FR2799551A1 - CIRCUIT AND METHOD FOR DETERMINING A MAGNETIC FIELD - Google Patents

Abstract

Circuit and method for determining an external magnetic field, for forming an angle sensor having four magnetoresistive elements (3a, 3b, 3c, 3d) which form two voltage dividers in bridges (3). Flexible wiring means of the elements (3a, 3b, 3c, 3d) allow, in a first state to two elements (3a, 3b) to form a first divider, and to the other two elements (3c, 3d) to form a second voltage divider. In a second state, the first and fourth magnetoresistive elements (3a, 3d) form a first voltage divider while the second and third magnetoresistive elements (3b, 3c) form a second voltage divider.

Description

I The present invention relates to a circuit for

  determine an external magnetic field, in particular for

  sea an angle sensor, having between one and four elements ma-

  gnétoresistifs which, by forming two tension dividers, can be combined in a bridge. The invention also relates to a method for determining the alignment of an external magnetic field using one to four magnetoresistive elements combined to form two voltage dividers constituting an assembly in

l0 bridge.

  We know for example, according to the document

  DE 196 14 460 Al, a circuit for determining a magnetic field

  tick, in which magnetoresistive elements are combined

  born in the form of a bridge. The magnetoresistive elements thus used can be produced for example by the application of Spin valve materials. Spin valve elements are,

  in the simplest case, three-layer systems ex-

  extremely thin comprising two magnetic layers having

  each a thickness of the order of 0.1 to 10 nm, and a

  non-magnetic intermediate che having an analog thickness

  ford. One of the two magnetic layers has a magnetization

  extremely soft and easily aligned in a magnetic field

  outdoor tick. The second magnetic layer has a hard magnetic characteristic and, in the ideal case, its amplitude does not depend on the direction of external magnetic fields. The second magnetic layer thus functions as a reference magnetization. By an appropriate choice of

  layer thicknesses, there will be a variation in resistance

  pendant from the magnetic field, which depends on the direction a of the external magnetic field. The resistance Ri (a), that is to say the resistance of such a magnetoresistive element is expressed by the formula:

Ri (a) = Ro + ARcos (c + pi).

  In this formula, Ro represents the offset resistance which itself depends on the specific resistance of the material as well as the length and width of the

  resistant path; AR corresponds to the amplitude of the varia-

  resistance and vi represents the angle between a direction

  taring of the external field and the direction of the mo-

  magnetic in the reference layer. The function co-

  sinus is defined in a one-to-one manner in the range between 0 and 180 and thus a sensor which, in the simplest case, consists of a single strip of such a Spin valve material, makes it possible to measure angles included

between 0 and 1800.

  To generate a resistance independent of Ro, four resistance bands are generally combined in the form of a bridge. This can be done both on a chip (the structure of the sensor consists of four resistant paths)

  or as four independent components. Have them-

  reference mantations of the magnetoresistive elements of the

  bridge must, at least in part, be different.

  To make a 360 angle sensor, it is necessary so far to have another turned bridge

  of 90 compared to the first bridge. We can then measure if-

  simultaneously sine and cosine signals. Based on if-

  general sine and cosine known, we can then in the simplest way, define by the tangent arc function, an angle

  one-to-one in the range of 0 to 3600.

  However, due to the increasing miniaturization, it is sought to produce such sensors in the space-saving manner possible. In addition, it can be seen that with a reduced overall surface of such a sensor, there will be less sensitivity to local inhomogeneities of the direction of the

  field and more precise operation.

  The present invention aims to develop an angle sensor, of construction as small as possible and allowing a one-to-one definition of the angle in a

  angular range between 0 and 3600.

  This problem is solved according to the invention by a circuit of the type defined above, characterized in that

  by means of flexible wiring of the magnetic elements

  toresistifs, in a first operating state, a first and a second magnetoresistive elements form a first voltage divider while a third and a

  fourth magnetoresistive elements form a second di-

voltage sight, and

  * in a second operating state, the first and fourth

  third magnetoresistive elements form a first divi-

  voltage generator while the second and third magnetoresistive elements form a second voltage divider. This problem is also solved by a method of the type defined above, characterized in that * in a first operating state, to obtain a signal associated with the first magnetization field, a first magnetoresistive element and a second element are connected

  magnetoresistive to form a first voltage divider

  sion, as well as a third magnetoresistive element and a fourth magnetoresistive element to form a second voltage divider, and

  * in a second operating state, to obtain a se-

  cond signal associated with the magnetic field, connect the first magnetoresistive element and the fourth element

  magnetoresistive to form a first voltage divider

  and connect the second magnetoresistive element and the third magnetoresistive element to form a second

voltage divider.

  The invention thus allows, using only

  a bridge assembly comprising four magnetoresistors

  sistives, to indicate the direction of an external magnetic field

  unequivocally laughing, in a range of 3600. The circuit according to the invention is much smaller than the circuits

  known because it only requires four magnetoresistive elements

  instead of the eight currently used.

  Following advantageous developments of the invention

tion:

  * the magnetoresistive elements have magnetizations of re-

ference of different alignments,

  * the reference magnetizations of the magnetoresist elements -

  tifs are rotated 90 times,

  * in the first and second operating states, we manage

  generates signals each phase out of phase by 90, in particular cosine and sine signals, * the alignment of the external magnetic field is determined using an arc-tangent function by forming the quotient

900 phase shifted signals.

  According to a preferred embodiment of the pro-

  assigned of the invention, during the first and second operating states, phase-shifted signals are generated each time

  90. From such signals, one can generate sequentially-

  measurement values from which to determine,

  in the simplest way, the alignment of a magnetic field

  outdoor tick. So it is for example possible, in the

  first operating state, to determine a cor-

  corresponding to the cosine of the alignment angle of the magnetic field

  tick sought and, during the second operating state, a signal corresponding to the sine of the alignment angle of

this magnetic field.

  Advantageously, the alignment angle of the magnetic field sought by the arc-tangent function is determined by forming the quotient of the phase-shifted signals from. It is known per se to determine the angle using the arc-tangent function from the known sine and cosine values, and to execute this determination by a

relatively small calculation.

  According to a preferred embodiment of the circuit

  of the invention, the magnetoresistive elements have

  reference magnetizations of different directions. The magnet-

  reference station designates, as already indicated, for example

  in the case of magnetoresistive elements formed of three layers

  ches, the magnetic alignment of a hard magnetic layer which, in the ideal case, retains its original magnetization alignment even for external magnetic fields

  of relatively large amplitude.

  Advantageously, the reference magnetizations

  of the respective magnetoresistive elements are rotated

  each time 90. If the reference magnetizations of the

  three magnetoresistive elements of a bridge are for example

  gnées on the angles 0, 90, 180 and 270, one can exploit

  signals with particularly simple calculations.

  The present invention will be described below from

  in more detail using the accompanying drawings in the-

  which: * Figure 1 is a diagram used to describe the

  known circuit for determining the alignment of a magnetic field

  outdoor tick comprising two juxtaposed bridges,

  * Figure 2 shows a pre-

  of the invention circuit in the first and second

cond operating states.

  Figure 1 shows a circuit for de-

  complete alignment of an external magnetic field. The circuit consists of a first bridge 1 and a second bridge 2 turned 90 relative to the first bridge. The first bridge 1 is made up of four magnetoresistive elements, in particular

  in the form of resistant bands. The four magnified elements

  toresistifs bearing the references la, lb, lc, ld can be produced on a chip or in the form of four independent components. The magnetoresistive elements la, lb, lc, ld have different reference magnetizations (1, (D2, D3, (4 (as shown in the figure). The reference magnetizations of two opposite resistors la, lc or lb, ld are

rotated or phase shifted by 180.

  The magnetoresistive elements 1a, 1b form a first voltage divider; magnetoresistive elements

  lc, ld form a second voltage divider in bridge 1.

  By applying an external voltage Uo and

  comparing the partial voltages of the two voltage divisors

  To obtain a voltage Ubrl, we provide, depending on the alignment of the external magnetic field to be observed, a

  Ubrl cosine signal curve like that of the

  lower part of Figure 1. Such a bridge used as a cap-

  angle sensor or angle generator gives an unequivocal associated angle in an angular range between 0 and. A 360 angle sensor can be achieved by completing the construction described by another turned bridge

  of 90 with respect to the bridge shown. Such a bridge carries glo-

  balance reference 2 in figure 1. Bridge 2 is made up

  magnetoresistive resistive elements 2a, 2b, 2c, 2d

  resistances R1, R2, R3, R4 or reference magnetizations () i, () 2, () 3, () 4. The construction of this second bridge corresponds to that of the first bridge 1, which makes it possible not to repeat

  this description. Bridge 2 gives a second curve of si-

  general Ubr2 of sinusoidal shape. Using the arc-

  tangent, based on sine signals and cosi- signals

  obtained, we can calculate the field alignment angle

  magnetic outside by proceeding in a simple way.

  The circuit according to the invention, allowing in particular

  ment the implementation of the method of the invention, will be described below using Figure 2. The circuit of the invention

  generally bears the reference 3. In FIG. 2, we have represented

  felt on the left a first operating state and on the right

  in FIG. 2, a second operating state has been shown.

  ment of circuit 3. The main difference with the reference below to the circuit described in FIG. 1, according to the state of the art, lies in the fact that, according to the invention, there

  there are only four resistant elements 3a, 3b, 3c, 3d. The ele-

  magnetoresistive resistant elements 3a, 3b, 3c, 3d have values

  their respective R1, R2, R3, R4 or magnetizations of

  reference (1D, c) 2, (D3, (4 like those represented in the fig-

  res 2a, 2b. The reference magnetizations are rotated or phase shifted by 900 relative to each other (00, 90,

   , 270). In a first operating state, the elements

  magnetoresistive elements 3a, 3b form a first divider of

  voltage and the elements 3c, 3d a second voltage divider.

  By applying an external voltage Uo, we obtain, as for the first bridge of FIG. 1, a voltage signal in

cosine form Ubrl.

  Bridge 3 is switched to present a second operating state; the magnetoresistive elements 3a, 3b

  form a first voltage divider and the magnetic elements

  resistors 3b and 3c form a second voltage divider.

  On the basis of this arrangement of the bridge 3, a sinusoidal signal Ubr2 is obtained, taking into account the respective reference magnetizations. The respective curves of the signals, for different alignments of an external magnetic field,

  are shown in the lower part of Figure 2.

  The flexible circuit, shown, of the magnetoresistive elements can be produced for example using diodes. We are thus able to sequentially form different bridges which

  on the one hand give a signal corresponding to a cosi-

  naked and on the other hand a signal corresponding to a curve if-

  naked. These means make it possible to build an angle sensor

  one-to-one with only four resistant elements for an angular range of 3600.

  Although we are free in the choice of magnet-

  References of the magnetoresistive elements 3a, 3b, 3c, 3d of the bridge, it is interesting, as shown, to choose

  reference magnetizations phase shifted by 900. Such signals are, as already described with reference to FIG. 1, ex-

  easily exploited by forming the arc-tangent function of the quotients.

Claims (4)

CLAIMS) Circuit for determining an external magnetic field, in particular for forming an angle sensor, having between one and four magnetoresistive elements (3a, 3b, 3c, 3d) which, by forming two voltage dividers can be combined into a bridge (3), characterized in that * by means of flexible wiring of the magnetoresistive elements (3a, 3b, 3c, 3c), in a first operating state, first and second magnetoresistive elements (3a, 3b) form a first voltage divider, while a third and a fourth magnetoresistive element (3c, 3d) form a second voltage divider, and * in a second operating state, the first and fourth magnetoresistive elements (3a, 3d) form a first voltage divider, while the second and third magnetoresistive elements (3c, 3c) form a second voltage divider.   20) Circuit according to claim 1, characterized in that   the magnetoresistive elements (3a, 3b, 3c, 3d) have magnets   reference positions of different alignments.   3) Circuit according to one of claims 1 or 2,   characterized in that the reference magnetizations of the magnetoresistive elements   (3a, 3b, 3c, 3d) are rotated 900 each time.   4) Method for determining the alignment of a magnetic field   only outside using one to four magnetoresis-   tifs (3a, 3b, 3c, 3d) combined to form two voltage dividers constituting a bridge arrangement (3), characterized in that * in a first operating state, to obtain a signal associated with the first magnetization field, we plug   a first magnetoresistive element (3a) and a second element   magnetoresistive element (3b) to form a first voltage divider, as well as a third magnetoresistive element (3c) and a fourth magnetoresistive element (3d) to form a second voltage divider, and   * in a second operating state, to obtain a se-   cond signal associated with the magnetic field, connect the   first magnetoresistive element (3a) and the fourth element   magnetoresistive (3d) to form a first divider   of voltage, and we connect the second magnetoresistive element   tif (3b) and the third magnetoresistive element (3c) for   form a second voltage divider.    ) Method according to claim 4, characterized in that in the first and second operating states, one generates   signals each phase 90 by phase, in particular signals cosine and sine gnals.   6) Method according to claim 5, characterized in that the alignment of the external magnetic field is determined using an arctangent function by forming the quotient of 90 phase shifted signals.