US2521878A

US2521878A - Sector scan circuit

Info

Publication number: US2521878A
Application number: US604038A
Authority: US
Inventors: Merle A Starr
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-07-09
Filing date: 1945-07-09
Publication date: 1950-09-12
Anticipated expiration: 1967-09-12

Description

Sept. 12, 1950 M. A.-STARR 2,521,878

SECTOR SCAN CIRCUIT Filed July 9, 1945 SAWTOOTH GENEQATOR AMPLIFIER L,

SAWTOOTH L GENERATOR AMPLBIFIER i INVENTOR. MERLE A. STARR WM; QM.

ATTORNEY Patented Sept. 12, 1950 Merle A. Starr, Belmont, Mass, assignon by mesne assignments, to. the United States .of America as represented by the Secretary-of Var Application July 9,1945, sh i'al Na. stin s This invention relates to electrical means for producing an output voltage or current which is a given function of an input voltage or current, and more particularly to electrical means whose output variation with respect to the input may be expressed as an equation of the second degree.

One object of this invention is to provide as an output from an electrical circuit a voltage whose magnitude varies as the sum (or difference) of first and second power functions of a variable input voltage. Another object of the invention is to provide simple, accurate, and reliable'means for achieving a variation of the kind mentioned: A further object of the invention is to provide means for changing the angle at which a radial sweep of a cathode ray tube electron beam em'a-j nates from the center of the cathode ray tube and yet maintain the amplitude of the sweep unchanged. H

Other objects and advantages of the invention will appear more fully from the detailed description contained herein.

Referring now to the drawings: Fig. 1 is a circuit diagram illustrating one em? bodiment of the invention; Fig. 2 illustrates in diagrammatic form a yolr'e' used in producing electromagnetic deflection of the electron beam of a cathode ray tube; and Fig. 3 illustrates the vector field components resulting from currents in the coils of Fig. 2.

Referring now to Fig. 1, there is illustrated a preferred embodiment of this invention having a particular application which will appear more fully herein. A signal is fed through condenser I l, thus appearing across potentiometer l5, 'and a portion thereof is picked up by sliding contact it of potentiometer l5 and, fed to grid I2 of vacuum tube 10, which has also a plate H and cathode l3. Cathode resistor 11 and plate resistor iii are equal in value, and thealternating component of voltage at plate I l is equal and out of phase with the alternating component a pean ing at cathode [3. The alternatin components of plate and cathode voltages are fed through condensers l9 and 20, respectively, to grids 2] and 22 of tubes 23 and 24 across grid resistors 25 and 2t. Cathodes 2! and 2B of tubes-23 and 24 are joined to sliding contact 23 of potentiometer 36 and thus have a variable cathode resistor in common. Resistors 3i and 32, chosen equal in this embodiment, are connected to a resistor 33 at their junction 34, and the other sides of resistors 3| and 32 are connected to

plates

35 and 36, respectively, of tubes 23 and 24. Plate voltage supply is fed through resistor,

Claims. (01. 315 -24) so that 'iesist'on33 forms a common plate load for tubes 23 and 24, and resistors 3| and 32 form separate plate loads, for said tubes respectively. The outputs from this'circuit are taken from junctions 35fand 36" of resistor 3.! with nlateiill and ;resistor.;32 with plate 36,respectively.' Lead. 3! conductsthe output voltage from junction 35 to saw-tooth'generator'and amplifier 39, and lead 38 conducts the output voltage from junction'tti to saw-tooth generator and amplifier 4! Both of the saW-toothgenerators and amplifiers 39 and '43 in this instance have like characteristics and areadapted .t provide currentsof. saw-to th form," rather than voltages of saw-tooth form, as it is contemplated that the output be used to provide electromagnetic sweep deflection of a, oathode ray tube circuit. Furthermore, the sawtooth generators and

amplifiers

39 and 40 are adapted to respond With output currents the peak values of which'are respectively modulated by the alternatingvOItagecQompQnents of the signals applied through leads 3? and 38. This may be accomplished, fouinstance by constructing sawtooth generatoriaiid amplifier 39 (andsimilarly 40) of any standard saw-tooth generator coupled with an amplifier the peak current output of which is varied, by the alternating voltage on lead 31. I

Referring noWto Fig. 2-,-there is illustrated a yoke of some mag'netic substance' such as soft iron wound -by 'coils 42 and '43. AS current h from amplifier- 39 passes through the windings of coils 42;flux Withiuthe' yoke M has the'direc'tion shown 'by arrows for the-direction of current shown for'h; Thus, a leakage flux' is produced lnslde the yoke'having a direction and magnitude indicated bythe vector H1. Likewise, a vector flux is produced by current i2 in space quadra ture with H1 which will be termed I-Iz, these vegtors and the resultant vector being shown in Figi 3." I-Iowev'er, saw-tooth generators and

ainplifiers

39 and 40 are in time-phase, and thereiorevector's H1 and l lz are in timephaseand. it

wi1l be'pbviously Sufi cientito treat of their-mash mutn'values' Vectors Hl and Hz. as shown are assumed-equal in magnitude when no signal is introduced at grid 12 of tube I0 and consequently Since the displacement of the electron beam is proportional to the magnitude of the flux vector, although at right angles thereto, the maximum displacement of the electron beam corresponds to a maximum range scale indicated by the amount of radial deflection of the electron beam. When the resultant flux H is shifted an angle A from resultant H, it is desirable to have-the magnitude of H remain the same as the magnitude of H, so that range representation will not be distorted or out of scale. The present invention affords a highly accurate means of obtaining such result without rotating the yoke.

To analyze the variation desired in the modulating voltages on leads 3! and 38, we will let h represent the difference in absolute value between H2 and H2. Referring to absolute values, if H1 and H2 are each increased and decreased respectively by it so that the new resultant H is rotated an angle A from the old resultant H, then the following relations can be written:

However, a new resultant having these components is too great in magnitude, and to correct this discrepancy the right-hand terms of Equations 1 and 2 should be multiplied by cos A. This gives:

(3) H1'=H1(1tan A) cos A=H1(COS Asin A) (4) H2'=H2(1+tan A) cos A=Hz(cos A-i-sin A) If angle A is not large, it may be established Therefore, currents 2'1 and i2 should have the form:

wherein K is some constant. This form of current is readily achieved by the invention if a signal is applied to grid l2 of tube of an alternating component proportional to A. Assuming that currents flow in tube III in linear fashion with the signal voltage on grid l2 of tube H), the signals at grids 2| and 22 of tubes 23 and 24 will be proportional to -A and A respectively. The current flowing in tube 23, including'second order terms, has the form:

(9) z's=abA-cA I and the current flowing in tube 24 has the form:

(10) i4=a+bA-cA Let V represent the value of plate supply voltage to resistor 33, then the voltage V1 at junction 35' has the form:

where m is the value of resistor 3| or 32, and 11 is the value of resistor 33.

Therefore, by choosing appropriate values for resistors 3| and 32 (which are equal to each other in this embodiment) and resistor 33, and by 4 choosing an appropriate bias through adjustment of the common cathode resistance 30, it is possible to obtain the proper ratio between the coeflicients in Equations 11 and 12 so that these have the form of Equations 7 and 8, respectively, except for the constant voltage term and the inversion of sign. A change in sign of the alternating current components is obtained in amplifiers'39'and 40. In this fashion, currentsii and 2': may be modulated so that vector H maintains a fixed magnitude, and angle A changes in accordance with the input signals to grid 42.

The system is particularly valuable where angle A changes rapidly up to values both positive and negative as high as 22 /2, and represents the angle from a, reference direction in the horizontal plane in radio echo detection apparatus. The electron beam of the cathode ray tube will accordingly change path in exact synchronism with the variations of the angle in the horizontal plane and yet maintain the proper range scale. A similar analysis shows that the input signal to grid I2 of tube l0 may be proportional to the tangent of the angle A, and a like approximation is possible, expressed in powers of the tangent of the angle. The invention is thus highly useful in depicting on a cathode ray tube complicated scanning motions in radio echo detection apparatus which involve rapid angular deviations from a given axis. For one such apparatus reference is made to copending application of Albert M. Grass, executed March 20, 1945, for scanning apparatus. In the Palmer scan motion mentioned in that case, a sine wave generator having a frequency of 30 C. P. S. may complete one cycle for each revolution of the antenna axis in its conical search pattern. This voltage is then proportional, with a high degree of accuracy for reasonably small angles of the axis of the cone with the horizontal plane, to the tangent of the angle which the projection of said axis on the horizontal plane makes with the axis of radiation. Thus, the sine Wave generator is used to provide a signal proportional to tan A, where A is the said angle of the axis of radiation with the axis of conical search pattern projected on the horizontal plane. Using an approximation correct to terms including tan A, it is readily shown that Equations '7 and 8 have the same form for tan A, if A is small, as for A. That is, A may be replaced by tan A in all the Equations 7, 8, 11 and 12 when the signal is proportional to tan A. With re gard to design considerations which may be involved in the type of circuit disclosed herein, it is not essential that both plate voltages be utilized as outputs, nor that

resistors

31 and 32 be equal. This was done in the present instance because the desired voltage variation for controlling the flow of current in the yoke coils is easily obtained by using both plate voltages. In general, the plate current through a tube may be considered in the form of a Taylor's expansion in terms of signal voltage, and the coefficients may be calculated or estimated by methods known in the art either experimentally or from tube char acteristic curves. For example, see Principles of Radio Engineering, by R. S. Glasgow, p. 337 et seq., McGraw-HillBook Co., Inc., 1936. Thus, once the principles of the invention are understood, it is not difiicult to apply them in order to obtain a desired result, when the output voltage is taken from the plate of one tube which has part of its plate load in common with another tube, and the relation between the grid signals is known. Such devicesas the variable cathode resistor in the circuit of Fig; 1 will assist in obtaining the desired result by changing the ratio of the coefficients in the series.

Many variations will be apparent to those skilled in the art, and therefore it is not desired. to restrict the scope of the appended claims to the precise embodiment as shown.

What is claimed is:

1. The method of obtaining a voltage which varies with a signal voltage in accordance with the terms of a second degree equation, said method comprising the steps of supplying said signal voltage 180 out of phase to the grids of two vacuum tubes, causing the current in both of said vacuum tubes to pass through a single resistance, and causing the current of one of said tubes to pass through a resistance which carries only the current passing through said one tube, the characteristics of said vacuum tubes in conjunction with the arrangement of said resistances bein eifective to produce a voltage which is substantially the sum of terms representative of a fixed voltage, terms proportional to the signal voltage, and terms proportional to the square of the signal voltage.

2. An electrical circuit for producing two output voltages, the first of which varies substantially in accordance with an input voltage, A, and equals the algebraic sum of (Z+bA+CA and the second of which varies substantially in accordance with said input voltage, A, and equals the algebraic sum of abA+CA a, b, and being constants, said circuit includin two vacuum tube amplifiers having a common cathode resistor connected to ground, two equal and separate plate loads, a source of positive potential, and a common resistor connecting said plate loads to said source of potential, paraphasing means for deriving from said input voltage, A, two equal components 180 out of phase from one another, means for impressing one of said components on the control grid of one of said amplifiers and the other of said components on the control grid of the other of said amplifiers, and utilization means coupled to the plate of each of said amplifiers, for utilizing the output voltages of said amplifiers.

3. A circuit as set forth in claim 2, wherein said utilization means comprises two sets of sawtooth current generators and amplifiers, and also including a magnetic yoke and two coils arranged thereon so as to produce two sets of lines of magnetic flux separated by 90, each of said coils being coupled to the output of one of said sets of generators and amplifiers, whereby said coils produce two perpendicular magnetic fields having magnitudes varying, respectively, in accordance with the two equations set forth in claim 2.

4. A circuit as set forth in claim 3, wherein said paraphasing means is a paraphase amplifier having plate and cathode loads, the two 180 out of phase components being taken from said plate and cathode loads, respectively.

5. A circuit as set forth in claim 2, wherein said equal and separate plate loads are resistive means and said common cathode resistor is vari- 6 able.

6. An electrical circuit for producing an output 6 J voltage which varies substantially in accordance with an input voltage representing a given angle and equals the algebraic sumof a constant, a second constant multiplied by said input voltage,

and a third constant times the square of said input voltage, said circuit including two vacuum tube amplifiers having a common cathode resistor connected to ground, two separate plate loads, a source of positive potential, and a common re- 10 sister connecting said plate loads to said source of potential, paraphasing means for deriving from said input voltage two equal components 180 out of phase from one another, means for impressing one of said components on the control grid of one of said amplifiers and the other of 7. A circuit as set forth in claim 2, wherein said utilization means includes sawtooth current generator and amplifier means, and also including a circular magnetic yoke and two coils arranged thereon so as to produce two sets of lines 5 of magnetic flux separated by 90, one of said coils being coupled to the output of said amplifier means, whereby said coils produce two perpendicular magnetic fields the resultant of which varies in accordance with said given angle.

8. A circuit as set forth in claim 7 wherein said paraphasing means is a paraphase amplifier having plate and cathode loads, the two 180 out of phase components being taken from said plate and cathode loads, respectively.

5 9. A circuit as set forth in claim 6, wherein said plate loads are resistive means and said common cathode resistor is variable.

10. An electrical circuit for producing a, magnetic field at a desired angle, comprising a first circuit for producing a voltage A, representative of the desired angle, a second circuit, connected to said first circuit, for generating an output voltage having the magnitude abA+cA where a, b and c are constants, a third circuit con- 5 nected to said first circuit, for generating an output voltage having the magnitude a-l-bA-l-cA a pair of mutually perpendicular deflection coils, and means for generating currents in said two coils varying in accordance with said output voltages of said second and third circuits, respectively, whereby the resultant of the magnetic fields of said coils is at said desired angle.

MERLE A. STARR.

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

UNITED STATES PATENTS Number Name Date" 1,907,225 Van Der Pol et al. May 2, 1933 2,265,848 Lewis Dec. 9, 1941 2,395,966 Goldberg Mar. 5, 1946 5 FOREIGN PATENTS Number Country Date 476,067 Great Britain Dec. 1, 1937