US2220712A - Saw-tooth wave generator - Google Patents

Description

Nov. 5, 1940. n M, GEIGER 2,220,712

SAW-TOOTH WAVE GENERATOR Filed Aug. 30, 1938 INVENTOR l Amig/G BY j /I/U'bd/l/ ATTORNEY Patented Nov. 5, 1940 UNITED STATES PATENT OFFICE SAW-Toorn WAVE GENERATOR many Application August' 30, 1938, Serial No. 227,453 In Germany June 21, 1937 2 Claims.

A saw-tooth generator has been disclosed in the prior art comprising a parallel resonance circuit in the grid circuit of a controlled tube, the inductance branch of the said resonance circuit comprising a rectier, with voltage feedback being established between the plate circuit of the said controlled tube and its grid circuit. According to this suggested arrangement, the deflector coil of; a cathode-ray tube is connected between the lament and the plate of the controlled tube by capacitive means.

The present invention has as its object to connect, in saw-tooth Wave or time-base generators predicated upon the same principle as the said organization disclosed in the earlier art, a resistance in series With the control grid of the tube, in a Way as shall hereinafter be described in more detail, with the result that the chances of disturbing actions arising in the circuit organization are greatly diminished.

To more fully and clearly explain the invention, the layout and the operation of a circuit arrangement Without the said resistance shall first be discussed.

My invention will best be understood by reference to the drawing in which Fig. 1 is an example of the prior art,

Fig. 2 is an explanatory curve, and

Fig. 3 is an embodiment of my invention.

Referring to Fig. 1, there is shown an embodiment of the prior art. A thermionic vacuum tube I0, which in this instance is illustrated as a triode, has connected to the control grid thereof three parallel circuits which are shunted across 35 the control grid-cathode path of the tube. The

rst comprises a resistor I5 and a source of positive biasing potential I6 connected serially each to the other. A condenser II is connected in shunt with the resistor I5 in the source of bias- 40 ing potential I6, and the third shunt circuit is a coupling coil I2 connected serially with a rectier I3. vThe anode circuit of the tube is connected serially With a coil I4 which is inductively coupled With the coil I2, and the circuit is completed through a source of energizing potential indicated, the negative side of the source of potential being connected to the cathode of the tube.

To more clearly explain the operation of an organization as illustrated in Fig. 1, the assumption shall be made vthat at the condenser Il prevails a strong charge Withgthe terminal thereof directly connected to the coil I2 being negative. The said charge shall be supposed to be so high that the tube as a result is biased to a point below the bottom knee of its plate current grid voltage characteristic. The coil I4 in the plate circuit of tube I0 as a result carries no current, and hence, no potential exists across the coil I2. 'The rectifier I3 is subject tovoltage action in its backward sense. The condenser II is then charged through the resistance I5 from the D. C. voltage source I6, the potential at the upper condenser coat being such as indicated by .curve K in Fig. 2. Over the zero line which corresponds to the iilament potential of tube I0 there is plotted in Fig. 2 the potential of the D. C. voltage source I 6 indicated by the straight line G in addition to the potential at the upper condenser coat. Graph K obeys an e function, with the straight line G being the asymptote. When the curve K intersects the dotted (dash) line C Which corresponds to the bottom knee of the plate current-grid voltage characteristic of tube Ill, a rise of current is initiated in the plate circuit of this tube Which is indicated by I in Fig. 2. To this rising current in the Winding I4 corresponds a constant voltage across the coil I2, the latter to have by assumption a polarity such that the terminal thereof connected directly to. condenser II has a positive polarity. 1 This lastrmentioned potential is designated by S, in Fig. 2. It is also a blocking potential-for the rectifier I3. When graph K crosses the zero line, the potential at condenser II is reversed, with the result that the condenser voltage now has a sign so that the rectier I3 is acted upon in its for- Ward direction. The voltage `at the condenser I I must then rise to a level which lies above the voltage to occasion incipient current flow in the rectifier I3. However, as the rectifier I3 con? ducts current again, the voltage at the condenser II diminishes again because of the discharge through the rectifier, and simultaneously with the decline of the plate current of tube I0 a voltage reversal will happen across the coil I2. Incidentally, the magnetic energy of the coil I4 will be discharged through the rectier I3 and re-appears in the form of an electric charge at the condenser II of= a polarity such that the terminal thereof directly connected to the inductance coil I2 has a negative polarity.

Under practical operating conditions, the process as hereinbefore outlined is not exactly as described on the ground that a grid current begins the coil I2, that is, vin a sense so that the polarity thereof is such that the terminal connected directly to the condenser I I has a positive polarity, While the size thereof diminishes. The instant of incipient current flow in rectifier I3, as Will be seen, is governed by the instant at which the line exhibiting a flatter rise than curve K, Fig. '2, has assumed a greater amplitude than the reduced voltage across the coil I2. This flat intersection of the curve which represents the potential actually prevailing at the upper condenser coat across the horizontal line which corresponds to the altered potential at the coil I2 is attended With a serious uncertainty of the time of initiation of the short stroke of the sawtooth Wave. For one has to figure With the chance that a certain noise or disturbing (stray) voltage level prevails at the control grid of the tube I0, which has this consequence that the incipiency of the saw-tooth return or iiyback stroke, comparatively speaking, may happen far earlier or later, according to the noise voltage level.

Hence, it is here suggested to insert a resistance Il in series with the control grid of the tube lo as shown in Fig. 3. The result and action of the said resistance is two-fold, namely, the curve K after crossing the zero line O Will continue to rise With practically unvaried slope or rate. Moreover, the grid potential of the tube I0 because oil incipient grid current flow, Will now stay practically constant and stable. As a consequence, however, the voltage across the coil I2 disappears, so that, as soon as the condenser has assumed a small charge of such polarity that the terminal thereof connected directly to the inductance coil I2 has a positive polarity, the rectifier I3 is rendered conducting so that the return stroke is caused to commence. As will be noticed, the noise level will then have far less chance to cause a shift in the time of initiation of the saw-tooth return stroke inasmuch as the curve K and the graph giving the potential shape as a function of the `time at the coil I2 nov longer intersect at a comparatively sharp angle.

Referring to Fig. 3, there is shown an embodiment of my invention in which similar reference numerals refer to similar parts as explained hereinbefore With respect to Fig. 1. In this case, the cathode of tube Ill is grounded and the anode of tube i0 is connected to ground through a coupling coil I4 and a source of energizing potential indicated, the negative terminal of the source of energizing potential being grounded. The control grid is connected serially to a resistor I'I, the terminal of the resistor I1 remote from the termination thereof connected to the control grid of tube I0 being electrically connected to the cathode of the tube through the three parallel circuits referred to in regard to Fig. l. These circuits compriser a serially connected resistor I5 and source of energizing potential I8, condenser II connected in shunt with said resistor and source of energizing potential, and a series circuit comprising coil I2 which is inductively coupled to coil I4 and rectifier I3 connected in series therewith, the combination of the inductance I2 and the rectifier I3 being connected in shunt with condenser II and resistor I5 and source of potential I6.

In an arrangement of circuits according to the invention a saw-tooth voltage wave is obtained at the condenser II, While moreover, if desired, a saw-tooth current Wave may be obtained from the plate circuit of tube IU, that is, when the bottom point of curve K is made to coincide with the incipient flow of plate current of tube I0. The coil I4 may be used directly as the deector coil in a cathode-ray tube.

It is, moreover, readily feasible tol synchronize a saw-tooth wave generator according to the invention by impulses. These impulses, to the said end in View, must be made to act upon the plate current of tube I0 in a sense to cause a reduction thereof, and this is accomplishable, for instance, by a further control grid of tube I0. For television purposes, therefore, a sawtooth wave generator according to the present disclosure may be readily controlled with line or lineseries impulses.

It is also to be emphasized that the invention is useful not only with generators for which potential feedback is eifected by a transformer, but that the invention is useful also with sawtooth wave generators comprising any desired regeneration scheme which furnishes a potential of suitable phase such as is insured, for instance, by a reversing tube or a device presenting negative slope.

' What is claimed is:

l. A saw-tooth Wave generator comprising a thermionic vacuum tube comprising anode, cathode and at least one control electrode, a parallel resonant circuit comprising an inductance and a condenser connected in the control electrodecathode path of said tube, a uni-directional conductor connected serially With said inductance and condenser comprising the parallel resonant circuit, a series circuit comprising a resistor and a source of potential connected substantially in shunt with said parallel resonant circuit, resistive means connected to said control electrode and connected serially to said parallel resonant circuit, means for feeding back a portion of the anode-cathode circuit energy to said parallel resonant circuit.

2. A saw-tooth wave generator comprising a thermionic vacuumv tube having anode, cathode and at least one control electrode, a rst in ductive member, a uni-directional conductor, condenser means, said first inductive member and said uni-directional conducting means being serially connected each With the other and connected in parallel with said condenser means, a source of fixed potential, an impedance means, said source of fixed potential and said impedance means being serially connected each with the other and connected in shunt with said condenser means, said condenser means being connected in the control electrode-cathode circuit lof said thermionic tube, impedance means connected serially With said control electrode and said condenser means, and a second inductive member coupled tosaid rst inductive member and connected in the anode-cathode path of said thermionic tube.

' MAX GEIGER.

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