US2131443A - Signaling - Google Patents

Description

Sept. 27, 1938. w. KUMMERER ET AL ,4

SIGNALING Filed May 16, 1954 2 Sheets-Sheet 1 -F l29 I i INVENTOR W/U/ELM mam/m5? 01/00 era-w ATTORNEY Sept. 27, 1938. w, KUMMERER ET AL 2,131,443

SIGNALING 2 Sheets-Sheet 2 Filed May 16, 1934 CARR/67? W4l/E SOURCE O/RECT CURRENT SOURCE #LT g INVENTOR Mil/ELM lfl/MME/Pf/P ATTORNEY Patented Sept. 27, 1938 SIGNALING Wilhelm Kummerer and Rudolf Giirtler, Berlin,

Germany, assignors to Telefunken Gesellschaft' fiir Drahtlcse Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application May 16, 1934, Serial No. 725,846 In Germany May 18, 1933 10 Claims.

This invention relates to an arrangement to change grid biasing voltage in tube circuits as a function of the signal strength.

In a great number of electric circuits comprising tubes it is desirable that the static value of the voltage of a tube stage should adjust itself in a definite way as a function of the signal strength or an electrical quantity controlled or governed thereby. The general requirement in cases like these is that in the presence of signal amplitudes falling below a certain minimum limit or level, the static value of the voltage of a tube, say, the grid biasing voltage, should have a selected constant, while being also constant and of higher value in the presence of amplitudes above a definite upper limit. For signal amplitudes located midway between the said two limiting values, the said biasing voltage is to adjust itself as a function of the signal amplitude.

Now, according to this invention, control of the static voltage value to be acted upon is insured by utilizing the fall of potential in a resistance caused by the plate direct current of an auxiliary tube, there being provided in the grid circuit of the said auxiliary tube an additional resistance in series with a rectifier which is given a negative biasing voltage, across which additional resistance current of the rectifier controlled by the signal currents produces a potential which is a function of the signal amplitude.

The novel features of the invention have been pointed out in the claims attached hereto as required by law.

The nature of my invention and the operation thereof will be better understood from the following detailed description thereof and therefrom. when read in connection with the attached Fig. 3 is a modification of the arrangement of Fig. 2. In the arrangement of Fig. 3, the controlling potentials are derived from the modulating potentials and the carrier wave amplitude is controlled by controlling the static voltage on the grid of the modulator in accordance with energy characteristic of the modulating poten: tial amplitudes; while Figs. 4 and 5 are modifications of a portion of the controlling circuits of Figs. 1, 2. and 3.

The signal amplitude or else a voltage which is a function thereof, is impressed upon the terminals I, 2, of the arrangement shown in Figure 1. By means of the rectifier 4 there is produced across the terminals of capacity 6 a'direct current voltage which isnegative with respect to the grid of the tube 9-, the said direct current voltage acting, through its control of the grid potential, upon the plate current of the tube 9 flowing through the resistance Ill, thereby influencing the fall of voltage across the resistance NJ, to which generally a condenser II is connected in parallel, and consequently across the terminals I4, 15. The potential drop across I4, I5, is caused to act in the grid circuitof the particular stage whose grid biasing voltage is to be a function ofthe signal strength in a way as has hereinbefore been indicated. As a general rule, the grid circuit also contains in series with l4, l5, a direct current source IS. The static value of anode current of the tube 9, apart from the direct current caused by the voltage of source l2, and the plate resistance I0, is further a function of the size of the biasing voltage of source 8. If desired, the source of biasing potential 8 may be dispensed with.

In the case of all voltages across I, 2, whoseamplitude falls below a predetermined critical negative biasing potential of the rectifier 4 as adjusted at the source of direct current potential 5, the said rectifier will be blocked so that no direct current voltage will arise across the condenser 6. The grid bias is now supplied wholly by source 8. The consequence is that the working point of the tube will not be shifted by signals of amplitude below said critical value, and .thus the voltage across [0 remains constant. It is only in the presence of signal amplitudes which exceed the said lower critical value that the source 5 is overcome so that the rectifier 4 becomes conductive; and there arises across the capacity 6 a potential which, according to its size, diminishes the plate current of tube 9 and thereby the fall of potential acrossthe resistance 50 I0. In the presence of the selected critical maxi-- mum signal strength the direct current voltage arising at t is so high that. the tube 9 is out off or is blocked, no current flows-through Sand the potential drop across to will be -of.zero value. v

Signals which exceed the said upper limit will, to be sure, cause a higher direct current voltage across the terminals of 6; but since the tube 9 is already blocked and the voltage at I4, I5 is zero, it follows that the grid biasing voltage of the above mentioned tube connected to I4, I5 will not be altered by these signal potentials.

One practical application of the invention is illustrated in Figure 2. In this case the arrangement hereinbefore described serves the purpose to lessen the distortions occasioned by the curved portions of the modulation characteristic in a transmitter. The plate direct current of tube I8 is conducted by way of the resistance I3. The resistance I9 which is traversed by the plate current of the auxiliary tube 9 is connected in series with the source of voltage I6 andthe modulation transformer I! in the grid circuit of the tube I9. The source I6 and/or resistance I I) shifts the working point of the tube I9 into thelower portion of its characteristic curve so that the tube is working in the region of and above the lower knee. In lieu of the voltage sources 5 and 8 of Figure 1, the biasing voltage 5a is provided in the circuit scheme of Figure 2. The resistance Ia as a general rule is high compared with the resistance I3 and the internal resistance of the valve 4. By the plate current of the tube 9 an additional biasing voltage for the tube I9 is occasioned across the external resistance II]. Inasmuch as the plate direct current of the tube I8 grows with the amplitude of the alternating current amplitude or the percentage of modulation, it will be seen that also the potential across the resistance I3 will increase. If then, in the course of operation of the modulator circuit the admissible modulation percentage is extended or increased so that the wave amplitudes grow to such degree that they extend as far as the lower knee of the characteristic curve. of tube I8, there is produced a growth of the plate current of the tube I8 and also due to the said rectification in tube I8 the same is negatively biased to a corresponding degree. Due to increase in plate current in I8 the fall of potential across the resistance I3 in the plate-to-cathode circuit of I8 also grows. Past a certain point, the potential drop across resistance I3 will exceed the electromotive force produced by source 5a and the rectifier 4 will become conductive. This permits the negative biasing voltage produced across resistance I3 to reach the grid of tube 9. Consequently, the plate current through 9 and the voltage produced by the potential drop across the resistance I0 are both diminished. The resultant biasing voltage of the tube I9 becomes less negative and the working point of tube I9 climbs up along the characteristic curve. A working point located above the lower bend at closer proximity to the middle of the characteristic curve results in 'a greater freedom from distortion. My novel circuit insures operation of the tube I9 at such working point. The arrangement is so dimensioned in this instance that the valve 4 remains blocked as long as the operation takes place somewhere above the lower bend of the characteristic curve upon the rectilinear part of the modulation characteristic. And for the same length of time, also the grid biasing voltage will remain constant in the tube I9. In other words this modulation percentage is exceeded with the result that operation takes place in the curved portion of the modulation characteristic,,then the fall of potential across I3 will go beyond and exceed the biasing voltage 5a, the valve 4 becomes conducting and the higher voltage from I3 will reach and become active at the grid of tube 9, with the result that the plate current decreases and therewith the fall of potential across Ill and thus the biasing voltage of the tube I9. As a result the latter will be modulated to a higher degree or percentage, as the alternating current amplitude grows, and the modulation characteristic of the tube I9 becomes straighter. In other words, inside certain limits a correction of the distortion is brought about. By choosing dimensions appropriately, conditions may be so made that in the presence of modulation the tube 9 will just be blocked. In that case the fall of voltage across I0 becomes zero, .and the biasing voltage of the tube I9 can not be changed any further. When the plate current in I8 assumes larger values, this will cause no additional efiect upon the tube I 9 because the lower negative biasing voltage of I9 is limited by the source I6.

Another exemplified embodiment of the basic idea of the invention is illustrated in Figure 3. This is the fundamental scheme of the modulation stage of a transmitter of the thermionictube type whose carrier is controlled or modulated in proportion to the signal strength. For the purpose of insuring carrier control recourse is had fundamentally to a scheme of the kind shown in Figure 1 which in the present instance is somewhat expanded and developed for the sake of example. The signal voltage is impressed upon the terminals I and 2, and on the transformer I'I. When the amplitude of the signal voltage is at a low critical value, or below, rectifier 4 is blocked by the source 5 and the bias potential on the grid of 9 is due substantially solely to the voltage of Ba as modified by resistors 20, etc., and 9 is conductive. Plate current flowing through 9 and through resistance I9 produces a potential drop in ID. The potential drop in II] adds to the voltage of source I6, as in Figure l, and the plate current through I9 falls. Now, if the modulating voltage amplitude equals a critical value, or more, the rectifier valve 4 becomes conductive and current flows in the resistance I producing a voltage drop which modifies the potential supplied from 8a to bias the grid of 9 more negative, thereby lowering 9s conductivity and reducing the flow of current through ID. This makes the control grid of I9 less negative and increases the flow of plate current in I9. In this manner we produce across the resistance II] a fall of potential which is a function of the signal strength. The size of the capacities 6 and II and of the resistances I and I0 govern the particular rate of speed at which the direct current voltage across I4, I 5, will increase and diminish. Contradistinct to known circuit schemes used for the control of the carrier wave, it is possible in the present invention to adjust to a large extent the speed of carrier growth regardless and independently of the rate of speed of the reduction of the carrier. If the ripples of the direct current voltage across I 4, I5 can not be suificiently suppressed or smoothed by the capacities 6 and II seeing that the values of the latter can not be raised ad libitum because of the resultant time-constants, it would be recommendable to use filter circuits of the kind as shown, for instance, in Figure 3 where instead of 6 the filter circuit 6, 2|, 22 is connected.

. Figure 3 shows a further development of the arrangement residing in the provision of the resistance 29 which is traversed by the plate current of tube 9 and which is included in the grid circuit of the tube 9, said resistance serving the purpose of compensating the curvature of the characteristic of the tube 9. The said resistance will have to be used whenever the desideratum is to insure as linear as feasible an interrelationship between the signal amplitude across I and 2, and the biasing voltage across M and I5.

Cases may arise in which the voltage across the resistance I0 is not desired to bear a linear dependence upon the signal amplitude. In that instance, at the point marked 9 one or more tubes possessing suitable characteristics are provided. Also the frequency curve of the transformer 3 may be so chosen that between the signal amplitude across I, 2, and the voltage across l4, it, the desired non-linear relationship will be fulfilled.

The lower and the upper limit or levels depend upon the choice of the rectifier bias, in Figures 1 and 3, and the turn-ratio of the transformer 3 or the adjustment of the potentiometer l3, in Figure 3. Hence, what is essential is that the voltage at 5 and in some suitable manner also the ratio of transformation of the applied voltage and the one transferred to the rectifier should be adjustable.

If an extensive suppression of the voltage ripples is desired, then as illustrated in Figure 4, two tubes 9, 9a, are connected push-pull fashion in the grid, while their plates are connected in parallel. The rectifier 4 works upon the capacity 6 and the resistance 1 in the grid circuit of the tube 9 and upon the capacity 60. and the resistance la. in the grid circuit of the tube 9a. The voltage ripples across to are of opposite phase compared with the voltage ripples across 5 so that they will largely be neutralized at the plate end. The condenser l I may be chosen so small that it will practically exercise no effect upon the time constant under certain circumstances it may be dispensed with. So far as the dimensioning of the condensers 6 and 6a and of the resistances 7, la, are concerned there is a good deal of latitude in the case of this circuit scheme.

When using tubes having their grids connected push-pull fashion the rectifier 4 may be dispensed with, while the grid biasing Voltage of the tubes 9, 9a, which is to be a function of thesignal may be obtained by means of grid rectification. One exemplified embodiment of such an arrangement is schematically shown in Figure 5. By selection of the biasing potential 5 and adjustment of the potentiometer E3, the upper and the lower control limits or levels are fixed.

Having thus described my invention and the operation thereof, what I claim is:

1. A signaling system comprising, a thermionic tube having a control grid and a cathode, a circuit for applying carrier waves to said control grid, a source of modulating potentials, a transformer having its primary winding connected to said source of modulating potentials, a resistance and a source of potential connecting the secondary winding of said transformer between the control grid and cathode of said first named tube, a rectifier having its input electrodes energized by said modulating potentials, an additional tube having an anode, a cathode and a control grid, a second resistance, a filter circuit connecting the output electrodes of said rectifier in parallel with said second resistance, a connection between said second resistance and the control grid and cathode of said additional tube, and a connection between the anode and cathode of said additional tube and said first named resistance.

2. In a signaling system, an electron discharge device having a controlling electrode and a cathode, a circuit applying carrier wave energy to said controlling electrode, a source of modulating potentials, an impedance and a source of direct current potential connecting said source of modulating potentials between the controlling electrode and cathode of said first named device, a rectiher having input electrodes energized by said modulating potentials, an additionaltube having an anode, a cathode, and a controlling electrode, a second impedance, a filter circuit connecting the output electrodes of said rectifier with said second impedance, a connection between said second named impedance and the controlling electrode and cathode of said additional tube, and a connection between the anode and cathode of said additional tube and said first named impedance. 7

3. In a modulation system, an electron discharge modulating device having electrodes ineluding input electrodes on which wave energy to be modulated is impressed, a source of modulating potentials connected with an electrode in said device and means to regulate the static value of the operating voltages of said device as a func tion of the strength of said modulating potentials comprising, an auxiliary'tube having an anode, a cathode and a control grid, at resistance connected between the anode and cathode of said auxiliary tube, a capacity connected in parallel with said resistance, said capacity being suitable to the frequency of said modulating potentials, means for coupling said resistance to an electrode in said discharge device, the voltage applied to which is to be regulated, a second resistance and a rectifier and a source of direct current potential in series connected with the control grid and cathode of said auxiliary tube, said source of potential being of such avalue and so connected as to normally block said rectifier, means for biasing the control grid of said auxiliary tube relative to its cathode by a potential such that current normally flows in said auxiliary tube and first resistance, and a circuit for ap-'- plying energy characteristic of the modulating potentials to the input electrodes of said rectifier for overcoming said blocking potential when the amplitude of the modulating potentials exceeds a selected value.

4. A system as recited in claim 3 in which said second resistance connected with the control grid and cathode of said auxiliary tube is connected with said rectifier by way of a filtering circuit comprising capacity.

5. In a modulation system, an electron discharge modulating device having electrodes including input electrodes on which wave energy to be modulated is impressed, a source of modulating potentials connected with an electrode in said device and means to regulate the static value of the operating voltages of said device as a function of the strength of said modulating potentials comprising, a pair of auxiliary tubes each having an anode, a cathode and a control grid, a resistance connected between the anodes and cathodes of said auxiliary tubes, a capacity connected in parallel with said resistance, said capacity being suitable to the frequency of said modulating potentials, means for coupling said resistance to an electrode in said discharge device, the voltage applied to which is to be regulated, a rectifier and a source of direct current potential in series connected with the control grid and .cathode of each of said auxiliary tubes, said source of direct current potential being of such a value and so connected as to normally block said rectifier, means for biasing said auxiliary tubes by potentials such that current normally flows in said auxiliary tubes and first resistance, and a circuit for applying energy characteristic of the modulating potentials to the input electrodes of ,said rectifier for overcoming said blocking potential when the amplitude of the'modulating potentials exceeds a selected value.

6. In a modulating system an electron discharge modulating device having electrodes including input electrodes on which wave energy to be modulated is impressed, a source of modulating potentials connected with an electrode in said device and means to regulate the static value of the operating voltage applied to an electrode of said device as a function of the strength of the modulating potentials comprising a pair of auxiliary thermionic tubes each having an anode, a cathode and a control grid, a resistance connecting the anodes and cathodes of said auxiliary tubes in parallel relation, a circuit for coupling said resistance to an electrode in said modulating device, a circuit connected between the control grids of said auxiliary tubes, means for coupling said circuit to said source of modulating potentials, a rectifier connecting a point on said circuit between the control grids of said auxiliary tubes to the cathodes of said auxiliary tubes, and means connected with said rectifier for normally blocking said rectifier.

'7. An arrangement as recited in claim 6 in which the control grid and cathode of each of said auxiliary tubes is shunted by a resistance and by a condenser and in which direct current potentials are applied to the anodes of said auxiliary tubes to charge the said anodes relative to the cathodes by potentials such that said auxiliary tubes are conductive in the absence of signals to be amplified.

8. In a modulation system a thermionic modulator tube having electrodes including a control grid and cathode, a source of wave energy to be modulated and a source of modulating potentials coupled to said control grid and cathode and means to regulate the static value of the biasing potential applied to the control grid of said thermionic modulator tube as a function of the strength of the modulating potentials comprising, an auxiliary tube having an anode, a cathode and a control grid, a resistance connected between the anode and cathode of said auxiliary tube, means for biasing said control grid of said auxiliary tube relative to its cathode by a potential such that current flows in said tube and resistance to produce in said resistance a potential drop, a source of potential coupling said resistance to the control grid and cathode of said modulator tube to apply therebetween said potential drop and potential from said source of potential, a rectifier having its anode circuit connected to the control grid of said auxiliary tube, said rectifier being normally biased to cut off, and means for applying moduated wave energy from said first tube to the input electrodes of said rectifier to control the conductivity thereof.

9. In a modulating system, an electron discharge modulator device having a control electrode and a cathode and an output electrode from which modulated energy is derived, a source of wave energy coupled to said control electrode, a source of signal voltage coupled to an electrode in said device, and means to regulate the static value of the operating voltage applied to the control electrode of said electron discharge device as a function of the amplitude of the signal voltage to be impressed on an electrode of said device and to limit said regulating action between upper and lower voltage amplitudes comprising a source of biasing potential and an impedance for applying to said control electrode relative to said cathode of said device a selected biasing potential, means for changing said biasing potential when the amplitude of said signal voltage exceeds a selected critical lower value commensurate with said selected biasing potential, said last named means comprising an additional discharge device having output electrodes connected to said impedance and having input electrodes, a rectifier having an output connected to the input electrodes of said additional discharge device and an input excited by voltages characteristic of said signal voltages, and means for normally biasing said rectifier to out off in the presence of signal voltages equal to or lower than said selected critical value.

10. A system as recited in claim 9 including means for rendering said means for changing said selected biasing potential inoperative when said voltages characteristic of signal voltages exceed a predetermined upper amplitude value whereby the biasing potential on said control electrode of said first discharge device is controlled in accordance with the amplitude of said voltages characteristic of signals between said upper and lower limits.

WILHELM KUMMIERER. RUDOLF GI'JRTLER.

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