US2159818A - Oscillator - Google Patents

Description

May 23, v1939; D.. l.. PLAlsTowE ET AL .2,159,818

OSCILLATOR Filed Oct. 2, 1957 SIGNAL INVENTORS DOA/ALD .PLA/.S'TOWE DA V/D J VNGS TORNEY OSCILLATOR Donald Leopold Plaistowe and David John FewffPa'tented May 23, 1939 PATeNT OFFICE.

o ings, VChelmsford, England, .I assignors to` RadioV Corporation of America, a corporation of Dela- Ware `Application October `2., 1937, Serial No. 166,930 In Great Britain November 30, 1936 Claims. (Cl. Z50-F36) This invention relates to electrical time base lcircuitsfand more particularly, though not exlclusively, to time .base circuits suitable for use yforfproducing or controlling scanning action in "1"" ftelevision and like cathode ray tube apparatus.

Considerable diniculty is experienced with .knowntime base circuits for use in television and `like cathode ray tube apparatus in obtaining the "required degree of constancy of frequency, var- 10ious causes, notably changes in the ambient and operating conditions, tending to produce frey quency` drift. In order-to meet this difliculty itis c at present usual` in television systems to lock the I time base circuits rigidly in step by synchroniz- 5 ning signals ofconsiderable amplitude. The necessity for the provision of powerful'synchronizing .signals is obviouslya disadvantage and such gnals may, moreover, result in distortion of the ogcalled television raster i. e., the scanning 2O pattern.

` fFw'I'he present invention seeks to provide time `basecircuits wherein a highdegree of constancy c of `frequency is obtainablea'nd which can be easily synchronized by synchronizing signals of `Lyrelatively small amplitude, although, las will be c, erful synchronizing signals such as are now ordinarily employed in television systems. c

c c odeyof` said valvefor discharging said capacity .I c Iperiodically, the whole arrangement being such l lthat (when the voltageacross said capacity arises ltoja'Hopredetermined value iand/or-when a syn- ;gi xchronizing` signal is'received, the electron beam `ntlie electronrbeam valve is deflected so as to be incident upon said other anode `whereupon the fductive and dischargels'thecapacity; c Y `The invention is illustrated inthe accompanybodiment of the invention.` Referring to the -drawinglthere is employed an `seen later apparatus in accordance with this invention may be arranged to be'controlled. by powdischarge spacetoysaid other `anode becomes conng drawing `which-shows diagrammatially one.`

a electron beam valve of.` somewhat llspecial conx 55 struction whichwillirst be described. "I"l1`isele:`:.z4

tron beam valve I includes within an evacuated envelope an electron gun system `of any known convenient kind (for example it may consist as shown of a cathode 2 and an associated electrode 3 having an aperture 4 throughV which a jet or beam of electronsis` projected); a first anode 5 in the form of an apertured plate having an aperture 6 and positioned opposite the electron gun; a second anode 'I in the form ofa plate situated behind the rst anode,i.e.,on the side thereof remote i from the electron gun; and three deilector electrodes 8, 9, I two (8, 9) on one side and the third (IU) on the other side of the electron beam path. 'I'he rst and second deector electrodes 8, 9 are side by side andopposite the third deflector Il), said first and second deflectors being at different distances from the gun and in a common planeat right angles to the parallel planes in which the two anodes 5, I lie and the third deilector I0 being in a'plane parallel to the said common plane. v c

In the time base circuit shownv and the above described electron beam valve I, the positive terminal II of a source of potential (not shown) is connected through a resistance I2, which is preferably adjustable,to`the second anode 1r and this 'anode is connected through two condensers I3, I4

in series to thecathode 2. The anode 'I is also connected to one contact I of a two-position I switch having another contact I6 connected to a tapping point I1 (whichmay be adjustable) upon a potentiometer I8 shunted acrossthe source of potential whose negative terminal is marked I9. The armature 20 of this switch is connected to the deiiectoi" 9 (which is nearer the two anodes 5, 'l than is the deiiector 8) and the dellector 8 is connected through a coupling condenser 2| to the rst anode `5 and is also connected to an adjustable tapping point 22 upon a second potentiometer 23 connected across the source of potential. .The first anode 5 is connected through a resistance 24 to the positive terminal II of the source of potential. The third deflector I 0 is connected to an adjustable tappingpoint 25`upon a third potentiometer 26 connected across the potential source, said third deflector I0 being alsoconnected to a terminal 21 which constitutes one ofthe input terminals 2'I and 28 for synchronizingv signals, the other inputfterminal 28 being connected to the gun cathode 2. In use, approximately saw-tooth Waves generated by the time base circuitmay be taken at terminals 29 and I-9 which are connectedacross the condenser I4. The whole arrangementis suchthat normally (gthatisfrwhen there isno charge in the condensers I3, I4) the electron beam in the electron beam valve is incident upon the rst anode only, because the internal resistance between the electron gun and the second anode 1 is so very high that this discharge path is, practically speaking,

n non-conductive.

Suppose the` switch arm 20 is on contact I5 connecting the deflector 9 to the anode 'I and the condenser I3. Then the operation of the device is as follows: current flows from the positive terminal II through the resistance I2 to charge the condensers I3 and I4, and these condensers will accordingly charge at a rate determined by the constants of the charging circuit. It will be noted that during this charging action (which corresponds to the longer face of a sawtooth wave) the electron beam is not incident upon the second anode l, and accordingly there is no load across any part of the charging circuit. As the potential across the twocondensers I3 and I4 rises, the potential applied to the deflector 9 also rises and accordingly the electron beam is increasingly deiiected. When the charging has continued to a predetermined extent the electron beam has become deflected far enough for it to pass through the aperture S in the anode 5 and strike the anode l. Accordingly the condensers I3 and I4 will be discharged through the electron beam. When the electron beam reaches the aperture 6 and leaves the first anode 5 for the second anode 'I the consequent cutting off of the current to the first anode 5 causes a positive pulse to be applied (through the coupling condenser 2 I) to the deilector 8 and this tends to maintain the beam on the second anode 7 until the positive voltage on the said delector 8 has fallen away (in accordance with a substantially exponential law) sufciently to enable the beam to become once more incident upon they rst anode 5. When this happens current reappears in the circuit of the rst anode 5 and accordingly the second deflector 8 receives a negative pulse which deiiects the beam further back towards its original position. Thus the condensers I3 and I4 charge relatively slowly while the electron beam is incident on the first anode 5 and are discharged rapidly as soon as the electron beam strikes the second anode 1. Because there is no load across any part of the charging circuit during charging, successive chargings will occupy substantially the same time. l

In practice the parameters of the circuit are so arranged that the voltage across condensers I3 and I4 rises almost to the predetermined value just before a synchronizing signal is due to be received so that the reception of a synchronizing signal (which is applied to the third deector It) produces the small amount of extra deflection necessary to cause the electron beam to pass through the aperture 6 in the rst anode 5 to the second anode 1. Thus synchronizing signals of quite small amplitude are sufficient to produce reliable synchronization.

The circuit is readily adjustable for different operating conditions. Adjustment of the resistance I2 in the charging circuit adjusts the charging period while the various potentiometer tappings provide additional and obvious operating adjustments. Adjustment of the static potential applied to the third deiiector plate I3 adjusts the amplitude of the sweep.

If the above described circuit arrangement is desired to be employed with strong incoming synchronizing signals the switch arm maybe moved to contact I5 in which the defleotor plate 3 is connected to the tap I'I on the resistance potentiometer I8. With the switch in this position the circuit is no longer a self-operating time base circuit, that is to say, it will not generate sawtooth Waves whether or not synchronizing signals are received, but can be driven by the signals.

When a circuit arrangement such as the above described is employed for synchronizing a television receiver of the kind in which picture signals and synchronizing signals are transmitted together in the same channel but with opposite senses or polarities, the combined synchronizing and picture signal wave may be applied directly without any preliminary separation, to the defiector Ill, for, by suitably choosing the polarity or sense of the application, the result may be achieved that only the synchronizing signals will be of the correct sense or polarity to deflect the electron beam in the required direction to cause it to pass to the second anode 'I. Thus When applied to such a television receiver the apparatus offers the advantage that the hitherto normally provided valve for separating picture signals from synchronizing signals may be dispensed with.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:

l. An electrical time base circuit comprising a capacity, means for charging said capacity at a predetermined rate, an electron beam valve including two anodes or electron collector electrodes, means for so operating said valve that normally theelectron beam therein passes to one of said anodes, means for utilizing a potential proportional to the instantaneous potential across said capacity for deflectng the electron beam in said valve, and means for utilizing the discharge space to the other anode of said valve for discharging said capacity periodically, the Whole arrangement being such that when the voltage across said capacity rises to a predetermined value the electron beam in the electron beam valve is deected lso as Vto be incident upon said other anode whereupon the discharge space to said other anode becomes conductive and discharges the capacity.

2. An electrical time base circuit comprising a capacity, means for charging said capacity at a predeterminedrate, an electron beam valve including two anodes or electron collector electrodes, means for so operating the said valve that normally the electron beam therein passes to one of said anodes, means for utilizing a potential proportional to the instantaneous potential across said capacity for deflecting the electron beam in said valve, means adapted to be operated by synchronizing signals for providing said beam with deflections supplementary to that caused by the instantaneous potential across said capacity and means for utilizing the discharge space to the other anode of said valve for discharging said capacity periodically, the whole arrangement being such that after the voltage across said capacity has built up to at least a predetermined minimum, reception of a synchronizing signal causes the electron beam in the valve to be deflected so as to be incident upon said other anode whereupon the discharge space to said other anode becomes conductive and discharges the capacity. K

3. A circuit as claimed in claim 1 wherein the anode upon which rthe beam normally falls is an apertured anode situated in front of the second anode between it and the electron gun of the i Valve, the electron `beam passing to the second anode only when it is suiciently deflected to pass through the aperture in the apertured anode.

4. A system for producing oscillations of sawtooth wave form comprising a discharge tube,

` means for producing a beam of electrons includ- @said condenser to cause the beam to impinge said lsecond anode upon a predetermined charged coning a cathode and a rst and second anode, a rst deflecting electrode positioned between said cath- `ode and said anodes, and at one side of the pro- `condenser connected between said second anode and said cathode, means for maintaining said third deiiecting electrode at the charge potential of said condenser whereby the produced beam may be deflected in accordance with the charge of dition to substantially instantaneously discharge said condenser, and means for maintaining said `:rst and second deiiecting electrodes positive with respectto said cathode.

5. An electrical time base circuit comprising a capacity, means for charging said capacity at a `predetermined rate, an electron beam tube includingtwo anodes, means for operating said tube so that normally the electron beam therein is directed on to one of said anodes, additional beam deflecting means adapted to be controlled by synchronizing potentials, means whereby said synchronizing potentials and said capacity potentials operate to deflect the beam on to the other anode for substantially instantaneously discharging said capacity.

6. A system for producing oscillations of sawtooth wave form comprising a discharge tube including a cathode and a pair of anodes, a ccndenser, means for charging said condenser at a predetermined rate, means for producing an electron beam in said tube and normally directing the beam against one of said anodes, means for utilizing a potential proportional to the instantaneous potential across said condenser for deiiecting the electron beam in said tube, means for utilizing the discharge space to the other of said anodes of said tube for discharging said capacity periodically, whereby when the potential across said condenser rises to a predetermined value the electron beam in the discharge tube is deflected so as to impinge upon said other anode to substantially instantaneously discharge said condenser.

DONALD LEOPOLD PLAISTOWE. DAVID JOHN FEWINGS.

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