US2281948A - Relaxation oscillator - Google Patents

Description

May 5, 1942. H. PIEPLOW RELAXATION OSCILLATOR INVENTOR HA NSF/ERA? P/EPLOW Filed Dec. 50, 1938 ATTORNEY Patented May 5, 1942 UNITED STATES PATENT OFFICE RELAXATION OSCILLATOR Application December 30, 1938, Serial No. 248,488 In Germany January 8, 1938 6 Claims.

The invention relates to a relaxation oscillation arrangement for producing voltages exactly proportional to time.

The prior art discloses means for producing voltages that are proportional to time such as those utilized in the television field and in cathode ray oscillographs, by charging a condenser with a constant current. This constant current is obtained by using tubes, for example pentodes which operate in the region of saturation.

My invention will best be understood by reference to the figures in which Fig. 1 shows an embodiment of the prior art,

Fig. 2 is an explanatory curve,

Fig. 3 is a prior art embodiment,

Fig. 4 is an explanatory curve,

Figs. 5, 6 and '7 are embodiments of my invention, and

Fig. 8 is an explanatory curve.

Referring to Fig. l, a source of potential is connected in parallel to a potentiometer l, and connected to the potentiometer is a vacuum tube 2 having anode, cathode, control, screen and suppressor grids; the arrangement being energized by the potential drop across the resistance. The control grid 5 is biased negatively with respect to the filament, and the screen grid 6 is biased positively with respect to the filament. The grid 1 is connected to the cathode. A condenser 3 is connected in parallel with a discharge tube 4, and this parallel arrangement is connected in series with the anode of the tube.

The plate current-plate potential characteristic field (is/Va) of 2 is shown in Fig. 2. It is seen that no absolute saturation is present and that the characteristics still have a slight tendency to increased steepness. A voltage that is exactly proportional to the time hence cannot be produced by means of such a circuit.

Attempts have been made to come nearer to the production of a voltage exactly proportional to time by inserting a variable resistance in the cathode branch of the discharge tube. Fig. 3 shows this circuit in which the resistor is designated by 8. The exact proportionality aimed at is not completely achieved since the influence of the screen grid current entails a falling characteristic of the cathode current (ik) in dependence on the plate potential (Va) (see Fig. 4), so that when controlling the control grid potential of the discharge tube, the resistance does not act fully.

In accordance with the invention, the linearity of the relaxation potential is essentially improved in that the control grid of the discharge tube is controlled only by the plate current or by the plate potential of this tube.

Fig. 5 shows an example of construction of the relaxation circuit arrangement according to the invention in which the control of the control grid of the discharge tube takes place only by the plate current. The reference characters have the same significance as those in the preceding figures. According to the invention, the resistor 8 is herein inserted in the control grid circuit and in the plate current circuit. The cathode connection of the screen grid 6 is directly to the cathode so that the screen grid current flows no longer across the resistor 8. It was found from tests that a substantial improvement of the linearity which is three times greater as compared with an arrangement according to Fig. 1 can be attained.

An absolutely accurate proportionality to time cannot however be achieved in general with a circuit arrangement according to Fig. 5. The relaxation condenser 3' has never actually an ideally insulating dielectric, and furthermore there are always resistors in parallel thereto as for instance in the case of the connection to a Braun tube, so that the condenser entails a loss resistance which would preclude a voltage proportional to time even where the charging current would be exactly constant. In this case, the control resistor 8 could not effect a control of the charging current since despite the loss resistance a charging of the relaxation condenser which is proportional to time will take place. A charging of the relaxation condenser which is proportional to time can be effected in that the control of the control grid 5 eifected by 2 is rendered dependent on the plate potential instead of on the plate current.

Fig. 6 shows an example of construction for this case. The plate potential of the tube 2 controls the auxiliary tube 8, the latter tube having an anode resistance 9, while the plate potential of 8 reacts upon the control grid of 2. The resistors Ill and H as well as I2 and I3 form the voltage dividers which bridge the anode and the cathode of the charging tube as well as the auxiliary tube. The arrangement functions in the following manner: At a decrease of the plate potential at 2, the positive part of the control grid potential of 8 appearing at H becomes smaller, hence the potential at I3 and therefore at the control grid of 2 increases in the positive direction so that the plate current of 2 has the tendency to increase. As can be seen, by setting the resistance relations H]; H and l2; l3 there exists the choice either to control an exactly constant plate current (ia) of 2 in dependence of the plate potential (Va) (Fig. 8, curve a), or even to control a plate current which decreases with an increase in the plate potential (see Fig. 8, curve b). The Working point of 8 Will be so set that the curve a or b in Fig. 8 becomes straight. Furthermore, the tube 2 will be so controlled that the inclination of the curve b in Fig. 8, that is, the apparent negative inner resistance, is equal to the total resulting leakage of the condenser 3. In this case, the condenser potential is accurately proportional to time. Then, if the loss resistance of the condenser is not appreciable, the tube 2 is so to be controlled that a constant plate current appears.

The example of construction according to Fig. 7 can be used in the case where periodic alternating potentials which are proportional to time appear at the condenser 3. In this case, the D. C. coupling of the tubes 2 and 8 (which obviously is also suited for alternating potentials) can be replaced by an A. C. coupling so that a saving in batteries can be attained. The voltage dividers I and II and I2 and I3 are blocked. against D. C. by the condensers I4 and I5, so that at II and at I3 only parts of the alternating plate potentials appear. The tube 8 receives its negative grid biasing potential by a cathode resistance I 6 which is known as such while the tube 2 is negatively biased by a potentiometer I! at which the means value of the charging current and hence the frequency of the relaxation potential will be controlled.

What I claim is:

1. A sawtooth wave generator comprising electrical energy storage means, a discharge path connected substantially in parallel with said electrical energy storage means, a first multi-grid vacuum tube having anode, cathode, and at least two grid electrodes, means connecting said electrical energy storage means in the anode-cathode path of said multi-grid tube, a second thermionic tube comprising anode, cathode and at least one control electrode, resistive means connected across the anode-cathode circuit of said multigrid tube, means connecting said resistive means to the control electrode of said second thermionic tube, resistive means connected across the anodecathode path of said second thermionic tube, said latter resistive means being electrically connected to said electrical energy storage means, and means electrically connecting at least one of the grid electrodes of said multi-grid tube to said latter resistive means.

2. Apparatus in accordance with claim 1, wherein said electrical energy storage means comprises a condenser.

3. Apparatus in accordance with claim 1, wherein the discharge path connected in parallel with said electrical energy storage means comprises a thermionic tube.

4. Apparatus in accordance with claim 1, wherein the resistive means connected in the anode-cathode circuit of said multi-grid tube comprises a pair of resistive members.

5. Apparatus in accordance With claim 1, wherein the resistive means connected across the anode-cathode circuit of said multi-grid tube comprises a pair of resistive members, and wherein the resistive means connected in the anodecathode circuit of said second thermionic tube comprise a pair of resistances.

6. Apparatus in accordance with claim 1, wherein the resistive means connected across the anode-cathode circuit of said multi-grid tube comprises a pair of resistive members, and wherein the resistive means connected in the anodecathode circuit of said second thermionic tube comprise a pair of resistances, and. wherein there is also provided a capacity member connected isaerially with each of said pairs of resistive meme ers.

HANSWERNER PIEPLOW.

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