Патент USA US3098989код для вставки
July 23, 1963 J. R. ASHLEY ETAL 3,098,979 DEPRESSED POTENTIAL OPERATION OF ELECTRON BEAM TUBES Filed Aug. 25, 1961 10 ENVELOPE DETECTOR R-F OUT COLLECTOR ODULATOR R" 22 12 26 W3 25 '"H I RIN-PFUT | k mxi PIC-3.3. ENVELOPE Z1 DETECTOR 31 SWITCH TUBE DRIVER #1 32 To ENVELOPE DETECTOR 20 38 #1 éD|_GATEx1 1 39 I40 it <i GATE § 31 2 (xrxz) 33 X2 Ff (o-x1) 41 ‘ PIC-1.4. #3 INVENTORS JAMES 5’. ASHLEY YCA/POL M. VERO/VDA " 30 3,098,979 Patented July 23, 1963 2 munications system wherein the input is an amplitude 3,098,979 modulated carrier wave. DEPRESSED POTENTIAL OPERATIQN 0F ELECTRON BEAM TUBES The di?iculty which has been encountered in the past results from the fact that when the collector is depressed to ya ?xed voltage in order to achieve optimum e?iciency James Robert Ashley and Carol McCauley Veronda, Gainesville, Fla, assiguors to Sperry Rand Corporation, for signals of relatively low magnitude, this collector Great Neck, N.Y., a corporation of Delaware Filed Aug. 23, 1961, Ser. No. 133,463 ' 5 Claims. (Cl. 330-44) This invention relates to the operation of velocity ' modulation electron tubes with depressed collector poten tials, and more particularly relates to the linear operation of such tubes when the tubes are employed in communi~ In an electron beam ‘velocity modulation device such velocity spread between slower moving and faster moving electrons is greater. It is for this reason that depressed collector operation of velocity modulated tubes has not been completely successful and has resulted in non linearity in the output of the tube when the tube is op cation system as linear ampli?ers for amplitude modu lated waves. potential is not su?icient to attract the low velocity elec trons in the beam and the secondary electrons produced when the input signal is of greater magnitude and the 15 erated in communications systems as a linear ampli?er for amplitude modulated waves. It therefore is an object of this invention to overcome as a traveling wave tube or a klystron, for example, it has been a common practice to electrically bias the col lector electrode at or very near the potential of the micro the above-mentioned di?iculty in the operation of velocity modulation tubes. wave structure of the tube. The R.F. properties of the 20 It is another object of this invention to operate a ve— device require that the microwave structure be at a high locity modulation tube with ‘a depressed collector poten potential with respect to the cathode of the tube. This tial when the tube is used as a linear ampli?er for am in turn requires that the collector also be at a high poten plifying amplitude modulated waves. tial with the result that the electrons in the beam have A further object of this invention is to obtain optimum considerable energy when they strike the collector. This 25 e?iciency in the operation of ‘a depressed collector ve energy is converted largely into heat in the collector and locity modulation tube when the input thereto is com_ causes considerable power loss and low e?iciency of prised of amplitude modulated waves. operation of the tube. In high power tubes additional These and other objects and advantages of the inven tion, which will become more apparent from the speci?ca~ tion and claims below, are achieved by providing means for applying a depressed potential to the collector of the cooling means must be provided to cool the collector. This cooling equipment is often expensive, bulky, and requires a considerable amount of power to operate. A further disadvantage of operating the collector at a poten velocity modulation tube, and means for detecting the tial near the potential of the microwave structure is that envelope of the amplitude modulated input waves to said tube. The envelope of the detected input wave then the high velocity electrons striking the collector generate X-rays and give rise to a shielding requirement. Because of the above-noted problems, considerable is combined with the depressed potential biasing voltage effort has been devoted to attempts to operate electron beam velocity modulation tubes such as traveling wave tubes and klystrons with a depressed potential on the col on the collector in the presence of stronger input signals and to lower the collector potential in the presence of lector, i.e., the collector potential is considerably lower than the potential of the R.F. structure. Although the above-mentioned di?icult-ies are largely solved by lower ing the potential on the collector, a new problem is cre applied to the collector so as to increase the potential 40 lower amplitude input signals. In this manner, the col lector potential is raised to collect the electrons with greater velocity spread produced in response to the higher amplitude input signals, and lowered to collect the elec trons when there is very little velocity spread. The col ated because the collector potential no longer is high lector potential, throughout its varying amplitude, is su?i— enough for the collector to attract all of the low velocity 45 cient to maintain the operation of the tube in the linear electrons in the beam and the secondary electrons which region of its characteristic curve, and yet maintain op are produced when the beam strikes the collector. These timum e?iciency, i.e. lowest collector potential possible, electrons are drawn to the higher potential R.F. structure in view of the changing amplitude of the input wave. and cause noise, non-linearity and instability in the opera The invention will be described by referring to the 50 accompanying drawings wherein: tion of the tube. FIG. 1 is a schematic illustration of one embodiment The R.F. input-output performance curve of a velocity of this invention; modulation klystron tube has a shape which is similar to FIG. 2 is a schematic illustration 0st‘ another embodi that of a J1 (X) Bessel function curve (i.e., somewhat similar to a sine curve in the region 0-11‘). When oper 55 ment of the present invention; FIG. 3 is a graph used in explaining the operation of ating the tube as a linear ampli?er in a communication the embodiment of the invention illustrated in FIG. 2; system it is required that the tube operate on the approxi and mately linear leading edge of the curve in order to avoid FIG. 4 is a simpli?ed schematic diagram of the switch distortions in the output therefrom. Deviation from tube driver illustrated in block form in FIG. 2. linear operation in a klystron tube is caused by re?ected Referring now more particularly to FIG. 1, the velocity beam electrons and secondary electrons traversing the modulation tube 10 is represented in a highly schematic tube in the backward direction and being collected in the form and is comprised of electron emitting cathode 1-1 electron beam-R.F. wave interaction portion of the tube. and collector electrode 12. The electron lbeam-electro A very small backward beam current can cause serious regenerative or degenerative e?’ects depending upon the 65 magnetic wav-e interaction structure 15 may be comprised of a number of resonant cavities in the event that tube phase of the backward traveling bunches of electrons in 10 is a klystron ampli?er, or may be comprised of a slow the beam. It therefore is desired that this backward ‘wave propagating structure in the event that said tube is beam current be as small as possible. This is di?icult a traveling wave tube. R.-F. input waves are coupled to achieve md to maintain with a depressed potential collector when the R.F. input is applied, and is increas 70 into the tube on input line 16 and are coupled therefrom on output line 17. In practice, lines 16 and 17 may be ingly di?icult to maintain in the presence of an R.F. input coaxial or uniconductor waveguide transmission lines. whose magnitude continually varies as it would in a com Collector electrode 12 is electrically :biased at a depressed 3,098,979 potential, ie a potential that is lower than the potential of the electron beam-microwave interaction structure 15, as may be seen drom the respective connections to volt age source V and ‘ground as illustrated in FIG. 1. The R.-F. input wave is coupled into tube 10 on line 16, is sampled at point 20 by means of a probe or directional ‘coupler, is’ detected in envelope detector 21 and the ampli tude modulation envelope is applied through collector modulator 22, which may be a power ampli?er, and to detector 21 which is coupled in parallel to diodes 32., 33 and 34. Said diodes are respectively back-biased by the potentials 0 volts, x1 volts and x2 volts, these potentials be ing those illustrated on the curve of FIG. 3. When the mag nitude of the input wave is in the region 0-x on the curve of FIG. 3, only diode 32 will be conductive because the back-‘biasing potentials x1 and x2 on the remaining di odes 33 and 34 will prevent those diodes from conduct ing. When the magnitude of the input wave is in the primary winding 25 of transformer 26. The secondary 10 region x1—x2 on the curve of FIG. 3, diode v33 will be conductive, and similarly when the magnitude of the in winding of said tranformer is series connected in the biasing circuit between collector 12 and voltage source V. The wndings of transformer 26 are poled so that a varia tion of the voltage across primary Winding 25 will be coupled through secondary winding 27 to vary the po 15 tential on collector electrode 12 in a corresponding man ner. In the operation of the embodiment of this invention illustrated in FIG. 1, collector 12 is biased at a depressed potential that is some fraction or’: voltage source V. This potential is su?icient to permit e?icient, linear operation of the tube with an input signal of moderate amplitude. An amplitude modulated input wave will be coupled into put wave is within the region x2—x3 on the curve of FIG. 3, diode 34 will overcome its back-biasing and will con duct. Exclusive energization of only one of the output lines #1, #2 or #3 is provided by means of normally open gates 38 and 39. When diode 33 is rendered con ductive the potential coupled to gate 38 on lead 40 will be su?icient to close the normally opened gate 38. Similarly when diode 34 is rendered conductive the potential applied to gate 39 on lead 41 and will be su?icient to close nor mally opened gate 39. In this way exclusive energization of only one of the output lines #1—#3 is provided. While the invention has been described in its preferred embodiments, it is to be understood that the words which tube 10 on input line 16 and will cause velocity modula have been used are words of description rather than limi‘ 25 tion of the electron beam in the tube. The input waves tation and that changes within the purview of the append are coupled from input line 16 at point 20, are detected ed claims may be made without departing from the true in detector 21 and coupled through transformer 26 to scope and spirit of the invention in its broader aspects. What is claimed is: be amplitude modulated to follow the amplitude modula l. The method of achieving linear operation of a de 30 tion of the input signal. In this manner, when the elec~ pressed collector velocity modulation electron tube when collector 12 so that the potential on said collector Will trons in the beam are propagated with a relative high used as a linear ampli?er for amplitude modulated waves velocity spread as a result of a relatively high magnitude comprising the steps of abstracting a sample of the input input signal, the collector potential also is at a relatively wave to be ampli?ed, passing the sampled wave through high potential so that as to substantially completely col a detector to obtain the envelope of the amplitude modula lect the beam electrons and substantially eliminate back 35 tion of said input wave, and controlling the potential on ward ?owing beam electrons. When the magnitude of the the collector of said tube in accordance with the ampli input signal is low, the voltage coupled through trans tude of said envelope to increase the potential on the former 26 to collector 12 will lower the potential on col collector when a high amplitude signal is coupled to the lector 12 and permit substantially complete collection of 40 input of said tube and decrease the potential on said col the electrons moving with little velocity spread. 'Ihus lector when a lower amplitude signal is coupled to the e?icient and linear operation of the tube is established input of said tube. and maintained irrespective of changes in amplitude in 2. Means for voperating a velocity modulation electron the input signal. tube with a depressed potential on its collector electrode An alternative embodiment of the present invention is 45 and for obtaining linear operation of said tube when said illustrated in FIG. 2 wherein velocity modulation tube tube 'is used as an ampli?er :for amplitude modulated .10, its input and output lines 16 and 17 and envelope de waves comprising the combination of means for applying tector 21 are substantially identical to the corresponding a biasing voltage to the collector electrode of said tube, components illutrated in FIG. 1. In FIG. 2, however, said voltage being below the voltage of the electron beam the potential applied to collector 12 may be either one 50 electromagnetic wave interaction structure of said tube, of the potentials V1, V2 or V3, depending upon which of means for coupling amplitude modulated waves to be the switch tubes T1, T2 or T3 is rendered conductive by ampli?ed into said tube, means for deriving a signal rep switch tube driver 30. Switch tube driver 30 is a circuit resenting the amplitude modulation envelope of said in which is responsive to the amplitude of the detected sig put waves, means for applying said envelope signal to the nal from envelope detector 21 and, for example, when 55 collector electrode to increase the potential on said col the amplitude of the detected signal is within the region lector when a high amplitude signal is coupled to said o-x1 on the curve of FIG. 3, only tube T1 is rendered tube and to decrease the potential on said collector when conductive and the potential V1 is applied to collector a lower amplitude signal is coupled to said tube. 12. When the magnitude of the input wave is within the 3. Means rfor ‘operating a velocity modulation electron region xr-xz on the curve of FIG. 3, switch tube driver tube with a depressed potential on its collector electrode 30 will cause only triode T2 to conduct so that the poten and for obtaining linear operation of said tube when said tial V2 is applied to collector 12. Similarly, when the tube is used as an ampli?er for amplitude modulated magnitude of the input signal is within the region x2-x3 waves comprising the combination of means for applying a biasing voltage to the collector electrode of said tube, on FIG. 3, switch tube driver 30 will render only triode T3 conductive so that the potential on collector 12 is the 65 said voltage being below the voltage of the electron beam-electromagnetic wave interaction structure of said fin-ll potential V3 of the biasing voltage source. In this tube, means for coupling amplitude modulated waves to manner, switch tube driver 30 and switch tubes T1~T3 will be ampli?ed into said tube, means for deriving a signal choose a depressed collector potential which will allow representing the amplitude modulation envelope of said the tube to operate in the linear portion of its characteris tic curve while at the same time permitting optimum de 70 input waves, means for controlling the potential applied to said collector electrode in accordance with said enve pression of collector potential in order to achieve optimum lope signal to increase the potential on the collector when e?iciency of operation consistant with desired linearity. said envelope signal is of a high magnitude and to de A schematic illustration of the switch tube driver 30 crease the potential on said collector when said envelope of FIG. 2 is shown in FIG. 4 of the accompanying draw ings, and is comprised of input line 31 from envelope 75 signal is of a lower magnitude. 5 3,098,979 4. Apparatus ‘for achieving linear operation of a de pressed collector velocity modulation eleotron tufbe when said tube is operated as a linear ampli?er for amplitude modulated input Waves, comprising detector means for deriving a signal ‘representing the amplitude modulation component of said input waves, a transformer having its 6 deriving a signal representing the envelope of the ampli tude modulated input waves, means for providing a plu rality of tbiasing voltage potentials, means for connecting anyone of said plurality of voltage potentials to the col lector electrode of said tube, all of said potentials being lower than the potential of the electron beam-electnomag primary winding coupled to pass said amplitude modula netic wave interaction structure of the tuibe, means re tion signal component and its secondary winding coupled sponsive to the magnitude of envelope signal to select one in a voltage biasing circuit for ‘the collector of said tube, of said connecting means ‘for coupling a respective one said secondary winding being so coupled and arranged to 10 of said voltage potentials to said collector, said con-nect increase and decrease the 'biasing voltage on said collector ing means and said envelope signal responsive means co in accordance with the respective increase and decrease operating to couple a higher potential to said collector in the magnitude of said amplitude modulation signal when the amplitude of said envelope signal is high and component. to couple a lower potential to said collector when the 5. Apparatus for achieving linear ‘operation of a de amplitude of said envelope signal is lower. pressed collector velocity modulation electron tube when 15 said tube is operated as a linear ampli?er :Eor amplitude modulated input waves, comprising detector means for No references cited.