US3725772A

US3725772A - Circuit arrangement for generating a phase-shiftable voltage

Info

Publication number: US3725772A
Application number: US00162037A
Authority: US
Inventors: D Ratzel
Original assignee: Bruker Biospin GmbH
Current assignee: Bruker Biospin GmbH
Priority date: 1970-07-30
Filing date: 1971-07-13
Publication date: 1973-04-03
Anticipated expiration: 1990-04-03
Also published as: DE2037762B2; DE2037762A1; GB1345274A

Abstract

A circuit arrangement for the generation of a voltage, the phase position of which relative to a reference voltage can be shifted within wide limits, preferably between 0* and 360*, characterized in that said circuit arrangement comprises a device for generating from the reference voltage at least three auxiliary voltages having a certain phase shift relative to each other, that an ohmic resistor with taps is provided to which the auxiliary voltages are supplied, that the geometric distance of the taps from each other is proportional to the phase angle of the auxiliary voltages connected to the taps, and that the ohmic resistor is provided with a wiper to which the output terminal of the circuit arrangement is connected.

Description

United States Patent [191 Ratzel [541 CIRCUIT ARRANGEMENT FOR GENERATING A PHASE-SHIFTABLE VOLTAGE [75] lnventor: Dieter Ratzel, Forchheim, Germany [73] Assignee: Bruker Physik AG, Karlsruhe, Germany [22] Filed: July .13, 1971 [21] Appl. No.: 162,037

[30] Foreign Application Priority Data July 30, 1970 Germany ..P 20 37 762.2

[52] U.S. Cl. ..323/10'5, 318/693, 323/44 F,

323/125 [51] Int. Cl. ..G05f 1/12 [58] Field of Search ..318/693; 323/44 F, 94,10 S, 323/109,124,125,126

[56] References Cited UNITED STATES PATENTS 3,056,921 10/1962 Flarity ..323/125X 2,864,924 12/1958 Mayer.....

mm HIE/Midi? l 8 51 Apr. 3, 1973 Schooley et al. ..318/693 3,196,368

Potter ..323/124 X FOREIGN PATENTS OR APPLICATIONS 57 ABSTRACT A circuit arrangement for the generation of a voltage, the phase position of which relative to a reference voltage can be shifted within wide limits, preferably between 0 and 360, characterized in that said circuit arrangement comprises a device for generating from the reference voltage at least three auxiliary voltages having a certain phase shift relative to each other, that an ohmic resistor with taps is provided to which the auxiliary voltages are supplied, that the geometric distance of the taps from each other is proportional to the phase angle of the auxiliary voltages connected to the taps, and that the ohmic resistor is provided with a wiper to which the output terminal of the circuit arrangement is connected.

6 Claims, 2 Drawing Figures PATENTEUAPR3 H973 SHEET 1 OF 2 IN VENTOR DIET'ER RATZEL.

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ATTORNEYS CIRCUIT ARRANGEMENT FOR GENERATING A PHASE-SHIFTABLE VOLTAGE The present invention relates to a circuit arrangement for the generation of a voltage the phase position of which can be shifted in relation to a reference voltage within wide limits, preferably between and 360.

Circuit arrangements of this type, frequently called phase shifters, are known in various embodiments. They comprise, for example, combinations of effective resistance and reactance means, i.e. combinations of ohmic resistance means with capacitors and/or inductance means. Phase shifters, in particular for higher frequencies, are also known, said phase shifters using lines of a length corresponding to the half of or to the total wave length of the provided frequency range and from which a voltage of any phase position with respect to the input voltage, serving as reference voltage, can be tapped by means of a wiper. However, the disadvantage of all these phase shifters is that the arrangement must be readjusted to achieve the same phase position if the feed-frequency changes, since the mechanical angle of rotation at the setting member for different frequencies corresponds to different electrical phase rotation angles. This is attributable to the fact that, in the case of combinations of effective resistance the reactance means, the resistance value of the reactance means and, in the case of phase shifter arrangements with lines, the wave lengths on the lines are both frequency-dependent.

Consequently, in the case of frequency changes or frequency changeovers the phase shifter must be readjusted accordingly to achieve the same phase position with respect to the reference voltage again at the phase shifter output. This characteristic of the known phase shifters leads to a very time-consuming adjustment of sets which are equipped with such phase shifters and is considered inconvenient by users of such sets.

It is the object of the present invention to provide a circuit arrangement in which the phase shift of the output voltage in relation to the input voltage is mainly independent of the frequency.

The object according to the present invention is achieved by providing the circuit arrangement with a device for generating from the reference voltage at least three auxiliary voltages which are shifted in phase with respect to each other, by providing an ohmic resistor having taps to which the auxiliary voltages are applied, by spacing the taps at geometric distances which are proportional to the phase angles of the auxiliary voltages connected to the taps, and by providing the ohmic resistor with a wiper to which the output terminal of the circuit arrangement is connected.

The auxiliary voltages applied to the taps generate a periodically alternating field at the ohmic resistor, said field having at any point of the ohmic resistor a constant phase position relative to the reference voltage, which is independent of the frequency. Adjustment of the wiper, independently of the frequency, is only required for shifting the phase position of the output voltage relative to the reference voltage. A particularly advantageous embodiment is achieved by employing a ring-shaped film resistor as ohmic resistance. An alternating rotary field is produced on this film resistor, the corresponding voltage of which can be picked up by the wiper at any point of the resistor. In this connection, the phase position of the voltage picked up by the wiper in a given angular position is phase-locked to the reference voltage. The alternating rotary field is produced by using at least three auxiliary voltages. However, it is also possible to employ any higher number of auxiliary voltages and any correspondingly higher number of taps. If a ring-shaped resistor is not used, the two terminal points of the resistor are preferably supplied with the same auxiliary voltage; the remaining auxiliary voltages are applied to the other taps.

The auxiliary voltages need not be shifted in phase with respect to each other by the same angle. However, the phase rotation angles of the auxiliary voltages relative to each other will generally correspond to a common value and the taps of the ohmic resistor will be spaced at correspondingly equal distances. In a preferred embodiment of the present invention four auxiliary voltages, each being shifted by relative to each other, are employed and the ohmic resistor is provided with four taps which are spaced at equal distances from each other. In this embodiment, the ohmic resistor is also designed as ring-shaped film resistor having taps at four points which are staggered by 90. However, it would also be possible to use a rectilinear ohmic resistor, for example a taut slide wire which is provided with equidistant taps and the two ends of which are connected to each other to form one of the taps.

As far as low frequencies are concerned, three auxiliary voltages which are shifted relative to each other by can be generated in a simple manner by means of electromagnetic machines, as also used for generating industrial three-phase current, for example in synchro systems and the like. The use of four auxiliary voltages, each being in phase quadrature, offers the advantage that phase-locked generation of said auxiliary voltages is also possible in the high frequency range independently of the frequency. In a preferred embodiment of the invention the device for generating the four auxiliary voltages is provided with two voltage dividers which are supplied with the reference voltage and consist of an ohmic resistor and of a reactance means having the same resistance value, the taps of said voltage dividers being connected to the primary winding of one transformer each, said transformers each having a winding for generating two voltages which are shifted in phase relative to each other by In this case, the two voltage dividers are designed such that their voltage divider taps are connected to voltages which are shifted in phase relative to the reference voltage by 45 the voltage at the tap of the one voltage divider being shifted relative to the reference voltage in the opposite direction as is the voltage at the tap of the other voltage divider. The two voltages at the voltage divider taps therefore have a phase difference of 90. These voltages are applied to the primary windings of the two transformers each of which generates two voltages which are shifted in phase by 180. Consequently, this device generates a total of four voltages which are oppositely phased in pairs; in this connection the voltage pairs have a phase spacing of 90 relative to each other: consequently, four voltages in phase quadrature are obtained.

In a preferred embodiment of the invention a buffer amplifier is connected between the voltage divider tap and the transformer in both cases. This prevents the transformers from reacting upon the voltage dividers, which is advantageous because loading of the voltage dividers causes a certain phase rotation which should be avoided as far as possible.

One of the two voltage dividers may, for example, by provided with an inductance means and the other one with a capacitance means; in this case the ohmic resistors of the two voltage dividers are connected to a common terminal of the reference voltage source. The phase rotations at the two voltage divider taps, relative to the reference voltage, are +45 and/or 45, if the ohmic resistance of each voltage divider is equal to the reactance value of the same voltage divider. In a preferred embodiment of the invention the two voltage dividers have equal reactances and are connected antiparallel. The two voltage dividers in this case either comprise one capacitance means and one effective resistance means or one inductance means and one effective resistance means. In order to achieve oppositely directed phase rotations, the voltage dividers are connected antiparallel; i.e. the reactance means of the one voltage divider and the ohmic resistor of the other voltage divider are each connected to the same terminal of the reference voltage source. At the same time at least one resistor of each voltage divider is variable in order to achieve the same effective resistance and reactance values of the voltage dividers even in the case of different frequencies.

In a particularly preferred embodiment of the invention electrically variable reactance means, in particular capacitance diodes, are provided, controlling of the reactance value of said diodes being dependent on the difference of the amplitudes of the voltages at the voltage divider taps or one the voltages at the buffer amplifier outputs which are proportional to said difference. This embodiment of the present invention offers the special advantage that the reactance value is automatically maintained at the same value as the ohmic resistance. If the frequency of the reference voltage changes, for example, the amplitudes of the voltages at the voltage divider taps also change but in the opposite direction. The amplitude of the one voltage increases and the amplitude of the other voltage decreases. This difference'controls the electrically variable reactance.

means in such a manner that the variation is compensated for again so that after controlling, the voltages at the voltage divider taps have the same amplitudes.

In a preferred embodiment an automatic gain control amplifier is provided which responds to the difference in the amplitudes of the voltages at the voltage divider taps or of the output voltages of the buffer amplifiers, the control terminal of the variable reactance means being connected to the output of said automatic gain control amplifier. Anappropriate design of the automatic gain control amplifier permits the design of the circuit in such a manner that resetting of the value of the reactances is sufficiently precise in the case of frequency changes that the differences in the voltage amplitudes at the voltage divider taps remain negligeably small.

In preferred embodiments of the invention, wherein two voltages which-are shifted in phase relative to each other by 180 are generated by means of a transformer, each of said transformers has a secondary winding with a center-tap connected to ground. In the circuit ar rangements having four auxiliary voltages the two free ends of the secondary windings of both transformers are connected to the four taps of the ohmic resistor.

Further details and embodiments of the invention will become apparent from the following specification in which the invention is described and explained in detail, reference being made to the accompanying drawing. In other embodiments of the invention, the features apparent from the specification and the drawing may be applied either individually or in any combination of a plurality of such features. In the accompanyin g drawing FIG. 1 is a basic circuit diagram of a phase shifter according to the present invention, and

FIG. 2 is a schematic circuit diagram of a circuit arrangement for the generation of four auxiliary voltages each being in phase quadrature relative to the other.

The output terminals 2 and 3 of a reference voltage generator 1 supply a reference voltage the frequency of which can be adjusted or selected. Output terminal 3 is connected to ground; from output terminal 2 a line 4 leads to a device 5 for the generation of a plurality of auxiliary voltages which are shifted in phase relative to the reference voltage by a given angle. These auxiliary voltages are picked up at

output terminals

6, 7, 8, and 9 and applied to a ring-shaped film potentiometer 14 which has a continuous ring-shaped resistive film to which four taps 15, 16, 17, and 18 are connected, said taps being staggered relative to each other by The ring-shaped film resistor 14 is provided with a wiper 19 which can be turned through 360, said wiper sliding on a resistance path and being connected to an output terminal 21 via line 20. The device 5 has a common ground connection 22 for all output terminals 6 through 9; the second output terminal 23 is also connected to ground.

Consequently, the ring-shaped film resistor 14, at four points staggered by 90, is supplied by four voltages which are continuously in phase quadrature relative to each other. Thus, an alternating rotary field is generated on the ring-shaped film resistor. Consequently, it is possible to pick up a voltage from any point of the ring-shaped film resistor 14, the phase position of said voltage relative to the reference voltage being adjustable at the output terminals 2 and 3 over a maximum range of 360. In this connection continuously variable adjustment is possible since an appropriately selected film resistor permits continuous scanning with very high resolution.

The device 5 for generating the four auxiliary voltages which are in continuous phase quadrature is shown in detail in FIG. 2. Line 4 leads from output terminal 2 of the reference voltage source 1 to the two voltage dividers 24 and 25 which comprise

ohmic resistors

26 and 27 and reactance means 28 and 29, respectively. The ohmic resistor 26 of the voltage divider 24 and the reactance means 29 of the voltage divider 25 are both connected to line 4. The reactance means 28 of the voltage divider 24 and the ohmic resistor 27 of the voltage divider 25 are both connected to ground. A line 32 leads from a voltage divider tap 30 of voltage divider 24 to a buffer amplifier 34. From a voltage divider tap 31 of voltage divider 25 a line 33 leads to the input of a buffer amplifier 35. These

buffer amplifiers

34 and 35 are high frequency amplifiers with constant amplification which is independent of the frequency over a large frequency range. In the effective frequency range these

high frequency amplifiers

34 and 35 have no phase rotation of the output signal relative to the input signal. Even if phase rotations occur in the high frequency amplifiers, they have no negative effect as long as the phase rotations are equal in the two high frequency amplifiers. A line 38 leads from one output 36 of the buffer amplifier 34 to a transformer 40. Similarly, a line 39 leads from one output 37 of the buffer amplifier 35 to transformer 41. The transformers 40 and 41, which are identical to each other, have a primary winding 42 or 43 into which the output signal of the

buffer amplifiers

34 or 35 is fed. In addition, each of the two trans-formers 40 and 4lhas a secondary winding 44 or 45 with a center-tap 46 or 47 which is connected to ground. The free ends of the windings 44 and 45 lead to the

output terminals

6 and 8 or 7 and 9. The voltage at terminal 6 is shifted in phase by 180 relative to the voltage at terminal 8. The same applies to the voltage at terminal 7 in relation to the voltage at terminal 9.

Two voltages are present at the voltage divider taps 30 and 31 and are shifted in phase by 90 relative to each other and by 2 45 relative to the reference voltage as long as the condition R X is fulfilled. This con dition can be easily met for a given frequency by varying the effective resistances or reactances. However, the reactance changes with frequency so that, in the case of frequency changes, the voltages at the voltage divider taps 30 and 31 have different values. The volta ges at the voltage divider taps only have exactly l/ V2 times the value of the reference voltage if the value of the effective resistances is the same as that of the reactances. If the resistance value of the reactances changes as a result of frequency changes, the amplitudes of voltages at the voltage divider taps 30 and 31 change inversely: the one voltage increases and the other voltage decreases. These two voltages are amplified by the same factor and consequently, different voltages are present at the output terminals 36 and 37 of the two

buffer amplifiers

34 and 35. From the output 36 of the buffer amplifier 34 and from the output 37 of the buffer amplifier 35 series connection arrangements, each comprising a diode 48 or 49 and a resistor 50 or 51, lead to the input of an automatic gain control amplifier 52. In this arrangement the anode of diode 48 and the cathode of diode 49 are connected to the output of the

buffer amplifier

34 or 35, respectively. Consequently, a voltage, which is proportional to the difference of the voltages at the outputs 36 and 37 of the

buffer amplifiers

34 and 35, is applied to the input of the automatic gain control amplifier 52. From automatic gain control amplifier 52 a line 53 leads to the reactance means 28 and 29 of the two voltage dividers 24 and 25. A control voltage is fed via line 53 to the two reactance means 28 and 29 for which capacitance diodes are preferably used, said control voltage varying the capacitance and hence the reactance of said capacitance diodes until the two voltages at the outputs of the

buffer amplifiers

34 and 35 practically have the same amplitudes. Premagnetized inductance means can be also utilized instead of capacitance diodes, the inductance of the former being adjustable by means of a d.c. control current. By means of the control signal via line 53 the two reactance means 28 and 29 are changed in the same direction, i.e. increased or decreased. However, as the reactance means are arranged at different points in their respective voltage dividers due to the antiparallel connection of the latter, the reactance changes act as oppositely directed voltage variations at the voltage divider taps 30 and 31 such that the amplitudes of the voltages at the voltage divider taps 30 and 31 are matched. I

The automatic gain control amplifier 52 serves as proportional controller at the input of which a certain signal must always be present in order to generate a desired output signal. Said input signal corresponds to a small amplitude difference of the two output voltages of the

buffer amplifiers

34 and 35, said difference being always present. This amplitude difference, however, is negligeably small if the automatic gain control amplifier has a very high amplification, which is always possible.

The phase shifter described offers the advantage that the angle of rotation of the wiper 19 corresponds to the electrical phase rotation for all frequencies employed, i.e. that, irrespectively of the frequency being employed at any given time, the wiper 19 can be provided with a scale which is directly graduated in degrees of electrical phase rotation. The circuit arrangement according to the present invention can be easily employed for very large frequency ranges. For this purpose it is necessary only to switch over the phase shifter elements in device 5 when the frequency band is switched over. Another advantage of the circuit arrangement described is that a high resolution can be obtained which practically depends only on the resolution of the resistive film and on the fine adjustment of the wiper 19. The resolution of the resistive film can be kept at a very high level by means of an appropriate surface treatment. It is also possible to achieve a very fine adjustment of the wiper by using an appropriate design of the gear driving the wiper and by choosing a wiper shape with an appropriate inherent rigidity.

Instead of device 5, which supplies four auxiliary voltages being in phase quadrature, other devices can also be used to supply at least three auxiliary voltages the phase position of which is maintained relative to each other independently of the frequency.

Having thus fully described our invention, what we claim as new and wish to secure by Letters Patent is:

1. Circuit arrangement for producing a voltage, the phase position of which is adjustable within wide limits with respect to a reference voltage, preferably between 0 and 360, comprising means for producing four auxiliary voltages from the reference voltage, exhibiting a phase shift of with respect to one another, an ohmic ring resistor having four taps which are spaced by 90 on the surface of said ring resistor and are connected to receive a respective one of said auxiliary voltages, the ring resistor being provided with a wiper to which is connected the output terminal of the arrangement, wherein said means for producing the four auxiliary voltages includes two voltage dividers supplied with the reference voltage and consisting of respectively one resistor and one reactance element, a pair of transformers, the primary winding of each respective transformer being connected to the center connection of a respective one of the voltage dividers, each transformer having a winding for the production of two voltages phase shifted with respect to each other by 180, and at least one resistor of each voltage divider being variable, and means for controlling the resistance value of the variable resistor of each voltage divider in dependence on the difference of the amplitudes of the voltages at the voltage divider center connections in such a manner that the resistance and the reactance element are equal in impedance value.

2. The circuit arrangement according to claim 1, characterized in that one buffer amplifier each is connected between the voltage divider center connections and the transformers.

3. The circuit arrangement according to claim 1, characterized in that each of the two transformers has a secondary winding with a cententap which is connected to ground and that the two free ends of the secondary windings of both transformers are connected to the four taps of the ohmic resistor.

4. The circuit arrangement according to claim 1,

characterized in that the two voltage dividers are provided with identical reactance elements and are arranged in antiparallel connection.

5. The circuit arrangement according to claim 4, characterized in that electrically variable reactance elements, in particular capacitance diodes, are provided, the reactance value of said reactance elements being controlled as a function of the difference of the voltage amplitudes at the voltage divider center connections and/or as a function of the voltages at the A

Claims

1. Circuit arrangement for producing a voltage, the phase position of which is adjustable within wide limits with respect to a reference voltage, preferably between 0* and 360*, comprising means for producing four auxiliary voltages from the reference voltage, exhibiting a phase shift of 90* with respect to one another, an ohmic ring resistor having four taps which are spaced by 90* on the surface of said ring resistor and are connected to receive a respective one of said auxiliary voltages, the ring resistor being provided with a wiper to which is connected the output terminal of the arrangement, wherein said means for producing the four auxiliary voltages includes two voltage dividers supplied with the reference voltage and consisting of respectively one resistor and one reactance element, a pair of transformers, the primary winding of each respective transformer being connected to the center connection of a respective one of the voltage dividers, each transformer having a winding for the production of two voltages phase shifted with respect to each other by 180*, and at least one resistor of each voltage divider being variable, and means for controlling the resistance value of the variable resistor of each voltage divider in dependence on the difference of the amplitudes of the voltages at the voltage divider center connections in such a manner that the resistance and the reactance element are equal in impedance value.

3. The circuit arrangement according to claim 1, characterized in that each of the two transformers has a secondary winding with a center-tap which is connected to ground and that the two free ends of the secondary windings of both transformers are connected to the four taps of the ohmic resistor.

4. The circuit arrangement according to claim 1, characterized in that the two voltage dividers are provided with identical reactance elements and are arranged in antiparallel connection.

5. The circuit arrangement according to claim 4, characterized in that electrically variable reactance elements, in particular capacitance diodes, are provided, the reactance value of said reactance elements being controlled as a function of the difference of the voltage amplitudes at the voltage divider center connections and/or as a function of the voltages at the buffer amplifier outputs which are proportional to said difference.

6. The circuit arrangement according to claim 5, characterized in that an automatic gain control amplifier is provided which responds to the difference of the voltage amplitudes at the voltage divider center connections or to the difference Of the output voltages of the buffer amplifiers, the control terminal of the variable reactance means being connected to the output of said automatic gain control amplifier.