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Патент USA US3098989

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July 23, 1963
J. R. ASHLEY ETAL
3,098,979
DEPRESSED POTENTIAL OPERATION OF ELECTRON BEAM TUBES
Filed Aug. 25, 1961
10
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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.
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