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March 30, 1948.
' 2,438,638
L. 1.. LAKATOS
PULSE TO RECTANGULARv WAVE CONVERTER
2 ‘Sheets-Sheet 1
Filed March 30, 1945
DEC/{191E625
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March 30, 1948.
‘
|_.' |_. LAKATOS
2,438,638
PULSE TO RECTANGULAR WAVE CONVERTER
Fil'ed March 5'0, 194;
2 Sheets-Sheet 2
_159/76P70I15W!’0/
lentil. Za/z’afqg
2,438,638
?atented Mar. 30, 1948
UNITED STATES PATENT OFFICE‘.
2,438,638
'
PULSE TO RECTANGULAR WAVE
CONVERTER
,
Louis L. Lakatos, Bala Cynwyd, Pa., assignor to
Radio Corporation of America, a corporation of
Delaware
Application March 30, 1943, Serial No. 481,176’
9 Claims.
(Cl. 250--27)
1
' 2
My invention relates to apparatus for utilizing
or for indicating the reception of electrical pulses
of short duration which recur at different repeti
tion rates and particularly to apparatus which is
effective to increase the energy content of such
pulses.
'
The invention is useful in pulse-echo recogni
tion systems, for example, where the received
the two periods are approximately equal whereby
a substantially square wave is produced within
the operating range of the apparatus regardless
of the repetition rate of the received pulses. The
circuit constants are such that the relaxation cir
- cuit always goes through oneful] ‘cycle of opera
tion between successive received pulses.
The invention will be better understood from
the following description taken in connection
pulses are of only a few micro-seconds duration
and where their repetition rate may be any one 10 with the accompanying drawing in which
Figure l is a circuit diagram of a preferred em- '
of a large number of preassigned repetition rates.
One of the problems in designing such equipment
bodiment of the invention,
_
Figure 2 is a group of graphs illustrating the
is to obtain an output signal from the receiver
results obtained with the apparatus of Fig. 1,
which contains su?icicnt energy at the repetition
rate of the received pulses to operate the asso 15 Figure 3 is a group of graphs that are referred
ciated equipment such as a decoder and/or a
to in explaining the operation of the‘invention,
recorder or to obtain a strong audiblesignal.
Figure 4 is a group of graphs illustrating the
An object of the invention is to provide an im
operation of the circuit of Fig. 1 for the ?rst few
proved method of and means for converting pe
cycles when it is functioning according to the in
riodic short electrical pulses into a-correspond 20
ing periodic signal of increased energy content.
A further object of the invention is to provide
improved apparatus for, converting short elec
vention, and
,
_
"
‘
I
Figures 5 and 6 are graphs that are referred to
in explaining theinvention. _
,
Referring to Fig. 1, the. short received pulses
trical pulses recurring at a. certain frequency into
indicated at ID are supplied through a vacuum
an approximately square wave signal having the 25 tube VI to a relaxation circuit comprising a pair
same fundamental frequency as’ said repetition
of vacuum tub-es V2‘ and V3. In this particular
frequency and of increased energy content at this
embodiment of the invention the pulses II) are
frequency.
applied to the tube VI with positive polarity and
each pulse is immediately followed by a short
the short electrical pulses are supplied through 30 negative pulse due to the grid-leak biasing action
an ampli?er to a-‘relaxation circuitcomprising a
of the grid capacitor CI and the grid-leak re
In a preferred embodiment of the invention
pair of tubes which are direct-current connected
sistor RI in the input circuit of tube VI. This
plate-to-grid in multivibrator fashion and which
negative pulse, which appears reversed in polar
block- and unblockalternately. One of the plate
to-grid connections includes a coupling capacitor 35 ity at the anode of the tube VI, is the pulse that
triggers the‘ relaxation circuit V2—V3. This
shunted by a resistor, the capacitor and resistor
method of applying triggering pulses to the cir
having a suitable time constant to permit partial
cuit V2—V3 is not an essential feature of the
charge of the capacitor between successive re
invention but it has certain advantages and will
ceived pulses. ‘In the absence of received pulses,
,
the coupling capacitor .has a direct-current 40 be discussed in detail hereinafter.
Referring more particularly to the circuit com
charge thereon, having been charged by a flow
prising the tubes V2 and V3, the anode of tube
of grid current. The other plate-to-grid connec
V2
is connected to the grid of tube V3 through a
tion includes a resistor only. .Upon reception of
capacitor C which is shunted by a resistor R.
the ?rst short pulse, the ?rst tube is unblocked
and the second tube is blocked and held blocked 45 The anode of tube V3 is connected to the grid of
.tube V2 through a resistor I I. Operating voltage
by the coupling capacitor for a short time. Mean_
is supplied to the anodes of tubes V2 and V3
while, the coupling capacitor discharges until the
through anode resistors I2 and I3, respectively.
second tube is unblocked at which time the ?rst
The cathodes of tubes V2 and V3 are connected
tube is again blocked. Meanwhile the coupling
capacitor receives an'additional charge. Upon 50 to ground through a common cathode biasing re
sistor I4.
‘
'
reception of the next short pulse the cycle of op
The short triggering pulses appearing on the
eration is repeated.
anode of the tube VI are impressed upon the grid
The periods available for charge and discharge
of the tube V2 through a direct-current connec
of the coupling capacitor are interdependent
and, as a result, after a few Cycles of operation 55 tion I6. Operating voltage‘is, applied to the anode
7 2,438,638
4,
3 V
of the tube VI through the anode resistor 13, and
sumed in Fig. 3, the discharge time for capacitor
the coupling resistor l l.
be such that tlregridoi tube V2 will be su?iciente
C is substantially constant whereas if the pulse
period is shorter, as is assumed in Figs. 2 and 4,
the discharge time for capacitor C is a function’
of the charging time of capacitor C and the ap
paratus will function as“ ‘desired.
I
ly negative with respect‘ to its associated cathode
, The reason that my circuit operates as illus
holds its grid positive with respectt'o its cathode. .
The capacitor C has a D.-C. charge because of
the grid current ?ow in the tube V3.
Upon the reception of a positive pulse It, the ‘ j
the coupling capacitor C plotted against its
-
r
In the absence of incoming pulses III, the rela
tive voltage drops in anode resistor 13 and cou
pling resistor II and in cathode resistor I 4 will
t'r'ated in Figs‘. 2‘ and 4 may be seen more clearly
to block the tube v2‘. The anode 'of tube v2 is
by referring to the graphs of Figs. 5 and 6. The
now at its maximum positive potential and the
1 tube V3 is conducting since the RC coupling’ ‘ graph l in Fig. 5 shows the discharge time of’ ‘
charging time. As here used, discharge time
means theitimefollowing an input pulse which is '
required-'toudischarge capacitor C to a potential
grid of tube VI draws current and the ‘small ‘grid
‘ which wiiipermit the two tubes v2 and v3 to
capacitor Cl is charged. Atthe end of pulse ID,
capacitor Cl discharges through the. grid re
switch; while the "charging time refers to the
time fromithefswit'ching point to the next im
sistor Rl to put a short negative pulse. on the . a
pulse, during which capacitor C charges. 1
Referring to the graph of Fig. 5, it will be
grid of tube VI, thus making the plate‘of tube
noted‘ that‘if the charging time for capacitor C
vligo‘mprepositiveto apply a positive-pulse to the r
‘
is greater‘ than 1'04 micro-seconds, jthe_~-discharge
time is 'siibstaiitially‘cons'tahti; but if- ‘the ‘charg
ihgjti-i-he less than, 1'03 mere-seconds. the dis
charge timeis' alrnest e linear-function ‘or the
makes‘ tubYeVi’. conduct
:sitive whereby the grid
' posimve and the anode of
snare. eqs'it’i‘ve- This change in
charging time- It'Yis
e kvo’ltag‘e‘qf ?ute v3 is fed back to the
vi» ‘third h the__coup_ling resistor ll;
or-ne'ar the latter region
of the graph that my invention applies.’ '7
j Referringnowto Fig. 6~,*th'e graphs "2,33, 74. and
'_ on the tube V3 is almost
5 are ior diiferent repeti on rateso?th‘e received
pulses it and they are 'pldttedfora'circhitliaving.
'» the constants indicated in rig;
In Fig. 1 the - '
capacity and resistance ival-ues, given by way of
V3,. asaiaig.soilsiyetegode, @urrent at which’
time the ‘reverse action takes place whereby the
if and is held at cut-off
hit‘ "v'gfiiowiiigi thrbugh thecathcae ‘resistor: It.
Meanwhile‘t-he depict l'g'rid- current in tube vs
' example, Tar'eindicat'ed ‘in .microfara'cfis, pm'icro- ,7
mioifofalrads, ohms Iand ‘meg
.
V.
.
,7
,
.
andiordihates are lfractions ‘0
e-"The absiéis'sas,
pulse period; 5i. e,
-‘ fractions orthepertinent-guises 'l‘pi fiEach'ofithe
. graphs wsl'1ciy'v_s:_('b‘y its ‘ordinate values) the frac
tion of 7a f'icértainfpiilse period
required‘ {for
applie an- additional charge to capacitor C.
whehithenéxt'puise ‘I'm-booms, "the. tube v2 is ‘
the discharge ‘time efeeapeeiter "C "y ‘en- :‘in the
preceding pulse lperiod ' the :fraction for the “pe4
again unblocked and the cycle of operation; 're
ridd-Nrlr‘eduir"
peats.
» i1 '
w
'
timed-semis.
"
.
‘
' ‘
For
The discharge and chargeiperiods for successive ‘
cycles o?‘rop'eration "are iinlik'eiand changing’. in
duration 'rfoit-fsevéral iiiuls‘etp'eriods or cycles-as ‘1 and assumeithat the repetition rate 'iSjIOO‘QcycIes '
illustratedfin?li‘ig.
"During the. ?rst cycle the " "
per second. TheffractionfoftheneXtcycleor pe
riod-jlVii-‘jlreqiiire'd frprv discharge-1 of: capacitor {Cfis
chargingrperiodQTz, butduring the second :cycle ‘ ' indicated'onIthe-graph?’bythearroWat'the right,
the discharge'rperiodT'siis' "short compared with
this ordinate, value being a2=0_.19. .Now taking
thegchargihg, period 154,. :Duringfthe third cycle .
the discharge period..-T5:a'g‘ain is longer_ than-the "
the mesa p‘er'h, 'th'e'lfriéti " ‘of-the period required
chargin'gjperiodk'l‘e but. it willbe noted that by
d2 as ‘the abscissa ‘value, ‘fit ~will {bet-‘seen that Ior
for discharge arcane" 'tore'cjjis‘l a'aéoa'. i‘simi;
this‘tim'e the-two periods are-:more nearly equal.
Aiter~ abqut. five . cycles. :for ‘example, the. dis
charge. and. ‘charge’ periodsare :Qi. substantially
1 .Qonstant
the waveforms?
‘ duratiqn. and
the. pptput,
are so. nearly,
wave _, I5,
,equal?hat
is. fairly
close “to, the of‘ , “symmetrical square ‘wave.
Wi'?iiathé1épératins- miigei ‘of the, equipment
thisaction"takesjplacenregardlgs ofwthe Irepetié ‘
tion.’ rate of the receivedpulses,ll],~ Thisfact is "
massage in; 371%’..- was‘: “Magnets 01 P111588
afiter'réhddt the. ?fihjmils .periodjandfthat ‘the
convergent‘;
'e’d" gills. holds fIQr: "graphs s2.
Ii} are shown aslioccurring at, two di?ere'nt rates.
3''and“5 ‘ ‘were rq, travail, .lt'may‘hgn'étsd
However, the'output'w'aye fl5 is appreximeteiy ‘ thet'atith higherpws‘ejrates;thisi?xea'vaiueiis
‘ajsyiml?siiwal 'squaiefjwave in each instanceand ,
' each s'quare‘waye has the‘isame.repetition‘rate as '1
that‘o'f thépul'se's l'0_ beingapplied to the‘circuit. j
'_ _It may be noted that, ‘withapparatus ‘having
.st'a’ritsg a" the raiigéjififiésmsnciss‘cen‘becorered., '
given, circuitii'consta’nts, if" the _'r'epetition ' rate of
Forexample;over‘alfréquéncy‘ jngefof 5.00‘.c;jp.fs. .
the receiyed'pulses l0 is t'ooIl‘ow,‘ the apparatus
will not functiohas described abo'veehd aslillusé ‘
trated inFigl. {1. Instead, itwill operate as shown
‘iniFiig.y‘3bedaiuse theI'c‘oupli‘ng'zfEapacitor. C will
"
"
e"'a"'full.'charge'before the
centages" ‘of “a r1311 ;‘ half ' ‘cycle :1 '
10.2090 “cjipgis-gasjpercent; ‘15,000.
90 percent.
~ »
"As previous-1y "statedfit "is " n61; heeessary’te '
.
disease
utilize the grid-leak biasing action at the input
circuit of the tube VI for triggering the relaxation
circuit V2—V3. For example, the tube VI may
be operated as a class A ampli?er drawing no grid
current, in which case the received pulses ID are
applied thereto with negative polarity. The ar
3. in combination a pair of vacuum tubes each
having a cathode, a grid and an anode, a cath
ode resistor common to said tubes, a coupling ca-
pacitor shunted by a resistor connected between
the anode of one tube and the grid of the other
tube, a coupling‘ resistor only connected between
the anode of said other tube and the grid of said
one tube, and means for applying short periodi
preferred, however, as it is a simple way of mak
cally'recurring pulses of positive polarity to the
ing certain that the triggering pulse which ap
grid of said one tube, the time constant of the
10
pears on the grid of the tube V2 is of suf?cient
charginggcircuit for said coupling capacitor be
duration to give the circuit V2—V3 time to switch
ing substantially greater than the period of said
to the alternate condition of tube blocking. It
recurring pulses.
~
will be understood that by selecting properly the
- 4. ,In' combination a pair of vacuum tubes each
values of Cl and RI, the negative pulse imme
diately following a positive pulse [0 may be given is having a cathode, a grid and an anode, an anode
resistor for each tube through which a direct-cur
a width or duration greater than that of the pulse
rangement illustrated and previously described is
rent voltage is applied to its anode, a cathode re
‘
sistor common to said tubes, a coupling capacitor
It has been found that for best operation of
shunted by a resistor connected between the anode
the speci?c circuit described the amplitude of the
input ‘pulses should be limited to values between 20 of one tube and the grid of the other tube, and a
coupling resistor only connected between the
3 volts and 15 volts positive. While speci?c circuit
anode of said other tube and the grid of said one
values have been given by way of example, the
tube, and means for applying short periodically
values are not critical and may, for instance, be
recurring pulses of positive polarity to the grid of
changed individually by plus or minus 50 per
cent with little change in operation. The +B 25 said one tube, the time constants of the charging
circuit and of the discharge circuit for said cou
voltage may be from 150 volts to 250 volts, for
It.
example.
pling capacitor being substantially greater than
meter by measuring the alternating current volt
connection from the anode ofgthe other tube be-v
ing substantially purely resistive and the time
constant of said series capacitor and shunting :
resistor being long compared with the period be-
the period of said recurring pulses.
Mention may be made of the fact that if the
5. In apparatus responsive to periodically re
tube V1 is omitted from the circuit, the remain
ing circuit comprising tubes V2 and V3 will os 30 curring electrical signals, a pair of ampli?er tubes
each having an anode and a grid, said tubes hav
cillate as a multivibrator with the frequency of
ing direct current connections from the anode of
oscillation determined largely by the time con
one tube to the grid of the other tube, the said
stant of the circuit R0.
connections from the anodeof one tube including
.The complete circuit comprising tubes VI, V2,
and V3 may be utilized as an electronic frequency 35 a series capacitor shunted by a resistor, the said
age appearing across the capacitor C. This A.-C.
voltage is a function of the repetition of the ap
plied pulses and is substantially independent of
the amplitude and of the wave form of the input 40 tween said successive electrical signals, means for
maintaining said one tube biased substantially
wave within the limits of circuit operation. The
to cut-o? in the absence of a signal voltage on its:
peak value of the said A.-C. voltage decreases
grid, and means for applying said electrical sig-*
as the frequency of the input signal decreases.
nals to the grid of said one tube.
I claim as my invention:
6. Apparatus for converting periodically re
1. The method of operating a pair of cross 45
curring short electrical pulses into pulses of
connected tubes wherein one of the cross-connec
longer duration recurring at the same rate as the;
tions consists of a capacitor shunted by a resistor
short pulses, said apparatus comprising a pair
and wherein the time constant for both charge
of ampli?er tubes each having an anode and a.
and discharge of said capacitor is long compared
grid, said tubes having direct-current connec
with the period between successive applied pulses,
tions from the anode of one tube to the grid of
said method comprising applying regularly re
the other tube, the said connection from the
curring short electrical pulses to said pair of
anode of one tube including a series capacitor
tubes and initiating the discharge of said capac
shunted by a resistor, the said connection from,
itor in response to the occurrence of a short pulse,
causing said capacitor to charge partially in re 55 the anode of the other tube being substantially
purely resistive and the time constant of said
sponse to said capacitor discharging to a prede
series capacitor and shunting resistor being long
termined voltage value, and again initiating the
compared with the period between said succes
discharge of said capacitor by the next succeed
sive short pulses, means for maintaining said '
ing short pulse while said capacitor is only par
tially charged whereby said charge and discharge 60 one tube biased substantially to cut-off in the
periods tend to become equal after a few cycles of
absence of a signal voltage on its grid, and
means for applying said short electrical pulses
operation.
I
with positive polarity to the grid of said one tube.
2. Apparatus for converting periodically recur
7. In apparatus responsive to periodically re
ring short electrical pulses into pulses of longer
curring
electrical signals, a pair of ampli?er tubes
65
duration recurring at the same rate as the short
each having an anode and a grid, said tubes
pulses, said apparatus comprising a pair of am
having direct current connections from the anode
pli?er tubes having cathodes and having anodes
of one tube to the grid of the other tube, the
and grids which are direct-current cross-con
said connection from the anode of one tube in
nected, one of said connections including a series
capacitor shunted by a resistor, the other of said 70 cluding a series capacitor shunted by a resistor,
the said connection from the anode of the other
connections being substantially purely resistive,
tube being substantially purely resistive and the
and a cathode resistor common to said tubes, the
time constant of said series capacitor and shunt
time constant of said series capacitor and shunt
ing resistor being long compared with the period
ing resistor being long compared with the period
between said successive electrical signals, means
75
between successive short pulses.
QASMQQ
7
' 8
1'02‘ maintai‘xii'ne said. one tube bmedsubs?afntm
having an anode that is
1y to cutr-offimthe rabsgnce of a £81m}. voltage ,
119 mg Hid.- of saidnpe tuhe- ‘
on its grid, and'mean‘s :fox' applying said smart
electrical pulses to the’ grid of saisl- on»? H1398
whereby there appears across said'seri? eapaeig
tor an alternating current manage having a peak
value that decreases as ism: mpeti?on rate oi
the electrical; signals increases.
- _>
I
,
direct-current connected
'
LOUIS L. LAKATOS.
REFERENCES CITED
‘The follgwing references are. of recQrd in thé
?le 91", this patent:
‘
‘
8. The invention according tq claim 3 whergin
UNITED STATES PATENTS
said means for applying short pulses inclugles fan 19
ampli?er‘ tube having, anoutput electrode that
Number .
Name
7
Date a ,
is direct-current connected to the‘gljid 9i said
22623338
Delorame et a1. --->. Nov. __18, 19M
one tubé.
'_
'
9. The invention according to claim 5 wherein
said means for maintaining saidgne tgbe bfilasled
FQREIGN‘PATENTS
’
substantiallyrto cut-off’ in the gbsencgoi a, sig
‘
Numbér
15 , 356,111
Great, Britain ___v~__ Aug. 24, 1931
nal voltage on its grid includes an ampy?gr tube
456,840
Great Britain ____ __ Nov. 12,‘ 1936
Country-
Date
' 7
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