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Патент USA US2410721

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Now}. 5, 1946.
v
R. B. DOME
‘ _
2,410,721
PHASE SHIFTING CIRCUIT
Filed Nov. 30, 1942
WA v:
SHAPING
\
APPAmn/s
PM
‘Inventor :
Robert BfDome, ’
by' 1/
His Attorney.
6f
General Electric Gompany, a corporation of
New York
Application November 30, 1942, Serial No. £67,421
5 Claims. (Cl. ire-23s)
My invention relates to, electric circuits and
more particularly to electric circuits for shifting
the phase of an alternating potential derived
from a source with respect to the potential of
that source.‘
"
>
2
M. The switch Hi, preferably, is of the double
pole, double-throw type and its use in my phase ‘
shifting circuit is explained in detail later. The
secondary winding l5 oithe transformer it has
a pair of terminal connections it and El and an
_
While my invention is of general application
in electric control and regulatingsystems, it is
electrically intermediate connection, or center
tap, it, the latter being connected to ground.
The terminal it of the secondary winding i5 is
connected to the input of the wave shaping ap
applications, particularly when used in ‘pulse 10 paratus l9 through capacitor 28. The wave
shaping apparatus l9 may be of a type commonly
systems, it is desirable to control the starting
particularly adapted for use in connection with
the sweep circuit of a cathode ray tube. In such
time of a trace so that a. selected image appears
used in deriving a wave form desired for sweep
circuits of cathode ray tubes and may comprise,
for example, means for clipping the top and bot
result he obtained, it is essential that the phase‘ 15 tom of the sine wave impressed across the input
of the apparatus to derive a square wave there
shifting device have a. range of substantially 360
from, means for integrating the square wave and
electrical degrees.
generating therefrom a saw-tooth wave, and
It is an object of my invention to provide a
means for amplifying this saw-tooth wave prior .
new and improved electric phase shifting circuit.
It is a further object of my invention to pro 20 to impressing it across the sweep coils 25 of the
cathode ray tube it.
vide an improved electric phase shifting circuit
Also connected to the terminal I6 is a poten-I
in whichv the output voltage may be varied
tiometer or resistance 26 having its other end
through 360 electrical degrees relative to the in
put voltage with substantially no change in rela- . connected to the terminal ll of secondary vwind
tive magnitudes.
25 ing l5. The potentiometer 2! has a movable
contact or slider 22 which is directly connected
Another object is to provide an improved elec
to the conductorv 23 between capacitor 26 and
trio phase shifting circuit which is simple in as
the input of the ‘apparatus id. The return cir
sembly and operation and the‘ component ele
cult for the apparatus i9 is connected to ground
ments of which are standard electrical circuit ele- '
ments and which may be replaced in the ?eld so by conductor 26 and the output of apparatus is
is directly connected to the sweep coils 2b of
with relatively little dimculty.
cathode ray tube I ll. '
The features of my invention which I believe to
The cathode ray tube may be of any well known
be novel are set forth with particmarity in the
form and the details thereof form no part of my
appended claims. My invention itself, however, ‘
both as to its organization and method of oper 85 invention. Brie?y, means are provided therein
for developing and projecting an electron ray 36
ation, together with further objects and advan
against ?uorescent screen 34 at the end of the
tages thereof, may best be understood by refer
tube envelope. The intensity of the ray 3!]
ence to the following description taken in con
emanating from the cathode i2 is controlled by
nection with the accompanying‘ drawing, in
which Fig. v1 diagrammatically illustrates an 40 the potential applied to the control electrode 3%.
The ray is caused to scan the target in a hori'
embodiment of my invention as applied to the
zontal plane in well known manner through the
sweep circuit of a cathode ray tube and Fig. 2
action of the sweep coils 25 supplied with scan
represents certain operating characteristics
ning potential from the source ll. When the
thereof.
'
tube I0 is used in a pulse’ signalling system of
Fig. 1 oi’ my invention is diagrammatically
the radio'echo type, for example, and is used in
illustrated as applied to the sweep circuit ofpthe
conjunction with a rotating antenna of such a
cathode ray tube Ill. The voltage for this cir
system, the coils 25 may be rotated about the
cuit is supplied from a source of sinusoidal oscil
neck portion of the tube l8 to effect scanning
lations “,the frequency of the source H prefer
ably being of a. value ordinarily used for such 50 at di?erent azimuth angles corresponding to the
circuits and lying in range between 325 and 650
position of such an antenna.
.
at the beginning of a trace and facilitates com
parison with other images. In order that this
cycles.
‘
The seaming voltages from the source ii. are
The operation of the embodiment of my inven
tion shown in Fig. 1 will be explained by consid~
impressed upon the primary winding I? of the
ering the voltage supplying circuit when the
transformer i8 through a phase reversing switch 55 sweep or scanning potential is being transmitted
4
plitude of the output voltages between positions
from the source I | to the coils 25 through trans
former I3 and apparatus l9. With the switch I‘
0A and OB and occurs near the point where re
sistance R1 is equal to R2, that is, substantially
at the middle of the movement of contact 22.
the secondary winding i5, that is, between the
Ultimately when contact 22 reaches the lower
terminal i6 and ground, may be represented as
most position on potentiometer 2| and the value
E volts. The voltage e impressed across the in
of R2 is zero, the voltage e has shifted 180° and
put of apparatus I9, that is, between movable
may be represented by the vector 0C. Other val
contact 22 and ground, can be shown mathe
ues of e for positions of contact 22 between the
matically to be
1
10 ends of resistor 2| are indicated by the remain
ing points shown on the full-line curve, the ratio
of resistance R1 to the resistance 2| being indi
where
cated for each of the points. For the practical
values mentioned previously, it should be noted
X=the reactance of capacitor 20,
R1=that portion of potentiometer 2| above the 15 that the greatest variation in' phase occurs dur
ing approximately the last 10 per cent of move
contact 22, and
ment of contact 22. Thus, ‘the change in e from
Rz=that portion of potentiometer 2| below the
the value 0A to the value OB occurs during ap
contact 22.
proximately the ?rst 90 per cent of movement of
To those skilled in the art, it is at once apparent 20 contact 22, while the shift from OB to 0C is
that the phase shift obtained, for any setting of
eifected during the last 10 per cent of the con
the movable contact 22 may be determined from
tact movement. This ion-linear relation between
shift of phase and variation in position of con
thrown to the left, the voltage across one-half of
tact 22 may be avoided by the use of a logarith
Since the value of the reactance X of capaci 25 mic type of resistor for potentiometer 2|, that is,
a resistor whose effective resistance does not vary
tor'20 is ?nite when contact 22 is at the upper
linearly with movement of contact 22, but instead
varies substantially in accordance with a logarith-é
mic curve, and 10 per cent of the resistance lies
is zero and the value of ¢ is also zero degrees.
Under such conditions‘, the voltage e is in phase 30 in the lower half of the resistance 2| and the re
maining 90 per cent in the upper half of resist
with the voltage E. As contact 22 is moved down ,
ance 2|.
'
'
potentiometer 2| and R1 is increased, a phase
It is thus seen that my invention provides a
shift of 90°‘is obtained when the denominator of
phase shift circuit effective to shift the phase of
Equation 2 passes through zero. Finally, when
point of potentiometer 2| and electrically is di
rectly connected to terminal I6, the value of R1
the movable contact 22 arrives on the lowermost 35 its output voltage through 360 electrical degrees
relative to the alternating voltage impressed
across its input circuit while maintaining the out
put voltage substantially constant in magnitude.
The component elements of my phase shift circuit
portion of potentiometer 2| and electrically is di
rectly‘connected to terminal |'|, R2 becomes zero
and the value of qi is 180°. Thus, in the move-—
ment of contact 22 between terminals 16 and H,
a shift of 180° is obtained.
If switch M be now 40 are readily available and are easily assembled.
thrown to itsright-hand position, a second shift
of 180° may be obtained. Thus, for the two po
sitions of switch I4, the output voltage of the
phase shift circuit which is impressed upon the
input of apparatus l9 may be varied through 360.
electrical degrees relative to the input voltage.
The variation of amplitude'of the output volt
age of the phase shift circuit may best be illus
trated by consideration of practical values for
potentiometer 2i and capacitor 20. If, for ex
ample, the' value of X, the reactance of capacitor
20, is 100,000 ohms and the value of resistor 2| is
1 megohm, it is seen from Equation 1 that the
maximum value of e is E and the minimum value,
approximately .895 E. This represents a voltage
drop of but 101,42 per cent and for practical pur
In the operation of phase shift circuits employing
variable resistors, the greatest percentage of
trouble is occasioned by failure of the resistors
used for the potentiometer 2|. As a result of pro
viding a phase shift circuit in which the resist
ance 2| is of the ordinary two-end control type,
having only the two contacts at the end of the
resistor and no intermediate taps to be connected,
' it may easily be replaced in the ?eldwith rela
tively little dif?culty.
1
While I have shown a certain application of my
invention, it will be apparent that modi?cations
may be made. Thus, instead of the apparatus i8
and the cathode ray tube 20, any other type of
utilization circuit may be employed in conjunc
tion'with my phase shift circuit. Also, where a
shift of 180 electrical degrees is sufficient, the
poses, the output voltage of the phase shift cir
phase reversing switch ll may be omitted. Thus,
cuit is maintained substantially constant in mag
while I have shown particular embodiments of my
nitude. Furthermore, if the size of capacitor 20
is doubled, the minimum value of e becomes ap 60 invention, it will of course be understood that I
do not wish to be limited thereto since various
proximately .95 E. It is to be observed that this
modifications may be made, and I contemplate by
increase in constancy of amplitude is obtained
the appended claims to cover any such modi?ca
at a sacrifice of linearity in the operation of' the
phase shift control.
'
tions as fall within the true spirit and scope of
'
For explanation of this effect, reference is 65
made to the curve of Fig, 2 in which the full-line
curve shows certain operating characteristics of
the phase shifting circuit and the broken-line
curve is a semicircle having a radius 0A. When
the movable contact 22 is at» the top of potenti
ometer 2|, the voltage e may be represented by
the vector 0A. The voltage OB, which repre
my invention.
1
What I claim as new and desire to secure by
Letters Patent of the United States is:
1. In combination, a source of alternating volt
age having -a pair of output terminals balanced
70 with respect to ground, a load connected between
ground and one terminal of said source through a
reactance, an impedance having two terminal con
nections, one of said terminal connections being
sents a shift of 90°, is obtained, as explained
- above, when the denominator of (2) is zero. A
connected to said source and said reactance and
secondary maximum point 35 appears in the-am 75 said one terminal and the other of said terminal ‘
2,410,781
connections being connected solely to the other of
e?ective to shift the phase of the alternating volt
said terminals, and a contact connected to a point
between said reactance and load and movable
along said impedance to vary the phase of volt
age supplied from said source to said load.
2. In combination, an alternating current cir
cuit. apparatus for producing an alternating volt
age variable in phase relative to the voltage of said
alternating current circuit and of substantially
constant magnitude and comprising an imped
ance in said circuit having a pair of terminals
and an electrically intermediate connection, a
resistance connected between said terminals ,and
having a movable contact, a capacitor connected
between one of said terminals and said movable
contact, the other of said terminals being con
nected solely to said circuit, and an output cir
cuit connected between said intermediate connec
age impressed across said output circuit'through
180 electrical degrees.
.
'
4. A voltage supply for the sweep circuit of a
cathode ray tube comprising, a source of alternat~
ing voltage, means for impressing across said cir
cuit a voltage derived from said source, and
means for shifting the phase of said derived volt
age relative to the voltage of said source compris
ing, a winding energized from said source and
having a pair of terminal connections and an
electrically intermediate connection, a resistance
connected between said terminal connections ‘and
having a movable contact, a capacitor connected
between one of said terminal connections and
saidlmovable contact, the other of said terminal
connections being connected solely to ’said resist
ance, and means connecting said circuit across
said intermediate connection of said winding and
of said contact between said terminal connections 20. said movable contact.
is effective to shift the phase of the alternating
5. In a voltage supply for a cathode ray tube
voltage impressed across said output circuit
having a sweep circuit, a source of sinusoidal volt
tion and said movable contact, whereby movement '
through 180 electrical degrees.
,
_
age, and means for deriving a voltage therefrom
for impressing across said sweep circuit, means for
3. in combination, an alternating current cir
cuit, apparatus for producing an alternating volt 25 adiustabiy shifting the phaseoi’ said derived volt
age relative to the voltage of said source com
age variable in phase relative to the voltage of said
prising, a winding energized from said source and
alternating, current circuit comprising a winding
energized from said circuit and having a pair 01
having a pair of terminal connections and an elec
terminal connections and an electrically inter
trically intermediate connection, a resistance con
mediate connection, a resistance connected be 30 nected between said terminal connections and
having a movable contact. a capacitor connected
tween said terminal connections and having a
movable contact, a capacitor connected between
between one of said terminal connections and said
one of said terminal connections and said mov
movable contact, the other of said terminal con
nectlons being connected solely to said resistance.
able contact, the other of said terminal connec
tions being connected solely to said resistance, 35 and output terminals ‘connected to said inter
mediate connection of said winding and said
and an output circuit connected across said in
termediate connection of said winding and said
movable contact.
contact of said resistance, whereby movement of
said contact between said terminal connections is
ROBERT B. DOME,
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