, means for producing substantially square-top voltage impulses periodically, a resistor and a capacitor connected in series, means for impressing said impulses across said resistor-capacitor combination, a three element vacuum tube having an input circuit and an output circuit, said tube having a low plate impedance, inductance coils coupled to said output circuit, and means for applying the voltage appearing across said capacitor and the voltage appearing across a portion of said resistor to said {input circuit, said resistor having such high impedance that the flow of current produced through said capacitor by said voltage impulses is substantially independent of the voltage built up across said capacitor.

6. Apparatus according to claim 5 characterized in that a resistor element is shunted across said inductance coils, and further characterized in that the voltage appearing across said resistor portion is of the proper polarity and magnitude to drive said tube beyond cut-off.

'7. In combination, means for producing substantially square-top voltage impulses periodically, a resistor and a capacitor connected in series, and means for impressing said impulses across said resistor-capacitor combination whereby a voltage having an impulse component and a saw-tooth component may be taken therefrom, said resistor having such high impedance that the flow of current produced through said capacitor by said voltage impulses is substantially independent of the voltage built up across said capacitor.

ARTHUR W. VANCE.

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