METHOD AND DEVICE FOR MEASURING AN ANGLE AT WHICH A MAGNETIC FIELD IS ALIGNED IN A PLANE RELATIVE TO A REFERENCE AXIS
[0001] The invention relates to a device for measuring an angle at which a magnetic field is aligned in a plane relative to a reference axis, with at least two magnetic field sensors which are aligned with their measurement axes in and/or parallel to the plane and oriented perpendicular to each other. The invention further relates to a method for measuring an angle, at which a magnetic field is aligned in a plane relative to a reference axis, wherein a first magnetic field component and a second magnetic field component aligned perpendicular thereto are measured in and/or parallel to the plane.
[0002] A device of the aforesaid type is disclosed in Reymond, S. et al., "True 2D CMOS integrated Hall sensor", IEEE SENSORS 2007 Conference, pp. 860-863, which has a semiconductor substrate in which are integrated so-called vertical Hall sensors as magnetic field sensors 64. The magnetic field sensors are equidistantly arranged relative to each other on a circular ring residing in the chip plane of the semiconductor substrate in such a way that the planes in which the magnetic field sensors extend are always radially aligned relative to an imaginary center axis, which passes through the center point of the circular ring and is aligned at right angles to the chip plane. The magnetic field sensors are connected to a scanning device in such a way that the measurement signals of the individual magnetic field sensors are capable of being applied successively to a differential output terminal for a rotation scanning signal. Cyclically rotating, successive scanning of the magnetic field sensors is thus carried out. The differential output terminal is connected via a differential amplifier to a low pass integrated in the semiconductor substrate. By means of the low pass, the analog output signal of the amplifier is smoothed to an

approximately sinusoidal signal. The zero crossing of the analog measurement signal thus achieved is determined, and the angle at which a magnetic field flowing through the semiconductor substrate in the chip plane is aligned relative to a reference axis is determined from the zero crossing point.
[0003] A disadvantage resides in the device in that the scanning of the many magnetic field sensors is time-consuming. In spite of the complex circuitry, the device enables only a small band width. A further disadvantage resides in the fact that the non-degenerative, analog low pass must meet stringent requirements in terms of linearity and frequency response, which entails a considerable use of surface area on the chip and a high power consumption.
[0004] A device of the aforementioned type is also disclosed in DATA SHEET UZZ9001, Sensor Conditioning Electronic, Product Specification, Philips Semiconductors, 27 November 2000, which has two magnetoresistive sensors integrated as magnetic field sensors in a semiconductor chip, which are aligned with their measurement axes in a plane at right angles relative to each other. Each magnetic field sensor is in each case connected to an analog-digital convertor, which is configured as a sigma-delta modulator. A decimation filter, at whose output is emitted a magnetic field measurement value in the form of a 15 bit digital word, is always disposed downstream relative to each analog-digital convertor. The digital words are transmitted to a calculator, which calculates the angle at which a magnetic field flowing through the semiconductor substrate is aligned in the chip plane relative to a reference axis from the arctangent of the quotient of the digital words. The relatively highly complex circuitry is also disadvantageous herein. The calculation of the magnetic field angle results in a latency, which poses a disadvantageous when the device is used in a control circuit.
[0005] The object is therefore to create a device of the aforesaid type which enables a simple construction and a high measurement precision. A further object is

to design a method of the aforesaid type with which the angle can be easily
determined with high precision.
[0006] With regard to the device, the object is achieved wherein the device has a
PLL phase control circuit with a follow-on oscillator arranged in a phase control loop,
wherein the follow-on oscillator has at least one oscillator output for a digital
oscillating signal, wherein the magnetic field sensors are coupled to the phase
[written] over an angular range of 360o control loop so that the digital oscillating signal is phase synchronous with a rotation
scanning signal formed by rotary scanning of the measurement signals of the
magnetic field sensors, and wherein the oscillator output for determining the phasing
of the digital oscillating signal is connected to a phasing detector.
[0007] The device thus has a simply designed, economically manufacturable
phase-locked loop (PLL) phase control circuit, which is synchronous with the phase
of a rotation scanning signal formed by rotary scanning of the measurement signal
outputs of the magnetic field sensors. "Synchronous" is understood to mean that the
phasing of the digital oscillating signal is identical to that of the rotation scanning
signal or displaced by a known, constant angle. The angle at which the magnetic field
is aligned relative to the reference axis in the plane spanned by the axes of the
magnetic field sensors can thus be easily measured by determining the phasing of
the digital oscillating signal.
[0008] It is advantageous if the magnetic field sensors are connected to a
scanning device in such a way that the measurement signals of the individual
magnetic field sensors are capable of being applied successively to an output
terminal for the rotation scanning signal, and if the output terminal is connected to a
synchronization signal input of the PLL phase control circuit. The scanning device
can thus be disposed downstream of the measurement signal terminals of the
magnetic field sensors. However, it is also conceivable that the magnetic field
sensors or their circuitry components are switched on or off by means of the

scanning device, in order to activate or deactivate the respective magnetic field sensor.
[009] In an advantageous embodiment of the invention, each magnetic field sensor always has a measurement signal output connected to a multiplexer, wherein the multiplexer has an output capable of being connected to the individual input terminals, which forms the output terminal for the rotation scanning signal. The construction of the device is thus further simplified.
[0010] In a preferred embodiment of the invention, the output terminal for the rotation scanning signal is connected to a first input of a frequency mixer and the oscillator output of the follow-on oscillator is connected to a second input of the frequency mixer, wherein a mixer output of the frequency mixer is connected to a frequency control input of the follow-on oscillator via at least one low pass and at least one synchronized comparator. By means of the frequency mixer and the low pass disposed downstream relative thereto, an analog signal is generated for the difference frequency between the rotation frequency of the rotation scanning signal and that of the digital oscillating signal. Said analog signal is then converted by means of the comparator to a digital control signal for the follow-on oscillator. The analog low pass of the phase control loop enables a high loop amplification in the signal band of the angle change with simultaneous low loop amplification in the rotation frequency, so that a spectral displacement of the quantization noise from the signal band, or noise shaping, takes place. As with any sigma-delta modulator, the arrangement and the frequency response of the low pass can be adapted to the specific conditions of the application.
[0011] It is advantageous if the phasing detector has a quadrant detector, which has a first polarity detector and a second polarization detector, that an input of the first polarization detector is connected to a measurement signal output of a first magnetic field sensor and an input of the second polarization detector is connected to a measurement signal output of a second magnetic field sensor, and if the second

magnetic field sensor is aligned with its measurement axis orthogonal to the measurement axis of the first magnetic field sensor. In this way it is possible to assign the measured magnetic field angle to a precise quadrant and thus determine the amount and the sign of the angle.
[0012] In an improvement of the invention, the magnetic field sensors are Hall sensors, which have a switch device for the orthogonal switching of the Hall sensor supply current and the Hall voltage taps, wherein the switch device has a clock input connected to a clock for a switching clock signal. The invention can therefore also be combined with the so-called spinning current technique.
[0013] It is advantageous if the pulse frequency of the switching clock signal of at least one magnetic field sensor is selected so that within a scanning cycle during which the measurement signal of this magnetic field sensor is coupled to the phase control loop, the orthogonal switching device assumes at least two and preferably four different switching statuses. By averaging the four possible polarities of the Hall sensors, it is possible to reduce a measurement-induced offset substantially. The mixer bandwidth increases due to the higher pulse frequency of the switching clock signal.
[0014] In another advantageous embodiment of the invention, the pulse frequency of the switching clock signal of at least one magnetic field sensor is selected so that the Hall sensor supply current of the magnetic field sensor changes its direction once after each rotation cycle of the rotation scanning signal. A spinning cycle is then completed after four rotation cycles of the rotation scanning signal. The spinning frequency fspin is then expressed as fspin = (frot /4) = (fCik/4N), wherein frot is the rotation frequency of the rotation scanning signal and fdk is the pulse frequency of a clock. The individual phase offsets of the magnetic field sensors are thus displaced from f=0 to fspln. A decimation filter can suppress these frequency components, thus enabling the averaging of the sensor offsets without additional expenditure.

[0015] Preference is given to the comparator having a clock signal input
connected to a clock signal generator, wherein the clock signal generator is
configured so that the pulse frequency of a comparator clock signal residing at the
clock signal input is at least twice as large as the rotation frequency of the rotation
scanning signal. The finding that the output signal of the frequency mixer oscillates
with the frequency fmix = 2 frot when the phase control loop is engaged is thus
exploited. By the faster pulsing of the comparator, the angle of the magnetic field can
be measured even more quickly.
[0016] In an advantageous embodiment of the invention, the follow-on oscillator
has a number of oscillator outputs for digital oscillating signals phase-displaced
relative to each other corresponding to the number of magnetic field sensors aligned
with their measurement axes at right angles to each other, wherein a number of
frequency mixers corresponding to the aforesaid number is arranged in the phase
control loop, wherein each frequency mixer always has a first input connected to a
measurement signal output of a magnetic field sensor allocated to the frequency
mixer and a second input connected to one of the oscillator outputs, and wherein the
mixer outputs of the frequency mixers are connected via an adding element, at least
one low pass, and at least one synchronized comparator to the frequency control
input of the follow-on oscillator. Preference is given to the scanning rate of the
comparator having a frequency four times higher than the rotation cycle. The angle of
the magnetic field can thus be measured even faster.
[0017] Mention should still be made that the measurement precision of the device
can also be increased by always providing, for each measurement axis, several
magnetic field sensors aligned parallel relative to each other, and by averaging the
measurement signals of these magnetic field sensors.
[0018] Regarding the method of the aforementioned type, the object mentioned in
the preceding is achieved by generating at least one digital oscillating signal, by
(written)over an angular range controlling the phasing of the digital oscillating signal so that/* it is phase of 360°

synchronous with the phasing of a rotation scanning signal formed by rotary scanning
of the measurement signals of the magnetic field sensors, and by measuring the
angle of the phasing of the digital oscillating signal.
[0019] In an advantageous manner, it is thus possible to measure easily the angle
at which the magnetic field is aligned in the plane spanned by the axes of the
magnetic field sensors relative to the reference axis by determination of the phasing
of the digital oscillation signal.
[0020] Illustrative embodiments of the invention are explained in more detail in the
following, with reference to the drawing. Shown are:
[0021] Fig. 1 a first illustrative embodiment of a device for measuring an
angle at which a magnetic field is aligned in a plane relative to a reference axis,
[0022] Fig. 2 a second illustrative embodiment of the device, and
[0023] Fig. 3 a graphic illustration of a rotation scanning signal Vrot, a digital
oscillating signal Svco and an oscillating signal Vmix at the output of a frequency mixer
of the device, wherein on the abscissa is plotted the time and on the ordinate is
plotted the amplitude of the corresponding signal.
[0024] A device designated in its entirety by 1 for measuring an angle at which a
magnetic field B is aligned in a plane 2 relative to a reference axis has two magnetic
field sensors 3, 4 configured as Hall sensors, which are aligned with their
measurement axes at right angles to each other. A first magnetic field sensor 3 is
sensitive to an x-component of the magnetic field B and a second magnetic field
sensor 4 is sensitive to a y-component of the magnetic field B.
[0025] The magnetic field sensors 3, 4 are integrated in a semiconductor chip,
which is not shown in any greater detail in the drawing. They each have a Hall plate
monolithically integrated in a semiconductor substrate, which is aligned with its
extension plane perpendicular to the plane of the semiconductor chip.

[0026] In Fig. 1 and 2 it can be discerned that the device 1 has a PLL phase
control circuit 5 with a [missing text] in a phase control loop, in which is integrated a
follow-on oscillator 6. The follow-on oscillator 6 in the illustrative embodiment of Fig.
1 has an oscillator output 7 for an approximately rectangular digital oscillating signal
8. The follow-on oscillator 6 has a frequency control input 9 for adjusting the base
frequency of the digital oscillating signal 8. The fundamental frequency of the digital
oscillating signal 8 is dependent on a voltage residing at the frequency control input 9.
[0027] The magnetic field sensors 3, 4 are coupled to the phase control loop in
such a way that the digital oscillating signal is phase synchronous with a rotation
scanning signal 10 formed by rotary scanning of the measurement signals of the
magnetic field sensors 3, 4. In Fig. 3, the scanning values contained in the rotation
scanning signal 10 detected by the measurement signal of the first magnetic field
sensor 3 are designated in each case with X+ or X- and the scanning values
detected by the measurement signal of the second magnetic field sensor 4 are
designated in each case with Y+ or Y- . It can be clearly discerned that with each
rotation cycle 11 of the rotation scanning signal 10, scanning values X+, Y+, X-, Y-
allocated in each case to the different magnetic field sensors 3, 4 are successively,
cyclically generated. A sinusoidal curve allocated to the rotation scanning signal 10,
whereon the detected measurement values reside, is also illustrated with dashes in
Fig. 3.
[0028] In the illustrative embodiment shown in Fig. 1, the measurement signal
outputs 12, 13 of the magnetic field sensors 3, 4 are in each case connected to an
input terminal of a multiplexer 14. By means of the multiplexer 14 the measurement
signal outputs 12, 13 are each successively, cyclically connected to an output
terminal 15 for the rotation scanning signal 10 provided on the multiplexer 14. In Fig.
1 it can be further discerned that the multiplexer 14 has a control input 16 at which a
rotation clock signal resides. The rotation clock signal is formed by means of a
frequency divider 17 from an internal clock of a clock signal generator 18. In Fig. 1

the frequency of the rotation clock signal is designated with frot and the frequency of the internal clock is designated with fclk . The division ratio N of the frequency divider 17 corresponds to the number of clock pulses that a rotation cycle lasts. [0029] The output terminal 15 for the rotation scanning signal 10 is connected to a first input of a frequency mixer 19 serving as a synchronization signal input for the phase control circuit 5 and the oscillator output 7 of the follow-on oscillator 6 is connected to a second input of the frequency mixer 19. At a mixer output 20 of the frequency mixer 19 resides a mixed signal 21, which corresponds to the product of the rotation scanning-signal Vrotand the digital oscillating signal 8 (Fig. 3). [0030] The mixer output 20 of the frequency mixer 19 is connected via an analog low pass 22 to an input of a comparator 23 synchronized with the rotation clock signal. The comparator evaluates the analog filtered signal after each rotation cycle. In the simplest case, its resolution can equal 1 bit. At the output of the comparator 23 resides a digital signal, which is transmitted to the frequency control input 9 of the follow-on oscillator 6 in order to form a control loop.
[0031] It can be discerned in Fig. 3 that when the phase control circuit is engaged the digital oscillating signal 8 is phase synchronous with the rotation scanning signal 10 or with the sinusoidal curve illustrated with dashes. The unique properties of the follow-on oscillator give rise to a ca. 90° phase displacement between the digital oscillating signal 8 and the rotation scanning signal 10.
[0032] To determine the angle at which the magnetic field B is aligned in the plane 2 relative to the reference axis, the device 1 has a phasing detector. The latter has a counter 24 for the clock pulses of the internal clock. The counter 24 is started by a start pulse, which marks a virtual zero phasing 25 corresponding to the reference axis for measurement of the angle. The counter 24 stops once a slope or a zero crossing arises in the digital oscillating signal. At the output of the counter 24 resides a digital signal φVco corresponding to the phase angle of the digital oscillating signal 8. The output of the counter 24 is connected to a first input of a low-pass filter 26.

[0033] The phasing detector further comprises a quadrant detector, which has a first polarity detector 27 and a second polarization detector 28. An input of the first polarization detector 27 is connected to the measurement signal output 12 of the first magnetic field sensor 3 and an input of the second polarization detector 28 is connected to the measurement signal output 13 of a second magnetic field sensor 4. [0034] An output of the phasing detector is connected to a second input of the low-pass filter 26. At the output of the low-pass filter 26 resides a measurement signal φout corresponding to the angle of the magnetic field.
[0035] In Fig. 3 it can be discerned that, with the phase control loop engaged, the mixer output signal Vmix oscillates with the frequency fmix = 2frot. With omission of the rotation phases 2 and 3 it is thus possible to exert an influence without the functionality. The follow-on oscillator 6 then only executes half periods. The comparator is likewise twice as rapidly synchronized with the frequency fCOmP = 2fCik/N, thus doubling the loop band width and the scanning rate.
[0036] An additional doubling of the loop band width is possible with the illustrative embodiment shown in Fig. 2. In this embodiment the follow-on oscillator 6 has oscillator outputs 7a, 7b for two digital oscillating signals. A first digital oscillating signal resides at a first oscillator output 7a and a second digital oscillating signal resides at a second oscillator output 7b of the follow-on oscillator 6. The first digital oscillating signal and the second digital oscillating signal are thus phase displaced by 90° relative to each other (quadrature signals).
[0037] It can be further discerned in Fig. 2 that two frequency mixers 19a, 19b are arranged in the phase control loop. A first input of a first frequency mixer 19a is connected to the measurement signal output 12 of the first magnetic field sensor 3 and a second input of the first frequency mixer 19a is connected to the first oscillator output 7a. In an analogous manner the first input of a second frequency mixer 19b is connected to the measurement signal output 13 of the second magnetic field sensor 4 and a second input of the second frequency mixer 19b is connected to the second

oscillator output 7b. The multiplexer 14 or the rotary switch provided in Fig. 1 is thus
lacking in Fig. 2.
[0038| The mixer outputs 20a, 20b of the frequency mixers 19a, 19b are in each
case connected to an input of an adding element 29. The output of the adding
element 29 is connected via an analog low pass 22 to an input of a comparator 23
synchronized with a clock signal. The frequency of the clock signal is four times
higher than the clock frequency fdkof the clock 18 divided by the number of clock
pulses N that a rotation cycle lasts. The scanning rate fs of the follow-on oscillator 6
thus equals fs = 4fclkN, and the resolution is equal to ld(N) bit.
[0039] The phasing detector in Fig. 2 corresponds to that in Fig. 1, and therefore
reference is made to the corresponding description.

we Claims
1. Device (1) for measuring an angle at which a magnetic field (B) is aligned in a plane (2) relative to a reference axis with at least two magnetic field sensors (2, 4) [sic], which are aligned with their measurement axes in and/or parallel to the plane (2) and oriented at right angles to each other, characterized in that the device (1) has a PLL phase control circuit (5) with a follow-on oscillator (6) arranged in a phase control loop, further characterized in that the follow-on oscillator (6) has at least one oscillator output (7) for a digital oscillating signal (8), further characterized in that the magnetic field sensors (3, 4) are coupled to the phase control loop in such a way that the digital oscillating signal (8) is phase synchronous with a rotation scanning signal (10) formed by rotary scanning of the measurement signals of the magnetic field sensors (3, 4), and still further characterized in that the oscillator output (7) is connected to a phasing detector for determining the phasing of the digital oscillating signal (8).
2. Device (1) as in claim 1, characterized in that the magnetic field sensors (3, 4) are connected to a scanning device in such a way that the measurement signals of the individual magnetic field sensors (3, 4) are capable of being applied successively to an output terminal (15) for the rotation scanning signal (10), and further characterized in that the output terminal (15) is connected to a synchronization signal input of the PLL phase control circuit (5).
3. Device (1) as in claim 1 or 2, characterized in that each magnetic field sensor (3, 4) always has a measurement signal output connected to an input terminal of a multiplexer (14), and further characterized in that the multiplexer (14) has an output capable of being connected to the individual input terminals which forms the output terminal (15) for the rotation scanning signal (10).

4. Device (1) as in any one of claims 1 through 3, characterized in that the output terminal (15) for the rotation scanning signal (10) is connected to a first input of a frequency mixer (19) and the oscillator output (7) of the follow-on oscillator (6) is connected to a second input of the frequency mixer (19), and further characterized in that a mixer output (20) of the frequency mixer (19) is connected via at least one low pass (22) and at least one synchronized comparator (23) to a frequency control input (9) of the follow-on oscillator (6).
5. Device (1) as in any one of claims 1 through 4, characterized in that the phasing detector has a quadrant detector, which has a first polarity detector (27) and a second polarization detector (28), further characterized in that an input of the first polarization detector (27) is connected to a measurement signal output (12) of a first magnetic field sensor (3) and an input of the second polarization detector (28) is connected to a measurement signal output (13) of a second magnetic field sensor (4), and still further characterized in that the second magnetic field sensor (4) is aligned with its measurement axis orthogonally to the measurement axis of the first magnetic field sensor (3).
6. Device (1) as in any one of claims 1 through 5, characterized in that the magnetic field sensors (3, 4) are Hall sensors, which have a switching device for the orthogonal switching of the Hall sensor supply current and the Hall voltage taps, and further characterized in that the switching device has a clock input connected to a clock for a switching signal.
7. Device (1) as in any one of claims 1 through 6, characterized in that the pulse frequency of the switching clock signal of at least one magnetic field sensor (3, 4) is chosen so that within a scanning cycle, during which the measurement signal of this

magnetic field sensor is coupled to the phase control loop, the orthogonal switching device assumes at least two and preferably four switching statuses.
8. Device (1) as in any one of claims 1 through 7, characterized in that the pulse frequency of the switching clock signal of at least one magnetic field sensor (3, 4) is chosen so that the Hall sensor supply current of the magnetic field sensor changes its direction once after each rotation cycle of the rotation scanning signal (10).
9. Device (1) as in any one of claims 1 through 8, characterized in that the comparator (23) has a clock signal input connected to a clock signal generator, and further characterized in that the clock signal generator is configured so that the pulse frequency of a comparator clock signal residing at the clock signal input is at least twice as high as the rotation frequency of the rotation scanning signal (10).
10. Device (1) as in any one of claims 1 through 9, characterized in that the follow-on oscillator (6) has a number of oscillator outputs (7a, 7b) corresponding to the number of the magnetic field sensors (3, 4) with their measurement axes aligned perpendicular relative to each other for digital oscillating signals phase displaced relative to each other, further characterized in that a number of frequency mixers (19a, 19b) corresponding to the aforesaid number are arranged in the phase control loop, further characterized in that each frequency mixer (19a, 19b) always has a first input connected to a measurement signal output (12, 13) of a magnetic field sensor (3, 4) allocated to the frequency mixer (19a, 19b) and a second input connected to one of the oscillator outputs (7a, 7b), and still further characterized in that mixer outputs of the frequency mixers (7a, 7b) [sic] are connected to the frequency control input (9) of the follow-on oscillator (6) via an adding element (29), at least one low pass (22) and at least one synchronized comparator (23).

11. Method for measuring an angle at which a magnetic field (B) is aligned in a plane (2) relative to a reference axis, wherein a first magnetic field component (Vx) and a second magnetic field component (Vy) aligned at right angles thereto are measured in and/or parallel to the plane (2), characterized in that at least one digital oscillating signal (8) is generated, further characterized in that the phasing of the digital oscillating signal (8) is controlled so that it is phase synchronous with the phasing of a rotation scanning signal (10) formed by rotary scanning of the measurement signals of the magnetic field sensors (3, 4), and still further characterized in that the angle is determined from the phasing of the digital oscillating signal (8).

A device (1) for measuring an angle at which a magnetic field (B) is aligned in a plane (2) relative to a reference axis has at least two magnetic field sensors (2, 4) [sic], which are aligned with their measurement axes in and/or parallel to the plane (2) and oriented at right angles to each other. The device (1) has a PLL phase control circuit (5) with a follow-on oscillator (6) arranged in a phase control loop, which has at least one oscillator output (7) for a digital oscillating signal (8). The magnetic field sensors (3, 4) are coupled to the phase control loop in such a way that the digital oscillating signal (8) is phase synchronous with a rotation scanning signal (10) formed by rotary scanning of the measurement signals of the magnetic field sensors (3, 4). The oscillator output (7) is connected to a phasing detector for determining the phasing of the digital oscillating signal (8).