US2093177A

US2093177A - Cathode ray tube deflecting cir

Info

Publication number: US2093177A
Authority: US
Publication date: 1937-09-14
Anticipated expiration: 1954-09-14

Description

Sept. 14, 1937. A. w. vANcE GATHODE RAY TUBE DEFLECTING CIRCUITS 2 Sheets-Sheet 1 Filed March 30,. 1935 INVEN'I'OR HrthurW Vance BMM;

H'T'T'ORNEY Sept. 14, 1937.` A, w, VANCE 2,093,177

CATHODE RAY TUBE DEFLECTING CIRCUITS Filed March 50, 1935 2 Sheets-Sheet 2 Plate Gaf/etui rlowr VII/100e,

Patented Sept. 14, 1937 Parar Frlc CATHODE RAY TUBE DEFLECTING CIR- CUITS Arthur W. Vance, Haddoniield, N. J., assigner to Radio Corporation of America, a corporation of Delaware Y Application March 30, 1935, Serial N0. 13,'815

9 Claims.

My invention relates to cathode ray tube deflecting circuits and particularly to circuits for supplying to deilecting coils a iow of current having a saw-tooth wave form.

One object of my invention is to provide an improved defiecting circuitl for producing a ow of current in cathode ray tube deilecting coils which has a substantially pure saw-tooth wave form.

m A further object of my invention is to provide a simplified deflecting circuit which can be synchronized easily and which will supply current having a saw-tooth wave form.

A still further object of my invention is to provide a defiecting circuit having the minimum number of vacuum tubes for supplying current having a substantially pure saw-tooth wave form.

In one of the preferred embodiments of my invention, two electric discharge tubes are employed, the output circuit of one tube being coupled to the input circuit of the second tube through a wave shaping network. The output circuit of the second tube includes a pair of deiiecting coils and the voltage appearing across these coils is fed back to the input circuit of the iirst tube in such phase that the complete circuit is self-oscillatory. The first tube is biased substantially to cut-oil, while the second tube is preferably of a larger size which may be biased o for operation along the linear portion of its characteristic.

lOther objects, features and advantages of my invention will appear from the following description taken'ln connection with the accompanying drawings, in which l Figure 1 is a circuit diagram of a deiiecting circuit embodying my invention;

Figs. 2 and 3 are circuit diagrams of other embodiments of my invention;

Fig. 4 is a characteristic curve of a tubeshown in Fig. 1; and

Figs. 5 and 6 are curves which are referred to in explaining the operation of my improved deilecting circuit.

Referring to Fig. `1, the deecting circuit inciudes two electricv discharge tubes I and 2 which may be oi the three electrode type as illustrated. Preferably, the second tube has 'a considerably greater power rating than the first tube, the

50 tube being of the 245 type and the other tube being of the 227 type in the speciiic circuit being described.

The iirst tube has an indirectly heated cathode 3. a control grid 4 and a plate 6. 'I'he plate 6 u is supplied with a suitable positive potentialy (Cl. Z50-27) through an impedance unit such as a resistor 'I from any suitable source of potential.

The inputcircuit of the tube I includes a grid resistor 8 and a self-biasing resistor 9, the selfbiasing resistor being shunted by a condenser 5 II having a suitable capacity value.

The second tube 2 comprises a directly heated cathode I2, a control grid I3 and a plate I4. The cathode I2 is supplied with current from any suitable source (not shown), the current source and the cathode being shunted by a. potentiometer I8.

'I'he input circuit of the tube! includes a grid resistor I1 and a self-biasing resistor I8 which is connected to the midpoint of the po- 15 tentiometer I6 in accordance with well known practice. The self-biasing resistor I8 is shunted by a condenser I9 which has a capacity of the proper value to maintain a substantially steady bias on the control grid I3. 20

The plate I4 of the tube 2 is supplied with a positive potential through an impedance unit such as a choke coil 2l from a suitable voltage source (not shown). A pair of defiecting coils of a cathode ray tube (not shown) are indicated 25 at 22, these coils being coupled to the output circuit of the tube 2 through a blocking condenser 23 and a conductor 24.

The output circuit of the rst tube I is coupled to the input circuit of the second tube 2 through 30 a wave shaping network 25 which comprises a resistor 26 and a condenser 21 connected in series. This network is connected across the output circuit of thefirst tube through a coupling condenser 28. 'I'he input circuit of the second 35 tube is connected across the network 25 through variable tap 29 on the resistor 26. v

It will be evident that if a positive voltage impulse is impressed upon the grid 4 of the iirst tube, a positive voltage impulse will appear in 40 the output circuit of the second tube 2. Thereiore, by coupling the output circuit of the second tube to the input circuit of the rst tube the deiiecting circuit is made self-oscillatory. In the preferred embodiment, this coupling is made through a coupling condenser 3i but it should be understood that this coupling may be made through a transformer if desired.

One of the features of my invention is that the nrst tube I is normally biased substantially to 5o plate current cut-of! `while the second tube 2 is normally biased to operate along substantially the linear portion of its characteristic. The

characteristic oi the rst tube is shown by the curve 82 in Fig. 4, the dotted line 33 indicating 55 the bias point about which the tube works. It will be apparent that if the grid is swung positive, there will be a large flow of plate current, while if the grid is swung negative, there will be only a small plate current iiow.

Before explaining the manner in which the deecting circuit oscillates to produce a ow of saw-tooth current through the deflecting coils 22, it may be pointed out that if the deflecting coils 22 are substantially purely inductive, (which they are in the preferred circuit) when current having a saw-tooth wave form flows through them, the voltage appearing across the coils will have the rectangular wave form shown by the curve 3@ in Fig. 5. If a voltage having this wave form is impressed upon the input circuit of the rst tube I, a Voltage having the same wave form will be impressed across the wave shaping network 25. This voltage will produce a current flow through the resistor 26 and condenser 2l whereby a voltage impulse having a rectangular wave form will appear across the resistor 26 as indicated by the curve 36 in Fig. 6 and a voltage having a sawtooth wave form will appear across the condenser 2l as indicated by the curve 3l in Fig. 6. As ex- 'plained in my VCanadian Patent No.. 346,227, issued November 20, 1934, by moving the tap 28 along the resistor 2'6 to obtain the proper ratio of rectangular voltage to saw-tooth voltage, current having a substantially pure saw-tooth wave form will iiow through the deecting coils 22. If the plate impedance of the tube 2 is low, only a small saw-tooth component is required in the voltage impressed upon the grid I3 of that tube. However, if the plate impedance of the tube is high, as in the case of a screen grid tube, the saw-tooth component which is required may be much greater than the impulse component.

Referring now to the manner in which the circuit oscillates, if we assume a small change in a decreasing direction of the plate current of the second tube 2, this will swing the grid d of the rst tube positive through the coupling condenser 3l. This positive voltage, of course, is put on the grid t as a result of the charging current of the coupling condenser flowing through the grid resistor 8. As a result of the positive voltage on the control grid 4, there will be an increase in the -plate current of the tube I whereby there will "be a less positive or .a more negative voltage applied to the control grid I3 of the second tube, thus further decreasing the plate current of that tube. This further decrease in plate current applies a still more positive potential to the grid 4 of the first tube through the coupling condenser 3l. It will be seen that this is a curnulative action and that it will `continue until either the plate current of the second tube can decrease no more or until the plate current of the iirst tube can increase no more, probably the latter in this particular circuit where the second tube has a much greater power rating .than the first tube.

As the first tube reaches the condition of plate current saturation v(or the second tube the condition of cut-off), less charging current is fed through the coupling condenser 3I and through the grid resistor ilv whereby less positive voltage is applied to the grid t. This causes the grid I3 of the second tube to become less negative whereby the plate current of the tube 2 begins to increase.

As a result a negative voltage is applied through the coupling condenser 3I to the grid d. This causes the grid I3 of the second tube to become This action is also cumulative and continues either until the plate current of the first tube can decrease no more or until the plate current of the second tube can increase no more, probably the former condition because of the high bias on the first tube.

From the above description it will be seen that the voltage which appears across the deflecting coils 22 is impressed upon the grid t of the first tube and that, if there were no resistance in the defiecting coil circuit, the rectangular voltage impulse appearing across the deilecting coils (as the result of saw-tooth current flowing therethrough) would have exactly the wave form required for the voltage which is to be impressed upon the grid I3 of the second tube. Since the deflecting coil circuit includes the plate resistance of the second tube 2 as well as a certain amount of resistance in the coils, the wave shaping network 25 is essential because otherwise it would be impossible to give the deflecting coil current a saw-tooth wave shape; and, consequently, the voltage appearing across the deflecting coils 22 would not have the rectangular wave shape shown in Fig. 5. Furthermore, even if it did have this rectangular wave shape, the voltage impressed upon thegrid I3 of the second tube would not have the proper wave form since the vrequired sawtooth component would be missing.

From the above remarks it will be apparent that in order to obtain a voltage across the wave shaping network 25 which consists of a rectangular component and a saw-tooth component, a rectangular voltage Wave must be impressed on the grid of the rst tube, and that a voltage having this wave form can be obtained from the output circuit of the second tube only by passing a substantially pure saw-tooth current through the deflecting coils, the wave shape of the deecting coil current, in turn, being dependent upon the Voltage obtained across the wave shaping network. It might appear that with one unit in the circuit dependent upon another unit in this manner it would be impossible to obtain a satisfactory circuit adjustment. Experience has shown, however, that it is not especially difcult to so adjust a circuit of this character that the current flowing through the deflecting coils will have a perfect saw-tooth wave form. To adjust the circuit, the coupling condenser 3l is adjusted to a capacity value such that the circuit oscillates at approximately the desired frequency. Then the variable tap 29 is moved along the resistor 26 of the wave shaping network until the wave form of the deecting coil current is made as close to a sawtooth as possible. This causes a slight change in the frequency of oscillation which is corrected for by readjusting the coupling condenser 3l. The change in the capacity of the coupling condenser also causes a slight change in the wave form of the deecting coil current. The adjustment of the wave shaping network is again changed to produce a still more perfect saw-tooth current. After several such circuit adjustments, the current passing through the deecting coils has a perfect saw-tooth wave form.

The reason that the positive voltage impulse impressed upon the grid t of the rst tube through the coupling condenser 3l is of much shorter duration than is the negative voltage impulse, may be explained by the fact that the coupling condenser 3I cannot transfer any direct current energy. Therefore, the energy in the positive cycle must equal that in the negative cycle, or expressing in a diierent way, the area of a positive impulse must equal the area of a negative impulse as indicated in Fig. 5. Since the iirst tube is biased substantially to cut-off, a positive voltage impressed upon the grid causes a much greater change `in voltage in the output circuit of the second tube than does a negative voltage of equal magnitude. For the areas under the positive and negative cycles to be equal, the time taken by the negative swing `rnust be considerably longer than the time taken by the positive swing.

The difference in the duration of the positive and negative cycles may also be `explained if we assume that the positive impulse fed back to the grid 4 of the first tube causes the coupling condenser 3I to charge to a voltage more than sumcient to block the tube i at the end of the positive impulse. The positive impulse lasts for the time required for the deiiecting coils 22 to discharge their stored energy through the second tube 2.

The first tube remains blocked until the charge on the coupling condenser 8i has had time to leak oil through the grid resistor 8 sumciently to raise the grid bias above the cut-oil value. This determines the comparatively long duration of the negative cycle.

It should be understood that it is diiiicult to determine the exact operation of a circuit oi this character, and that, for this reason, I do not wish t? be limited to any particular theory of opera- The operation of the circuit as described above l depends upon using a coupling condenser 8| which has sumciently small capacity. However, if a coupling condenser of large capacity is used. a capacity so large as to have a very small alternating current impedance at the frequencies involved, the same result can be obtained by givingv the condenser il shunting the self-bias resistor 8 a suillciently small capacity. If this embodiment of my invention is employed, the circuit is adiusted the same as previously described except the capacity of the shunting condenser Il is adjusted iarstead of the capacity of the couplingrcondenser When the capacity values indicated in Fig. 1 for condensers Ii and 8l are employed, the frequency of oscillation is determined mainly by the capacity of the coupling condenser 8| and to a less extent by the capacity of the condenser I i.

The above-described detlecting circuit was utilizedfor generating saw-tooth deiiecting wavesfor the comparatively high frequency horizontal deflection in a television receiver. The circuits shown in Figs. 2 and-3 were designed i'o'r providing the comparatively low frequency saw-tooth waves required for vertical deection.

Referring to Fig.r2, the deflecting circuit comprises two screen grid tubes 4i and 42 connected as a direct current ampiier. The first tube 4i has an indirectly heated cathode 48. a control grid 44, a screen grid 46 and a plate 41. A positive potential is supplied to the plate 41 through a plate resistor 48 from a voltage divider 48. The screen grid 48 is supplied with a suitable positive potential.

The input circuit of the tube 4I includes a grid resistor 5I and a biasing resistor 82, the-grid end of the vbiasing resistor 52 being connected to the negative terminal of the source of biasing voltage (not shown). I

The secondtube 42 includes an indirectly heated cathode |58, a control grid 84, a screen grid 88 and a plate 61. The plate 81 is supplied with a positive potential through a choke coil 58 and a resistor 89 from the voltage divider 49. The

screen grid 58 is supplied with a lower positive potential from a point on the voltage divider 48.

The control grid 54 is connected through a conductor 6I directly to the plate 41 oi the first tube. The cathode 58 is connected through a resistor 82 A to the cathode 48 of the iirst tube whereby the ilow of plate current through the resistor 62 maintains the cathode 68 positive with respect to the control grid 54. The resistor 62 is shunted by a suitable by-pass condenser 68.

A wave shaplngnetwork 64, similar to the one previously described and comprising a resistor 6E and a condenser 61, is connected across the input circuit of the second tube 42.

Cathode ray tube deecting coils indicated at 68 are connected across the output circuit of the tube 42, the Yupper terminal of the coils being connected to the plate 51 through a coupling condenser 68 and the other terminal of the coils being connected to the cathode 53 through a con-l ductor 1 i.

The output circuit oi the second tube 42 is coupled to the input circuit of the rst tube 4i through a coupling condenser 12. this condenser having one plate connected to the junction point of the inductance coli 58 and th/e resistor 59 and having the other plate connected to the control grid 44.

In the particular circuit illustrated, synchronizing impulses are applied through a resistor 13 and a condenser 14 to the plate 41 of the nrst tube. A condenser 18 is connected between the plate end of the resistor 18 and ground so that it, in con- Junction with the resistor 13, separates vertical synchronizing impulses irom horizontal synchronizing impulses. In this circuit. as in the circuit shown in Fig. 1, theldeilecting circuit may be synchronized by impressing the synchronizing im- 4 pulses upon either the plate or the grid of the iirst 18, a control grid 8|, a screen grid 82 and a plate 83.

The plate 88 is supplied through a resistor 84 with a positive potential from a suitable voltage source. The input circuit of the tube 11 includes a grid resistor 88 and a self-biasing resistor 81, the self-biasing resistor being shunted by a condenser 88 which, as stated in connection with Fig. 1, may have a large capacity value if a small coupling or feed-back condenser is employed. but which must have a comparatively small capacity value if the coupling condenser has a lange capacity.

The second tube 18 includes a cathode 88, a control grid 8| and a plate 82. The plate 92 of the second tube is supplied through a choke coil 88 with a positive voltage from a suitable voltage source. The input circuit of the tube 18 includes a grid resistor 84 and a suitable biasing source such as a biasing battery 88.

The output -circuit oi the first tube 11 is coupled to the input circuit of the tube 18 through a coupling condenser 81. In this embodiment o! the invention, a wave shaping network 85 comprising a resistor 88 and condenser 89 in series are connected across the output electrodes of the viirst tube 1l. It will be noted that in this circuit the coupling condenser 91 is located between the wave shaping network 95 and the grid 8l of the second tube, instead of between the wave shaping network and the plate of the iirst tube as in Fig. 1. Either arrangement gives satisfactory operation. Cathode ray tube deiiecting coils indicated at lill are connected through a coupling condenser I 02 and a Aconductor I 0 3 across the output electrodes of the second tube 18. If desired, they may be shunted b'y a resistor ills for the purpose of improving the eiciency of the circuit as described and claimed in my copending application, Serial No. 741,230, filed August 24, 1934, and assigned to the same assignee as this application. When using the particular circuit illustrated, it was found desirable to shunt the coils lill by a small by-pass condenser |06 for the purpose of eliminating certain undesirable transients in the saw-tooth wave passed through the delecting coils.

As in the circuit shown in Fig. l, the output circuit of the second tube i8 is coupled to the input circuit o f the first tube il through a coupling condenser ll, one plate of the coupling condenser being connected to the upper terminal of the deilecting coils itl and the other plate of the condenser being connected to the control grid Si of the rst tube. In any of the circuits described, satisfactory synchronization may be obtained by impressing synchronizing impulses upon either the grids or the plates of either the first tube or the second tube.

It will be understood that the synchronizing voltage impulse should be impressed upon a, tube electrode in phase with, that is, with the same polarity as, the voltage appearing on said plate due to the self-oscillation of the circuit. The operation of the circuit shown in Fig. 3 as an oscillator for producing a iiow of saw-tooth current through the deecting coils is substantially the same as that of the circuit shown in Fig. 1.

On' the drawings the values of the circuit elements are indicated in ohms, megohms, microfarads, henrys, and number of turns.

From the foregoing description it will be seen that many modications 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:

1. In combination, a cathode ray tube deecting coil having substantial inductance, an electric discharge tube having an input circuit and an output circuit, a second electric discharge tube having an input circuit and an output circuit, the output circuit of said second tube being coupled to said coil, a Wave shaping network, means for coupling the output circuit of said rst tube to the input circuit of said second tube through said network, and means for coupling the output circuit of said second tube to the input circuit of said nrst tube in such phase as to produce oscillations, the wave form of said oscillations being determined in part by the inductance of said deecting coil, said rst tube being biased substantially to plate current cut-off, and said network being so designed and adjusted as to cause a saw-tooth current to iiow through said deflecting coil. v

2. The invention according to claim i characterized in that said network consists of a resistor and capacitor in series connected across the input circuit of said second tube.

3. In apparatus of the class described, an electric discharge tube having an input circuit and an output circuit, a second electric discharge tube having an input circuit and having an outq put circuit which is substantially purely inductive, a wave shaping network, means for coupling the output circuit of said rst tube to the input -circuit of said second tube through said network,

and means for coupling the output circuit of said second tube to the input circuit of said iirst .tube in such phase as to produce oscillations,

5. In combination, an electric discharge tube having aninput circuit and an output circuit, a second electric discharge tube having an input circuit and an output circuit, a cathode ray tube defiecting coil having substantial inductance, said coil being coupled to said second output circuit, a wave shaping network, said irst output circuit being coupled to said second input circuit through said network, and means for coupling said second output circuit to said rst input circuit whereby oscillations are produced, the wave form oi said oscillations being determined in part by the inductance of said deiiecting coil, said network being so designed that in response to a rectangular impulse being impressed upon said first input circuit there appears across said network a voltage having a rectangular component and a saw-tooth component.

6. 'Ihe invention according to claim 5 characterized in that the output circuit of said rst tube includes a plate resistor connected in series with a source of plate potential, and further characterized in that said network consists of a resistor and condenser in series and connected in shunt to said plate resistor and said source.

7. In apparatus of the class described, an electric discharge tube'having an input circuit and an output circuit, a second electric discharge tube having an input circuit and having an output circuit which is substantially purely inductive, a wave shaping network, means for coupling the output circuit of said rst tube to the input circuit of said second tube through said network, and means for coupling the output circuit of said second tube to the input circuit of said i'lrst tube in such phase as to produce oscillations, said network including means for producing a voltage Wave having a saw-tooth component.

8. In apparatus of the class described, an electric discharge tube having an input circuit and an output circuit, a second electric discharge tube having an input circuit and having an output circuit which is substantially purely inductive, a wave shaping network, means for coupling the output circuit of said rst tube to the input circuit ci.' said second tube through said network, and means for coupling the output circuit of said second tube to the input circuit of said first tube in such phase as to produce oscillations, said network including means for producing a voltage wave having a rectangular impulse component.

9. In combination, an electric discharge tube having an input circuit and an output circuit, a second electric discharge tube having an input circuit and an output circuit, a cathode ray tube deecting coil having substantial inductance, said coil being coupled to said second output circuit,

a wave shaping network, said rst output cirsaid network being so designed that in response cuit being coupled to said second input `circuit to a rectangular impulse being impressed upon through said network, and means for coupling said iirst input circuit there appears across said said second output circuit to said rst input cirnetwork a voltage having the proper wave shape cuit whereby oscillations are produced, the Wave to produce a ow of saw-tooth current through form of said oscillations being determined in said deiiecting coil.

part by the inductance of said defiecting coil, ARTHUR W. VANCE.