DE102006046739A1 - Magnetic field sensor for use in magneto resistive element, particularly four elements in bridge connection, has chip arranged on substrate or even formed on substrate - Google Patents

Abstract

The magnetic field sensor has a chip (50), which is arranged on the substrate (40) or even formed on the substrate. The magneto resistive element (41 to 44) has a hysteresis-afflicted characteristic and a magnetic current is detected by a magneto resistive element as a magnetic field signal. The magneto resistive element has a medium, by which the characteristic of the magneto resistive element is improved and hysteresis is reduced. The hysteresis-characteristics is reduced over the signal current by superimposed of a high frequency demagnetizing pulse.

Description

The The invention relates to a magnetic field sensor of at least a magnetoresistive element according to the preamble of claim 1. For a practical realization are preferably four magnetoresistive Elements in bridge circuit available.

To the magnetoresistive effect working magnetic field sensors are in particular as so-called GMR (Giant Magneto Resistance) and TMR (Tunnel Magneto Resistance) known. Such sensors set in the magnetic field-based position, speed, speed, Field or current sensors an alternative to the commonly used in practice Hall sensors.

In front Everything in the field of position and current sensors are during the reinforced in recent years MR-based sensors have become known. The main advantages lie Compared to Hall sensors in the simpler system design, the greater interference immunity - conditional by the possibility a design with greatly reduced external field sensitivity - and the less noise. They are available with MR-based sensors all fully integrated solutions on, since the magnetoresistive elements as a backend process, for example can be applied in CMOS technology and therefore no additional chip area is claimed.

For practice-relevant Applications, especially in position, speed and current sensors, each four elements become one known from electrical engineering Wheatstone bridge interconnected to a more accurate, by temperature fluctuations, extraneous fields or other disturbances more independent To achieve measurement.

Indeed it comes especially at room temperature (T = 20 ° C) increased Temperatures (T> 70 ° C) - conditional by the temperature dependence intrinsic material properties of hysteresis - too partial very significant inaccuracies in the magnetic field measurement. In particular, the required in the current sensor tolerance to overcurrents, i. Stream, which are larger by a factor of 5 to 12 as the nominal maximum value of the current to be measured, sets great Problem.

Overcurrents can, if they occur simultaneously with high temperatures, what interspersed warming effects as a result of the overcurrent often the Case is over the property of hysteresis too many applications lead to more tolerable measurement errors.

As you know, that depends Effect on the output signal of the sensitive element or the sensitive elements for magnetic field / current measurement strongly from the history of the magnetic field and the temperature at the location of the sensor, the influence can practically not be numerically eliminated. In addition to the reduced accuracy over temperature and current range will therefore also the possible Offset calibration difficult.

In In practice, MR sensors achieve high accuracies, i. ± 1% error at room temperature, only in the temperature range up to 85 ° C. An increase in the specified maximum temperature on z. 150 ° C, e.g. for automotive applications is desired at the same time high bandwidth can with MR sensors with increased expenditure and costs over a continuous regulation, so-called "closed loop" circuit, achieved become. But such a circuit has the disadvantage of a very high Power consumption (1 W at a measuring current of 25 A). Furthermore is in a closed loop process without the use of an expensive flux concentrator the measuring range is limited to approx. 150 A

A another solution consists in the use of Hall effect sensors, which, in order to high accuracy always need an expensive flux concentrator and further disadvantages, in particular piezoelectric effect and strong thermal or semiconductor noise, have.

Furthermore, from the DE 41 21 374 C1 a compensated magnetic field sensor, which is constructed with respect to a sensor plane of thin-film strip, with means for compensation, in which the compensation by trained in specific geometry layer strip conductor takes place on both sides of the sensor plane.

From Based on the above prior art, it is an object of the invention to provide an improved magnetic field sensor.

The Task is inventively by the features of claim 1 solved. Advantageous developments are in the subclaims specified.

The invention relates to the reduction and in particular the minimization of the hysteresis properties in magnetic field sensor with magnetoresistive elements which are subject to hysteresis. Advantageously, by superimposing a high-frequency magnetic field pulse on the measuring current - preferably with decaying amplitude - which is generated by means of a particular integrated current-carrying conductor, a current-carrying conductor loop or a current-carrying coil assembly, the hysteresis of a individual magnetoresistive element or a bridge constructed therefrom can be considerably reduced. The final magnetization field is chosen so that a maximum effect of hysteresis reduction is achieved with reasonable energy expenditure.

At the subject to the invention magnetic field sensor the hysteresis is not as strong the influence of the random sequence of values of the measuring field. This becomes the magnetic memory of the individual magnetoresistive element through the temporarily superimposed demagnetizing fields reduced or overwritten and thus minimized.

With The invention can in particular by high-frequency superposition an alternating field in the magnetic system a hysteresis-reduced characteristic be won. In MR-based current sensors, this can be superimposed on the measuring field Alternating field or the current pulse, in particular with decreasing amplitude, generated by an internal conductor loop.

Especially advantageous in the invention that by superposition of a high-frequency Pulse, the undamped or abating, in an internal conductor loop to one significant reduction of hysteresis is achieved.

Further Details and advantages of the invention will become apparent from the following Description of the figures of exemplary embodiments based on the drawing.

It demonstrate

1 a diagram with magnetic hysteresis curves,

2 a diagram to illustrate the invention,

3 a diagram for determining the hysteresis as a function of the current amplitude and the measuring method,

4 in sectional view the structure of an improved magnetic field sensor and

5 the top view of the magnetic field sensor according to 4 ,

In 1 the magnetic field H is plotted on the abscissa and the magnetic induction B is plotted on the ordinate. For magnetic materials results in a known manner a characteristic 1 as a so-called new curve after the alternating field demagnetization, whereby in each case a remanence remains after individual cycles, whereby the known hysteresis curves are realized. This effect is known from the prior art.

A Hysteresis can be reduced by superimposing a demagnetizing pulse respectively. In this case, the reduction of the hysteresis or the remanent Magnetization of ferromagnetic materials expediently performed with an alternating field of decreasing amplitude.

In 2 For this purpose, the current I is shown on the abscissa and the sensor signal V is shown on the ordinate. This results in a hysteresis characteristic 21 respectively. 21 ' and the ideal, hysteresis-free characteristic 22 ,

By the high-frequency overlay of the alternating field can reduce hysteresis in the magnetic system Characteristic can be obtained. It is advantageous that in magnetoresistive Elements that overlaid the measurement field Alternating field or the current pulse with decreasing amplitude by an internal conductor loop can be generated.

Experimental results are in 3 reproduced, in which the current level is plotted on the abscissa and on the ordinate, the respectively determined hysteresis in mV. They are graphene 31 to 33 for different methods of hysteresis reduction.

From the 3 Specifically, it results that by superimposing a high-frequency pulse, which may be unattenuated or decaying, a significant reduction of the hysteresis is achieved in an internal conductor loop. The graphs 31 to 33 show that in a conventional construction of an output amplitude of about 1 A, an effective reduction of the hysteresis by a factor of 3 can be achieved.

In 4 and 5 is a substrate with 40 designated. On the substrate are four identically constructed, magnetoresistive elements 41 . 42 43 and 44 arranged, which together form a Wheatstone bridge. Such bridge circuits for magnetic field sensors made of magnetoresistive elements 41 . 42 43 and 44 are known in the art.

In 4 / 5 is a loop with a current-carrying conductor 45 present, which is designed as a rectangular current loop, each with several turns so that in each case two magnetoresistive elements 41 . 42 43 and 44 arranged in pairs in the longitudinal leg of the loop. This results in a U-shaped arrangement.

Out 4 it can be seen that the magnetoresistive elements 41 . 42 43 and 44 in the substrate 40 themselves are introduced, the substrate 40 from a non-conductive layer 46 for electrical insulation of the conductor loop 45 is covered.

On or in the substrate 40 is still an arrangement 50 for pulse current generation, which is a discrete circuit of a filter 51 , an A / D converter 52 , a computing unit 53 and a control unit 54 or forms an integrated chip topography with these functions. The chip topography can also directly form the substrate for the magnetoresistive elements. The voltage signal U _B passes through the filter 51 with assigned A / D converter 52 on the arithmetic unit 53 and control unit 54 to the subsequent pulse current source 55 , The current signal I _S feeds the conductor loop 45 and generates the alternating field or the pulses with decreasing amplitude.

substratum and chip topography is advantageously realized in CMOS technology, which the possibility a miniaturization as far as possible.

Because the magnetoresistive elements 41 . 42 43 and 44 are introduced into the CMOS structures of a chip and thereupon the conductor loop 45 is applied, I _{s can} from the ic, which is on the substrate 40 integrated, be removed. In the current-carrying conductor 45 Thus, when imprinting an alternating field, the Abmagnetisierungspulse be generated. These act as a control panel in 5 With 47 is designated, which on the measuring field, the in 4 With 48 is called, acts.

With an arrangement according to 4 / 5 Thus, the hysteresis error can be reduced, whereby the resolution and accuracy of the arrangement is significantly increased. With a suitable design, a reduction of up to a factor of 4 can be achieved. Since the Abmagnetisierungsphasen can be very short, even a comparatively low amplitude is sufficient, the power consumption in the arrangement according to 4 / 5 significantly lower than in the known close loop method. In addition, no control is needed, so that the sensor maintains its quasi-passive character.

It can in the arrangement according to 4 / 5 also demagnetization phases targeted at a so-called "power on reset" approach or after particularly critical operating conditions, such as short circuit with very high magnetic fields, are used to create a defined, reproducible initial state of the waveforms.

Claims (12)

Magnetic field sensor of at least one magnetoresistive element, preferably four elements in bridge circuit, wherein the at least one magnetoresistive element has a hysteresis characteristic and as a magnetic field signal a measuring current through the at least one magnetoresistive element is detectable, characterized in that the at least one magnetoresistive element ( 41 . 42 . 43 . 44 ) a means ( 45 . 47 ), by which the characteristic curve ( 21 . 22 . 22 ' ) of the at least one magnetoresistive element ( 41 . 42 . 43 . 44 ) can be improved and the hysteresis can be reduced. Sensor according to claim 1, characterized in that the hysteresis of the characteristic ( 21 . 22 . 22 ' ) can be reduced by superimposing at least one high-frequency degaussing pulse on the measuring current. Sensor according to claim 1 or claim 2, characterized that the hysteresis is reduced by a factor of 3 to 5. Sensor according to one of the preceding claims, characterized characterized in that the reduction by the hysteresis by several stamped one after the other Demagnetization occurs, thereby minimizing the hysteresis properties is reachable. Sensor according to claim 4, characterized in that Magnetic field pulses are impressed with decaying amplitude. Sensor according to claim 3 or claim 4, characterized in that the / the magnetic field pulse / e by means of a current-carrying conductor, a current-carrying conductor loop ( 45 ) or a current-carrying coil arrangement is / are generated. Sensor according to claim 1, characterized in that as a current-carrying conductor, a conductor loop ( 45 ) on or in the substrate ( 40 ) for the at least one magnetoresistive element ( 41 - 44 ), wherein the conductor loop ( 45 ) a pulse current source ( 55 ) is assigned to generate high-frequency current signals. Sensor according to claim 7, characterized in that the pulse current source ( 55 ) with the associated supply units ( 51 - 54 ) on a chip ( 50 ) is integrated. Sensor according to claim 8, characterized in that the chip ( 50 ) on the substrate ( 40 ) or even the substrate ( 40 ). Sensor according to one of the preceding claims, wherein four magnetoresistive elements are present in bridge circuit, characterized in that the current-carrying conductor ( 45 ) several rectangular conductor loops ( 45 . 45 ' . 45 '' ), in whose longitudinally opposite conductor regions in each case two magnetoresistive elements ( 41 . 41 ; 43 . 44 ) of the bridge circuit are arranged in pairs one behind the other. Sensor according to one of the preceding claims, characterized by integration in the chip ( 50 ), especially in CMOS technology. Sensor according to claim 11, characterized in that for the power supply of the conductor loop ( 45 ) in the chip ( 50 ) generated current (I) is usable