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„Euäy ì, i946. o. H. SCHADE 2,404,099 AMPLIFYING SYSTEM Filed Aug. 16, v1941 2 Sheets-Sheet 1 ' vVEN-rn r l ` July 16, 1946. O. H. SCHADE 2,404,099 AMPLIFYING SYSTEM Filed Aug. 16, 1941- 2 ShfeetsFShee'f,v 2 Patented July 16», A1946 i „ 2,404,099 UNITED STATES >PA'I‘ENTÍ OFFICE 2,404,099' _ 4 AMPLIFYmG SYSTEM Y Otto H. Schade, West Caldwell, N..I., assigner to Radio Corporation of America, a corporation of . Delaware Application August 16, 1941, Serial No.4077,1370 » l 7 claims. My invention relates to high efficiency ampli (o1. 315-28) l ` 2 power limiting devices to limit the power outputy fying circuits for uni-directional signals and par from at least one of the said tubes to a prede ticularly to amplifiers for amplifying recurrent termined maximum value. These and other ob phenomena for portrayal in cathode ray oscillo jects, features and advantages of my invention scope equipment. UY will become apparent when taken in connection In many applications for the ampliñcation of with the following description and with the' ac recurrent phenomena, it is desirable .tol provide a companying drawings wherein: ’ , linear amplified output characteristic with mini Figure 1 is a schematic circuit showing the mum of equipment and power dissipation. In portable aircraft position indicators it is neces 10 -prin’cipalieatures of my new „and improved amplifying system for use in cathode ra'y deñec sary to provide circuits having a high degree of tion oscillographs; ‘ . frequency response as well as high precision so that the absolute distance between approaching Figure 2 is a dynamic characteristic curve show ing operation wave forms of a conventional am aircraft or from an aircraft to ground station may plifying system; be portrayed on a luminescent screen of a cathode 15 Figure 3 is a similar dynamic characteristicV ray tube with accurate precision. It is also desir able, especially when such equipment is to be located on the aircraft, to provide a minimum of showing my improved method of operation, andA Figure 4 is a graphical diagram of certain static anode characteristics of my amplifying system. weight and power dissipation. While certain of It will be appreciated that in circuits for- ob the objects of my invention may be obtained by 20 taining high output voltages of square and asym other methods and means, such is true only by metric wave forms, it is necessary to provide very the use of larger and higher power dissipating equipment. Thus in circuits for obtaining high output voltages of square wave form severe limi high frequency band widths up to and including a band Width such as 10 megacycles per'second. Whilel large amplifying output tubes may be ’ tations are incurred by the fact that the ampli 25 utilized `with relatively low -load resistors to fier tube dissipation becomes excessive. It was obtain such wide band widths, such-tubes and therefore found necessary in the past to use rela circuits are usually characterized by high power tively large tubes when the required output volt- dissipation and relatively high tube and circuit age exceeds a certain value by providing tubes of increased size and larger power dissipating 30 capacitance. The plate dissipation in such tubes is proportional to the second power ofthe capaci capability. Such use also increases the amplifier tance so that for a -given frequency band, tubes circuit capacitance which in turn necessitates in having kvery large continuous power dissipation creased power dissipation. are necessary even though the useful integrated It is therefore an object of my invention to . power output is relatively small. In vso-called increase the obtainable linear voltage output over “class B” operation the continuous power con» a relatively high frequency band with low power sumption may be reduced but only at the sacri dissipation. It is another object of my invention lice of nonlinearity. Therefore, in accordance to provide a system wherein high linear output with my invention I provide a counterphase voltage wave forms may be obtained and wherein amplifying circuit having at least two amplifying a minimum of power dissipation is required. It is tubes, each Vhaving at least a cathode, control a still further object to provide a System wherein grid, and anode or plate electrode, and I adjust uni-directional signals may be ampliñed efli the` grid and anode potentials so that a greater ciently by the use of conventional low power dissi negativegrid bias may be applied to the tube pation tubes, and it is a still further object to with the higher anode potential, and a lower nega provide a system of high frequency band width tive grid bias may vbe applied'to the tube having wherein the power dissipation may be maintained the lower anode potential. , In operation the at low values while retaining the advantages of first tube operates near cut-off current at zero low output loads which are required for high fre signal and hence operates with low orzero plate quency response. dissipation. 'I’he second tube operates with a In accordance with my invention I provide an low negative grid bias and a moderately high amplifying system utilizing at least two ther plate current at low plate voltage and hence also mionic amplifying tubes and control the operation operates with moderate plate dissipation.Y Eur-_ of the tubes so that the parameters determining ther in accordance with my invention I_ utilize the power dissipation are divided unequally be tween the tubes in combination with additional voltage measuring control tubes which auto matically vary the »grid bias on each ofthe-_ 2,404,099 3 counterphase amplifier tubes to limit the maxi mum plate dissipation of one tube and maintain a linear summation characteristic. Obviously, my to maintain the two tubes at different bias values comprising a manually adjustable potential divider 20 connected between ground and cathode l2 and I5 and a source of negative potential. system is applicable only to the amplification of The grid I3 of the tube I6 is connected through a uni-directional wave forms such as square waves, grid resistor 2| of approximately 250 K. ohms either of the symmetrical or asymmetrical type, with low average components such as impulses of short duration with respect to their repetition to a point on the potential divider 20 which is highly negative with respect to the cathode I2, whereas the grid I5 of the tube II is connected through a similar resistor 22 to a point on the time. The principles embodied in my system will be 10 potential divider 2B which is at a less negative understood to better advantage by referring to potential. In this manner the grid bias on the Figure 1 which shows in schematic form one Inod tube I0 is maintained at a greater negative value iflcation of an amplifying circuit employing my than that of the >grid of the tube l I. Further in invention and particularly adapted for the am-V accordance with my invention each of the grid plification of square wave forms which may be resistors ZI and 22 are shunted by a peak volt applied to cathode ray indicating equipment. Re age reotifying device, such as the diodes 23 and ferring to Figure 1, the tube I, which may be of 2d. These diodes rectify the peak voltage shown the single or multiple grid thermionic type, serves as ein and en on the wave forms I8 and I9 and modify the grid biases by an equivalent D. C. as a phase inverter for a square wave form-shown > at 2 for which ampliiication is desired. The wave voltage appearing across the resistors 2 l-22. To form is applied across the grid-cathode input cir obtain this mode of operation I connect the diode cuit and appears in unmodified form except for 23 with its cathode to the grid I3 and the plate phase inversion across the plate cathode circuit. to the potential divider 2€), and conversely the Thus a wave form similar to that shown at 2 is diode 24 is connected with its plate to the grid developed across the capacitor 3 and a similar I6 and the cathode to the potential divider 2€). wave form except for phase inversion across the In operation any signal I3 applied to the input capacitor 4. The relative amplitude of these wave circuit of the tube II! will cause a decrease of the forms may be varied by a variable resistor 5 con negative bias applied to this tube, and conversely nected as shown. In order to preserve the high any signal I9 will cause an increase in the nega frequency components comprising the square wave 30 tive bias applied to the tube II. Further details form shown at 2, the resistors in the input and of the operation of the voltage measuring devices output circuits of the tube I are of relatively low 22 and 23 will be more fully described below. The value. The output from the capacitor 3 may be anodes of the tubes I0 and II are likewise, in further amplified by use of a conventional am accordance with my invention, supplied with def plifying tube 6, and similarly the output from 35 inite potentials, that of the tube I0 being con the capacitor 4 may likewise be ampliñed in con siderably higher than that applied to the tube I I. ventional manner by an amplifier tube l. Each The tubes I0 and I I may be of the 6L6 type with of these tubes may likewise be of the single or an isolated anode lead, such as the commercially multiple grid types. rEhe outputs from each of available tube Type 807, in which case a poten the tubes (i and 'I are applied through conven 40 tial of 1500 volts may be applied to the plate I4 tional coupling networks to output capacitors 8 through a load resistor 25 of relatively low value and 9. Likewise, following current high fre to maintain proper frequency response in series quency circuit principles in the design of the load with a load impedance 26; similarly, a potential circuit, tubes S and 'I are preferably of the low of 500 volts may be applied to the anode I'I power consumption beam type, such as the tube through a similar load resistor 2'I and load imped known commercially as Type GLS operating at a ance 23. The ampliñed outputs of the tubes iii plate potential supply of approximately 250 volts as shown. In accordance with my invention the and II are preferably capacitively coupled through capacitors 29 aid 39 through suitable signals to be further amplified and appearing at nonattenuating circuits and. to one set of deflec the capacitors ß and 9 which are preferably of 50 tion plates ill-_32 of a conventional high voltage 0.1 microfarad value are applied to the input cir cathode ray tube 33. These amplified square wave cuit oi‘ two tubes IIJ and II operating in counter potentials contain substantially all of the high phase arrangement. In accordance with my frequency harmonics originally contained in the principles of operation I apply a relatively high signal shown at 2 and appear across the respec 55 negative bias to tube I0 and a relatively low neg tive plates 3I-32 as shown at Sli-_35. A con ative bias to the tube II, and likewise apply a ventional sawtooth voltage wave form may be ap relatively high plate potential to the tube ID and relatively low plate potential to the tube II. plied to the quadrature deñection plates 36-«31 as well known in the art for the portrayal of the More particularly, the tube Ii) includes a cat-h combined wave forms Sil-35 on the conventional ode I2, a control grid I3 and an anode lf3, while 60 luminescent screen of the tube 33, and the por the tube I I includes a cathode I5, grid I6 and an trayal of the square wave form may be centered anode I'I; each of these tubes likewise may be on the luminescent screen by applying a positive of multi-grid as shown, including a screen grid potential to the plate 3| from the potentiom I3’ and I6', in which case suitable operating po 38. tentials may be applied to the additional grid elec 65 eter The principles underlying the operation of my trode or electrodes. The signal appearing be system will be more fully appreciated with ref~ tween the capacitor 8 and ground is applied di erence to Figures 2 and 3 wherein Figure 2 is rep rectly to the grid I3 of the tube Iû, the wave resentative of a balanced bias and anode poten form being such as shown at I3, and similarly the tial condition between the tubes Ill and II, and wave form appearing between the capacitor 9 Figure 3 is representative of an unbalanced con and ground is applied directly to the grid IE of dition of bias and anode potentials whereby the the tube II. The average potentials or bias po objects of my invention are obtained. Refer tentials of these grid electrodes, however, are ring to Figure 2, the dynamic load characteris maintained at definite values, one of which is tic of the tube I0 is represented by the line AB 75 higher than the other. I therefore provide means 2,404,099 and that of the tube II by the line A’B'. Since the characteristics of the two tubes I0 and II are similar, the summation characteristic is substan tube II). _'I‘he load line AioBio is drawn with a' slope corresponding to the resistance of resistor 25 throughrth'e assumed Imax value which is lo cated'on the knee line 50 of the tube I0. This knee line is the envelope curve of all plate volt age-plate current characteristics with control tially linear and represented by the line BB', a portion of which is shown in dashed line detail. The grids of the tubes I0 and I I for the assumed balanced condition have applied thereto a sig grid; or screen grid voltage or voltages as pa nal, such as shown at 40 in Figure 2, the line CC’ rameters. ‘ This ' will determine the necessary being representative of the average grid signal. anodepotential Eb'for the tube Iû. To determine It is here also assumed that the diodes and their 10 theïcorresponding anodev potential for tubeV .II circuits are not used in the balanced condition. theîload'lineÍis-lextended so as to be 1/4 as long For this balanced condition the grid bias on 'each as ' A101310/- which .determines the point Bn of the tubes I0 and II would be of the same through which the perveance characteristic 5I of amount and the average grid signal represented theïtube'll is drawn. The values Enf, I’max and by the line CC’ remains stationary, always pass 15 Ep'f'mina're thus “derivedì ` - ¿ ’ ' ing through the point O. Consequently, even in ~ The dynamic characteristics for .the tubes I0 the absence of signals applied to the tubes Ill and YII -shown vin' Figure 3 are then drawn using and II, the plate dissipation of both tubes will these assumed and derived parameters, adjust be high because both of the tubes operate with ingftheirv position to give the linear summationV a plate current represented by the intersection 20 characteristicl ' 'If the tubes' I0 and II are of the multi-grid Vtype as shown, the screen potential at a high anode potential applied to both tubes. required _for tube II will be found to- have a Figure 3, which shows the dynamic character lower Value lthan tube Ill'becaus’e of' the'lower istic under unbalanced conditions, portrays the current requirements’. The line EE’ of Figure 3 of line CC" with the characteristic AB and A'B’ operation of the system when operated in ac cordance with my invention. The line EE’ may be made to coincide always with one of the peak values of the grid signals by means of the di is now drawn through the current value of I’max intersecting the characteristic AB of tube I0 a't the zero signal current value. The zero signal power dissipation is given for tube- Ill by this zero odes 'i3-24. The average value of the grid sig signal current IQ multiplied by the anode voltage nals DD' is eifectively shifted to the right by the 30 of the tube I0: ` rectiñed peak voltages ein, en adding to the ñxed grid bias of the two tubes I0 and I I. By increas ing the bias on one tube by an amount en and The power dissipation for tube I I is similarly ob- . at the same time decreasing the bias‘on the other tube by the amount ein, the linearity of summa 35 tion characteristic is not altered but the grid voltage axis is shifted to DD' as shown in Figure If these dissipations do not exceed the tube rating, the derived values represent one possible operat 3. Thus with the tubes 23 and 24 in operation the average moves according to the signal leav ing condition. yIf the dissipation ’of tube VIl) eX ing EE’ in a predetermined position. A ñxed 40 ceeds the tube rating, the line EE’` must be moved toward cut-offY until a dissipation conforming to maximum current cannot, therefore, be exceed ed in tube II regardless of signal. It is there the rating is not exceeded. ' The required current fore obvious from Figure 3 that a square wave I’max for tube I Iv is thus increased as seen from Figure 3 and can be determined from Figure 3 as form, such as the signal shown at 40, will cause a high current and low plate voltage lon tube II, L the intersection. of line EE' with a linear sum and a low or Zero current with corresponding mation characteristic. Consequently, the inter high plate voltage on tube I0 for the long inter val between the signal pulses. Both of these conditions represent low plate dissipation in the section of the load line AnBn in Figure 4 with the perveance characteristic 5I must be corrected respective tubes. Therefore, for zero signal con- ' ditions the tube I0 has the same low dissipation as between signal impulses. The tube I I, when operated with low negative bias and relatively low anode potential, operates with a moderate anode current at zero signal, . and since the signal is uni-directional toward its cut-off voltage and beyond, the required anode supply voltage for the tube II is considerably less than that required for the tube I0. The necessary anode supply voltage on each tube is 60 given by the expression: solving for the required higher plate potential Eb' of tube I I. The zero power dissipation of tube I I is redetermined' with these new values. If the resultant dissipation of tube II exceeds the rat ing, it is not possible to obtain the assumed sig nal output for the tubes chosen and the process must beV repeated for a signal output lower than the desired output referred to above. In this manner the maximum signal output may be de termined for the chosen type oftubes Il) and II. While I havedisclosed my invention with par ticular reference to the amplification of square wave forms, it will be obvious that-it is also of particular advantage in the ampliñcation of any pulse-type wave forms wherein the average value . These voltages and currents may be shown between reoccurrence of the pulses is relatively ï graphically on the static anode potential-anode 65 long with respect to the pulse time. It will like current characteristics as in Figure 4. This wise be obvious that my system possesses consid static characteristic may be used to determine erable merit inthe ampliñcation of wave forms the operating parameters for the tubes I0 and of the pulse type having a smaller and larger ' II. The load resistors 25 and 21 are chosen in amplitude of opposite polarities. Therefore, accordance with the tube characteristics to give 70 while I have described my invention with refer the desired band width, these resistors being ence to the amplification of vsignals of particular identical for similar tubes. The output signal wavev form and have likewise disclosed only one of tube Ill may be assumed as 4/5 of the total de particular modification of which my invention is sired output signal swing and hence furnishes susceptible, _it will be obviousthat my invention the maximum current (Imax) to be supplied by 75 is ' suitable’for 'use' in amplifying other Íwavef 2,404,099 7 immediately occur to those skilled in the art, and I am therefore not to be limited to the particular use or modification set forth above except as set forth in the following claims. I claim: appearing between said anodes is applied to said deñection plates for portrayal of said combined wave form. 1. A counterphase amplifying system for am plifying signals of square wave form comprising a 5. A system for portraying a square wave form on a cathode ray tube comprising a counterphase pair of thermionic amplifying tubes of the multi grid type, each having a cathode, grid and anode, means to apply dilîerent negative biasing poten amplifying circuit including a pair of amplifying tubes having a cathode, input grid, screen grid and anode, a source of bias potential of different tials with respect to the cathode between the cathode and grid of said two tubes, means to ap ply different positive potentials between the an ode and cathode of each of said tubes, the positive potential applied to the tube having the most neg ative biasing potential being higher than that ap plied to the other tube, means to apply the square magnitude connected between the cathode and input grid of each of said tubes, a positive po tential source of diiîerent magnitude connected to each of said screen grids, a positive potential source of different magnitude connected to each of said anodes through a load resistor to form an output circuit for each of said tubes, the screen wave form between the cathode and grid of one tube and means to simultaneously apply a similar wave form to be amplified, but of opposite polar ity thereto, to the other of said tubes, whereby the ouput wave form from each of said tubes is an amplified signal component of the said square wave form. 2. A system for amplifying a square wave volt 8. other, a cathode ray tube having a pair of op positely disposed deflection plates and means con necting each of said deflection plates to one of said anodes whereby the combined wave form forms and that other modiications thereof will grid and anode sources of the tube having the lower negative bias being of lower magnitude than those connected to the screen grid and anode of the tube having the greater negative bias, means to apply to each of said input grids mutually in 25 verted components of a square wave form, each age impulse comprising a pair of amplifier tubes having input and output electrodes, means to apply the square wave form to be amplified to the of said components having two different ampli tudes, to develop signals having different ampli tudes in the output circuits of said tubes, means to modify the bias of each of said tubes in pro input electrode of one of said tubes, means to 30 portion to the smaller amplitude of the signals applied to each of said tubes, a cathode ray tube apply an inverted wave form of the wave form having a pair of oppositely disposed deflection to be amplified to the other of said tubes, means plates and means connecting said anodes respec to maintain the input electrodes of said tubes at tively to said plates whereby the ampliñed in a predetermined average potential, means to ap ply a bias potential more negative than the said 35 verted components of said square wave form are applied between said deflection plates for por predetermined potential on the input electrode trayal of said wave form. of said one tube to the input electrode of the other 6, A counterphase amplifying system for por tube, and means to apply a positive potential to traying a square wave form on a cathode ray tube each of the output electrodes of said tubes, the potential applied to said one tube being lower 40 comprising an amplifying circuit including a pair of similar amplifying tubes, each having a cath than that applied to the said other tube. ode, input grid, screen grid and anode, a direct 3. A system for amplifying a square wave form electrical connection between the cathodes of each for portrayal on a cathode ray tube comprising of said tubes, a source of bias potential of differ a pair of similar amplifying tubes, each having a cathode, grid and anode, means to apply differ 45 ent magnitude connected between the cathode and input grid of each of said tubes, a positive ent grid bias and anode potentials to each of said potential source of different magnitude connected tubes, means to adjust the bias on each of said to each of said screen grids, a positive potential tubes such that the tube having the higher anode source of different magnitude connected to each potential has applied thereto the more negative bias potential to displace the operating point on ç of said anodes through a load impedance to form an output circuit, the screen grid and anode the dynamic summation characteristics of said sources of the tube having the lower negative tubes in opposite directions, means to apply the bias being of lower magnitude than those con square wave form to be amplified between the nected to the screen grid and anode of the tube cathode and grid of each tube in inverted form, one with respect to the other, a cathode ray tube having a pair of oppositely disposed deflection plates and means capacitively connecting each of said deflection plates to one of said anodes whereby the combined wave form appearing be tween said anodes is applied to said deñection plates for portrayal of said combined Wave form. 4. A counterphase amplifying system for am plifying pulse wave forms for portrayal on a cath ode ray tube comprising a pair of amplifying tubes, each having a cathode, grid and anode, means to maintain the anodes of each ofv said tubes at different positive potentials with respect to the respective cathodes, means to displace the operating point on the dynamic summation char acteristic towards cut-off on the tube with the higher anode potential and towards higher anode current on the tube with the lower anode poten tial, means to apply the pulse wave form to be having the greater negative bias, means to apply to each of said input grids a mutually inverted component of a square wave having a smaller and larger amplitude of opposite polaritiës, a diode having a cathode and grid connected between each of said input grids and the cathode of said tubes in series with the said sources of bias po tential of different magnitude to modify the bias of each of said tubes in accordance with the smaller amplitude of the square wave form ap plied to each of said tubes, a cathode ray tube having a pair of oppositely disposed deflection plates and means connecting said anodes respec tively to said plates whereby the ampliñed in verted components of said square wave form are applied between said deflection plates for por trayal of said wave form. 7. A system for portraying a square wave form on a cathode ray tube comprising a counterphase amplifying circuit including a pair of lamplifying amplified between the cathode and grid of each tubes, each having a cathode, input grid, screen 75 tube in inverted form, one with respect to the , Y 9 2,404,099 10 , grid and anode, a source of bias potential of dif wave form, means to modify the bias of each of ferent magnitude connected between the cathode said tubes in accordance with the smaller ampli and input grid of each of said tubes, a positive tude of the square wave forms applied to said tubes potential source of different magnitude connected comprising a diode connected with its anode to to each of said screen grids, a positive potential 5 the source of higher grid bias and its cathode to source of dilîerent magnitude connected to each the input grid cf the tube with higher anode po of said anodes. the screen grid and anode sources tential and a second diode inversely connected of the tube having the lower negative bias being with respect to the lower bias source and the in of lower magnitude than those connected to the put grid of the tube with lower anode potential, screen grid and anode of the tube having the 10 a cathode ray tube having a pair of oppositelydis greater negative bias, means to apply to the input posed deñection plates and means connecting said grid of the tube having the lower anode and screen anodes respectively to said plates whereby the grid potentials an input square wave form to be amplified inverted components of said square portrayed with such polarity that the higher am wave form are applied between said deflection plitude of said square wave decreases the current of said tube, means to apply to the other of said tubes a counterphase component of said input plates for portrayal of said wave form. ` O'I'I'O H. SCHADE.