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Патент USA US3079524

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Patented Feb. 26, 1963
ripple free, and permits the generation of pulses of long
In the present invention, ?rst and second switching ele
Martin Fischman, Wantagh, N.Y., assignor to General
Telephone and Electronics Laboratories, Inc., a corpo
ration of Delaware
Filed Apr. 29, 196%, Ser. No. 25,757
4 Claims. (Cl. sci-sen
ments are provided each having a cathode, an anode, and
a control electrode. The cathode of the ?rst switching
element is connected to a voltage reference point through
an output impedance while the cathode of the second
switching element is connected to a source of negative
\voltage through a pulse forming network or other energy
This invention relates to pulse generators.
In my Patent 2,942,190, issued June 21, 1960, there is 10 storage device. The plates of the ?rst and second switch
ing elements are coupled to a source of positive voltage.
disclosed a pulse generator designed to produce output
Normally both switching elements are essentially non
voltage pulses having extremely steep leading and trailing
conducting and, therefore, the voltage across the output
edges. In this apparatus, ?rst and second grid controlled
impedance is zero. When a ?rst input signal is applied
thyratrons are provided. The cathode of the ?rst thyra
tron is connected to an output resistor while the cathode 15 to the control electrode of the ?rst switching element, the
?rst switching element becomes highly conductive and a
of the second thyratron is coupled directly to a source
voltage is produced across the output impedance. After
of negative voltage. The plates of both tubes are con
a predetermined interval equal to the desired duration of
nected to a delay line and to a source of positive voltage.
the output pulse a second input signal is applied to the
When a positive signal is applied to the grid of the ?rst
thyratron, the ?rst thyratron conducts producing a volt 20 control electrode of the second‘ switching element. The
second switching eiement then becomes conductive, its
age across the output resistor. After a predetermined
plate voltage dropping to a negative value thereby revers
interval a second positive signal is applied-to the grid
ing the polarity of the voltage across the ?rst switching
of the second thyratron causing it to conduct and its
element causing it to return to its non-conductive state.
plate voltage to drop to a negative value slightly above
Application of the second input signal also causes a wave
its cathode potential. Since the plates of the two thy
to travel down the pulse forming network, be re?ected
ratrons are coupled together, the ?rst thyratron is out
from‘ its far end, and return to the cathode of the second
off sharply and the output voltage falls rapidly to zero.
switching element._ This reduces the voltage across the
second switching element and switches it from its con
The drop in theplate voltage of the second thyratron
also causes a wave front to travel down the delay line,
ductive to ‘its non?~conductive state.‘ Since the voltage
surge down the pulse forming network-is initiated by the
second input signal, the electrical length of the network
he re?ected at the far end, and return tov the input of
the line with a magnitude'and polarity large enough to
cut off the second thyratron.
does not a?ect the duration of the output pulse. Also,
While this, circuit has been found entirely satisfactory
for the'generation'of pulses of moderate duration, some
since the pulse forming network is effectivelyv out of the
dif?culties have arisen in obtaining very long or very '
short pulses. When a pulse of long duration is to be
generated, the electrical length of the delay line must
circuit during the'time the output pulse is being produced,
no spurious re?ections or other disturbances are generated
by the network and no distortion appears in the output
voltage waveform.
be such that the time for a pulse to travel down the
In a preferred embodiment of the invention the ?rst
line and return is greater than the desired duration of
‘the pulse. This is because a voltage wave front surges 40 and second switchingvelements are comprised of solid
down the line when the ?rst thyratron is ?red producing ._ I
a re?ected .wave which will cut off the ?rst tube when
it returns, if the ?rst tube has not already been rendered
non-conductive by the action of the second thyratron.
Longer pulses may be obtained by increasing the elec
trical length of the delay line but this solution results in ..
expensive and bulky components. In addition, it has
been found that unless great care and high quality parts
are used in the design of the delay line, ripple voltages
will be superimposed on the output voltage regardless of
cathode voltage below the holding value.
The above objects of and the brief introduction to
the present invention will be more fully understood and
further objects and advantages will become apparent
from a study of the following description in connection
with the drawings, wherein:
sultant re?ections in the line. These ripple voltages
occur because the delay line is connected directly to the
plate circuit of the ?rst thyratron while the output pulse
Extremely short duration pulses on the order of a
to the control electrode, or gate, the plate-to-cathode im
pedance is abruptly switched from a high to a low value
andv the recti?er conducts freely. The recti?er is rendered
non-conductive again by brie?y reducing the plate-to
the duration of the pulse due to discontinuities and re
is being generated.
state gate controlled recti?ers. As will be explained .in
greater detail hereinafter, this type of solid-state recti?er
normally has a very high impedance between its Plate and
cathode. However, when an apropriate signal is applied
FIG. 1A is a schematic representation of a type PNPN
FIG. 1B is a typical plot of the voltage-current char
acteristics of the device shown in FlG. 1A;
FIG. 2 is a schematic diagram of the invention; and,
'FIG. 3 depicts waveforms useful in explaining the
second thyratron.
operation of the circuit of FIG. 2.
Accordingly it is an object of this invention to provide
In FIG. 1A there is shown a schematic representation
apparatus for generating voltage pulses of any duration.
of a controlled recti?er, having an anode 10, a cathode
Another object of the invention is to provide a pulse
11 and a control, or gate, electrode 12 consisting of an
generator in which the duration of the output pulses is 65 ohmic contact to the center P region. The recti?er con
fraction of a microsecond are also quite dif?cult to obtain
with the circuit described in the aforementioned copend
ing application due to the ?nite ionization time of the
continuously variable and in which the output pulses have
rapidly rising and decaying leading and trailing edges.
sists of three rectifying junctions 13, 14, and 15 which
divide regions of P and N type semiconductor material.
The impedance between the anode 10 and cathode 11 is
pulse generator using a delay line in which the electrical
initially very high and the recti?er is essentially non
length and other characteristics of the line are not critical. 70 conducting in both directions. However, when current
A further object of the invention is to provide a pulse _ is caused to ?ow between the control electrode and the
athode by application of a suitable signal to the con
generator which is small in size, relatively inexpensive,
Still another object of the invention is to provide a
trol‘ electrode 12, the recti?er breaks down at a positive '
until the forward current falls below the value required
below ground (FIG. 3D) and recti?er 20 ceases to con
duct. The output voltage across resistor 23, therefore,
abruptly falls to zero. The transfer of recti?er 21 from
its non-conducting to its conducting state also causes a
voltage surge down the pulse forming network 25 which
is re?ected from the other end and returns to the cathode
24 after a time interval TL. This re?ected wavefront
to maintain conduction.
The recti?er may also be caused to conduct With
potential thereby cutting o? recti?er 21. The network
anode-to-cathode voltage greater than a few volts. After
breakdown the impedance of the recti?er is very low and
the current is essentially limited only by the load. The
input signal loses control after breakdown and the recti
?er is cut o? by reducing the anode-to-cathode voltage
causes the cathode of recti?er 21 to assume a positive
out applying an input signal by increasing the plate-to
25 then recharges along a curve 50, cathode 24 ultimate
cathode voltage beyond the forward breakover volt 10 ly reaching its initial value —V2, as shown in FIG. 3B.
age VB. This is illustrated by the voltage-current char
Listed below are typical values for the components
acteristics curve of FIG. 1B. As shown, the forward
current IF remains constant with increasing forward volt
used in the circuit of FIG. '2.
age VF until the voltage VB is reached. At this point
the recti?er impedance suddenly decreases, as indicated 15
by the dashed line, and thereafter the forward current
increases sharply with small ‘increases in forward volt
The magnitude of the forward and reverse cur
rents corresponding to voltages between the peak inverse 20
voltage Vmv and the breakover voltage VB has been
greatly exaggerated in FIG. 1B for increased clarity.
FIG. 2 is a circuit diagram of one embodiment of the
invention and FIGS. 3A-3E depict idealized wave
forms of ‘the voltages appearing at corresponding points 25
in the circuit of FIG. 2. In the embodiment shown in
FIG. 2, a pair of gate controlled recti?ers 20 vand 21
V are provided.
The cathode 22 of recti?er 20 is con
23 ___________ __ ______ __ohms__
Inductor 26 _____________ __.microhenries__
Inductor 27
Capacitor 28 ______________ --microfarad-..
Capacitor 29__________________ _..do____
Resistor 30 ____________________ __ohms__ 10,000
Resistor F33 _________________ _._~___d0__....
Resistor 36 ____________________ __do____
Resistor 39 ___________ __>_______ __d ____
Using "the values listed for inductors '26, 27 and capac
itors 28, 29 the characteristic impedance of ‘the pulse
forming network is 50 ohms and the round trip delay
‘time is about 6 microseconds. Type 'ZJ-39a controlled
nected through a load impedance 23 to ground, while
recti?ers may be used for recti?ers '20 and ‘21.
the cathode 24 of recti?er 21 is connected through a 30
The duration TD of the output pulse is determined by
pulse forming network 25 to a source of negative voltage
the differences in delay time of delay circuits 35 and 38.
The pulse forming network shown comprises
For pulses of long or moderate duration, delay circuit
inductors 26, 27 and capacitors 28, 29 and is of the type
shown in FIG. 6.23 (b), page 203 of the book “Pulse
35 may be omitted and .the output of the trigger source
40 coupled directly to resistor 136. However, ‘to obtain
Generators,” by Glasoe ‘and Lebacqz, published by Mc 35 extremely short pulses, delay circuit 35 is used in con
Graw-Hill Book Co. Inc, although ‘any other suitable
junction with delay 38 since a short time diiference be
energy storage network may also be used. A shunting
tween vthe outputs of two networks is more easily obtained
resistor 30 is connected between the cathode '24 and
than is a short absolute delay from a single delay circuit.
the source of negative voltage —V2. The plates 31 and
An important feature of the invention is that a pulse
32 of recti?ers 20 and 21 ‘respectively are coupled to 40 generator is provided which is capable of obtaining an
‘a source of positive voltage +V1 through a common
output pulse of any desired duration. Also, the trailing
resistor 33. The control, or gate, electrode 34 of recti
edge of the pulse has a very rapid rate of decay thereby
?er 20 is coupled to a delay circuit 35 through a current
providing the sharp cut-off required in many applications.
limiting resistor 36, while the control electrode 37 of
Furthermore, the pulse forming network used ‘to obtain
recti?er 31 is coupled to a delay circuit 38 through a 45 the steep trailing edge cannot affect the waveform of the
resistor 39. The inputs of delay circuits 35 and 38 are
output pulse,,since the network is only connected to the
connected 'to the output of a trigger pulse source 40.
circuit after the output pulse has been terminated and vthe
Delay circuits 35 and 38 may consist, for example, of
?rst recti?er is open-circuited.
multivibrators while trigger pulse ‘source 40 may be ‘a
blocking oscillator.
‘When the circuit is ?rst energized, both recti?ers 20
and '21 are non-conductive since the voltage across each
is less than the breakover voltage VB. The ‘application
What is claimed is:
l. A pulse ‘generator comprising ?rst and secondswitch
ing elements, each of said switching elements having an
anode, a cathode, and a control electrode, the ‘impedance
between ‘said anode and cathode being switched from
of a trigger voltage from source 40 to delay circuits 35
a high value to a low value by the ?ow of control cur
‘and 38 produces a ?rst'input signal at control electrode 55 rent from the control electrode to the cathode of said
'34 and then, after a predetermined interval TD, produces
switching element, an outputimpedance connected be
"a second input signal at the control electrode 37. The
tween the cathode of said ?rst switching element and. a
input signal applied to electrode 34 causes recti?er 20
common voltage reference point, a pulse forming net.
to immediately conduct thereby producing an output
work having one end connected to the cathode of said
Recti?er 20 60 second
switching element, impedance means for coupling
a positive voltage to the plates of said ?rst and second
switching elements, means for coupling a negative voltage
causes a holding current to exist which is greater than
to the other end of said pulse forming network, and means
In (FIG. 1B).
After the predetermined interval TD has expired, and 65 for selectively applying ?rst and second control signals
to‘ the control electrodes of said‘?rst and second switching
the second control signal is applied to electrode 37,
elements, said ?rst control signal causing said ?rst switch
recti?er 21 will conduct causing the voltage on plates
ing element to conduct thereby producing an output volt
31 and 32 to decrease abruptly to a value slightly greater
voltage (FIG. 3C) across impedance 23.
continues to conduct even after the pulse is removed,
since the voltage between its plate 31 and cathode 22
age pulse across said output impedance, said second con
than the voltage on the cathode 24 of recti?er 21. With
'trol signal causing said second switching element to con
the magnitude of voltage V2 somewhat greater than that 70 duct thereby rendering said ?rst switching element non
of voltage V1 and the characteristic impedance of net
work 25 approximately equal to resistances 23 and 33,
the voltage on cathode 24 rises from —V2 ‘to a smaller
conductive and abruptly reducing said output voltage to
zero, the interval between the applications of said ?rst
and second control signals determining the duration of
negative value, as shown in FIG. 4E.
said output voltage pulse, the re?ected pulse produced by
The voltage on plate 31 of recti?er 20 is then slightly 75 said pulse forming network rendering said second switch
ing element non-conductive a predetermined interval after
application of said second control signal thereto.
to the plates of said ?rst and second recti?ers, means re
sponsive to an input trigger pulse for coupling a ?rst
control signal to the control electrode of said ?rst rec
2. A pulse generator as de?ned in claim 1 wherein
said means for selectively applying ?rst and second con
trol signals to the control electrodes of said ?rst and
second switching elements comprises delay means, said
delay means applying said second control signal to the
ti?er, delay circuit means responsive to said input trigger
pulse coupled to the control electrode of said second rec
ti?er, means for coupling a ?rst voltage to said plate cir
cuit resistor, and means for coupling a second voltage to
the other end of said pulse forming network.
4. A pulse generator as de?ned in claim 3 wherein said
determined interval after said ?rst control signal is ap
plied to the control electrode of said ?rst switching ele 10 means responsive to an input trigger pulse for coupling
a ?rst control signal to the control electrode of said ?rst
ment, said predetermined interval being equal to the de
recti?er includes second delay circuit means.
sired duration of the ouput pulse appearing across said
control electrode of said second switching element a pre
output impedance.
3. A pulse generator comprising ?rst and second type
PNPN controlled recti?ers, each of said recti?ers having 15
a plate, a cathode, and a control electrode, an output
resistor connected between the cathode of said ?rst rec
ti?er and a common voltage reference point, a pulse form
ing network having one end connected to the cathode
of said second recti?er, a plate circuit resistor connected 20
References Cited in the ?le of this patent
Page ________________ __ May 31,
Pankove _____________ __ Apr. 21,
Pankove _____________ .._ July 14,
Russell et al ___________ __ Sept. 13,
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