Patent Description:
<FIG> shows a conventional 2D magnetic sensor for measuring an orientation angle of an external magnetic field <NUM>. Such a 2D magnetic sensor can be formed by combining two 1D magnetic sensors <NUM>, <NUM>, wherein each 1D magnetic sensor <NUM>, <NUM> can be formed from four magnetic sensor elements arranged (not shown) in a full (Wheatstone) - bridge circuit configuration. One of the 1D magnetic sensor <NUM> has a sensing axis <NUM> being orthogonal to the sensing axis <NUM> of the other 1D magnetic sensor <NUM>. A constant DC voltage (V) can be supplied to the two 1D magnetic sensors <NUM>, <NUM>. Each 1D magnetic sensor <NUM>, <NUM> generates a first output <NUM> and a second output <NUM>. The first and second output signals <NUM>, <NUM> of each of the 1D magnetic sensors <NUM>, <NUM> are supplied to the input terminals of a respective differential amplifier <NUM>. Each differential amplifier <NUM> outputs a differential amplifier output signal <NUM> that is supplied to an analog-to-digital converter <NUM> in order to obtain two digitized signals <NUM>. The two digitized signals <NUM> are inputted into a processing unit <NUM> where software routine solves the arctangent of the ratio of the two digitized signals <NUM> to extract the external magnetic field angle.

<CIT> discloses a displacement sensor using GMR elements for detecting a displacement of a physical quantity such as angle is to be provided wherein a waveform distortion of output voltage is diminished. There are installed at least two Wheatstone bridge circuits having a predetermined angular offset and each comprising a plurality of GMR elements, the GMR elements each having a fixed magnetic layer set to a predetermined magnetization direction. An AC power supply is used as a power supply of the Wheatstone bridge circuits and a displacement of a physical quantity such as a rotational angle is detected on the basis of AC-modulated outputs from the Wheatstone bridge circuits. An anisotropic self-bias effect of a free magnetic layer in each GMR element can be diminished and hence it is possible to remedy a waveform distortion of an output signal based on the anisotropic self-bias effect of the free magnetic layer.

<CIT> discloses an apparatus for determining rotational position of a rotatable element without contacting it, which includes a sensor device having two Hall or AMR sensor elements for sensing a magnetic field of magnetic field strength (B) generated by or influenced by the rotational position of the rotatable element and for producing output signals according to the magnetic field and thus the rotational position of the rotatable element. In order to easily detect the absolute rotational position of the rotatable element, the sensor device is constructed and positioned with respect to the rotatable element so that in every rotational position the field lines from the rotatable element extend at right angles to the sensor structures defined by the direction of an alternating current in the sensor elements. Using different embodiments of an electronic evaluation circuit, the direction components of the magnetic field are evaluated to determine the rotational position by comparing the input current to one of the sensors and the sum of the output signals of the respective sensor elements. Either sinusoidal or rectangular alternating voltages or direct voltages are input to the sensor elements.

A disadvantage of the conventional 2D magnetic sensor is that it must perform cumbersome and lengthy mathematical operations which require a powerful processing unit <NUM>.

According to the invention, an electronic circuit for measuring an angle and a field intensity of an external magnetic field, comprises:.

The electronic circuit according to the invention uses the principle of quadrature amplitude modulation (QAM). The angle of the external magnetic field can be determined directly from the analog conditioned signal.

The first voltage waveform Q(t) and the second voltage waveform I(t) can be represented, respectively by equations (<NUM>) and (<NUM>): <MAT> <MAT> where θ is the angle of the external magnetic field, A<NUM> is the amplitude of the first magnetic field sensing unit and A<NUM> is the amplitude of the second magnetic field sensing unit. The amplitudes A<NUM>, A<NUM> of the first and second sensing output signal are modulated by the external magnetic field angle and intensity.

By combining the two quadrature signals, i.e., the first and second voltage waveforms, each having a defined amplitude, one obtains a new periodic signal (conditioned signal) which phase is defined by arctangent of the amplitudes ratio of initial first and second voltage waveforms.

The conditioned signal can correspond to a monoharmonic signal having a phase and an amplitude. Both amplitude and phase of the monoharmonic conditioned signal carry the information of the angle and field intensity of the external magnetic field. The phase shift of the conditioned signal relative to the first and second voltage waveform contains information about the angle of the external magnetic field.

If the amplitudes A<NUM>, A<NUM> are equal, the phase in the conditioned signal is equal to the magnetic field angle φ (t) given by equation (<NUM>): <MAT>.

The amplitude Ac of the conditioned signal is then equal to: <MAT> which is independent on the angle of the external magnetic field. Thus, if the first and second magnetic field sensing units work in the linear regime, the amplitude Ac of the conditioned signal can be used as a measure of external magnetic field intensity. Otherwise a linearization procedure can be applied to recover magnetic field amplitude.

In an embodiment, the first voltage waveform comprises a sine wave and the second voltage waveform comprises a cosine wave.

The first and second sensing output signals are substantially in-phase with the first and second voltage waveforms, and the amplitude of the first and second sensing output signal is proportional to the cosine of the angle between the first and second sensing axis and to the angle of the external magnetic field.

The signal conditioning unit is configured to add the first sensing output signal to the second sensing output signal in the ratio <NUM>:<NUM> or with different ratio which considers possible difference in sensitivity between two sensing units. The signal conditioning unit can also admix a certain part of the input signal driving sensing unit to its output to cancel possible electrical offset stemming from electrical misbalance of four sensing elements comprising a Wheatstone full bridge - i.e. a sensing unit. The signal conditioning unit can also apply a correction to the summed signal in case of non-orthogonal configuration of sensing axes of two sensing units. Finally, the signal conditioning unit can apply filtering to the summed signal to filter out higher order harmonics from the signal and to improve thereby the accuracy of the electronic circuit.

For fixed amplitude of magnetic field, each sensing unit gives an output differential voltage which is proportional to cosine of the angle between external magnetic field direction and sensing axis direction of a sensing unit.

The electronic circuit according to the invention does not require lengthy mathematical operations and a powerful processing unit. The angle and field intensity of the external magnetic field are determined directly from the analog conditioned signal.

An electronic circuit <NUM> for measuring an angle θ and an intensity H of an external magnetic field <NUM> is shown in <FIG>, according to an embodiment. The circuit comprises a voltage generator <NUM> configured to supply a first generator signal <NUM> and a second generator signal <NUM>. Each of the first and second generator signals <NUM>, <NUM> has a periodic voltage waveform of fixed generator frequency fg and amplitude. A phase shift between the first generator signal <NUM> and the second generator signal <NUM> is of substantially <NUM>°. The voltage generator <NUM> is further configured to supply a synchronization signal <NUM> having the generator frequency fg. Alternatively, in an example not covered by the claims, the electronic circuit <NUM> can further comprise a clock generator <NUM> generating the clock synchronization signal <NUM>. The synchronization signal <NUM> synchronizes the operation of the voltage generator <NUM>.

The electronic circuit <NUM> further comprises a first magnetic field sensing unit <NUM> outputting a first sensing output signal <NUM> and a second magnetic field sensing unit <NUM> outputting a second sensing output signal <NUM>. The first magnetic field sensing unit <NUM> has a sensing axis <NUM> that is substantially orthogonal to a sensing axis <NUM> of the second magnetic field sensing unit <NUM>.

The first generator signal <NUM> is supplied to an input of the first magnetic field sensing unit <NUM> and the second generator signal <NUM> is supplied to an input of the second magnetic field sensing unit <NUM>. The first magnetic field sensing unit <NUM> outputs a first sensing output signal <NUM> and the second magnetic field sensing unit <NUM> outputs a second sensing output signal <NUM>. The amplitude of the first and second sensing output signals <NUM>, <NUM> is changed relative to the amplitude of the first and second generator signals <NUM>, <NUM>, depending on the orientation of the external magnetic field <NUM>, i.e., relative to the angle θ of the external magnetic field <NUM> and its intensity when the sensor is operating in the linear range.

The electronic circuit <NUM> further comprises a signal conditioning unit <NUM>, <NUM> into which the first and second sensing output signals <NUM>, <NUM> are inputted. The signal conditioning unit <NUM>, <NUM> is configured to add (or sum) the first sensing output signal <NUM> to the second output signal <NUM> and to output a conditioned signal <NUM>. The conditioned signal <NUM> can correspond to a monoharmonic signal having the generator frequency fg.

The first generator signal <NUM> and the second generator signal <NUM> can also be inputted into the signal conditioning unit <NUM>, <NUM> in order to compensate possible Wheatstone bridge electrical misbalance in modules <NUM>, <NUM>, to compensate possible misorthogonality between sensing axes <NUM> and <NUM> and to filter higher order harmonics from the summed signal.

The electronic circuit <NUM> further comprises a magnetic field angle detection unit <NUM>. The conditioned signal <NUM> and the clock synchronization signal <NUM> are supplied to an input of the magnetic field angle detection unit <NUM>. The synchronization signal <NUM> thus further synchronizes the operation of the magnetic field angle detection unit <NUM>. The magnetic field angle detection unit <NUM> is configured for measuring a phase shift between the conditioned signal <NUM> and the synchronization signal <NUM>. The magnetic field angle detection unit <NUM> is further configured to determine the angle θ of the external magnetic field <NUM> from the measured phase shift. The magnetic field angle detection unit <NUM> outputs a digital angle output <NUM> comprising the information about the determined angle θ.

The first magnetic field sensing unit <NUM> and second magnetic field sensing unit <NUM> are configured such that an amplitude of the first and second sensing output signals varies linearly with a variation of the external magnetic field intensity H. In that case, the electronic circuit comprises a magnetic field intensity detection unit <NUM> configured to determine the external field intensity. The magnetic field intensity detection unit <NUM> is configured to measure an amplitude of the conditioned signal <NUM>, supplied to an input of the magnetic field intensity detection unit <NUM>, and determine the external field intensity H from the conditioned signal <NUM>. The magnetic field intensity detection unit <NUM> outputs a digital magnetic field intensity output <NUM> comprising the information about the determined external field intensity H. The synchronization signal <NUM> further synchronizes the operation of the magnetic field intensity detection unit <NUM>.

Each of the first magnetic field sensing unit <NUM> and second magnetic field sensing unit <NUM> can comprise a plurality of magnetic field sensing elements (<NUM>-<NUM>). Preferably, the magnetic field sensing elements are arranged in half-bridge or full (Wheatstone) -bridge circuit. In such configuration, the first and second magnetic field sensing units <NUM>, <NUM> can act as a voltage divider, where the divider ratio is a function of intensity H and angle θ of the external magnetic field <NUM>.

As used herein, the term "magnetic field sensing element" is used to describe a variety of electronic elements that sense a magnetic field. The magnetic field sensing element can be, but is not limited to, a Hall Effect element, a magnetoresistance element, or a magnetotransistor. As is known, there are different types of magnetoresistance elements, for example, a semiconductor magnetoresistance element such as Indium Antimonide (InSb), a giant magnetoresistance (GMR) element, an anisotropic magnetoresistance element (AMR), a tunneling magnetoresistance (TMR) element, a magnetic tunnel junction (MTJ), a spin-valve, etc..

In a possible configuration illustrated in <FIG>, the plurality of magnetic field sensing elements can comprise four magnetic field sensing elements arranged in a full-bridge circuit, comprising two magnetic field sensing elements <NUM>, <NUM> connected in series in parallel to two other magnetic field sensing elements <NUM>, <NUM> connected in series.

For example, the magnetic field sensing element <NUM>-<NUM> can comprise a MTJ, such as a self-referenced MTJ, comprising a reference layer having a reference magnetization <NUM> and a sense layer having a sense magnetization (not represented in <FIG>) that can be oriented relative to the (pinned) reference magnetization <NUM>, according to the orientation of the external magnetic field <NUM>. A sensing axis <NUM> of the magnetic field sensing unit <NUM>, <NUM> coincides with the direction of the reference magnetization <NUM>. The sensing axis <NUM> of the first magnetic field sensing unit <NUM> substantially orthogonal to the sensing axis <NUM> of the second magnetic field sensing unit <NUM> can be obtained by programming the (pinning) direction of the reference magnetization <NUM>.

In a possible variant, the signal conditioning unit <NUM>, <NUM> can be configured for filtering out higher order harmonics from the conditioned signal <NUM>. The signal conditioning unit <NUM>, <NUM> can be further configured for performing amplitude and offset correction of the first and second sensing output signals <NUM>, <NUM>.

In another variant, the magnetic field angle detection unit <NUM> is configured for using linear mathematical operations in order to determine the magnetic field angle θ. The magnetic field angle detection unit <NUM> can be further configured for determining the angle θ of the external magnetic field <NUM> from the measured phase shift, and outputting the corresponding digital angle output <NUM>.

In yet another variant, the magnetic field intensity detection unit <NUM> is configured for digitizing and linearizing the magnetic field strength value H when generating the digital magnetic field intensity output <NUM>.

<FIG> shows the electronic circuit <NUM>, according to an embodiment. Here, the voltage generator <NUM> is configured to supply the first and second voltage waveforms <NUM>, <NUM> having the same generator frequency fg. The first and second voltage waveforms <NUM>, <NUM> can comprise quadrature signals. For instance, the first voltage waveform <NUM> comprises a sine waveform and the second voltage waveform <NUM> comprises a cosine waveform. The voltage generator <NUM> can be further configured for supplying a generator synchronization signal <NUM> having the generator frequency fg, thus the same frequency as the one of the first and a second generator signals <NUM>, <NUM>.

In the configuration of <FIG>, the signal conditioning unit comprises an adder circuit <NUM> into which the first and second sensing output signals <NUM>, <NUM> are inputted. The adder circuit <NUM> is configured to add up the first and second sensing output signals <NUM>, <NUM> and output a corresponding summed signal <NUM>. The adder circuit <NUM> can be configured for adding the first sensing output signal to the second sensing output signal in the ratio <NUM>:<NUM>.

The signal conditioning unit comprises a phase comparator <NUM> into which the summed signal <NUM> is inputted. The phase comparator <NUM> is configured to detect the phase of the summed signal <NUM> and output a digital phase comparator signal <NUM> that is inputted in the magnetic field angle detection unit <NUM>. The phase comparator signal <NUM> may be a pulse width modulated signal wherein the duty period varies in proportion to the determined phase difference.

The magnetic field angle detection unit <NUM> can function as a counter that starts counting the pulses of the synchronization signal <NUM> coming from the clock generator <NUM> when comparator output <NUM> changes its state. The magnetic field angle detection unit <NUM> can stop counting the pulses of the synchronization signal <NUM> when the generator synchronization signal <NUM> arrives from the voltage generator <NUM>. The number of counted pulses is proportional to the phase shift of the summed signal <NUM>.

In the configuration of <FIG>, the summed signal <NUM> and the phase comparator signal <NUM> are further inputted in the magnetic field intensity detection unit <NUM>. The magnetic field intensity detection unit <NUM> can be configured for sampling the amplitude of the summed signal <NUM> at its maximum and obtaining a corresponding sampled magnetic field intensity output <NUM>. This is performed thanks to synchronization with the phase of the summed signal <NUM> and predefined delay which is set by the number of clock pulses and which corresponds to <NUM>° phase shift with respect to the phase comparator signal <NUM>. The sampled magnetic field intensity output <NUM> can be digitized and linearized.

<FIG> show the electronic circuit <NUM> according to other examples not covered by the claims, wherein the magnetic field sensing units <NUM>, <NUM> comprise magnetic field sensing elements having the reference magnetization <NUM> in the saturated state. In such configuration, the electronic circuit <NUM> does not require the magnetic field intensity detection unit <NUM>.

In the example of <FIG>, the electronic circuit <NUM> corresponds to the one of <FIG> without the magnetic field intensity detection unit <NUM>. The summed signal <NUM> is inputted only in the phase comparator <NUM> and the phase comparator signal <NUM> is inputted only in the magnetic field angle detection unit <NUM>.

<FIG> shows the electronic circuit <NUM> according to another example. The electronic circuit <NUM> corresponds to the one of <FIG>, wherein a DC blocking capacitor <NUM> is provided at each input of the adder circuit <NUM>, i.e., in the electrical path of the first and second sensing output signals <NUM>, <NUM>. The capacitors <NUM> increases the angular resolution of the electronic circuit <NUM>, i.e., increases the resolution of the determined angle θ of the external magnetic field <NUM>.

<FIG> shows the electronic circuit <NUM> according to yet another example. The electronic circuit <NUM> corresponds to the one of <FIG>, further comprising a low-pass filter <NUM> placed between the output of the adder circuit <NUM> and the input of the phase comparator <NUM>. The low-pass filter <NUM> is configured for suppressing higher order harmonics, except the first harmonic (fundamental frequency) of the summed signal <NUM>. The higher order harmonics can be introduced by the voltage generator <NUM> and/or by first and second magnetic field sensing units <NUM>, <NUM>. The low-pass filter <NUM> increases the angular resolution of the electronic circuit <NUM>, i.e., increases the resolution of the determined angle θ of the external magnetic field <NUM>.

<FIG> represents the electronic circuit <NUM> according to yet another example. The electronic circuit <NUM> corresponds to the one of <FIG>, further comprising a sensor correction module <NUM> connected to the output of the first magnetic field sensing unit <NUM> and the second magnetic field sensing unit <NUM>. The sensor correction module <NUM> is configured for alleviating the imperfections of the first and second magnetic field sensing units <NUM>, <NUM>. In particular, the sensor correction module <NUM> can be used for matching the sensitivity of the first and second magnetic field sensing units <NUM>, <NUM> by setting the internal gain (or resistive divider ratio).

In practice, a conventional magnetic field sensor has offsets that affect the voltage across the sensor. The presence of the voltage offset in the magnetic field sensing unit <NUM>, <NUM> reduces the precision with which the logic state of the magnetic field sensing unit is read. The sensor correction module <NUM> can be used for at least partially eliminating that offset. The sensor correction module <NUM> can further be used for adding or subtracting part of the signal coming from the voltage generator <NUM>.

The sensor correction module <NUM> can further be used for reducing departure in the orthogonality between the sensing axis <NUM> of the first magnetic field sensing unit <NUM> and the sensing axis <NUM> of the second magnetic field sensing unit <NUM>. Reducing departure in the orthogonality between the sensing axis <NUM> and <NUM> can be further, or alternatively, realized either by programming the reference magnetization <NUM> of the magnetic field sensing element <NUM>-<NUM>, or by resistor trimming, for example using laser trimming.

<FIG> represents the electronic circuit <NUM> according to yet another example. The electronic circuit <NUM> corresponds to the one of <FIG>, wherein the first sensing output signal <NUM> from the first magnetic field sensing unit <NUM> and the second output signal <NUM> form the second magnetic field sensing unit <NUM> are inputted directly into the phase comparator <NUM>. The phase comparator <NUM> provides the functions of summing the first sensing output signal <NUM> to the second output signal <NUM> and of detecting the phase of the summed signal. The conditioned signal corresponds to a digital phase comparator signal <NUM> outputted by the phase comparator <NUM>. The electronic circuit <NUM> is simpler than the other circuit configurations.

<FIG> shows the electronic circuit <NUM> according to yet another example. The electronic circuit <NUM> corresponds to the one of <FIG>, wherein the magnetic field angle detection unit <NUM> comprises a RS trigger (or RS flip flop) circuit into which the phase comparator signal <NUM> and the generator synchronization signal <NUM> are inputted. In this configuration, the information corresponding to the determined angle θ of the external magnetic field <NUM> is coded in a pulse width modulated signal. The electronic circuit <NUM> configuration of <FIG> can be advantageously used in auto regulating applications.

<FIG> illustrates the electronic circuit <NUM> according to yet another example not covered by the claims. The electronic circuit <NUM> corresponds to the one of <FIG>, wherein the first and second magnetic field sensing units <NUM>, <NUM> are connected such as to form a differential magnetic field sensor arrangement. In this configuration, there is a direct connection of the first sensing output signal <NUM> to the second output signal <NUM>. The electronic circuit <NUM> further comprises a differential amplifier <NUM> comprising two analog input terminals to which the first and second sensing output signals <NUM>, <NUM> are connected. The differential amplifier <NUM> outputs a binary digital differential amplifier output signal <NUM> that is inputted into the magnetic field intensity detection unit <NUM> such as to determine the intensity H of the external magnetic field <NUM> and output the magnetic field intensity <NUM>.

The configuration of the electronic circuit <NUM> shown in <FIG> simpler that the circuit of <FIG>. This configuration further avoids the use of a single-ended-to-differential transformation circuit.

<FIG> shows the electronic circuit <NUM> according to yet another example not covered by the claims. The electronic circuit <NUM> corresponds to a simplified variant of the circuit of <FIG>, wherein the magnetic field sensing units <NUM>, <NUM> comprise magnetic field sensing elements having the reference magnetization <NUM> in the saturated state. In comparison with the configuration of <FIG>, the electronic circuit <NUM> does not comprise the differential amplifier <NUM> and does also not comprise the magnetic field intensity detection unit <NUM>.

<FIG> shows the electronic circuit <NUM> according to yet another example not covered by the claims. The electronic circuit <NUM> corresponds to a simplified variant of the circuit of <FIG>, wherein the voltage generator <NUM> comprises a single output monoharmonic voltage generator. In other words, the voltage generator <NUM> is configured for supplying the first generator signal <NUM>, for example a sine waveform, and for supplying a generator synchronization signal <NUM> having the same frequency as the first and a generator second signals <NUM>. The electronic circuit <NUM> further comprises a phase shifter (or quadrature booster) <NUM> configured for phase-shifting by <NUM>° the first generator signal <NUM> and generate the second generator signal <NUM>.

Claim 1:
An electronic circuit for measuring an angle and an intensity of an external magnetic field (<NUM>), comprising:
a first magnetic field sensing unit (<NUM>) being configured to output a first sensing output signal (<NUM>) and a second magnetic field sensing unit (<NUM>) being configured to output a second sensing output signal (<NUM>), a first sensing axis (<NUM>) of the first magnetic field sensing unit (<NUM>) being substantially orthogonal to a second sensing axis (<NUM>) of the second magnetic field sensing unit (<NUM>);
a voltage generator (<NUM>) configured to supply a synchronization signal (<NUM>) having a generator frequency (fg) and to supply a first voltage waveform (<NUM>) to the first magnetic field sensing unit (<NUM>) and a second voltage waveform (<NUM>) to the second magnetic field sensing unit (<NUM>);
a signal conditioning unit (<NUM>, <NUM>) into which the first and second sensing output signals (<NUM>, <NUM>) are inputted and configured to add the first sensing output signal (<NUM>) to the second sensing output signal (<NUM>) and output a conditioned signal (<NUM>);
wherein the first and second voltage waveforms (<NUM>, <NUM>) have substantially the same amplitude and the same generator frequency (fg), and are phase shifted by about <NUM>° with respect to each other; and
a magnetic field angle detection unit (<NUM>) configured to receive the conditioned signal (<NUM>) and the synchronization signal (<NUM>), and configured to measure a phase shift between the conditioned signal (<NUM>) and the synchronization signal (<NUM>) and to determine the angle (θ) of the external magnetic field from the measured phase shift;
wherein the first and second magnetic field sensing units (<NUM>, <NUM>) are configured such that an amplitude of the first and second sensing output signals (<NUM>, <NUM>) varies linearly with a variation of the intensity of the external magnetic field (<NUM>);
characterized in that the electronic circuit further comprises a magnetic field intensity detection unit (<NUM>) configured to determine the intensity (H) of the external magnetic field (<NUM>) from an amplitude of the conditioned signal (<NUM>).