US2451796A

US2451796A - Phase shifting circuit

Info

Publication number: US2451796A
Application number: US503545A
Authority: US
Inventors: Berkoff Seymour
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1943-09-23
Filing date: 1943-09-23
Publication date: 1948-10-19
Anticipated expiration: 1965-10-19
Also published as: FR945118A

Description

Oct. 19, 1948. s, BERKOFF 2,451,796

PHASE SHIFTINGCIRGUIT Filed Sept. 23, 1945 FigJ.

Inventor: SCBTTIOUT' BeTkoff,

by WW5.

H is Attorney.

than 180 degrees.

Patented Oct. 19, i948 PHASE SHIFTING CIRCUIT Seymour, Berkofi, Bridgeport, Conn., assignor to General Electric Company, a corporation of New York Application September 23, 1943, Serial No. 503,545

6 Claims. (Cl. 323-119) My invention relates to electric circuits and, more particularly, to electric circuits for shifting the phase of the alternating potential derived i'rom the source with respect to the potential of that source. It is an object of my invention to provide a new and improved electric phase shifting circuit.

It is another object of my invention to provide a new and improved phase shifting circuit in which the output voltage may be varied through 360 electrical degrees relative to the input voltage with substantially small change in relative magnitudes.

It is a further object of my invention to provide an improved electric phase shifting circuit which is simple in assembly and operation and the component elements of which are standard electrical circuit elements and which may be replaced in use with relatively little difllculty.

While my invention is of general application in electric control or regulating circuits, it is particularly adapted to use in connection with the sweep circuit of a cathode ray tube. In such applications, particularly when used in pulse signalling systems, it is desirable to control the starting time of a trace so that a selected image appears at the beginning of a trace and facilitates comparison of other images. In order that this result be obtained, it is essential that the phase shifting device have a range of substantially 360 electrical degrees.

Accordingly, it is another object of my invention to provide a new and improved means for shifting the phase of a sine wave over a range greater than 360 degrees and which requires only a combination of resistors, condensers, and electron discharge tubes.

One of the features of my invention is the employment of an electronic discharge tube as a phase splitter in a phase shifting circuit to avoid the necessity of employing transformers and the use of the combination of capacitances and resistances in the output circuit of the electronic discharge device to obtain a phase shift of more In another of its aspects, my invention employs two electronic discharge devices having similar output circuits and connected serially to obtain a phase shift of more than 360 electrical degrees.

The features of my invention which are be- .lieved to be novel are set forth with particularity reference to the following description taken in connection with the accompanying drawing in which Fig. 1 diagrammatically illustrates an embodiment of my invention in which the phase shifting circuit illustrated provides an adjustablephase shift of more than 180 electrical degrees; Fig. 2 is a vector diagram illustrating certain voltage and current relationships in the phase shifting circuit of Fig. 1; and Fig. 3 is a modification of the circuit of Fig. 1 and illustrates a circuit capable of producing a phase shift of more than 360 electrical degrees.

In Fig. 1 there is shown a source of alternating voltage I and apparatus for producing an alternating voltage variable in phase relative to the phase of this source and of fairly constant magnitude and comprising the electronic discharge device 2 having an output circuit which includes the output terminals 3 across which a suitable load circuit, such as the sweep circuit of a cathode ray tube, may be connected.

'The electronic discharge device 2 comprises an anode 4, a control electrode 5, and a cathode 5, the cathode 8 being connected to ground through a cathode resistance I. The source of alternating voltage I is connected between control electrode 5 and ground. Operating potential for the anode 4 may be supplied from any suitable source, such as the battery 8, through an anode load resistance 9. In the portion of the circuit thus far described, the cathode resistance I and the anode resistance 9 have substantially equal ohmic values so that the electronic discharge device 2 operates as a phase splitting means and produces voltages across the resistances I and 9 which are equal and approximately 180 degrees out of phase.

In order to provide means for shifting the phase of the voltage impressed across the output terminals 3 with respect to the phase of the alternating voltage source I, a phase shifting resistance II is connected between anode l and cathode 6, this resistance having a movable contact l2. A capacitance i3 is connected between the anode 4 and the movable contact 12. Likewise, the upper terminal of the pair of output terminals 3 is connected to the juncture of capacitance l3 and contact l2. When the portion of the phase shifting circuit comprising resistance Ii and capacitance I3 is combined with device 2 and its load resistances, as the movable contact I: is moved along resistance [I from its upper to its lower terminal, a phase shift of substantially 180 degrees in the voltage impressed across the output terminals 3 is obtained. In order to increase this shifting of the phase of output voltage of the circuit to a value of greater than 180 electrical degrees, I provide a capacitance I4 connected between anode 4 and ground.

Operation of the circuit of Fig. 1 to produce a phase shift of more than 180 electrical degrees may best be explained by reference to the vector diagram shown in Fig.2. To assist in explaining the voltage-current relationships in the circult, the anode 4 has been designated as the point P, the cathode 6 as the point C, the grid 5 as point G, and ground as the point 0. In Fig. 2, therefore, the vector Ecp denotes the potential rise between cathode 6 and anode 4. It is assumed that the resistance II is a very large resistance so that a negligible amount of current passes therethrough when the movable contact I2 is at the anode end of resistance II and condenser I3 is short-circuited. The circuit behavior is then the same as though these elements, the resistance I I and capacitance I3, were not present. The alternating current anode-toground voltage rise, Eop, in terms of the input voltage E03, is given by the equation 'I- vr( EL j E p+#R+Rm.)j n In this equation and those which follow hereinafter, the designation of the circuit elements is as follows:

R =internal plate resistance of tube 2 Rc=cathode load resistance 1 Rat=equivalent plate load resistance,

On the other hand when the contact point I 2 is at the cathode end of resistance II, capacitance I 3 is effectively connected between the plate 4 and cathode 6. If we consider resistance I I to be of a very large value, the alternating current cathodeto-ground voltage rise E00 is then In Equation 2 it will be seen that E00 may either lead or lag Eog, depending on the sign of the 7 term in the denominator. If Xnr, is sufficiently large (reactance of capacitor I4 is sufficiently small) compared to REL, the sign of the 7' term will be negative, and Eoc will then lead E0 which condition is shown in the vector diagram of Fig. 2.

Also, from Equation 1, it may be seen that Eop must lag the vector Eog. whatever the value of XEL. This follows because the denominator of Equation 1 has a greater resistance component than the numerator, while containing the same reactance component.

If X121. is large enough to cause Eoc to lead E03, the vector relations are then as shown in Fig. 2. The anode-to-cathode voltage rise Ecp is applied 4 across the circuit comprising resistance II and capacitance I3 in which the phase is adjustable by varying the position of contact I2. A net current I, having a phase angle which leads the voltage Ecp, flows through the circuit comprising resistance II and capacitance I3.

Since Ecp is applied across this circuit, the current I may be varied in phase with Ecp when contact I2 is at the upper terminal of resistance II and the capacitance I3 is short-circuited to a condition where it leads the voltage Esp by degrees, which condition occurs when contact I2 is at the cathode terminal of resistance II. The locus of the potential of point D at the junction of capacitance I3 and contact I2 varies approximately along the arc of a semicircle having the voltage Ecp as its diameter. It should be noted that the resistance of the portion of potentiometer II which is across the capacitor I3 is large compared with the reactance of capacitor I3, and causes but small deviation from a true circle diagram. The output for each of the systems impressed across output terminals 3 is be tween ground and the point D, ground being denoted by the common point 0 of the vectors Eop and E00 in the vector diagram of Fig. 2. From the diagram, therefore, it is seen that the phase position of the vector Eon, the voltage across the output terminals 3, may be varied over a range greater than degrees. The variation in amplitude of the voltage Eop, of course, depends upon the phase angle between the voltages Eoc and E011. When this angle is 180 degrees, the amplitude of the output voltage remains substantially constant. This phase angle between E00 and Eop is determined by the value of the capacitance I4 which controls the value of the quantity XEL in the equations given above. The value of this capacitance need be only suflicient to make the angle between Eoc and Eop equal to 180 degrees, which value may be found by equating the resistive and reactive terms in Equations 1 and 2. Any value of XEL greater than this will allow the circuit to provide a phase shift considerably greater than 180 degrees; in fact, phase shifts up to slightly less than 270 degrees may be obtained. Of course, the amplitude variation increases as the obtainable phase shift increases over 180 degrees.

In the foregoing discussion, the vector diagram of Fig. 2 holds only for a given frequency. However, it may be seen by a study of Equations 1 and 2 that the total obtainable phase shift remains approximately constant over a large range of frequencies, since E00 and Eop maintain practically a constant phase position with respect to E0; as the frequency is varied. Thus the circuit is not limited to use at a single frequency.

In Fig. 3, I have shown a modification of my phase shift circuit in which a variation of greater than 360 electrical degrees may be obtained between the voltage source I and the voltage across any small load impressed across output terminals 3. In this modification of the phase shifting cir-' cuit, a pair of electronic discharge devices 2, 2' have circuit elements corresponding to the elements used in the circuit of Fig. 1 connected thereacross, In Fig. 3 impedance elements, associated with electronic discharge device 2 and corresponding to impedance elements shown in Fig. 1, are designated by similar characters, while corres nding impedance elements associated with electronic discharge device 2 are designated by similar numerals differentiated by priming.

The source of alternating voltage I, is connected between ground and control electrode Ii through a coupling capacitor and a voltage dividin resistance 2|. The use of resistor 2| is not necessary in all applications and this resistor may be omitted when the source of alternating voltage I does not swing the tube grid beyond class A operation, i. e., cause the tube 2 to be cut off during any portion of a cycle. A cathode bias resistor 22 is connected between cathode 6 and cathode load resistance 1 and a grid leak resistance 23 is connected between controlielectrode 5 and the common point of resistances 22 and I. The phase shifting potentiometer l l is connected between anode l and the common point of cathode resistances 22 and The movable contact I2 is connected to the control electrode 5' of electronic discharge device 2' through a coupling capacitance 25, The output terminals 3' of the phase shifting circuit are connected respectively to ground and the movable contact l2 on phase shifting potentiometer l I. In applications where desired. the contacts l2, l2 may be mechanically linked for unicontrol operation. When so connected, as the contacts l2 and I2 are moved from the anode terminals of their associated resistances to the cathode terminals thereof, the

voltage impressed across output terminal 5 is shifted with respect to the input voltage I through an angle greater than 360 electrical degrees, the exact angle of the phase shift being determined by the values ofcapacitances H, I 4' according to the considerations pointed out in connection with the discussions of the circuit of Fig. 1 and the vector diagram of Fig. 2.

By way of illustration only and not in any sense by way of limitation, the following representative values are those whichhave been found suitable in a particular phase shifting receiver embodying my invention and constructed according to the circuit of Fig. 3. In this receiver a type GSN'TGT tube was employed in the dual capacity of the discharge devices 2, 2". The values of the impedance elements used are as follows:

Load resistances I, I, 9, 9 ohms 22,000 Potentiometers II, II megohms 2 Capacitances ll, ll,

l3, I3 micromicrofarads 3,300

I The frequency of the input of the source of alternating voltage was of the range of 300to 600 cycles, and it was found that with the circuit elements given above, the amplitude of the output voltage and range of obtainable phase shift remained substantially constant over this frequency range. A phase shift of considerably more than 360 degrees was obtained, As the phase controls were rotated, the amplitude of the output varied about In applications where this amplitude variation is objectionable, capacitors l4 and H may be reduced in size to give only 360 degrees phase shift, in which case the amplitude variations with phase shift will be reduced to about 5%.

From the foregoing. it may be seen that my invention provides an improved phase shift circuit which may be employed to obtain shifts beages through a range of greater than 360 electrical degrees, a range particularly desirable for use in conjunction with sweep circuits of cathode ray tubes. The component elements of my phase shifting circuit are readily available and easily assembled and require no transformer connections with tap adjustments.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since various modifications may be made. and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent inthe United States is:

1. In a phase shift network, an electron discharge device having an anode, control electrode, and a cathode, a source of operating voltage having its positive terminal connected to said anode through a resistance and its negative terminal connected to said cathode through a resistance, means to supply an alternating voltage between said control electrode and cathode, a resistance connected between said anode and cathode, and

a load circuit connected between said negative terminal and a point variable along said last resistance in accordance with the phase shift desired.

2. In a phase shift network, an electrondischarge device having an anode, control electrode, and a cathode, a source of operating voltage having its positive terminal connected to said anode through a resistanceand its negative terminal connected to said cathode through a resistance, a source of alternating voltage connected between said control electrode and said cathode, a resistance connected between said anode and cathode, a load circuit connected between said negative terminal and a point variable along said last resistance in accordance with the phase shift desired, and means to increase said phase shift to a value in excess of 180 degrees as said point is moved from one end of said last resistance to the other.

3. In a phase shift network, an electron discharge device having an anode, control electrode, and a cathode, a source of operating voltage having its positive terminal connected to said anode through a resistance and its negative terminal connected to said cathode through a resistance,

means to supply an alternating voltage between said control electrode and cathode, a resistance connected between said anode and cathode, a reactance connected between said anode and said negative terminal, and a load circuit connected between said negative terminal and a point variable along said last resistance in accordance control electrode and cathode, a source of opertween the phases of incoming and outgoing voltating voltage having opposite terminals connected to said anode and cathode through respective resistances, a capacitance connected between said anode and the negative terminal of said source of operating voltage, a resistance connected between said anode and said cathode, a second capacitance connected between said anode and a movable contact on said last resistance, and an output circuit connected between said movable contact and said negative terminal, said capacitances having such values relative to said resistances that movement of said contact along said second resistance is effective to shift the phase of the alternating voltage impressed across said output circuit through an angle greater than 180 electrical degrees.

5. In combination, a source of alternating voltage, apparatus for producing an alternating voltage variable in phase relative to the voltage of said source and of substantially constant magnitude and comprising means connected to said source for producing equal and opposite voltages with respect to a point of fixed potential, said means including a pair of terminals, a resistance connected across said terminals and including a movable contact, a first reactance connected between said movable contact and one of said terminals, a second reactance connected between said one terminal and said point, and an output circuit connected between said movable contact and said point, said second reactance having such a value that the phase variation produced in said output circuit as said contact is moved between the terminals of said resistances is at least 180 degrees.

6. In combination, a source of alternating voltage, apparatus for producing an alternating voltage variable in phase relative to the voltage of said source and comprising a pair of electron discharge devices each having an anode, a cathode, and a control electrode, a source of operating voltage having its positive terminal connected to said anodes through resistances and its negative terminal connected to said cathodes through resistances, each of said devices having a resistance and a capacitance connected between the anode thereof and ground, each of said last resistances having movable contacts thereon, means connecting said source of alternating voltage between the control electrode of one of said devices and ground, means connecting the control electrode of the other of said devices to the movable contact associated with said one device, and output terminals connected between the other of said movable contacts and ground, said capacitances having such values that movement of said contacts along said resistances is efiective to shift the phase of the alternating voltage impressed across said output terminals through an angle of at least 360 electrical degrees.

- SEYMOUR BERKOFF.

REFERENCES CITED The following references are oi. record in the file of this patent:

UNITED STATES PATENTS