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Патент USA US3089968

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May 14, 1963
J. B. CHATTEN
3,089,959
SELF-LIMITING PHOTOMULTIPLIER AMPLIFIER CIRCUIT
Filed May 2, 1960
3,089,959
Patented May lli, i953
l
3,089,959
2
.
SELF-LIMITING PHOTOMULTIPLIER
AMPLIFIER CIRCUIT
John B. Chatten, Philadelphia, Pa., assignor, by :nesue
assignments, to Philco Corporation, Philadelphia, Pa.,
a corporation of Delaware
Filed May 2, 1969, Ser. No. 25,98l
14 Claims. (Cl. Z50-_207)
The present invention relates to photomultiplier am
plifier circuits and more particularly to self-limiting pho
tomultiplier amplifier circuits.
For a better understanding of the present invention
together with other and further objects thereof refer
ence should now be made to the following detailed de
scription which is to be read in conjunction with the ac
companying drawing in which:
FIG. 1 is .a schematic diagram of one preferred form
of .photomultiplier amplifier arranged in accordance with
the present invention;
FIG. 2 is a plot of the large signal characteristic curve
of the system of FiG. l; and
FIG. 3 is a partial schematic diag-ram of a circuit for
obtaining two signals at different »amplitude levels and
Photomultiplier amplifiers have been employed in con
junction with beam indexing systems of color television
reproduction to detect ultra violet indexing signals (here
inafter referred to generally as luminous indexing sig
different frequencies from the same photomultiplier
circuit.
In FIG. l the photom-ultiplier tube l0 includes 'a photo
emissive cathode l2, six dynodes 13 through 1S, and an
nals) generated by suitably placed indexing stripes on
anode 29. The bias source Afor the amplifier circuit of
the screen of the picture tube. In this application the
FÍG. l is schematically represented by batteries 22 and
intensity of the luminous energy falling on the photo
2li. However it is to be understood that in the usual
cathode may vary -by ‘a factor of 100'-to-1 depending upon 20 applications of the circuit of FIG. l, these potentials will
the intensity of the cathode-ray beam, the portion of the
be supplied by suitable rectifier circuits. lIf it is as
screen being scanned and other factors such las the varia
sumed by way of example that phototube lll is one sold
tion in efiiciency in the photo emissive material forming
under the commercial type number 6365, source 24 pref
the index stripes. Proper opera-tion of the indexing cir
erably provides a potential of the order of 2,000 volts
cuits responsive to this luminous indexing signal require
and source 22 preferably provides a potential of the order
that the variable Iamplitude luminous energy be converted
of 380 volts. The common terminal 26 of sources 22
to a substantially constant amplitude electrical signal at
and 24 is maintained «at `ground potential in order to
the indexing frequency. The limiting of the electrical
minimize the potential from the anode 20 to ground and
indexing signal must be accomplished without appreciable
to minimize the current requirement of the high voltage
phase shi-ft or time delay. This has been »accomplished 30 power supply.
.
in the past by cascaded vacuum tube limiting circuits fol
A voltage divider comprising resistors 28 through 31
lowing the photomultiplier tube. These .limiting circuits
is connected between the positive terminal of source 22
are relatively complex and costly and they are not en
and ground. Resistors 28-31 have a resistance such that
tirely satisfactory for all applications.
the bleeder current through these resistors is much greater
Automatic gain control circuits for controlling the am 35 than `the maximum dynode current. Thus the voltage
plitude of the output signals of multi-stage electronI mul
divider formed by resistors 28-31 may be termed a “stiff”
tiplier amplifiers per se »have been proposed. It has been
volta-ge divider, i.e. a divider inl which the potential at
suggested in the past that a form of limiting action can
each tap is substantially independent of changes in dy
be obtained in photomultiplier amplifiers by employing
node current. A `second voltage divider comprising re
a high impedance voltage divider to supply biasing po 40 sistors 35 `through 3@ is Aconnected between terminal 26
tential to the "dynodes near the anode.
This means of
and the negative terminal of source 24. Typical values
for the resistors in these two dividers are given in the
limiting the dynamic range of the output signal of a pho
tomultiplier amplifier is unsuited `for use in indexing sys
tems for color television reproducers since they cannot
following table:
provide satisfactory limiting action at the relatively high
frequencies employed in indexing systems. Means such
Resistor:
as voltage regulator tubes in the »dynode supply circuit
fail to provide sufficient control of the gain, render the
Impedance
(ohms)
28 __________________________________ __
1.5K
29 __________________________________ _ _
6K
3u __________________________________ __
10K
circuit unduly ycomplex .iand/ or introduce instabilities or
3.1 __________________________________ __
22K
phase shifts which make the known forms of photomul
35 __________________________________ __
820K
tiplier amplifiers generally unsuited for servo loops of
36 __________________________________ _ _
820K
the type mentioned above.
37 __________________________________ __
820K
,
Therefore, it is an object of the present invention to
38 __________________________________ _ _
1.2M
provide a self-limiting photomultiplier amplifier which
introduces relatively small phase shifts in the signal pass
39 __________________________________ _ _
470K
ing therethrough.
A further object of the present invention is to provide
photom-ultiplier amplifier circuits which are well suited
to beam indexing systems of Color television reproduction.
Still another object is to provide a photomultiplier
amplifier circuit which has very little degeneration of low
amplitude input signals but which limits the amplifica
tion of high amplitude signals.
In general these and other objects of the invention are
achieved by providing a relatively low impedance be
tween successive dynodes in the vicinity of the anode and
by selecting the potentials supplied to the dynodes so
that the voltage between the final idynode and the anode
>The cathode 12 and each of the dynodes except dynode
la is bypassed to ground lby one of the capacitors 42.
Each of the capacitors LEZ may have a value of the order
v0f .,002 nf. for an input signal having a frequency of
9 megacycles per second. Dynode 16 is connected
directly lto ground and hence needs no bypass capacitor.
Since the taps on the two voltage dividers 2.8-31 and
35-38 remain relatively Í'Lxed regardless of changes in
dynode current, it is obvious that the voltage divider may
be replaced 4by a voltage source having a plurality of
taps `corresponding in potential to the taps on the voltage
divider.
Anode 2li is connected to the junction of resistors
Z8 and 29 by way of the primary 44 of an interstage
and/or bet-Ween final dynode and the next precedingl 70 coupling transformer. The output signal from the ampli
dynode is relatively small compared to .the voltage dif
fier stage is taken from the secondary de of this trans
ference between idynodes inI the vicinity of the cathode.
former. The intensity modulated luminous input signal
3,089,959
`
d.
3
to the amplifier of FIG. l is schematically represented
by the arrow '48.
The general principles of operation of a photomulti
plier amplifier circuit are well known and hence require
no description. The circuit thus far described differs
from conventional photomultiplier amplifier circuits in
that the voltage between the final dynode and the anode
is much lower than the voltage between successive
dynodes. Furthermore this voltage is substantially inde
mentioned coupling circuit. For example, it may be
tuned to 6 megacycles.
It is believed that the operation of the circuit of FIG. 3
is obvious from the description of the operation of the
circuit of FIG. 1. It is to be understood that an output
signal at the two different frequencies can be obtained
only if the component frequencies are present in the
luminous signal supplied to the cathode 12. If the poten
tial between dynodes 16 and 17 is made substantially
voltage source 22 a relatively low impedance so that the
equal to the potentials appearing between the dynodes
13 through 16, respectively, there will be no appreciable
limiting of the signal supplied at transformer winding 84.
bleeder current through the voltage dividers 28, 29, 30
and 31 is relatively large compared to the maximum
dynode current which ñows from dynode 18. In the
believed to be the preferred embodiments of vthe inven
tion, it will be apparent that various modifications and
pendent of anode or dynode current.
This is accom
plished by making the voltage divider across the low
While there have been described what are at present
other embodiments thereof will occur to those skilled
example given above, the voltage between dynode 18
in the art within the scope of the invention. Accord
and anode 20 is of the order of 50 volts. The voltage
ingly I desire the scope of my invention to be limited
between successive dynodes is of the order of 100 volts.
only by the appended claims.
The voltage between cathode 12 and the first dynode 13
is somewhat greater than l0() volts. The photomultiplier 20 I claim:
1. A photomultiplier amplifier circuit comprising a
circuit described above has the non-linear transfer char
photomultiplier amplifier tube having as electrodes an
acteristic shown in FIG. 2. For input signal amplitudes,
anode, a cathode and a plurality of dynodes, said` photo~
i.e. light intensities, up to the value A1 the gain of the
photomultiplier amplifier is relatively high as represented
multiplier amplifier tube being subject to limiting of elec
by the slope of the curve 52. The slope of the portion 25 tron current fiow in an interelectrode space thereof in
response to a potential difference between the final dynode
54 of the characteristic is much lower than that of por
and an adjacent electrode which is less than a first value,
tion 52. Thus signals having an amplitude such as AZ
a source of bias potential having a plurality of taps, means
will be clipped or peak limited by this non-linear char
coupling said cathode, said anode and said dynodes to
acteristic. It is Ibelieved that the limiting which occurs
for large signals is caused by space charge limitation of 30 selected taps on said bias source, said means coupling said
However
anode to said bias source including means for deriving an
represented by terminals 62 and 64, respectively, in
tial difr’erence between the final dynode and an adjacent
the current in the final interelectrode spaces.
output signal from said amplifier circuit, said bias source
applicant does not wish to be limited by this explanation
including means for causing said taps to be at different
of the observed operation of this circuit.
potentials, said ylast mentioned means causing the poten
It has been determined empirically that the specific
non-linear transfer characteristic of the amplifier can be 35 tial difference between the said taps connected to said
final dynode and said adjacent electrode to be substan
controlled to some extent by choice of the interelectrode
tially less than the potential difference between taps
voltages between the dynodes 16, 17 and 18 and between
associated with other adjacent electrodes of said photo
dynode 18 and anode 24). Tests on photomultiplier tubes
multiplier amplifier tube and less than said first value.
bearing the commercial type number 6365 have indicated
2. A photomultiplier circuit as in claim l wherein said
that a useful non-linear characteristic is obtained for a 40
adjacent electrode is said anode and wherein space charge
final dynode-to-anode voltage in the range from 30 to
limiting occurs in the final interelectrode space of said
60 volts with optimum operation being obtained at
amplifier tube.
approximately 50 volts. It has been found that a photo
3. A photomultiplier amplifier circuit as in claim 1
multiplier amplifier having the characteristics mentioned
above is capable of reducing the dynamic range of the 45 wherein said adjacent electrode is the preceding dynode
and wherein limiting occurs in the interelectrode space
signals passing therethrough `by a factor of more than ten.
between said final dynode and said preceding dynode.
FIG. 3 is a schematic diagram similar to FIG. l of
4. A photomultiplier `amplifier circuit comprising a
a second preferred embodiment of the invention which
photomultiplier amplifier tube having an anode, a cathode
provides output signals at two different frequencies.
Parts in FIG. 3 corresponding to like parts in FIG. 1 50 and a plurality of dynodes, said photomultiplier amplifier
tube being subject to limiting of electron current flow
have been identified by the same reference numerals.
in an interelectrode space thereof in response to a poten
Bias sources 22 and 24 of FIG. 1 have been schematically
FIG. 3. In the circuit of FIG. 3, the anode 20 is con
nected to the junction of resistors 28 and 29 by a fre
quency` selective circuit which is diagrammatically repre
sented by winding 72 and circuit capacitance 68 in shunt
therewith. A resistor 66 provides sufficient damping to
obtain the desired bandwidth. A secondary winding 74
is coupled to primary winding 72 to provide means for
obtaining an output signal from the circuit. The output
circuit 66-72-74 may be tuned to resonate at one
of the component frequencies of the luminous signal
represented schematically by arrow 48. By way of an
electrode which is less than a first value, a source of bias
potential, a tapped voltage divider connected to the ter
minals of said source yof bias potential, means coupling
said cathode, said anode and said dynodes to selected
taps on said voltage divider, said means coupling said
anode to said voltage divider including means for de
riving
an output signal from said amplifier circuit, the
60
position of said taps on said voltage divider being such
that the potential ’between the final dynode and an adjacent
electrode is substantially less than the potential difference
between other adjacent electrodes of said tube and less
than said first value.
es 5. A photomultplier amplifier circuit comprising a
photomultiplier amplifier tube having an anode, a cathode
and a plurality of dynodes, said photomultiplier amplifier
tube being subject to limiting of electron current flow in
example, it may `be tuned to resonate at a frequency of
9 megacycles per second. It is to be understood that in
practice the output circuit may be a double tuned inter
stage coupling circuit or the like.
In the circuit of FIG. 3 the direct connection from
dynode 17 to the junction of resistors 30 and 31 is re 70 the final interelectrode space thereof in response to a
placed v'by a second coupling circuit of the type just
described. rI‘his second coupling circuit comprises re
potential difference between the final dynode and said
anode which is less than a first value, a source of bias
potential, a tapped voltage divider connected to the ter
minals of said source of bias potential, means coupling
may be tuned to a different frequency than the first 75 said cathode, said anode and said dynodes to selected
sistor 76, circuit capacitance 78, primary winding 82
and secondary winding 84. This second coupling circuit
3,089,959
5
6
taps on said voltage divider, said means coupling said
tween 'successive dynodes, the impedance of said first
anode to said voltage divider including means for deriv
voltage divider being such that the bleeder current com
ing an output signal lfrom said amplifier circuit, the posi
ponent through said voltage divider is substantially greater
tion of the said taps on said voltage divider being such
»than the maximum dynode current component through
that the potential between said anode and the final dynode
said first voltage divider.
is substantially less than the potential difference between
9. A photomultiplier amplifier circuit comprising a
other adjacent electrodes of said tube `and less than said
photomultiplier amplifier tube having an anode, a cathode
first value which will cause space charge limiting of elec
and a plurality `of dynodes, a source of bias potential,
tron fiow in the final interelectrode space of said amplifier
said source of bias potential having first and second ter
tube, the impedance of said voltage divider being such that 10 minals of opposite polarity and a third terminal at a
the bleeder current component through said voltage di
potential intermediate that of said first and second ter
vider is substantially greater than the maximum dynode
minals, a first tapped voltage divider coupled between said
current component flowing in said voltage divider.
first termina-l and said third terminal, a second tapped
6. A photomultiplier amplifier «circuit comprising a
voltage divider connected between said second terminal
photomultiplier amplifier tube having an anode, a cathode
and said third terminal, means coupling an intermediate
and a plurality of dynodes, a source of bias potential, a
dynode to said third terminal of said bias source, means
tapped voltage divider connected to the terminals of
said source of bias potential, means coupling said cathode,
coupling said cathode and the dynodes between said cath
ode and said intermediate dynode to selected taps on said
second voltage divider, means coupling the dynodes be
said anode and said dynodes to selected taps on said volt
age divider, said means coupling said anode to` said volt 20 tween said intermediate dynode and said anode to selected
age divider including means for deriving an output signal
taps on said first voltage divider, means including an
»from said amplifier circuit, the position of sai-d taps on
said voltage divider being such that the potential between
interstage coupling transformer coupling said anode to
a selected tap on said first voltage divider, the impedances
`between taps on said first voltage divider being selected
the potential between successive dynodes, the impedance 25 so that the potential between said anode and the final
of said voltage divider being such that the bleeder com
dynode is substantially less than the potential between
ponent of current through said voltage divider is sub
successive dynodes, and so that the bleeder component
stantially greater than the maximum dynode current com
of current through said first voltage divider is substan~
ponent through said voltage divider.
-tially greater than the maximum dynode component of
7. A photomultiplier amplifier circuit comprising a 30 current through said first voltage divider.
photomultiplier amplifier tube having an anode, a cathode
l0. A photomultiplier amplifier circuit as in claim 9,
said anode and the ñnal dynode is substantially less than
and a plurality 4of dynodes, a source of bias potential hav
ing first and second terminals of opposite polarity and a
third terminal at a potential intermediate said first and
wherein said means coupling 'one of said dynodes inter
mediate said intermediate dynode and said anode to said
first voltage divider includes a second interstage cou
second terminals, a first tapped voltage divider connected 35 pling transformer and wherein said first and second inter
between said first terminal and said third terminal, a
stage coupling transformers are tuned to resonate at dif
ferent frequencies.
second tapped voltage divider connected between said
second terminal and said third terminal, an intermediate
ll. A photomultiplier amplifier circuit :comprising a
one 4of said dynodes being yconnected to said third terminal
photomultiplier amplifier tube having as electrodes an
of said source of bias potential, means coupling said 40 anode, a cathode and a plurality of dynodes, a source of
cathode and the dynodes between said cathode and said
bias potential having a plurality of taps, said bias source
intermediate dynode to selected taps on said second volt
including means for causing said taps to be lat diñerent
age divider, means coupling said anode and the dynodes
potentials, means coupling said cathode, said anode and
between `said intermediate dynode and said anode to se'
said dynode to selected taps on said bias source, said
lected taps on said first voltage divider, said means cou 45 means coupling said anode to lsaid bias source including
pling said anode to said ñrst voltage divider including
means for deriving an output signal from said amplpifier
output signal coupling means, the said taps on said two
circuit, the potential difference between the taps associated
voltage dividers being selected so that the potential beL
with the final dynode and an adjacent electrode being not
tween said anode and the final dynode is such as to cause
greater than the approximately six-tenths the potential
space charge limiting of electron flow in the final inter 50 difference between other adjacent electrodes of said tube
electrode space of said amplifier tube, the impedance of
whereby limiting of the electron fiow occurs in the inter
said first voltage divider being such «that the bleeder com
electrode space across which said «lower potential exists.
ponent yof current through said first voltage divider is
l2. A photomultiplier amplifier circuit as in claim ll,
large compared to the maximum dynode current com
wherein said potential difference between said ñnal dynode
ponent t-hrough said first voltage divider.
55 and said adjacent electrode is Ifrom three-tenths to six*
8. A photomultiplier amplifier circuit comprising a
tenths the potential difference between the adjacent dy
nodes in the vicinity of said cathode.
photomultiplier amplifier tube having an anode, a cathode
and a plurality of dynodes, a source of -bias potential hav
13. A photomultiplier amplifier circuit comprising a
ing first and second terminals of opposite polarity and a
photomultiplier amplifier tube having as electrodes an
third terminal at a potential intermediate said first and 60 anode, a cathode and a plurality of dynodes, a source of
second terminals, a first tapped voltage divider connected
bias potential having at least first and second terminals,
a tapped Voltage divider connected to said termina-ls of
ond tapped voltage divider connected between said second
said source of bias potential, means coup-ling said cathode,
terminal and said third terminal, an intermediate one of
said anode and said dynodes to selected taps on said volt
said dynodes being connected to said third terminal of 65 age divider, said means coupling said anode to said Volt
said bias source, means coupling said cathode and the
age divider including means for deriving an output signal
dynodes between said cathode and said intermediate
from said amplifier circuit, the position of said taps on
dynode to selected taps on said second voltage divider,
said voltage divider Ábeing such that the potential differ
means coupling said anode and the dynodes between said
ence between the final dynode and an adjacent electrode
intermediate dynode and said anode to selected taps on 70 is not greater than the approximate six-tenths the poten
said first voltage divider, said means coupling said anode
tial differences between other adjacent electrodes of
to said first voltage divider including output signal cou
said tube.
pling means, the said taps on said voltage divider being
14. A photomultiplier amplifier circuit comprising a
so selected that the potential between said lanode and the
photomultiplier amplifier tube having as electrodes an
final dynode is substantially lless than the potential be 75 anode, a cathode and a plurality of dynodes, a source of
between said first terminal and said third terminal, a sec
3,089,959
l'
7
bias potential having at least ñrst and second terminals, a
tapped voltage divider connected to the terminals of said
source of bias potential, means coupling said cathode, said
8
between adjacent dynodes of said tube, the impedance of
said voltage divider being such that the bleeder current
component through said voltage divider is substantially
greater than the maximum dynode current component
anode and said dynodes to selected taps on said voltage
5
flowing in said voltage divider.
divider, said means coupling said anode to said voltage
divider including means -for deriving an output signal from
References Cited in the ñle of this patent
said amplifier circuit, the position of `said taps on said
UNITED STATES PATENTS
voltage divider being such that the potential diíîerence
Wouters ______________ __ Jan. 13, 1953
between said anode and the linal dynode is not greater
2,625,653
than approximately six-tenths the potential differences 10 2,815,453
Colson et al. __________ _.. Dec. 3, 1957
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