US2157533A - Oscillator - Google Patents

Description

M. GEIGE May 9, 1939.

OSCILLATOR Filed June 8, 1957 L Z/PUFF POTENT/AL INVENTOR YGER BY V? ATTORNEY Patented May 9, 1939 UNITED STATES PATENT OFFEQE OSCILLATOR Germany Application June 8, 1937, Serial No. 146,986 In Germany June 16, 1936 '7 Claims.

This invention relates in general to a relaxation oscillation generator.

A multivibrator is known to be a generator of relaxation oscillations in which two discharge paths are alternatively in action and whereby the one path puts the other one out of operation. Such relaxation oscillation generators can be utilized for the production of periodic electrical impulses employed in particular for purposes of television.

An object of my invention is to provide an oscillator which supplies a timing wave in which the impulses furnished by the multivibrator are rectangular in shape.

A further object of my invention is to provide means whereby the variation in anode current from the tubes of the multivibrator is substantially instantaneous.

Other features and advantages of my invention will appear from the following description taken in connection with the accompanying drawing in which:

Fig. 1 is a schematic diagram of my improved multivibrator.

Figs. 2 and 4 show curves of the grid potentials of the multivibrator as hitherto demonstrated.

Fig. 3 shows the characteristic grid voltageplate current curve for a tube such as used in a multivibrator.

Fig. 5 shows the plate potential curve for a multivibrator tube.

Referring now to Figure 1, those parts of the system which constitute a conventional multivibrator circuit will be explained. The multivibrator consists of discharge tubes and II, each of which includes a cathode, a control electrode and an anode. The cathodes of the tubes are connected together and are in turn connected to ground potential, whereas the anodes of each of the tubes are maintained positive with respect to the cathodes by an appropriate source of potential, the positive terminal of which is connected to the anodes of the tubes l0 and II through the resistances l2 and I3 respectively. Connected between the anode of each tube and ground is a resistance-condenser combination in order that the potential of the control electrodes of each of the tubes may be controlled. One plate of the condenser M, for instance, is connected to the anode of tube I l, the other plate of the condenser M being connected to ground by way of resistance l 5. The control electrode of tube I0 is connected to the junction of the condenser l4 and the resistance l5, this connection including a parallel.

arrangement of a resistance l9 and a condenser 2|, The purpose of the resistance l9 and the condenser 2| will become more apparent later. Likewise, one plate of condenser E6 is connected to the anode of tube H], the other plate of the condenser being connected to ground by way of "5 resistance IT. The control electrode of tube H is connected to the junction of the condenser l6 and the resistance H, the connection including a resistance 20 in parallel with which is connected a I condenser 22. The resistance 29 and the con- 10 denser 22 which are associated with tube l l correspond to the resistance [9 and condenser 2i which are associated with the tube l0. These elements are not necessary so far as the multivib-rator circuit and its operation is concerned, and, in order to explain the operation of the multivibrator system resistances l9 and 20, as well as the condenser 2! and 22, will be left out of consideration. There is also a certain inherent distributed anode- V cathode capacity within each of the tubes I U and II, which are represented in the drawing and the presence of this capacity will also be ignored at present, for the purpose of explanation.

Figure 2 shows the pattern of the grid potential of the tube It (Eglo) as hitherto demonstrated '25 for the multivibrator. In this figure, the pattern of the grid potential is shown as function of the time. In the point A the condenser M has a high charge such that its lower plate is negative with respect to its upper plate. The tube It has no 50 current while plate current flows in tube l I. The potential at the lower plate of condenser M then varies in accordance with an e-function whose time constant is determined by the capacity l4 and the value of the resistor l5. In point B the 3 ,5 Voltage at the condenser l l may be assumed to have decreased to such a degree that current also begins to flow in the tube Ill. The horizontal dotted line in Figure 2 thus corresponds to the lower bend of the plate current-grid voltage char- 4 acteristic of tube It] as represented in Figure 3. As soon as a small plate current flows in the tube lo, the plate potential of IE! decreases because of the drop of the voltage at the resistor l2, and since the charge of the condenser it cannot change suddenly, the grid potential of the tube H decreases at the same rate. This causes a decrease of the plate current of tube H and hence an increase of the plate potential of tube l l in view of the reduction of the voltage drop through the resistor l3, This potential increase in turn has the effect that the grid potential of tube 0 increases still further, since also the charge of the con denser I4 cannot vary suddenly. In this manner there takes place alternatively an increase in the grid potential of tube Hi and a decrease in the grid potential of tube ll, until grid current sets in in tube l0 and the plate current in tube ll disappears completely. This condition corresponds to the point C in Figure 2. Now, the grid potential of tube l0 remains substantially constant until the charge on condenser l6 has disappeared to such a degree that current sets in again in tube ll. This condition corresponds to point D in Fig. 2 and, at this time, the grid potential of tube lll will be displaced in the negative direction because of the decreasing plate potential of the tube l l, causing a potential increase at the anode of the tube ill, and hence, also an increase of the plate current of tube H. In this way the plate current of tube H increases rapidly to a point in which the grid current sets in, while the plate current of tube l0 disappears completely. The condenser 14 has then again a high charge in the sense of the plus-and-minus signs shown, so that the described performance repeats itself from point E in Figure 2. The pattern of the grid potential of tube H (Egll) is shown in Figure 4.

Now it was to be expected that the pattern of the plate potential of the two tubes would be absolutely rectangular, since it was believed that the plate current was always brought quickly to a constant value, while at the setting in of the discharge the plate current in the other tube was likewise believed to fall to zero in a very rapid fashion. However, a closer investigation shows that this does in fact not occur. It is true that in point B in Figure 2, as above described, a plate current sets in in the tube It which increases rapidly also on account of the feed back across the plate potential of tube H. Therefore, also the potential at the anode of tube H increases rapidly at first, but the course of the plate potential as a function of time is determined by the inherent cathode capacity 18 of tube ii (and by other distributed capacities), as seen in the following. When the plate current of tube ll decreases, the plate potential can only increase to the extent in which the plate-cathode capacity I8 is charged through the resistor l3. This takes place with the time constant of the resistor l3 and condenser l8 which are both comparatively small, so that the plate potential of tube ll first undergoes a steep increase tending to adjust itself to the potential of the positive terminal of the battery in accordance with an e-function. The initial part of this e-function is designated by the portion F-G of the curve shown in Figure 5, the following part of which is shown in dotted line. But, as already explained above, at an increase in the plate current of tube la, a grid current also begins to flow very soon in tube ill whereby the inner resistance of the grid cathode path is very low. In other words this signifies that the small condenser it has the comparatively large condenser M. practically placed in parallel thereto. At this point, therefore, the plate potential of tube l i can now increase but very slowly instead of rapidly as desired, since the time constant is a product whose one factor consists of the value of the resistor l3, and whose other factor consists of the sum of the capacity values of M and IS, and this time constant is considerably greater than the time constant existing before the grid of the grid current in tube III. This curve represents in fact an asymptote to the horizontal line representing the potential of the positive terminal of the battery, but this curve is produced with a much greater time constant.

It is therefore proposed in accordance with the invention, to insert resistors l9 and 28 respectively in the connection lines between the resistance-condenser members M, H) and it, I! and the connection terminals of the control grid. These resistances have the effect that the time constant of the curve part GI-I in Figure 5 will be increased to such a degree that, starting from the point G the plate potential can be considered as limited to the horizontal. (The part FG of the pattern of the plate potential has in fact a course that is still steeper than that shown in Figure 5.)

The resistors l9 and 2% completely fulfill the requirement to eliminate, in operation, the effect of the parallel connection of the condenser M to the condenser l8, but eventually they may lead to an undesirable decrease in the steepness of the current increase of tube 38 and thus cause a slow current decrease in tube H. The reason for this can be found by the fact that the gridcathode capacities of the amplifier tubes must, at an increase of their grid potentials, at first be charged across the resistors l9, 2% which can take place only with the time constant of the grid resistance and grid-cathode capacity. The voltage at the grid-cathode capacity thus increases in accordance with a rectangular potential pattern, but at the anode of the other tube it increases only with a finite steepness. In order to increase the rate of this increase of the grid potential the resistors l5, 2i may have condensers El, 22 connected in parallel thereto. These condensers have the effect that at the control grids a voltage appears through capacitive voltage division between the parallel condensers 2!, 22 and the grid-cathode capacities, which increases the plate current. The stationary condition lies in the fact that the potential increase at the anode of tube M will be distributed in accordance with the relationship between the ohmic resistances l9 and 20 and the inner resistances of the grid-cathode paths when grid current flows. The transition from the capacitive to the ohmic voltage division takes place in accordance with an e-function in the event that the inner resistance of the grid-cathode path can be considered constant as to time such as corresponds very favorably to the actual state at sufficient size of the condensers 2!, 22. That is, the time constant of the resistance and condenser !9, 2i and 2 22 should be about the same as the time constant as caused by the gridcathode resistance and capacity of the tubes ii] and H.

Various modifications 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 imposed by the prior art and are set forth in the appended claims.

I claim as my invention:

1. A multivibrator for producing rectangular wave form comprising a pair of vacuum tubes each having a cathode, an anode and a control grid, a condenser and a resistance connected in series between the anode and the cathode of each tube, a second resistance, said second resistance being connected between the control grid of one tube and the junction of the series condenser and resistance of the other tube, means connected to each anode and cathode for maintaining said anodes positive with respect to said cathodes, and a resistance in each anode connection.

2. In a relaxation generator, a pair of vacuum tubes each comprising a cathode, a control grid and an anode, a source of potential, circuit means for connecting said source of potential to said tubes to maintain the anodes positive with respect to the cathodes, a resistance in each anode circuit, a condenser and a resistance connected in series between the anode and the cathode of each tube, a conductor for connecting the control grid of each tube to the junction of the said condenser and resistance of the other tube, and a high resistance included in said conductor.

3. In a relaxation generator, a pair of vacuum tubes each comprising a cathode, a control grid and an anode, a source of potential, circuit means for connecting said source of potential to said tubes to maintain the anodes positive with respect to the cathodes, a resistance in each anode circuit, a condenser and a resistance connected in series between the anode and the cathode of each tube, a conductor for connecting the control grid of each tube to the junction of the said condenser and resistance of the other tube, a high resistance included in said conductor and a condenser in parallel with said high resistance.

4. In a relaxation generator, a pair of vacuum tubes each comprising a cathode, a grid and an anode, a resistance connected to each anode and a source of current one terminal of which is connected to the cathodes and the other terminal of which is connected to the resistances, a condenser and a resistance connected in series between the anode and the cathode of each tube and a second resistance connected at one end to the grid of one tube and at the other end to the junction of the series condenser and resistance of the other tube.

5. In a relaxation generator, a pair of vacuum tubes each comprising a cathode, a control grid and an anode, a resistance connected to each anode and a source of current one terminal of which is connected to the cathodes and the other terminal of which is connected to the resistances, means for connecting the anode of each tube to the grid of the other tube, said means including a condenser and a high resistance and a second resistance connected between the junction of said condenser and said high resistance and the cathode of each tube.

6. In a relaxation genera-tor, a pair of vacuum tubes each comprising a cathode, a control grid, and an anode, a resistance connected to each anode and a source of current one terminal of which is connected to the cathodes and the other terminal of which is connected to the resistances, a condenser and a resistance connected in series between the anode and the cathode of each tube and an impedance connected between the control grid of each tube and the junction of the series condenser and resistance of the other tube.

'7. In a relaxation generator, a pair of vacuum tubes each comprising a cathode, a control grid, and an anode, a resistance connected to each anode and a source of current one terminal of which is connected to the cathodes and the other terminal of which is connected to the resistances, a condenser and a resistance connected in series between the anode and the cathode of each tube and a time constant circuit connected between the control grid of each tube and the junction of the series condenser and resistance of the other tube, said time constant circuit being substantially equivalent to the time constant of the internal grid-cathode resistance and capacity of the associated tube.

MAX GEIGER.

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