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Патент USA US2411440

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Nov. 19, 1946.
W. R. LE PAGE
LIGHT SOURCE FEEDBACK SYSTEM
Filed April 50, 1945
2,41 1,440
Patented Nov. 19, 1946
2,41 1,440
"UNITED "STATES RATE-NT‘ QFFICEE, ‘
‘FLIGHT-l SOURCE FEED -BACK~ SYSTEM
Wilbur labile ,lPage, Pikesville, :Ma., assignonto,
fjtadio Corporation of America, yarcorporation
of " Delaware
iApplicationiApril'i-b’?, 1943, Serial No. 485,255
"5 ,Claims.
(Cl. 1250-415)
1
g
.
This invention relates “to. “photographic sound
:_2
‘
,
‘energy Vsuppliedit'o Ethe :lamp in vaccordancewvith
‘.‘recording and ‘reproducing systems, and, partic u
. "the variations inzthe ,deteotedgllight “for-stabiliza
.larly. to ,a system ,~forv stabilizing’ the 1 light, sources
.ztiongand in accordancewithsan applied signal for
.used. in suchsystems or anysystem iniwhich the
‘modulationcand ground noise ‘reduction. ,ziThe
light output shouldvvarydinearly with anapplied
, 5 general principle ,of suchan opticalieedback
.signal, :voltage ,or current which :may consist of
oscillations ,of :audio frequencies and unidirec
stabilizing systemkis knownrin the::art. Incer
tain‘ .of "these IDI‘iOI' ‘systems; which provide :both
tional-components.
i
‘direct current, andalternating-current feedback,
It ,is ‘W811 ‘known :that. in, photographic "sound
the impedance of anqelectronicsrdevice connected
erecording.systemsdight sources orlampsare-em .10 in series with the :lamp :and ithe "primary? power
.ployed ,toproduce lightibeamswhichmay. be either
:source'is varied inaccordance .with the:lig‘hti?uc
, directly,mod.ulated ,by varying the f energy sup
:tuations. i-The amountx'ofvfeedback ini‘suchra
plied ,togthelampsiinaaccordance with ,the varia
system "depends on ' theigain .Lof tth'e ‘ amplifiergthe
tionslof soundwavestobe recorded, or whichtmay
‘ eiiiciency of translationof .the :light 'JSEYISltlVSCdG
be modulated by vibrating the beaminaccordance 15 vice and the amount‘ of ilightgcollected; for acon
with thesoundwaves. Light. sources cfconstant
trol purposes. For a ?xed amount-otzampli?ca
.intensity are .use‘di'for ,recording both variable
tion and Ira ?xedramount :of; lightcreceived: by; the
,area-and ‘variable density sound tracks, the light
'photocell, :thefeedback can :only ;bex~.increased
‘being modulated ‘by the ‘vibrations :of agalvan~
:byvincreasin'g‘ the :rcell xload ~ resistance, :or for i a ;ometer mirror. "Light sourceaisuch as glowlamps, 20 1 ?xed-number of #stages ,of; ampli?catiomthe 'feed~
which vary ‘in intensity are also employed for
recording variable density records. For repro
ducing either type of record, *a light source of
‘constant intensity is used to produce the scan~
‘ning'beam.
I
'
- backmaybe increased by; increasingthe,interstage
coupling =resistors. ;However, these methods ‘of
increasing ifeedback have -_the ‘disadvantage :;of
rcausing _:phase shift ,‘and ilossiof again :at ;,high
is CA
‘
'
‘When alight of constantintensity is employed
ifrequencies.
.
i
'
l
'‘ rI'he zprincipalgobiectaoflthe invention; therefore,
'for'recording; it is necessary that it be maintained
,is'tor-improve ‘light ;source stabilizing, modulat
"accurately constantly to prevent undesired’varia
ing, and controlling systems.
. .
‘ti'ons inthe sound levels or modulations and the
:Another; obj ect.ofxgthezinvention“ is: torprovi‘de an
introduction of distortionin‘the recorded or re in CD optical feedback;stabilizing;‘modulating; and con
'produced sound. "Unwanted light variations may
;trolling "system vwhich rhas Iminimum i‘ distortion
‘be produced‘by'?uctuations in the lamp ener-.
‘gizing source,‘ by ‘deterioration 'of ‘the light-pro
‘and faxhighisensitivityrto the controlling light,
Y. makingrit: unnecessary to appreciably ‘reduce the
ducing elements, by‘the blackening ofthe lamp
useful,light,:tmObtaimSu?icient ‘control light. '
envelope 'and‘fother reasons. When the record
ingis done'by causing a variation of the light
source, "this variation must be linear with the
:A'furt-her‘object oft‘theiinvention is ‘to-provide
:an optical :lfeedback system "which is capable ;of '
:responding , tocrapi'dw changes innlight ioutput, was
applied signaL-voltage or current, and the linearity
well .asgto slow ,vari-ationsztherein.
must ‘be ‘maintained ‘for frequencies up to ‘the
highest frequency of sound to be recorded-While
vtot-be characteristic ,‘Of'ilhisf invention : are pointed
‘ ;out with {particularity-1m 1511116? claims "appended
the'averagellight remains constant or at a‘ con
i‘trollable ‘value. Thatis, the light'must follow an
‘ ‘ rhereta-gfthe ‘manner :jof 1‘ its rorganization :and the
averagevaluewhich-‘is determined by the ‘noise
“reduction'voltage an‘d'also thesoundsignal fre
quencies andthus linearly?respond to voltage or
rcurrent of~anyffrequencyin theband to‘b'e-re
rc‘ordedrand adirect-current‘or voltage. 'Thein
imodeloif iits ,,operation'vvill'cbe‘better understood
zbyzreferring" to :the following :description, :read
in conjunction withrthe iaccompanyinggdrawing,
inwhich:
{Fig :1 iisra
‘ ,rbiock :diagra-m showing
r
i :the
r ":general
" venti-onifurther provides-a feedback system which
1 arrangementofg thezsystenrembodyine the-inven
‘ ~-requiresveryJlittle‘light toproduce‘the necessary’ '
:tion.,
‘stabilization, modulation,:and control.
"The present inventiongtherefore, ' is directed to
- .detecting a Iportionxofftheflight;an‘drregulatingihe
‘
‘
V
_; ‘W
.Eig. ..-2 is ca ,rschema-tic 5 diagram-1 of ,rthefieedback
amoli?enof thei-invention-nand
'ia-system- for stabilizingand providing linearity of
‘light variation 1 with "an applied alternating and
;direct .;current signal. This is : accomplishedjby
1 ‘
:Althoughtthe; novelfeatures which are believed
“
‘ ‘
1
Fig.3 is‘. a schemat-imdetail ,;diagram; of ‘armodi
m?cation, of:.the,glastqstagezofuthe isystem ‘shownmof
-
55
IYEigJQZ.
c
-
._
,
.'
:Reierringmow to EEiaLl; blockimisran‘ampli?er
2,411,440
3
.
4
sistors 26, 21, and 28. The effective plate loading
which is capable of amplifying both direct cur
resistance of tubes l5 and I6 is produced by re
sistor 26 and resistor 30 in parallel for tube l5
and by resistors 21 and 34 in parallel for tube IS.
The constant voltage drops across gas-?lled
voltage regulator tubes 32 and 35 produce the
rent and alternating current, and P is a power
supply and other circuit elements necessary for
controlling a glow lamp 5 upon which the out
put of the unit P is impressed. A portion of the
light from lamp 5 is detected by a photosensitive
proper biaseson the tubes l5 and 16, respectively,
devicey? energized by battery 8. The energization
of thejcell' 6' generates a voltage across a load-re
. and effectively provide a'direct coupling between
tubes l5 and I6 and between tubes l6 and H,
sistor 9, which voltage is indicated as ‘e2. The
voltage across load resistor 0 is impressed over 10 a direct connection 33 being provided between
tubes I1 and I8. Regulator lamps 31, 38 and 39
conductors l0 upon the input of ampli?er A in are for the purpose of obtaining a negative bias
series with an external voltage which may bev
on the grids of the respective tubes, while lamp
considered as co, the total voltage thus appear
' 4i regulates the bias potential on tube 18.
ing across the input to ampli?er A being e1.
Since a sustaining current of about 5 mils is
The phase of the voltage ez is such'as'to‘de
necessary in the glow tube, thecoupling resistors
crease the energizing lamp current with an in
cannot be very large, and this is particularly de
crease in light output. '
, ~
7
sirable in order to provide the low coupling be
The entire system just described can be con
tween the amplifying stages. The abovee-men
sidered as a feedback ampli?er with 100 per cent
feedback. Without feedback, the gain G of the 20 tioned circuit operated satisfactorily to provide
I ampli?er may be considered as 62/61. It is evi
a’ ?at frequency response characteristic‘ up to
10,000 cycles per'second with negligible distortion.
dent that ez is considered the output voltage,
in order to deal with the circuit as an ampli?er.
To obtain ‘20 db. of feedback with resistor-"22
Actually, the light is the useful output, but since
having the small value of 10,000 ohms, only “one
fthe‘light islproportional to e; the discussion is 25 microampere of photocell current is necessary for
' valid.? Thus, in the usual notation in which the
each ten milliamperes of lamp current. - More
feedbackfact'or ‘5 equals (—1), the'wellwknown
formula G/(1—.GB)=G/(I+G) .for the'gain of
photocell current, (i. e. more detected light) will
give more feedback. The system may thus supply
.a' feedback ampli?er applies in this case. If G
a considerable amount of feedback with ‘a very
is large,‘th‘e gain'is nearly unity, and this is the 30 feeble photocell current, and therefore has a high
condition ‘desired. In this analysis the numeri
sensitivity to detected light. The modulating sig
' cal value of the overall gain is based on the as
' sumption that 13:1. Now, the optimum condi
‘ tionv of operation is that‘the valuev of G be su?i
introduced in the control grid circuit 'offtube
[5 instead of across resistors. .23 and 24 as men
nal and noise reduction voltages may also be
ciently large so thatthe net gain is very nearly
7 equal to unity.
In a single stage feedback system, the'amount
' of'feedback is‘ limited by the size of the photo
cell and ampli?er load'resistors and any increase
therein increases thev effects of stray capacity with
the associated di?iculties. ‘Of particular concern
in this application is the resulting phase shift at
the higher frequencies, which may contribute to
a tendency to'osoillate. This phase shift disad
tioned above.
I claim
difficulties by theruseof more‘stages of ampli?
cation'in ‘combination with low coupling resist
ances
I8, of amplification are shown,; the
to "ampli?er A of Fig. 1, and tube l8 vbeing com
parable to power unit Prof Fig. 1. The three
tubes l5, l6, and ' I‘! may be ampli?er tubes, such
as the RCA type‘ 6J7,"while tube IB‘may be of
' the‘ RCA type 6L6. The lamp 5 of Fig. 1 is shown 60
' connected in the platev circuit of tube I18, energy
for‘the lamp and tube being supplied by a bat
tery 20. The photoelectric cell 6 of /‘Fig. 1 is
shown connected back .to a low value load're
~
>
The external voltage represented by E6 in Fig. 1
“maybe impressed across either resistors 23 or .
24, onev of which may be used‘for'introducing a
modulating signal voltage and the other for in- '
ftroducing- a noise‘ reductionv voltage.' A poten
tiometer 42 is an intensity control for the lamp
.\ S'whi‘ch may'also'be obtained, if desired, by a
=volta'ge applied across I‘either resistor 23 ‘or re
sistor 24. A common source of B potential ‘is sup
»;pli'ed'to the 'platé's‘of tubes l5, l6, and ll 1 ‘over re
,.
stage of ampli?cation having its output con
?rst three tubes l5, l6, and I1 being comparable
'
a
50 nected to said light source, coupling means be
Referring‘ now to Fig.2, four stages l5, l6,
sistor22 in the input of tube l5.
'
cell, a light source to be’ controlled,‘ an .output
and a low photocell load resistance.
l1, . ‘and
as my invention:
?cation having its input connected tosaid photo
'
The present invention overcomes the above
- "
source for said photocell, an input stage of ampli
glow lamp since the ‘light modulation lags the
current modulation by a considerable angle at
'
'
i 1. A feedback ampli?er system ‘for stabilizing
a light source comprising a photocell, apotential
vantage may be more acute with the use of a
high audio frequencies'
'
In Fig. 3, an alternate‘ method of ' connecting the
6L6 into the circuit is shown, a method in which
the screen‘ grid of the tube is separately utilized.
The same low coupling resistances betweentubves
40
is obtained wherein the amount‘ of feedback'fis
,more nearly constant as a function of frequency.
tween said amplifying stages, said coupling
means having a low value of resistance, and cou
pling means intermediate said photocell and said
input stage of ampli?cation, said last mentioned
coupling. means including .a resistor .in; series
With. said photocell andlsaid potential‘ source,
said resistor having a resistance value of the .or
der of 10,000 ohms, said low value of resistance
minimizing phase shift and loss of gain-at high
frequencies.
.
__
-
,
a
2. A' feedback-ampli?er system for stabilizing
a light source comprising a photocell, an input
stage of ampli?cation having its input‘ circuit
connected to said photocell,’ a coupling resistor
in'said input circuit, a light source to be‘ con
trolled, an output stage of ampli?cation having
its output connected to said light soured-cou
pling means between said amplifying stages-said
coupling means having a low value of resistance,
a polarizing source of voltage for said'photo‘cell
and the anodes'of the tubes in said amplifying
stages, and a vdegenerative feedback‘ series-cir
cuit from said polarizing source of ‘voltage
‘ through said photocell through said coupling re~
sistor and back to said polarizingv source‘for cou
2,411,440
5
pling said photocell to said input stage of ampli
fication.
3. A feedback ampli?er system for stabilizing
a light source comprising a photocell, an input
6
?er stages, said coupling means having a low
value of resistance, and coupling means between
said photocell and said ?rst stage of ampli?ca
tion, said last-mentioned coupling means in—
stage of ampli?cation having its input circuit Ul cluding a resistor in series with said high poten- .
connected to said photocell, a coupling resistor
in said input circuit, a light source to be con
trolled, an output stage of ampli?cation having
its output connected to said light source, cou
tial source and said photocell to provide a de
generative ieedback circuit, the variations in
voltage across said resistor being ampli?ed by
said ampli?er stages.
5. A feedback ampli?er system for stabilizing a
pling means between said amplifying stages, said H)
light source comprising a light source to be stabi
coupling means having a low value of resistance,
lized, a photoelectric cell for detecting a portion
a polarizing source of voltage for said photocell
of the light from said source, a plural stage
and the anodes of the tubes in said amplifying
ampli?er including at least three stages inter
stages, and a series circuit from said polarizing
mediate
said photocell and said light source, glow
source of voltage through said photocell through '
lamp coupling means between said amplifying
said coupling resistor and back to said polarizing
stages, a high potential source for said photocell
source for coupling said photocell to said input
and the anodes of the tubes in said ampli?er
stage of ampli?cation, the value of said coupling
stages, said coupling means having a low value
resistor being of the order of 10,000 ohms.
20 of resistance, and coupling means between said
4. A feedback ampli?er system for stabilizing
photocell and said ?rst stage of ampli?cation,
a light source comprising a light ‘source to be
said last-mentioned coupling means including a
stabilized, a photoelectric cell for detecting a por
resistor in series with said high potential source ,
tion or” the light from said source, a plural stage
and said photocell, the‘ variations in voltage
ampli?er including at least three stages inter- .
across said resistor being ampli?ed by said am
mediate said photocell and said light source, glow
pli?er stages, the value of said resistor being of
lamp coupling means between said amplifying
the order of 10,000‘ ohms.
‘
stages, a high potential source for said photo
cell and the anodes of the tubes in said ampli
WILBUR R. LE PAGE.
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