USRE21400E

USRE21400E - blumlein

Info

Publication number: USRE21400E
Authority: US
Priority date: 1932-04-04
Publication date: 1940-03-19
Also published as: GB400976A; US2063025A

Description

A. D. BLUMLEIN SWEEP CIRCUIT Original Filed April 1.- 1933 2 Sheets-Sheet 2 Ml WTOH ALA/V DOM 8 BLl/MLE/N Reiuued Mar. 19, 1940 Alan Dower 'Blumlein, 'Ealing, London, England, asalgnor to "Electrical and Musical Industries Limited, Hayes, Middiesex, England, a company of Great Britain Original No. 2,063,025, dated December 8, 1936,

' Serial No. 663,977, April. 1. 1933. Application for reissue November 26, 1938, Serial No. 242,508. In Great Britain April 4. 1932 12 Claims.

vices, for the purposeof producing periodic deflection of the ray.

The invention is mainly concerned with the generation of non-sinusoidal oscillations adapted to produce deflection of the cathode ray of the kind in which each cycle of deflection comprises a relatively slow motion in one direction followed by a relatively rapid motion in the opposite direction. Arrangements of this kind are, for-example, used in television receivers inwhich reconstitution of a line of the transmitted image occurs during the slow motion of the ray and the rapid motion constitutes the return stroke which is necessary'before the next line of the image can be reconstituted. The requirements of such arrangements are, amongst other things, that the slow motion shall be a uniform one and that the return stroke shall be rapid."

According to the present inventionthere is provided an oscillation generator adapted to gen erate periodic electrical-oscillations of other than sinusoidal wave form in which'the'wave form of one'portion of each cycle of the generated oscil- 1 lations-is determined by a circuit comprising a reactive element or a plurality of reactive elements and in which the wave form of another portion 'of the cycle is determined by a circuit having different reactive properties from the first circuit, switching means being provided for transferring the control of wave form periodically from one of the circuits to the other. Where the natural frequency of the generated oscillations is high, the switching means may conveniently be in the form of a thermionic device and impulses serving to control the frequency of the generated oscillations may be applied to the grid circuit of the device. The wave form of the generated oscillations can thus be made independent df the wave form of the impulses within wide limits.

The thermionic device can be made to function as a switch by arranging that its anode-cathode impedance'is very small compared with the impedances with which'it is associated during the closed periods and very large compared with these impedances during the open" periods. Where lower frequencies are to be generated, the switching means may be mechanical.

The present invention further provides apparatus for generating periodic electrical oscillations of other than sinusoidal wave form, comprising means whereby the wave form ofthe generated oscillations is adapted, during the greater part of each cycle, to be controlled substantially by an inductance and, during the remainder of each cycle, by the resonant frequency of a tuned circuit. The apparatus may be such that the generated current, during the greater part of each cycle, is substantially that due to the voltage of a source applied across 'aninductance or it may be such that the generated voltage, during the greater part of each cycle, is substantially that built upacross a condenser due to the flow of current thereto from a source through an inductance. In both cases, however, the current or voltage during the remainder of each cycle may be that due to a half cycle of oscillation of a tuned circuit. i 'f According to a'feature of the present invention as applied to cathode ray devices, the rapid motion of the ray is effected under the control of one half cycle of oscillation'of a resonant circuit. Preferably, the rate of the-slow motion 'is determl-nedby the value of an inductance and the rate' of the rapid motion is determined by frequency. of a resonant 'circuit'. 7 According to a further feature of the present invention there is provided a source of electrical energy and means for applying from this source to the control coil or electrodes, which serve to the natural deflect a cathode ray, aperiodic voltage of pre-" determined wave form having a maximum voltage greatly exceeding that of the source. r

The invention will be described, by way of example, with reference to the accompanying drawings, in two embodiments but it will be realized that there are many other embodiments within erence to Fig. 1 is suitable for use with-a cathode ray tube in which the ray is deflected magnetically, by means of an electric current passed through a control coil. The periodicity of-the deflections is determined by electrical impulses, for example synchronizing impulses transmitted from a television transmitter.

The synchronizing impulses are appliedthrough a transformer I to the grid circuit of a'thenmionic triode 2 having a thermionic diode 3 shunted across its anode-cathode circuit, the cathode of the diode being connected to the anode of the triode. The anode of the triode is connected through a parallel resonant circuit 4 and a suitable impedance 5, such as a. resistance, to the positive terminal of a source of high tension 6, the negative terminal of the source below. A large condenser III is connected from the cathode of the triode to a point between the tuned circuit 4 and the resistance 5 for the purpose ofmaintaining the voltage of the high tension source at a steady value. Suitable biasing means II are provided to maintain the grid of the triode 2 slightly positive in relation to the cathode in the absence of a received impulse.

The operation of the circuit will be described with reference to Fig. 2 in which time is the abscissa and the ordinates are: in curve (a) the current IL in inductance 1; in (b) the voltage Vg impulses applied to the grid of triode 2; and (c) the voltage Vc developed across the tuned circuit 4.

The cycle of deflection will be assumed to begin with the ray in its midposition, that is to say with the scanning spot in the middle of the reproducing screen. Under these conditions the current through the control coil is zero. but increasing in a direction which will for convenience of description be referred to as positive and indicated by the arrow 11. in Fig. l. The ratio of the resistance of the coil 1 to its inductance is made low and the anode-cathode impedance of the triode 2 is also low due to the positive bias on its grid and therefore the rate of increase of current through the control coil and triode due to the voltage of the source 6 is determined substantially entirely by the inductance of the coil I. The current Ir. through the coil thus rises at a uniform rate from d to e (Fig. 2 (11)) until a scanning impulse is received (Fig. 2 (b)). This impulse serves to make the grid of the triode negative relative to the cathode and the anode-cathode impedance high. The flow of current through the control coil I cannot be stopped suddenly because of the inductance thereof and, since the path through the triode has become of high impedance, the current is deflected into'the condenser 8 of the tuned circuit 4 which is thereby charged. The voltageacross the anode-cathode of the triode will now rise to a high value and the grid thereof must therefore by this time have been raised to a sufficiently high negative value, by the received impulse, to prevent appreciable current flow through the triode. After a time interval, (measured from the moment when the synchronizing impulse was received) equal to that of one quarter of a cycle of oscillation of the tuned circuit at its resonant frequency'and represented by the distance along the abscissa in Fig. 2 (a) between points 2 and f, the current through the control coil 1 has fallen to zero and the condenser commences to discharge thus causing current to flow through the coil in a negative sense. By the time that the condenser 8 has become fully discharged a further quarter cycle of oscillation at the resonant frequency of the tuned circuit 4 has been executed and the current is at point g Fig. 2 (a). Due to the negative current now flowing in the coil, the condenser commences to charge in the reverse direction but this reverse charging ceases almost immediately due to flow of current through the diode 3. The high tension voltage of the source 6 opposes the flow of current in a negative direction through the coil 1 and this current is reduced at a steady rate to zero as represented by gd1 Fig. 2 (a), thus completing the cycle.

It will be noted that during the greater portion of each cycle (constituting the scanning stroke), namely 9 to e1 Fig. 2 (a), the wave form of the current through the control coil 1 is .determined substantially by the inductance of this coil and the voltage of the source and during this portion of the cycle the rate of change of current in the coil is, therefore, substantially uniform. The cathode ray is thus swept at a uniform 'rate across the reproducing screen. During the remainder of the cycle (constituting the return stroke), and represented between points e and a Fig. 2 (a), the wave form of the current in the coil is determined by the natural frequency of the tuned circuit 4 which during this period executes one half cycle of oscillation at its resonant frequency. Further, the voltage developed across the control coil reaches, during each cycle, a peak value greatly exceeding the voltage of the source 6. This is shown clearly in Fig. 2 (c) where the distance Vs represents the voltage of the source 6.

The wave form of the generated wave will be substantially independent of the wave form of the received impulse provided that this impulse makes the grid suiiiciently negative and that it does not maintain the negative grid polarization for. longerthan one half the scanning stroke.

The grid voltage may for example be anywhere within the shaded areas in Fig. 2 (b).

The circuit described depends upon a half cycle of oscillation of a tuned circuit to produce the back stroke and is liable to give alternate scanning strokes of different mean positions due to persistence of oscillations at one half the scanning frequency. The auxiliary tuned circuit 9 which is arranged in series with the condenser 8 of the main tuned circuit 4 is provided to prevent this. The auxiliary tuned circuit 9 is arranged to resonate at half the scanning frequency whilst the condenser and inductance constituting it are of low impedance and good efflciency. Further the value of the inductance is so chosen that series resonance with the condenser 8 of the main tuned circuit occurs at a frequency not lower than one third of the scanning frequency. The auxiliary tuned circuit may, if desired, be connected in the high tension supply between the large shunt condenser I 0 and the main tuned circuit 4.

In determining the capacity of the main tuned circuit 4 this should be taken as including, with the condenser 8 thereof, the self-capacity of the control coil 1 and the associated valves 2 and 3.

The diode 3 should be selected to have a reasonably low impedance and the triode 2 should also have a low impedance with a suitable value of positive grid bias. Both valves should be capable oi withstanding high voltages and should have high impedance, in the case of the triode capacity of the valve due to the "Miller" effect.

In order to decrease the amplitude of the neuative-pulse required, coupling in a suitable sense may be provided between the coil 1 and the' Ieoil together with the capacity of the triode 2 serves to delay the negative pulse.

'In the second embodiment of the invention illustrated inl'ig. 3, a triode I! of the gaseousdischarge time is used. This type of'triode has the property that its anode-cathode impedance remains high so long as its grid is maintained at a suitable negative potential relative to the oathode. 0n suitably reducing the negative .potential, however, the impedance falls to a low value and remains at this low value, irrespective of any potentials applied to the grid, until the anode voltage has been reduced to a certain value.

Between the anode and cathode of a triode of this kind there is connected an inductance il in series with a condenser ll constituting a tuned circuit. The condenser represented by M consists of the capacity between the electrostatic control electrodes of a cathode ray tube (not shown) increased by a parallel condenser to a suitable value, for example 0.002 microfarad. The point of connection between the inductance II and condenser I4 is connected through an inductance II and a resistance I. (which will be termed the feed impedance) to the positive terminal of a source "of high tension, the negative terminal of the source being connected to the cathode of the triode.

The curves of Fig. 4 illustrate the behaviour of this circuit. In each curve the abscissa is time and the ordinates are: in (a) the voltage V across condenser id; in (b) the voltage impulses V applied to the grid of the triode l2; and in (c) the current i flowing in inductance ll.

Once more assuming the cycle to commence with the scanning spot in the centre of the reproducing screen, as represented by point Ic Fig. 4 (a), the charge upon the condenser i4 is zero but increasing due to current from the source i1 flowing through the feed impedance ii, II. The grid of the triode i2 is held at a suitable negative value by biasing means II and the current through the inductance I! of the tuned circuit is thus' negligible. The voltage across the condenser i4 therefore rises until a positive synchronizing impulse is applied to the grid of the triode as represented by point I. The impedance of the triode I2 is now very small and the condenser discharges through the in- .ductance ll of the tuned circuit at a rate -dependent upon the natural frequency thereof. The feed impedance it, It is made sufficiently high to prevent appreciable flow of current through it during the short period of the condenser discharge. When the tuned circuit has executed one quarter of a cycle of oscillation (points i to m Fig. 4 (ml) the condenser It has discharged and, due to the current now within the shaded areas of Fig. 4

ilowingintheindnctance ll. charges upin-the reverse direction, the tuned circuit thus executingaaecondquartercycleoi'oscillation (points m-to n Fig. 4 (11)). The currentthr'oughthe inductance ilisnowaeroandthevoltageacross the anode circuit of the triode is therefore sero alsowhileduetothelowimpedance oscillatory nature of the circuit during thishalf cycle the polarity of the charge on the condenser i4 is reversed and is practically equal in opposite magnitude to the original charge. The impedance oftube' i! has accordingly returned to its original high value. The condenser cannot draw current through the inductance II of the tuned circuit and accordingly current commences to flow through the feed impedance II, I! until the voltage across the condenser is once more zero (point h) and the cycle has been completed.

In this arrangement the wave form of the voltand during the scanning stroke, by the flow current thereinto through the inductance i I of the feed impedance, and during the remainder of the cycle, that is during the return stroke. 1 to n or ii to m by the natural frequency of the tuned circuit ll, I which executes one half cycle of oscillation at its resonant frequency.

The positive impulse applied to the grid need only last for long enoughto trigger the Thyratron I! but it may if desired persist until the middle of the scanning stroke, after which the grid must be negative. The impulses may be anywhere (b), for example.

In this example also, the voltage developed across the control electrodes can exceed greatly the voltage of the source since the voltage is determined by the flow of current through the inductance of the feed impedance.

In this case also it is desirable to provide an auxiliary circuit to prevent persistence of oscillations at one half the scanningfrequency and this may take the form of an inductance II and a condenser II connected in series across the condenser id of the main tune circuit. The auxiliary circuit is arranged to resonate at the undesired frequency and thus makes the voltages acres the control electrodes, that is, the deflector plates II. at this frequency negligible. It should also be arranged that the inductance i8 and condenser 20 of the auxiliary circuit have individually a high impedance and that the inductance ll resonates with the condenser ll of the main tuned circuit at a frequency not higher than say two thirds the scanning fre- In determining the capacity of the main tuned circuit it should be taken as including the selfcapacity of the feed inductance l5.

Both the circuits described are such that there is, theoretically, no power dissipation. The actual power dissipation is therefore only that due to unavoidable losses and can be made relatively small.

Clearly, forms of switch other than thermionic valve such as i in Fig.1 or II in Fig. 3 may be used. At relatively low frequencies mechanical switches can be used and they can be operate substantially sparklessly.

Although the invention has been described as applied to the control of cathode ray tubes it is clearly not limited to such uses but may be employed in manyother fields where periodic oscilmodem lations oi predetermined but other than sinus-.

' an inductance for controlling, the wave form of the'generated oscillations during a part of each cycle thereof, a condenser constituting with said inductance a tuned circuit, said tuned circuit being operative to-control said wave form during another part of each cycle, means for supplying control electrical signal impulsesto said system, and means for transferring the control of said wave-form from the circuit including said inductance to said tuned circuit in response to control electrical impulse.

2. An oscillation generator for generating periodic electrical oscillations of other'than sinusoidal wave form comprising a circuit including a condenser forcontrolling the waveform of the generated oscillations during a part of each cycle thereof, an inductance constituting with said condenser a tuned circuit, said tuned circuit being operative tocontrol said wave form during another part of each cycle, means for receiving controlling electrical impulses, and means for transferring the control of said wave-form from said condenser to said tuned circuit in response to said electrical impulses.

3. An oscillation generator for generating, in response to applied electrical impulses, oscillations of frequency determined by the frequency of said impulses, comprising a source of electrical energy, a parallel tuned circuit, said tuned crrcuit-being conductively in series with said source, means for impulsing said tuned circuit to commence oscillation in response to one of said impulses'and rectifier means for automatically stopping said oscillation atter one half cycle thereof.

4. Apparatus for generating electrical oscillations of saw-tooth wave-form in response to electrical impulses, comprising a source of electrical energy, a timed circuit includingan inductance and a condenser arranged in parallel, normally conductive switching means responsive to said impulses and a unidirectionally conducting device in parallel with said switching means, said tuned circuit and said switching means being arranged in series across said source -and' means responsive to said electrical impulses for making the switching means momentarily non-conductive.

5. Apparatus for generating electrical oscillations of saw-tooth wave-form in response to electrical impulses, comprising a source of electrical energy, a condenser and an impedance connected in series across said source, an inductance and a switching device connected in series with one another and in parallel with said condenser and means for rendering said switching device conductive in response to said impulses.

6. Apparatus for generating electrical oscillations of saw-tooth wave-form in response to electrical impulses, comprising a source of electrical energy, a tuned circuit, an impedance, means causing a progressively increasing current from said source to flow through said impedance for the greater part of each cycle of the generated oscillation and means responsive to said impulses for causing said tuned circuit to execute one half cycle of free oscillation during the remaining part of each cycle of the generated oscillation.

7. Apparatus for generating electrical oscillations of saw-tooth wave-form in response to electrical impulses, comprising a source oi electrical energy, it tuned circuit, a condenser, means permitting a progressively increasing voltage, due to current flo'w from said source, to develop across said condenser during the greater part of each cycle of the generated oscillati'onand means responsive to said impulses for causing said tunedcircuit to execute one half cycle of free oscillationduring the remaining part of each cycle of the generated oscillation. L

8. Apparatus for generating electrical oscilla tions of saw-tooth wave-form in response to electrical impulses, each cycle of said saw-tooth wave-form comprising a substantially uniformly increasing current occupying the greater part of each cycle followed by a rapid decrease in current for the remaining part of eachcycle, said apparatus comprising a parallel tuned circuit, means conductively in series with said tuned circuit for impulsing the tuned circuit into oscillation in response to said impulses and rectifier means for limiting the duration of said rapid decrease in. current to a single half cycle of oscillation of said tuned circuit I I 9. Apparatus for generating electrical oscillations of saw-tooth wave form in response to electrical impulses comprising a source of electric en-' ergy, a parallel tuned circuit, a tube having a.

cathode, an anode and a control electrode, means connecting said tuned circuit and source in seriesmagnetically deflecting a cathode ray beam developed within a cathode ray tube comprising electro-magnetic energy storage means tuned to a frequency, substantially greater than the frequency of said generator system, said electromagnetic energy storage means comprising the magnetic control means for deflecting thecath- I ode ray in the cathode ray tube, means for storing energy in said electro-magnetic energy storage means, a uni-directional conductor coupled substantially in parallel with said electro-magnetic u energy storage means and means for intermittently interrupting the storing of energy in said electro-magnetic energy storage means.

11. Apparatus in accordance with claim 10 wherein said uni-directional conductor coupled substantially in parallel with said electro-magnetic energy storage means comprises a diode.

12. A sawtooth oscillation generator system for magnetically deflecting a cathode ray beam developed within a cathode ray tube which comprises electro-magnetic energy storage means tuned to a frequency greater thanthe frequency of the sawtooth oscillations generated in said system, said electro-magnetic energy storage means comprising the magnetic control means for deflecting the cathode ray beam inthe cathode ray tube, a thermionic vacuum tube having anode, cathode, and at least one control electrode, means'for producing an anode-cathode current in said tube, means for storing at least a portion having the cathode element thereof electrically connected to the anode of said thermionic tube, and means for intermittently interrupting the storing of energy in said electro-magnetic energy storage means.

ALAN DOWER BLUMLEIN.