US2182555A - Saw-tooth wave generator - Google Patents

Description

. 5, 1939. M. GEIGER SAW-TOOTH WAVE GENERATOR Filed July 24, 1937 2 Sheets-Sheet 1 INVENTOR MAX 65/ ER ATTORNEY Dec. 5, 1939. MLGHGER R 2,182,555

SAW-TOOTH WAVE GENERATOR Filed July 24, 1957 2 Sheets-Sheet 2 TIME INVENTOR MAX GE/GER ATTORNEY Patented Dec. 5, 1939 UITED STATES ATENT OFFiCE 2,182,555 SAW- TOOTH WAVE GENERATOR Germany Application July 24, 1937, Serial No. 155,456

In Germany 3 Claims.

l/Vhat has been called a multivibrator in the prior art of this nature is a saw-tooth Wave generator in which there are two thermionic discharge paths the control grids of which through a resistance-capacity mesh are driven or controlled by the plate circuit of the respective other thermionic discharge path. Relaxation or sawtooth wave generators of this kind are particularly valuable for the production of impulse trains of the sort required for instance, in television work. In their practical use, one fact that has often provide troublesome is that the duration or period of the generated impulses is a function of the value of the D-C potential supplied to the saw-tooth wave generator as shall be explained more fully further below. In order to overcome this difiiculty it is suggested according to the invention to excite by means of the current variations an oscillation circuit in one or in both of the two thermionic discharge branches, the oscillations of said circuit to affect the behaviour of the other thermionic discharge branch, or of both discharge branches, as the case may be.

My invention will best be understood by reference to the drawings in which,

Fig. 1 is an embodiment of my invention,

Figs. 2, 211,217, 20, 3 and 4 are explanatory curves, and

Fig. 5 is a further embodiment of my inventiOl'i.

By reference to Fig. 1 an exemplified embodiment is shown which generates impulses of practically constant duration. These impulses succeed one another at time intervalswhich are a function of the feed voltages of the multivibrator. The plate circuit of one of the discharge paths or tubes includes a choke coil which is in close coupling relationship with the choke coil of an oscillation circuit included in the grid lead of the other discharge path.

Referring to Fig. 1, l0 and ii are two tubes. Tube Hi contains in its plate circuit a choke coil 12 and a resistance It. The plate circuit of tube 4 1 contains only a resistance It. The control grid lead of tube Iii includes a resistance-capacity mesh l5 through which the control grid, in a way customary with multivibrators, is united with the plate of tube H, that is to say, through a condenser 18, while through a resistance ll connection is established with the filament of tube Iii. In the control grid lead of tube H is included an oscillatory circuit i8 comprising a choke coil !9 and a condenser 20. As to the rest, the grid circuit of tube H is also connected up in a way as known from the prior art of multi-- July 27, 1936 vibrators, that is to say, a condenser 2| is connected through lead 22 between the plate end of the resistance l3 and the oscillation circuit l8, and resistance 23 is in series with the said condenser 2i. Resistance 23 has its lower end con- 5 nected with a potential which is positive with respect to the filament of tube l I, that is, it is connected with tap P of the D. C. source of potential 2d. The connection 25 indicated by broken lines between the upper terminal of condenser 10 2! and the lower terminal of the choke coil It shall be discussed further below.

Disregarding for the present choke coil l2, the oscillatory circuit l8 and the resistance-capacity mesh-l5, the circuit organization shown in Fig. 15 1 represents a multivibrator which distinguishes itself from the conventional type of multivibrator known in the art in that the lower end of resistance 23 is positive in reference to the filament or cathode of tube M. This particular step 20 embodied in the circuit arrangement which is designed to reduce the liability of disturbing actions in the multivibrator has been disclosed in my copending patent application Ser. No. 145,974 filed June 2, 1937. The resistance-capacity mesh 25 i5 has the purpose of rendering the shape of the potential Waveof tube H as rectangular as possible as described in my copending application Ser. No. 146,986 filed June 8, 1937. In the usual type of multivibrator, as is well known, the shape 0 of the potential of the two tubes is as shown by curves Figs. 2a and 2b, the former representing the grid potential of tube l!) and the latter that of tube II. In both graphs, the horizontal coordinate stands for time, and from the line 35 marked 0 which corresponds to the filament potentialv of the two tubes, the potential of the control grid is plotted downwards. In both graphs, the broken line K corresponds to the lower knee of the plate current-grid potential characteristic of the tube. Both graphs show that the control grid potential of tube H. during the time interval between 151 and t2, and that of tube til during the time interval t2 and t3 rises slowly and that at instant t2 the flow of current in tube It is interrupted, while fiow of current is initiated in tube H but that at instant t3 the plate current of tube H disappears while the plate current in tube Ill resumes flowing. Owing to the connection of the lower end of resistance 5 23 with the positive potential at point P, Fig. 2a is not altered at all, while Fig; 2b must be replaced by Fig. 2c in which the rise of grid potential has a horizontal line located above the zero line. and marked P as its asymptote rather than line as shown in Fig. 2b. The resistancecapacity mesh l5, as already pointed out, acts in the sense of producing a greater steepness of the rise of potential at the grid of tube ill at the instant t1 and is. In Fig. 2a the rise of potential is shown perpendicular.

Now, across the choke coil l2, at instant ii a potential will arise in a sense as indicated in Fig. 1 by plus and minus signs. The close coupling of coil |2 with coil IQ of the oscillation circuit I8 is chosen in such a way that there then is developed a potential across the coil |9 whose direction is indicated by plus and minus signs. This leads to the production of a half-cycle in the oscillatory circuit N3, the shape of the potential being indicated by the sinuous alternation S, Fig. 3. The amplitudeA of this voltage alternation is assumed to be high compared with the drive range of tube 1|, in other words, great compared with the vertical distance of lines 0 and K, Figs. 2b and 20. Thus, at the grid of tube I the shape of the potential wave will first be as shown in Fig. 20 (which, as will be noted, corresponds to the potential of the lower terminal of condenser 2|), and additionally the potential shown in Fig. 3. The total potential of the control grid, therefore, is the sum of the ordinates in Figs. 2c and 3. If only the alternation shown in Fig. 3 acted at the grid of tube Ii, and if the drive range of tube H were small compared with the amplitude A, the line K would be intersected practically where the sine passes through Zero. This point of intersection would be independent of the Value of the D-0 potential 24 seeing that, while the amplitude A is a function of the value of the working voltage, this is not true of the duration of the alternation. In practice, however, the constant location of 152 still exists also when taking in consideration the grid voltage share according to Fig. 2c inasmuch as the grid potential at time i2 is far less steep than the sine curve S.

It thus follows that the shape of the grid potential of tube comprises a component which, as regards to the passage through zero is independent of the value of the D-C potential, and further a component which is a function of the value of the D-C potential, which latter, however, by choosing a convenient time constant for 2| and 23 may be so diminished that it is practically negligible. In other words, the time interval-ti, t2, the length of the impulses arising at the plate of tube II is independent of the value of the D-0 potential.

By reference to Fig. 4 it shall be shown that there is no such independence in the case of an ordinary multivibrator. Fig. 4 shows the shape of potential impressed on the grid of tube H in so far as the same is due only to the resistancecapacity mesh, that is, for two different potentials U1 and U2 of battery 24, U1 being assumed to be higher than U2, the further assumption being made that the change of potential as far as instant i2 is to proceed along the initial tangent. It will be seen that the line corresponding to U1 cuts the straight line K later than the onecorresponding to U2 intersects said straight line. In other words, it will be noted that as a matter of fact the length of the impulses greatly depends upon the voltage if the oscillation circuit of this invention is absent.

When the resultant potential of the control grid of tube H as shown in Figs. 2c and 3 cuts the line K, plate current starts to flow in the tube This plate current, for the reasons prevailing in the case of a multivibrator, will always rise rather rapidly until grid current begins to fiow. When this happens, parallel damping arises for the oscillation circuit l8, said damping consisting in the series arrangement of the grid-filament resistance of tube II, the vanishingly low inner resistance of the lower end of battery 24 and the resistance 23. Resistance 23 may be chosen far smaller without occasioning any change in the time constant of 2| and 23, for there is a chance to increase at will the value of the condenser 2| in a corresponding measure. By action of the parallel damping the second alternation or half-cycle is strongly damped with the result that its amplitude will be far lower than magnitude A, and that thus the third alternation which has the same sign again as the first alternation S turns out to be comparatively small. The resistance 23 may be made so small that for the third alternation in Fig. 3 the plate current of tube II will still be of finite size.

However, if then the upper terminal of the condenser 2| through the connection 25 shown by the dotted line in Fig. 1 is united with the plate end of the choke coil l2, there results at the grid of tube not only the sinuous potential arising in the coil IE, but in addition the potential developed across the choke coil I2 which reaches the grid capacitively by way of 2|.

An improvement in the operating conditions of the multivibrator as shown in Fig. 1 is obtainable also for the reason that a pentode, that is a tube having a screen grid, isused rather than an ordinary tube. This makes it permissible to make the choke coil 2 much larger so that a very large amplitude A, the arrangement producing the wave form of Fig. 4 may be used without the deleterious features of unsteadiness or discontinuance of the plate current in 'tube Ill producing undesirable results.

Referring to Fig. 5, there is shown an arrangement wherein an oscillatory circuit is provided in the grid circuit of both of the thermionic tubes. A multivibrator of this kind works in this manner that, after termination of the second alternation, Fig. 3, the tube I0 is started or ignited again, in other words, that impulses of like length are set up in both branches, the duration of which, for the reasons hereinbefore set forth, is independent of the potential.

Instead of including the resistances l3 and 4 and the choke-coil l2 in the plate circuit of discharge vessels, they could be connected also, for instance, in screen-grid circuits or, generally speaking, in circuits of current-carrying electrodes.

What I claim is:

1. An oscillation generator comprising a pair of thermionic discharge tubes having an anode, cathode and at least one control electrode, a time constant circuit connected in the grid-cathode circuit of the first of said thermionic discharge tubes, a resistor connected in series with said time constant circuit, an inductive member connected in the anode-cathode circuit of said tube, resistive means connected in series with said inductive member, a condenser for coupling the grid of said first tube to the anode-cathode circuit of the second thermionic discharge tube, a resonant circuit connected in the grid-cathode circuit of the second thermionic discharge tube, said resonant circuit being variably coupled to the inductive member connected in the anodecathode path of said first tube, a resistor connected in series with said resonant circuit, means for energizing the anodes of said tubes, a connection between the last named resistor and a point on said supply having a positive potential with respect to the cathode of the second tube, means coupling the grid of the second tube to the anode of the first tube, and a resistor connected in the anode-cathode circuit of the second thermionic discharge tube. 2. An oscillation generator comprising a pai of thermionic discharge tubes having anode, cathode and at least one control electrode, a resonant circuit connected in the grid-cathode circuit of the first of said thermionic discharge tubes, a resistor connected in series with said resonant circuit, an inductive member connected in the anode-cathode circuit of said tube, resistive means connected in series with said inductive member, a condenser for coupling the grid of said first tube to the anode-cathode circuit of the second thermionic discharge tube, a resonant circuit connected in the grid-cathode circuit of the second thermionic discharge tube, said resonant circuit being variably coupled to the inductive member connected in the anodecathode path of said first tube, a resistor connected in series with said resonant circuit, means for energizing the anodes of said tubes, a connection between the last named resistor and a point on said supply having a positive potential with respect to the cathode of the second tube,

means coupling the grid of the second tube to the anode of the first tube, and a resistor connected in the anode-cathode circuit of the second thermionic discharge tube.

3. An oscillation generator comprising a pair of thermionic discharge tubes having anode, cathode and'at least one control electrode, a resonant circuit connected in the grid-cathode circuit of the first of said thermionic discharge tubes, a resistor connected in series with said resonant circuit, an inductive member connected in the anode-cathode circuit of said tube, resistive means connected in series with said inductive member, a condenser for coupling the grid of said first tube to the anode-cathode circuit of the second thermionic discharge tube, a resonant circuit connected in the grid-cathode circuit of the second thermionic discharge tube, a resistor connected in series with said resonant circuit, means for energizing the anodes of said. tubes, a connection between the last named resistive and a point on said supply having a positive potential with respect to the cathode of the second tube, means coupling the grid of the second tube to the anode of the first tube, a resistor connected in the anode-cathode circuit of the second thermionic discharge tube, and. an inducive member connected in the anode-cathode circuit of the second tube.

MAX GEIGER.

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