U.S. patent application number 13/889365 was filed with the patent office on 2013-09-19 for apparatus, sensor circuit, and method for operating an apparatus or a sensor circuit.
This patent application is currently assigned to Infineon Technologies AG. The applicant listed for this patent is INFINEON TECHNOLOGIES AG. Invention is credited to Udo Ausserlechner, Christian Kolle, Mario Motz.
Application Number | 20130241540 13/889365 |
Document ID | / |
Family ID | 44858963 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130241540 |
Kind Code |
A1 |
Ausserlechner; Udo ; et
al. |
September 19, 2013 |
Apparatus, Sensor Circuit, and Method for Operating an Apparatus or
a Sensor Circuit
Abstract
A sensor system comprises a sensor element adapted to sense at
least one physical quantity, wherein the sensor element is adapted
to generate a sensor signal in response to the at least one
physical quantity, an evaluation circuit adapted to detect a
manipulation of the sensor system based on the sensor signal and
stored reference values and to output an indication signal in
response to a detected manipulation and a package, the package
housing at least the sensor element and the evaluation circuit.
Inventors: |
Ausserlechner; Udo;
(Villach, AT) ; Kolle; Christian; (Villach,
AT) ; Motz; Mario; (Wernberg, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INFINEON TECHNOLOGIES AG |
Neubiberg |
|
DE |
|
|
Assignee: |
Infineon Technologies AG
Neubiberg
DE
|
Family ID: |
44858963 |
Appl. No.: |
13/889365 |
Filed: |
May 8, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12771310 |
Apr 30, 2010 |
8442787 |
|
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13889365 |
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Current U.S.
Class: |
324/226 ;
324/260 |
Current CPC
Class: |
G01R 22/066 20130101;
G01N 27/72 20130101; G01R 31/2829 20130101; G01R 15/202 20130101;
G01R 15/181 20130101; G01D 3/0365 20130101; G01D 3/036
20130101 |
Class at
Publication: |
324/226 ;
324/260 |
International
Class: |
G01N 27/72 20060101
G01N027/72 |
Claims
1. A sensor system, comprising: a sensor element adapted to sense
at least one physical quantity, wherein the sensor element is
adapted to generate a sensor signal in response to the at least one
physical quantity; an evaluation circuit adapted to detect a
manipulation of the sensor system based on the sensor signal and
stored reference values and to output an indication signal in
response to a detected manipulation; and a package, the package
housing at least the sensor element and the evaluation circuit.
2. The sensor system according to claim 1, wherein the sensor
element is adapted to sense at least a first magnetic field
component in a first direction and a second magnetic field
component in a second direction, the first and second direction
being orthogonal.
3. The sensor system according to claim 1, wherein the sensor
element is a first sensor element adapted to sense a first physical
quantity and to generate a second sensor signal in response to the
first physical quantity, the sensor system further comprising a
second sensor element adapted to sense a second physical quantity,
wherein the second sensor element is adapted to generate a second
sensor signal in response to the second physical quantity; and
wherein the evaluation circuit is adapted to detect a manipulation
of the sensor system based on the first and second sensor
signal.
4. The sensor system according to claim 3, wherein the first and
second sensor elements are integrated in a same package.
5. The sensor system according to claim 3, wherein the first and
second sensor elements are integrated on a same chip.
6. The sensor system according to claim 3, wherein the first sensor
element is a sensor element adapted to measure a primary physical
quantity and the second sensor element is a sensor element adapted
to measure a secondary physical quantity.
7. The sensor system according to claim 6, wherein the secondary
physical quantity is a temperature
8. The sensor system according to claim 6, wherein the secondary
physical quantity is a mechanical stress.
9. The sensor system according to claim 8, wherein the sensor
system is adapted to compensate a drift caused by a variation of
the primary physical quantity.
10. An apparatus comprising: a magnetic field sensor, the magnetic
field sensor having a first sensing element to measure a first
magnetic field component, the first magnetic field component being
a primary physical quantity and a second sensing element to measure
a second magnetic field component, the second magnetic field
component being a secondary physical quantity, the first magnetic
field component being orthogonal to the second magnetic field
component; an evaluation circuit capable to indicate a manipulation
of the system based on an evaluation of an output signal of the
magnetic field sensor; and. a package housing at least the magnetic
field sensor and the evaluation circuit.
11. The apparatus according to claim 10, wherein the evaluation
circuit is configured to detect a difference between a
characteristic corresponding to a normal operation and a
characteristic not corresponding to a normal operation.
12. The apparatus according to claim 11, wherein the evaluation
circuit is configured to detect a difference between a
characteristic corresponding to a normal operation and a
characteristic not corresponding to a normal operation based on the
sensor signal and stored reference values.
13. The apparatus according to claim 10, wherein the evaluation
circuit is configured to determine a manipulation based on the
detection of a temporal characteristic of a manipulation magnetic
field.
14. The apparatus according to claim 10, wherein the apparatus is
capable to measure an electric current as a primary physical
quantity.
15. The apparatus according to claim 14, wherein the apparatus is
an electricity meter apparatus.
16. A sensor device comprising: a first sensing element to provide
a first sensor signal based on a sensed first physical quantity; a
second sensing element to provide a second sensor signal based on a
sensed second physical quantity; a circuit capable to evaluate the
first sensor signal with regard to an expected normal operation
signal characteristic of the first sensor signal and capable to
evaluate the second sensor signal with regard to an expected normal
operation signal characteristic of the second sensing element, the
circuit being capable to output a signal indicating a sensing
manipulation based on the evaluating of the first and second sensor
signals; a semiconductor package comprising encapsulating material,
the encapsulating material encapsulating at least the first and
second sensing element.
17. The sensor device according to claim 16, wherein the first
sensing element is a sensing element to sense a primary physical
quantity and the second sensing element is a sensing element to
sense a secondary physical quantity.
18. The sensor device according to claim 16, wherein the circuit is
configured to start an evaluation of the second sensor signal based
on an evaluation that the first sensor signal is not within an
expected normal operation signal characteristic.
19. The sensor device according to claim 16, wherein the first and
second physical quantity is selected from a group consisting of: a
magnetic field, a temperature and a mechanical stress.
20. The sensor device according to claim 16, wherein the circuit is
capable of evaluating the first and second sensor signals based on
an expected static characteristic or based on an expected dynamic
characteristic of the normal operation of the first and second
sensor signals.
21. The sensor device according to claim 16 wherein the circuit is
capable of evaluating the first and second sensor signals based on
a spatial characteristic.
22. The sensor device according to claim 16, wherein the circuit is
capable of evaluating the first and second sensor signals based on
a temporal characteristic.
23. The sensor device according to claim 16 further comprising: a
third sensing element to provide a third sensor signal based on a
sensed third physical quantity, wherein the circuit is further
capable of evaluating the third sensor signal with regard to an
expected normal operation signal characteristic of the third sensor
signal, wherein the circuit is capable to output a signal
indicating a sensing manipulation based on the evaluating of the
first, second and third sensor signals; and wherein the
encapsulating material encapsulates at least the first, second and
third sensing elements.
24. The sensor device according to claim 16, wherein the first
sensing element is provided on a first semiconductor chip and the
second sensing element is provided on a second semiconductor
chip.
25. The sensor device according to claim 16, wherein the sensor
device is a current sensor provided in an electricity meter.
26. The sensor device according to claim 25, wherein the circuit is
capable to indicate an attempt of manipulation based on an
evaluation of a background magnetic field.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/771,310 which was filed on Apr. 30, 2010
and claims the benefit of the priority date of this application,
the contents of which are herein incorporated in its full entirety
by reference.
TECHNICAL FIELD OF THE INVENTION
[0002] Embodiments of the present invention relate to apparatus
comprising a sensor element, sensor circuits and methods of
operating the same.
BACKGROUND OF THE INVENTION
[0003] Often sensors are used in applications, where ultimate
reliability and prevention of misuse or fraudulent manipulation is
crucial: life sustaining applications in medical treatment,
applications in transportation where lives may be endangered in
case of malfunction, metering, billing and remote payment systems
which need protection against forgery or fraudulent
falsification.
[0004] Applications for magnetic sensors in general and for
differential magnetic sensors in particular are, for example,
systems counting the rotations of a mechanical member, for example
for measuring the amount of water flowing through a pipe or
measuring the number of turns of a wheel in a car, that must be
protected against manipulation by electromagnetic stimuli. For
example, one could try to apply a rotating magnetic field to such a
sensor system to imitate the rotation of the mechanical member
thereby manipulating the number of rotations detected. The rotating
field could be generated by attaching a permanent magnet to a
handheld drilling machine or by using two orthogonal coils supplied
with two sinusoidal currents with 90.degree. phase shift.
[0005] Another example refers to electricity meters, where one
could try to attach a small permanent magnet nearby a sensor in an
intend to defraud. If the current through a conductor is measured,
for example using a magnetic sensor, one could try to bend the
conductor so that the current flows in opposite direction and close
to the original sensor thereby reducing the magnetic field on the
sensor which would decrease the measured value of apparent
current.
[0006] Besides intentional misuse as described above, it is
beneficial if these sensor systems are also robust against
unintended manipulation, or put more general, against abnormal
operating conditions. For example, if a rotational position sensor
is exposed to a large magnetic field this may impair its accuracy.
In an automotive system this may lead to a wrong ignition timing
with increased fuel consumption and increase air pollution. In
medical instrumentation this may lead to inaccurate determination
of a three dimensional location (3D-location) of a micro-surgery
tool during a delicate heart- or brain-surgery.
[0007] Therefore, there is a need to make sensors or systems using
such sensors robust against manipulation or against an abnormal
operating condition and/or to detect, whether a manipulation or an
abnormal operating condition occurs.
SUMMARY
[0008] Embodiments provide a sensor system comprising a sensor
element adapted to sense at least one physical quantity, wherein
the sensor element is adapted to generate a sensor signal in
response to the at least one physical quantity, an evaluation
circuit adapted to detect a manipulation of the sensor system based
on the sensor signal and stored reference values and to output an
indication signal in response to a detected manipulation and a
package, the package housing at least the sensor element and the
evaluation circuit. Embodiments provide an apparatus comprising a
magnetic field sensor, the magnetic field sensor having a first
sensing element to measure a first magnetic field component, the
first magnetic field component being a primary physical quantity
and a second sensing element to measure a second magnetic field
component, the second magnetic field component being a secondary
physical quantity, the first magnetic field component being
orthogonal to the second magnetic field component. An evaluation
circuit is provided capable to indicate a manipulation of the
system based on an evaluation of an output signal of the magnetic
field sensor and a package is provided housing at least the
magnetic field sensor and the evaluation circuit.
[0009] Embodiments provide a sensor device comprising a first
sensing element to provide a first sensor signal based on a sensed
first physical quantity, a second sensing element to provide a
second sensor signal based on a sensed second physical quantity, a
circuit capable to evaluate the first sensor signal with regard to
an expected normal operation signal characteristic of the first
sensor signal and capable to evaluate the second sensor signal with
regard to an expected normal operation signal characteristic of the
second sensing element, the circuit being capable to output a
signal indicating a sensing manipulation based on the evaluating of
the first and second sensor signals and a semiconductor package
comprising encapsulating material, the encapsulating material
encapsulating at least the first and second sensing element.
[0010] Embodiments of the evaluation circuit can be adapted to
output the signal, also referred to as an evaluation signal, only
in case abnormal operation conditions have been detected or can be
adapted to output the signal in any case, wherein, e.g., a first
value of the signal indicates a normal operating condition and a
second value different from the first value indicates the abnormal
operation condition. The signal generated by the evaluation circuit
in case it detects an abnormal operation condition can also be
referred to as an abnormal operation condition signal.
[0011] The signal or evaluation signal produced by the evaluation
circuit is not to be confused with a sensor signal or measurement
signal, e.g. a temperature value output by a temperature sensor
which represents the temperature but does not comprise any
evaluation or assessment of the temperature with regard to the
operating conditions at which the temperature signal was measured.
In other words, in contrast to sensor signals or measurement
signals, the evaluation signal does not represent the physical
quantity to be measured but comprises, e.g., information about an
evaluation or assessment whether the operating conditions at which
the sensor signals and measurements signals were obtained are to be
considered normal or not. In case the evaluation indicates that the
operating conditions are normal, the sensor signals and the
measurement signals (or any other output signal produced by the
signal processing unit) can be considered, e.g., "trustworthy" or
"reliable", whereas in case the evaluation signal indicates that
the operating conditions are not normal or abnormal, the sensor
signals and measurement signals (or any other output signal
produced by the signal processing unit) can be considered "not
trustworthy" or "unreliable".
[0012] Embodiments provide a sensor circuit comprising: a first
primary sensor element adapted to generate a first primary sensor
signal in response to a first primary physical quantity comprising
a first wanted part or a first unwanted ambient part; and a second
primary sensor element adapted to generate a second primary sensor
signal in response to a second primary physical quantity comprising
a second wanted part or a second unwanted ambient part, wherein the
second primary physical quantity is of a same type as the first
physical quantity; a signal processing circuit adapted to process
the first primary sensor signal and the second primary sensor
signal according to a first algorithm to obtain a measurement
signal; and an evaluation circuit adapted to evaluate the first
primary sensor signal and the second primary sensor signal
according to a second algorithm that is different than the first
algorithm and to generate a signal indicating an abnormal operating
condition in case the result of the second algorithm sensor signal
does not fulfill a predetermined normal operation criterion.
[0013] Embodiments ion provide a sensor circuit comprising: a
signal processing unit adapted to process at least one sensor
signal of a plurality of sensor signals generated by at least one
sensor element to obtain a measurement signal; and an evaluation
circuit adapted to evaluate the at least one sensor signal of the
plurality of sensor signals to derive a signal indicating an
abnormal operating condition in case the at least one sensor signal
does not fulfill a predetermined normal operation criterion,
wherein the predetermined normal operation criterion defines a
predetermined relation between a value of the at least one sensor
signal and a value of at least one other sensor signal of the
plurality of sensor signals during a normal operation, or a
relation between the value of the at least one sensor signal and a
value of a measurement signal during a normal operation.
[0014] In certain embodiments, the plurality of sensor signals can
be produced by the same sensor element or other sensor elements of
the same class of sensor elements over time to evaluate a temporal
relation between the at least one sensor signal and the at least
one other sensor signal or the measurement signal.
[0015] In further embodiments, the plurality of sensor signals can
be produced by different sensor elements of the same class of
sensor elements, i.e. by sensor elements adapted to measure the
same type of physical quantity, to evaluate a spatial relation
between the at least one sensor signal and the at least one other
sensor signal or the measurement signal.
[0016] In even further embodiments, the plurality of sensor signals
can be produced by different sensor elements of different classes
of sensor elements, i.e. by sensor elements adapted to measure
different types of physical quantities, and the evaluation circuit
can be adapted to evaluate a temporal or spatial relation between
the at least one sensor signal and the at least one other sensor
signal or the measurement signal. For example, in case a high
current flows through a magnetic current sensor, the temperature
due to internal heat generation increases. This effect or other
similar effects can be used to evaluate a primary sensor signal
based on a secondary sensor signal.
[0017] Embodiments of the invention provide a method for operating
an apparatus comprising a sensor element for sensing an
predetermined physical quantity, the method comprising: sensing the
predetermined physical quantity by the sensor element and
generating a sensor signal in response to the predetermined
physical quantity; processing an input signal to obtain an output
signal depending on the sensor signal; and evaluating the sensor
signal and generating a signal indicating an abnormal operating
condition in case the sensor signal does not fulfill a
predetermined normal operation criterion.
[0018] Embodiments of the invention provide a method for operating
a sensor circuit comprising a first primary sensor element and a
second primary sensor element, the method comprising: generating a
first primary sensor signal by the first primary sensor element in
response to a first primary physical quantity comprising a first
wanted part or a first unwanted ambient part; and generating a
second primary sensor signal by the second primary sensor element
in response to a second primary physical quantity comprising a
second wanted part or a second unwanted ambient part, wherein the
second primary physical quantity is of a same type as the first
physical quantity; processing the first primary sensor signal and
the second primary sensor signal according to a first algorithm to
obtain a measurement signal; and evaluating the first primary
sensor signal and the second primary sensor signal according to a
second algorithm that is different than the first algorithm and to
generate a signal indicating an abnormal operating condition in
case the result of the second algorithm sensor signal does not
fulfill a predetermined normal operation criterion.
[0019] Embodiments of the invention provide, for example, an
apparatus or a sensor system that is robust against external
disturbances. In other words, embodiments of the invention relate
to apparatus and/or sensor systems capable to detect abnormal
operating conditions, wherein "abnormal operating conditions" are
operating conditions which are significantly different from normal
operating conditions.
[0020] Normal operating conditions are, for example given in a
datasheet of the electronic system. The datasheet, for example
lists the supply voltage, the ambient temperature, for sensor
systems also a certain range of applied values for the physical
quantities to be measured. It may also comprise environmental
quantities like a maximum allowed radiation dose or ambient
pressure or humidity or a range of allowed altitudes or a maximum
acceleration or vibration. Those operating conditions can also be
referred to as "explicitly given normal operating conditions".
[0021] Many operating conditions are not given explicitly, but
rather implicitly, for example, if the datasheet explains a rule
for soldering or mounting a device into a module or how to fix it
to a heat slug or how to bend its leads. Any violation of this rule
may lead to operating conditions which are far from normal, for
example, lead to too high mechanical stress or temperature during
assembly and potentially also during operation, which again might
deteriorate the measurement quality.
[0022] The term "abnormal operating conditions" should not be
confused with "defects" or "defective systems". For example, (i) a
high density memory may detect that a certain address space of the
memory is stuck at zero or one, or (ii) a telecommunication system
may detect that errors have occurred during storage or transmission
of data which is done by error coding techniques like the well
known Reed-Solomon-Code for compact disks for audio recording, or
(iii) a sensor system may detect that part of a large array of
sensor elements may be defective because it renders signals which
differ significantly from the rest of the sensor array although the
entire array is exposed to the same pressure, temperature or
magnetic field, or whatever physical quantity is measured by the
sensor array. Neither such defects nor other internally generated
defects, for example, production flaws, nor defects caused by some
external origin like damage due to electrostatic discharge (ESD) or
insufficient cooling or too high supply voltage or reverse polarity
of voltage to certain input/output ports (I/O-ports) of the
electronic system shall be confused with the "abnormal operating
conditions" addressed by embodiments of the invention.
[0023] Abnormal operating conditions may also lead to a system
error, but this is not necessarily the case. Abnormal operating
conditions--in contrast to the defects detected in the system as
explained above--often cause less obvious effects compared to these
"defects", for example, reduced quality of the system which is not
yet classified as "erroneous" or faulty, for example, enhanced
noise, inaccurate processing of signals, inaccurate readings of
sensor values, reduced lifetime (e.g. due to increased stress on
the system), or reduced reliability (e.g. higher bit error rates,
reduced speed for data transmission). Moreover, the presence of
abnormal operating conditions may also be a sign that there is
something wrong with the environment or ambient conditions in which
the system is working. Finally, abnormal operating conditions may
also be the result of intentional misuse of the system by a user or
by sheer vandalism, for example in billing systems users may try to
manipulate the system.
[0024] To distinguish the "abnormal operating conditions" discussed
herein from the above "defects", the abnormal operating conditions
can also be referred to as "abnormal ambient conditions" or
"abnormal ambient operating conditions" as embodiments of the
invention relate to the detection of abnormal ambient conditions.
Such abnormal ambient conditions or environmental conditions have
the effect, typically only temporarily, i.e. without causing
lasting damage to the sensor or system, that the sensor or system
does not behave or perform as expected, e.g. as expected under
normal ambient conditions.
[0025] Therefore, there is also a need to detect, whether an
abnormal ambient operating condition occurs, e.g. whether the
abnormal ambient operating condition exceeds certain limits between
which the sensor or the system performs acceptably, and to signal
this exceeding of the certain limits, for example, to a controller.
By detecting an abnormal ambient operating condition, sensors or
systems using such sensors can be made more robust against
manipulation (e.g. against a manipulation by applying an external
physical quantity disturbing the normal operation of the apparatus
or system forming an intended case of abnormal ambient operating
conditions to achieve a specific effect at the sensor or system) or
unintended worsening of the ambient operating conditions such that
the ambient operating conditions become abnormal.
[0026] Sensors are used to transduce a physical quantity into a
sensor signal, the sensor signal representing a property of the
physical quantity. The physical quantity to be measured by the
sensor element may also be referred to as a physical measurand and
can be, for example a magnetic field, temperature, mechanical
stress, etc. The sensor signal can be, for example, a voltage or a
current which is primarily or essentially dependent on a physical
quantity to be measured. For example, in case of a Hall sensor for
measuring a magnetic field, the polarity and voltage value or
current value of the sensor signal output by the Hall sensor
primarily depends on the polarity and strength of a magnetic field
measured by the Hall sensor. In addition, the sensor signal
typically also depends on other ambient physical quantities, for
example a temperature or a mechanical stress applied to the Hall
sensor. However, the influence of a temperature and mechanical
stress is typically much smaller than the influence or dependence
of the sensor signal from the primary physical quantity to be
measured by the sensor element. Therefore, in case of a Hall sensor
which is designed for measuring the physical quantity "magnetic
field", the magnetic field may be referred to as the "primary
physical quantity" (the physical quantity the sensor is designed to
sense or measure) and these other physical quantities may also be
referred to as the "secondary physical quantities" (the physical
quantities the sensor is not designed to sense or measure but which
influence the measurement of the primary physical quantity of the
sensor, e.g. by causing a drift). The influence of these secondary
physical quantities on the measurement of the primary physical
quantity can be compensated, for example, by implementing secondary
sensor elements adapted to transduce these secondary physical
quantities into corresponding sensor signals and to adapt the
operation or readout of the primary sensor element to achieve a
measurement of the primary physical quantity that is essentially
independent of one or several of such secondary physical
quantities, e.g. by compensating the drift of a magnetic field
measurement signal generated by a magnetic field sensor due to
temperature or mechanical stress. In other words, the secondary
physical quantity can be any physical quantity that is different
from the primary physical quantity or belongs to a different type
of physical quantity, wherein, for example, the magnetic field
forms a first type of physical quantity, the temperature a second
type of physical quantity and the mechanical stress a third type of
physical quantity.
[0027] As the range of sensor signals and measurement values for
normal operation conditions are known, they can be evaluated with
regard to their expected characteristics or values (expected for
normal operation conditions). Therefore embodiments of the
evaluation circuit can be adapted to evaluate the sensor signal or
sensor signals based on static or dynamic expected characteristics
of the sensor signals and the measurement signals derived therefrom
to detect abnormal operation conditions.
[0028] Further embodiments of the apparatus or sensor circuit use
the fact that different sensor signals typically show a certain
relation during normal operation conditions which can be used to
detect whether an abnormal operation conditions is present. This
relation may be temporal or spatial.
[0029] Ambient physical quantities like ambient temperature
typically show a homogeneous spatial characteristic. This can be
used by embodiments, which comprise e.g. several (at least two)
temperature sensor elements as secondary sensor elements, to
evaluate continuously, whether these temperature sensor elements
really measure the same temperature. In case the difference between
at least two temperature sensor elements becomes too large, an
abnormal ambient condition can be signaled.
[0030] Magnetic fields of a current to be measured by a magnetic
field current sensor typically show an inhomogeneous spatial
characteristic. For example due to the radial characteristic of the
magnetic field and/or due to the structure or geometry of the
conductor, e.g. due to changing cross sections, notches within the
current conductor and/or due to bending of the current conductor.
In contrast thereto, the unwanted earth's magnetic field
superposing the wanted magnetic field of the current to be measured
is spatially (and temporally) homogeneous, at least with regard to
the dimensions of sensor circuits. Furthermore, other current
conductors near to the current sensor also produce an unwanted
magnetic field, which superposes to the wanted magnetic field
produced by the current to be measured. This unwanted magnetic
field may show an inhomogeneous spatial characteristic (radial,
etc), however, this inhomogeneous spatial characteristic is
different from the spatial characteristic of the current to be
measured. For example, in case of a magnetic current sensor with
two magnetic field sensor elements arranged on opposite sides of
the primary conductor of the magnetic current sensor and with the
same distance to the primary conductor, the wanted magnetic field
of the current to be measured has the same magnitude at both
magnetic field sensor elements but with a different sign. A
parallel other current conductor would also produce a radial
magnetic field, however, this unwanted magnetic field would have
different magnitudes at the locations of the two magnetic field
sensor elements and would have the same sign. Thus, the wanted and
unwanted magnetic field parts can be distinguished by their
different spatial characteristics.
[0031] Therefore, embodiments of the apparatus or sensor circuits
can use the knowledge of the specific spatial (or temporal)
characteristic of the wanted physical quantities and evaluate,
whether the sensed or measured physical quantity at least
essentially shows the expected characteristic, and signal an
abnormal operation condition in case the deviation of the sensed or
measured characteristic of the physical quantity differs too much
from the expected one. In other words, embodiments can verify,
whether the sensor signals and the measurement signal are
consistent, i.e. reflect the expected spatial or temporal
dependencies, and produce the abnormal operation condition signal
in case the signals or measurement signal are not consistent or at
least not sufficiently consistent.
[0032] Thus, further embodiments comprise a current sensor circuit
comprising: a signal processing unit adapted to process at least
one sensor signal of a plurality of sensor signals generated by at
least one magnetic field sensor element to obtain a measurement
signal; and an evaluation circuit adapted to evaluate the at least
one sensor signal of the plurality of sensor signals using the at
least one other sensor signal or the measurement signal to derive a
signal indicating an abnormal operation condition in case the at
least one sensor signal does not fulfill a predetermined normal
operation criterion, wherein the predetermined normal operation
criterion is derived from a predetermined temporal or spatial
relation between a value of the at least one sensor signal and a
value of at least one other sensor signal of the plurality of
sensor signals during a normal operation condition.
[0033] The larger the degree of the spatial or temporal
inhomogenity of the wanted physical quantity, the more difficult it
becomes for a person trying to manipulate the apparatus or sensor
circuit to imitate this characteristic and the better becomes the
protection of the apparatus or sensor circuit against intended
manipulation but also against any unintended disturbing physical
quantity.
[0034] Particular embodiments of the invention relate to a class of
systems which is particularly prone to operating conditions because
the systems measure environmental or ambient physical quantities:
sensor systems.
[0035] Typical electronic sensor systems are adapted to measure at
least one physical quantity and output the result of this
measurement by at least one signal. To this end sensors have to
interact more immediately with their environment than other
electronic systems. Therefore, sensor systems or sensors in general
are more susceptible to general environmental influences or ambient
conditions. In fact, typically, sensors are adapted to measure at
least one primary physical quantity, yet the measurement of this at
least one primary physical quantity is typically influenced by at
least one secondary physical quantity. For example, a Hall sensor
is adapted to measure a component of a magnetic field (i.e. a
magnetic field component which may comprise wanted and unwanted
parts) applied to it, yet it is also sensitive to temperature
changes or mechanical stress applied to it. A further example is a
magneto-resistive sensor that is adapted to measure one component
(i.e. a magnetic field component with a first three-dimensional
orientation) of the magnetic field, yet the magneto-resistive
sensor is also sensitive to a second perpendicular component of the
magnetic field (i.e. a second magnetic field component with a
second three-dimensional orientation orthogonal to the first
orientation).
[0036] According to a further aspect of the invention, embodiments
of the sensor circuit comprise more than one sensor element adapted
to measure the same physical quantity or the same type of physical
quantity. A particular class of such sensor systems comprising two
or more sensor elements of the same type or class are called
"gradiometers". Gradiometers detect a spatial variation of a
primary physical quantity. A simple example is a differential Hall
sensor which measures a difference in a magnetic field on two spots
or locations on the semiconductor substrate. The two spots are, for
example 2.5 mm spaced apart from each other. The advantage of
gradiometers is that they allow to separate disturbances or
unwanted parts or portions of the primary physical quantity from
the wanted part or portion of the physical quantity. An example is
a magnetic current sensor, which has two Hall plates and a wire in
between both of them. The current through the wire generates
circular magnetic field lines so that both Hall plates, which are
located symmetrical to the wire, for example, on opposite sides of
the wire with regard to the current flow through the wire, detect
the same magnitude of the field, yet with a different sign. The
signal processing circuit according to this differential sensor
principle subtracts the signals of both Hall plates, each of the
signals including, for example a wanted part (the magnetic field
produced by the current flowing through the wire) and an unwanted
part (the earth's magnetic field or any other background magnetic
field), which effectively doubles the contributions of the circular
field lines (the wanted parts), yet the earth's magnetic field (the
unwanted part) is identical on both Hall plates (identical with
regard to the sign and orientation of the magnetic field) and,
therefore, is cancelled after the subtraction of the two total
measured primary physical quantities. Therefore, the differential
sensor principle allows to separate the unwanted magnetic field
part from the earth from the wanted field part of the current
flowing through the wire.
[0037] This example, also shows a second property of gradiometers:
redundancy. The described system has two Hall plates to measure
only one current. The signal of the second Hall plate is redundant
in the absence of any background fields because it is the signal of
the first Hall plate multiplied by "-1". So the second Hall plate
renders no additional information on the current to be measured.
Yet, it renders information, if there is a background field present
because then it is different from the field on the first Hall plate
multiplied by "-1" and the difference is twice the background
field. In other words, adding the sensor signal of the first Hall
plate and the sensor signal of the second Hall plate cancels the
wanted signal part (because they are essentially equal in
magnitude, however not in sign) and results in providing a value
representing the strength and orientation of the earth magnetic
field or any other homogeneous magnetic field multiplied by 2. An
evaluation circuit (EC) may compare the value of this homogeneous
magnetic field with a predetermined value like e.g. 20 mT and it
outputs "abnormal operating condition" if the homogeneous magnetic
field exceeds this value. Then the system works perfectly (i.e.
with negligible error) at normal operating condition and it signals
"abnormal operating condition" when the homogeneous field is so
large that it endangers proper operation of the system.
[0038] In general terms, an n-th order gradiometer consists of n+1
sensor elements of the same type or same class. It can be used to
derive a primary physical quantity and to detect n spatial
derivatives of the primary physical quantity, namely the 0.sup.th
order spatial derivative (which corresponds to the homogeneous
portion of the primary physical quantity which does not depend on
the location), the first order spatial derivative (which
corresponds to the slope), the second order spatial derivative
(which corresponds to the curvature), etc. and finally the
(n-1).sup.th order spatial derivative. One out of all these spatial
derivatives can be used for the determination of the measurand and
all other spatial derivatives can be used to check for violation of
normal operating conditions. The n-th spatial derivate scales with
the n-th power of the size of the system, which for integrated
sensor systems is on the order of several millimeters or less.
[0039] Embodiments of the invention can be adapted to detect
manipulation or abnormal ambient conditions on an integrated
circuit through on-board sensors (like for magnetic field,
temperature or mechanical stress) by processing their readouts
through algorithms and comparing the results with predetermined
fixed or dynamic limits over a specific time and signal this via
output ports to an external controller.
[0040] In many cases it is good practice to use a differential
field measurement: to this end the system samples, for example, a
magnetic field component at two locations and subtracts both of
them. One important advantage of this measurement system is that it
cancels homogeneous background fields (like e.g. Earth's field or
the stray field of motors and other electro-magnetic
actuators).
[0041] Specific embodiments of the invention can be adapted to
detect manipulation on differential magnetic field sensors by using
the redundant information supplied by the multitude of sensor
elements on the die by processing their readouts through algorithms
and comparing the results with predetermined fixed or dynamic
limits over a specific time and signal this via output ports to a
controller.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] Embodiments are described herein after, and make reference
to the appended drawings.
[0043] FIG. 1A shows a schematic embodiment of an apparatus
comprising a sensor element and an evaluation circuit;
[0044] FIG. 1B shows a block diagram of an embodiment of an
apparatus according to FIG. 1A comprising additionally a time base
and a feedback of the output signal to the evaluation circuit.
[0045] FIG. 2 shows a block diagram of an embodiment of a sensor
circuit comprising a primary sensor element and an additional
(primary or secondary) sensor element and an evaluation
circuit;
[0046] FIG. 3 shows a block diagram of an embodiment of a sensor
circuit with two primary sensor elements arranged at two different
locations of the sensor circuit and an evaluation circuit;
[0047] FIG. 4 shows a top-view of a magnetic field current sensor
with two Hall sensor elements;
[0048] FIG. 5A shows a top-view of an embodiment of a magnetic
field current sensor circuit with three Hall sensor elements;
[0049] FIG. 5B shows a cross-sectional view of a magnetic field
current sensor package with two external sources for disturbing the
magnetic field.
[0050] FIG. 5C shows an exemplary current density distribution in a
part of the primary conductor of a magnetic field current sensor
according to FIG. 5A.
[0051] FIG. 5D shows an exemplary magnetic flux density
distribution of the vertical component of the magnetic field for a
part of the magnetic field current sensor according to FIG. 5A.
[0052] FIG. 6 shows a schematic view of a magnetic rotation sensor
circuit with 2 magnetic field sensor elements at 2 locations.
[0053] Equal or equivalent elements or elements with equal or
equivalent functionalities are denoted in the following description
of the Figures by equal or equivalent reference numerals.
DETAILED DESCRIPTION OF THE INVENTION
[0054] FIG. 1A shows a block-diagram of an embodiment of an
apparatus comprising a signal processing circuit (SPC) 110, a
sensor element (SE) 120 and an evaluation circuit (EC) 130. The
signal processing circuit 110 is adapted to process an input signal
110a to obtain an output signal 110b. The sensor element 120 is
adapted to sense a predetermined physical quantity 140, for example
an ambient physical quantity 140, which may have an influence or
impact on the signal processing circuit 110, wherein the sensor
element 120 is adapted to generate a sensor signal 120b depending
on or in response to the predetermined physical quantity 140.
[0055] The predetermined physical quantity, e.g. temperature or
mechanical stress, can have, for example, an unwanted influence on
the input signal 110a itself or on the processing of the input
signal by the signal processing circuit 110, e.g. may cause a
deviation of the input signal, e.g. a drift due to a variation of
the temperature. Therefore, the signal processing circuit 110 is
adapted to process the input signal 110a, to obtain the output
signal 110b depending on the sensor signal 120b (see arrow), for
example to compensate for the drift caused by the temperature
variation.
[0056] In a specific embodiment, as described later based on FIG.
2, the input signal 110a can be a signal generated by a primary
sensor, wherein the sensor signal 120b is used to compensate the
drift of the signal 110a to facilitate a measurement less prone or
essentially independent of temperature variations.
[0057] The evaluation circuit 130 is adapted to evaluate the sensor
signal 120b and to generate a signal 130b indicating an abnormal
operating condition in case the sensor signal 120b does not fulfill
a predetermined normal operation criterion or normal operation
condition, or defined in a positive way, in case the sensor signal
120b does fulfill a predetermined abnormal operation criterion or
abnormal operation condition.
[0058] In the following embodiments, the invention will be
primarily described based on a negative definition of the
criterion, i.e. the abnormal operation condition is obtained in
case a sensor signal does not fulfill a predetermined normal
operation criterion. However, it should be born in mind that both,
positive or negative definitions can be equally applied to achieve
the same result. Therefore, explanations given with regard to the
negative definition of the criterion apply in a corresponding
manner to the positive definition of the decision criterion.
[0059] In other words, the evaluation circuit 130 is adapted to
obtain a characteristic of the sensor signal and to generate the
signal 130b in case the characteristic of the sensor signal 120b
does not coincide with an expected characteristic of the sensor
signal that is indicative of a normal operation.
[0060] The sensor element 120 can be adapted to transduce a
secondary ambient physical quantity or a primary physical quantity,
for example, an unwanted primary ambient physical quantity, which
may be, e.g. an unwanted ambient part of a primary physical
quantity.
[0061] The sensor elements described herein can be adapted to
produce a sensor signal in response to a physical quantity the
respective sensor element is adapted to sense or measure, wherein
the sensor signal output by the sensor element can be a continuous
analogue signal representing the respective physical quantity
comprised of time continuous analogue values. In alternative
embodiments, the sensor elements can be adapted to comprise
analogue-to-digital-converters (ADC) and to convert the analogue
and continuous signal output, for example, by a Hall plate or
magnetic field measurement or a voltage produced by a negative
temperature coefficient resistor (NTC) or positive temperature
coefficient resistor (PTC) into a series of digital sensor signals
or sensor signal values, i.e. a sequence of discrete sensor signals
or sensor signal values over time, and to output these digital
values as sensor signal 110a or 120b.
[0062] The abnormal operation criterion may define or may be
derived from, e.g. a threshold the sensor signal shall not exceed
during normal operation (because the drift of the input signal
cannot be compensated sufficiently any more, or because the
measurement deviation or processing deviation of the input becomes
too large). The abnormal operation criterion may define or may be
derived from a maximum value and a minimum value, the sensor signal
shall not exceed (the normal operation range being defined as the
range between the minimum and the maximum value), or may define or
may be derived from a maximum temporal deviation magnitude the
sensor signal shall not exceed (the normal operation range being
defined by deviations of the sensor signal over time below the
maximum temporal deviation magnitude). Further, the abnormal
operation criterion may be derived from a sign or polarity the
signal should not have, an average value (e.g. in case wanted
ambient physical quantities have a known frequency f or period T
and unwanted or abnormal ambient physical quantities have a
different frequency or period), or frequency contributions the
sensor signal should not have (e.g. in case wanted ambient physical
quantities have a known frequency limited spectrum).
[0063] The abnormal operation criterion can further comprise or
define tolerances for the above or other criteria to consider noise
or other influences onto the sensor signal and the evaluation of
the sensor signal to avoid, e.g. false detections of abnormal
operation conditions due to the above influences, and to, thus,
achieve a more reliable detection of truly abnormal ambient or
operation conditions.
[0064] According to one embodiment, the predetermined normal
operation criterion defines a maximum value of the sensor signal
120b, and the evaluation circuit is adapted to compare a value of
the sensor signal with the maximum value and to generate the signal
130b indicating an abnormal operating or ambient condition in case
the value of the sensor signal is higher than the maximum value. In
addition or instead of the aforementioned maximum value, the
predetermined normal operation criterion may also define a minimum
value of the sensor signal 120b, and the evaluation circuit may be
adapted to compare the value of the sensor signal with the minimum
value and to generate the signal 130b in case the value of the
sensor signal 120b is smaller than the minimum value.
[0065] According to a further embodiment, the maximum value or the
minimum value is a zero value. Thus ambient physical quantities
that have a sign, polarity or orientation different from an
expected or acceptable sign, polarity or orientation of the ambient
physical quantity can be detected and the signal 130b to indicate
an abnormal ambient condition is generated and, e.g., output by the
apparatus 100. The expected or acceptable sign, polarity or
orientation of the ambient physical quantity defines, e.g., the
normal ambient or operation condition of the physical quantity.
[0066] In other embodiments, the sensor element is adapted to
generate a plurality of sensor signals 120b over time, for example
a temporal sequence of sensor signals, in response to the ambient
physical quantity, wherein the temporal sequence of sensor signals
represents the physical quantity over time, including any
variations of the physical quantity over time. To obtain the
temporal sequence of sensor signals the apparatus comprises, e.g.,
a time basis, either for each circuit element individually or
centrally for some or all circuit elements. The time base can,
e.g., be a oscillator or a simple RC low-pass filter, which
separates fast variations from slow variations.
[0067] In further developments of such other embodiments, the
predetermined normal operation criterion can define a maximum
magnitude for a change of the sensor signal over time, and the
evaluation circuit can be adapted to compare a magnitude of a
change of the sensor signal over time with the maximum magnitude
for a change of the sensor signal and to generate the signal 130b
in case the magnitude of the change of the sensor signal over time
is higher than the maximum magnitude for a change of the sensor
signal. The predetermined abnormal operation criterion can define,
for example, the maximum magnitude for a change of the sensor
signal between two consecutive sensor signals or between two sensor
signals with a predetermined time difference. This method can also
be referred to as a temporal gradient detection method.
[0068] In further developments of such other embodiments using a
plurality of sensor signals obtained at different time instants by
the sensor element, the predetermined normal operation criterion
can define an maximum average value of the sensor signal for a
predetermined duration, and the evaluation circuit can be adapted
to determine an average value of the sensor signal for the
predetermined duration and to generate the signal in case the
average value of the sensor signal is higher than the maximum
average value of the sensor signal. For such further developments
the predetermined normal operation criterion may
define--additionally or alternatively to the maximum average
value--a minimum average value of the sensor signal for a
predetermined duration (the same duration as for the maximum
average value or a different duration), and the evaluation circuit
may be adapted to determine an average value of the sensor signal
for the predetermined duration and to generate the signal in case
the average value of the sensor signal is lower or smaller than the
minimum average value of the sensor signal.
[0069] The predetermined duration may correspond to a period of the
predetermined or ambient physical quantity at normal operation
conditions, e.g. in case no unwanted part of the predetermined or
ambient physical quantity is present, or to an expected or wanted
physical quantity of the type of physical quantity to be measured
by the sensor element 120, whereas an abnormal or unwanted physical
quantity or part of the type of physical quantity to be measured is
not periodic at all or has a different period T and, thus, can be
detected because the average value obtained by the evaluation
circuit 130 is smaller than the minimum average value or higher
than the maximum average value.
[0070] In further developments of such other embodiments using a
plurality of sensor signals obtained at different time instants by
the sensor element, the predetermined normal operation criterion
can define a maximum frequency of the sensor signal, wherein the
evaluation circuit is adapted to process the plurality of sensor
signals to obtain a spectral representation of the plurality of
sensor signals and to generate the signal in case the spectral
representation has a significant contribution at at least one
frequency that is higher than the maximum frequency. In further
embodiments the predetermined normal operation criterion may
additionally or alternatively define a minimum frequency of the
sensor signal, wherein the evaluation circuit is adapted to process
the plurality of sensor signals to obtain a spectral representation
of the plurality of sensor signals and to generate the signal in
case the spectral representation has a significant contribution at
at least one frequency that is smaller than the minimum frequency.
A significant contribution can be, for example, any magnitude that
is higher than a 10% or 20% of a maximum magnitude of the spectral
representation.
[0071] In even further embodiments of the apparatus 100, the sensor
element 120 is located at a first position of the apparatus, and
the apparatus comprises a further sensor element (not shown in FIG.
1A or 1B) located at a second position of the apparatus for sensing
the ambient physical quantity at the second position. In this case,
the sensor element 120 is adapted to generate the sensor signal
120b depending on the ambient physical quantity 140 at the first
position, and the further sensor element is adapted to generate a
further sensor signal depending on the ambient physical quantity at
the second position. In addition the predetermined normal operation
criterion defines a maximum magnitude of a difference between the
sensor signal 120b and the further sensor signal, and the
evaluation circuit is adapted to evaluate a difference between the
sensor signal and the further sensor signal and to generate the
signal in case a magnitude of the difference is higher than a
maximum magnitude of the difference between the sensor signal and
the further sensor signal. This method can also be referred to as a
spatial gradient detection method. The sensor signal and the
further signal to be compared for the spatial gradient detection
are, for example, generated at the same time, i.e. synchroneously,
or essentially the same time, i.e. without significant delay,
wherein without significant delay means that the time difference
between the measurement or sensing of the two signals is much
smaller than the time scale of the disturbances that shall be
detected. The latter can also be referred to as real-time
measurement.
[0072] FIG. 1B shows a block-diagram of an embodiment of an
apparatus according to FIG. 1A, wherein the embodiment 100' of the
apparatus comprises additionally a time-base (TB) 180 and an output
port 190 for outputting the abnormal operation condition signal
130b. The dotted lines in FIG. 1B indicate optional features.
[0073] The output port can be any interface, for example, an
electrical contact-based interface, e.g. an external contact or pad
for electrically connecting the apparatus or sensor circuit to an
external device via connecting wires or bond connections, or
contact-less interface, e.g. an antenna or any other radio
frequency interface, or an optical interface. The apparatus or
sensor circuit is adapted to communicate the signal 130b via said
output port, either instantaneously or delayed after meanwhile
storage. Further embodiments of the apparatus or sensor circuit may
comprise separate output ports for the signal 130b and the output
signal or measurement signal 110b, or may use one common output
port to output both, the signal 130b and the output or measurement
signal 110b.
[0074] The time-base can be a filter element integrated into a
sensor element 120. In an alternative embodiment, the time base 180
can be a separate oscillator unit, which is adapted to provide the
sensor element 120 with a clock signal, for example, for
analogue-to-digital-conversion or any other processing performed by
the sensor element. In further embodiments, the time base 180
provides the clock signal 180b not only to the sensor element 120
but to other circuit elements of the apparatus, for example, to the
signal processing circuit 110, the evaluation circuit 130 or to
other sensor elements. In even further embodiments, each of the
elements has its own time base or shares a time base with other
elements of the apparatus.
[0075] In contrast to the apparatus according to FIG. 1A, the
apparatus 100' comprises an evaluation circuit 130 that is adapted
to receive the output signal 110b or measurement signal 110b and to
perform the evaluation of the sensor signal 120b, i.e. the
evaluation whether an abnormal operation condition exists, based on
the measurement signal or output signal 110b.
[0076] Embodiments of the apparatus or the sensor circuits
described herein can be adapted to evaluate the sensor signal using
static criteria or thresholds, e.g. static minimum or maximum
values or the sign of the sensor signal (i.e. criteria not
depending on other sensor signals or the measurement signal), or
using dynamic criteria or thresholds, e.g. criteria depending on
other sensor signals or the measurement signal, and/or can be
adapted to evaluate the sensor signal using only one or several
other sensor signals, using only the output or measurement signal
110b, or using one or several other sensor signals and the output
or measurement signal 110b for the evaluation.
[0077] Other embodiments of the apparatus and/or of the sensor
circuit, as for example described in the following based on FIGS. 2
to 6, can also comprise an evaluation circuit 130 that is adapted
to receive the measurement signal 110b for evaluating the sensor
signal 120b. These other embodiments may also comprise the output
port 190 to output the abnormal operation condition signal 130b,
and/or may comprise one or more time base units 180 for providing
clock signals 180b to the different elements of the sensor
circuits.
[0078] Even further embodiments comprise an evaluation circuit 130
that is adapted to not only use the input or a sensor signal 120b
for the manipulation evaluation but also the input signal 110a or a
further sensor signal 110a and/or the output signal 110b or
measurement signal 110b. The evaluation circuit can be further
adapted to evaluate the sensor signal 120b of the sensor element
120 only in case the input signal 110a or the output signal 110b
are small. For example, in case the apparatus 100 or 110' is a
current measuring unit or current meter and the signal processing
circuit 110 indicates a large current (i.e. a large signal or
signal value 110b), the current meter 100, 100' can be adapted to
not evaluate a sensor signal 120b to detect a manipulation.
However, in case a measured current indicated by the measurement
signal 110b is small (i.e. a measurement value 110b has a low
value), it might be more important to exclude a manipulation and to
perform an evaluation of the sensor signal 120b.
[0079] It should be noted that, in particular for apparatus with
integrated sensor circuits, it is easy to determine the spatial
distribution of a physical quantity over the chip surface because
(i) the position or location of the different sensor elements can
be controlled on a micrometer-level due to high-precision
production techniques, (ii) production variations of the sensor
elements can be kept small because the spacing of the elements
integrated on a single chip or a single semiconductor die is very
small, for example, only some few millimeters (in contrast to
lot-to-lot or wafer-to-wafer or chip-to-chip variations in case
different sensor elements are integrated into different chips or
semiconductor dies), and (iii) the remaining variation, for
example, of the sensor signal values due to the variation of the
position or due to other production variations of the sensor
elements themselves, can be equilibrated in an end-of-line test
because the individual sensor elements remain on the same chip and
are, thus, not mixed with sensor elements of other chips, which
would be the case for discrete sensor elements, wherein "discrete"
means that a single sensor element is implemented per chip.
[0080] It is further emphasized that in case a system, for example,
an apparatus or a sensor circuit as described herein, is disturbed
(intentionally or unintentionally) from external, the unwanted
external physical quantity or external disturbing physical quantity
has a spatial dependency that is smaller, the larger the distance
between the source of the disturbance and the sensor elements is.
One advantage of the integrated semiconductor technology now is the
aspect of the miniaturization. Therefore, it is possible to design
a current sensor such that the wanted primary physical quantity
(the magnetic field of the current to be measured and flowing
through a primary current conductor integrated into the package or
even into the semiconductor substrate) causes a relatively strong
spatial dependency on the sensor elements. For embodiments of
housed apparatus, housed sensors, housed sensor circuits or housed
sensor packages, the design of the housing or packaging is such
that external disturbers have a certain minimum distance to the
individual sensor elements so that the disturbing or unwanted
physical quantities applied from external to the sensor elements
only have a smaller spatial dependency. This can be easily
achieved, for example by a plastic encasing or plastic
encapsulation with sufficient dimensions, as will be described in
more detail later with reference to FIG. 5B.
[0081] FIG. 2 shows a block-diagram of a specific embodiment of the
apparatus 100, wherein the apparatus 100 is a sensor circuit 200.
The sensor circuit 200 comprises the signal processing circuit 110,
the sensor element 120, the evaluation circuit 130 and additionally
(compared to FIG. 1A) a primary sensor element 220. The primary
sensor element 220 is adapted to transduce a primary physical
quantity, or in other words, to generate a primary sensor signal
110a as input signal 110a in response to the primary physical
quantity 240. The signal processing circuit 110 is adapted to
process the primary sensor signal 110a depending on the sensor
signal 120b to obtain a primary measurement signal as output signal
110b, wherein the primary measurement signal 110b represents a
property of the primary physical quantity 240.
[0082] The sensor element 120 can be a secondary sensor element for
measuring a predetermined secondary physical quantity or ambient
secondary physical quantity, or can be a primary sensor element for
measuring a predetermined primary physical quantity or ambient
primary physical quantity or ambient part of a physical quantity of
the same type of physical quantity as the primary physical quantity
measured by the primary sensor element 220.
[0083] In case of a Hall sensor, the magnetic field to be measured
forms the primary physical quantity, the temperature or mechanical
stress form the secondary ambient physical quantity 140. The
voltage output by the Hall sensor 220 (e.g. a Hall plate) depends
on the field strength and polarity of the magnetic field measured
by the sensor element and on the variation over time of the
magnetic field 240 and, thus, comprises information about at least
one property or several properties, for example field strength,
polarity and variation over time, of the primary physical quantity.
The sensor element 120 can, for example, also be adapted to provide
a voltage signal as sensor signal 120b, wherein the voltage signal
120b represents at least one property of the secondary ambient
physical quantity, for example a temperature value or mechanical
stress value.
[0084] As explained previously, the signal processing circuit can
be adapted to compensate drifts of the primary sensor signal caused
by variations in temperature or mechanical stress with regard to
the measurement signal 110b to reduce the unwanted effect of a
secondary ambient physical quantities.
[0085] As for the apparatus 100, the sensor element 120 can be a
secondary sensor element adapted to transduce a secondary ambient
physical quantity (e.g. to compensate a drift of the primary sensor
signal 110a), or a primary sensor element adapted to transduce an
unwanted ambient part of a primary physical quantity, wherein the
sensor signal 120b is used, for example, to reduce the effect of
background magnetic field parts through differential measurement
principles. Embodiments of the sensor circuit 200 comprise an
output port, e.g. an external contact or pad or a wireless
interface, to output the primary measurement signal 110b.
[0086] Embodiments of the sensor circuit 200 may form a sensor
package, wherein the primary sensor element 220, the sensor element
120, the signal processing unit 110 and the evaluation circuit 130
are fully or at least partially encapsulated by an encapsulating
material, wherein the sensor circuit comprises an external contact
to output the primary measurement signal 110b and optionally
another external contact to output the abnormal operation condition
signal 120b, and wherein the two external contacts are not covered
or only partly covered by the encapsulation material. In further
embodiments the sensor circuit is adapted to output the abnormal
operation condition signal 120b via the same external contact or
interface as the primary measurement signal 110b.
[0087] The primary sensor element 220, the sensor element 120, the
signal processing unit 110 and the evaluation circuit 130 can be
arranged on different semiconductor dies or chips (multi-chip
package) or integrated on the same semiconductor die or chip
(single chip package or single die package). In further embodiments
all components of the sensor circuit, including further components
not shown in FIG. 2, except for the external contacts are
encapsulated or are hermetically sealed from the environment by the
encapsulation material.
[0088] Integrating the primary sensor element 220, the sensor
element 120, the signal processing unit 110 and the evaluation
circuit 130 on one semiconductor die makes it more difficult to
manipulate the sensor signals 110a and 120b from external (due to
the integration and small dimensions of the connecting lines
between the sensor elements and the signal processing circuit and
in particular the evaluation circuit).
[0089] Furthermore, providing an ambient operational condition
monitoring as provided by embodiments of such an integrated sensor
circuit provides highly reliable miniature sensors. Design
engineers using such integrated sensor circuit only need to read or
monitor the abnormal ambient condition signal to verify the correct
functioning of the sensor and may employ automatic or manual
countermeasures in case an abnormal operating condition is signaled
by the sensor.
[0090] The above explanations with regard to the packaging, the
external contacts or interfaces and the integration on different or
the same semiconductor dies applies in a corresponding manner to
the apparatus 100 and other embodiments of sensor circuits
described herein.
[0091] FIG. 3 shows a block-diagram of a specific embodiment of the
sensor circuit according to FIG. 2, wherein the sensor element 120
is a further primary sensor element 120. Thus, the sensor circuit
300 comprises a first primary sensor element 220 and a second
primary sensor element 120. First and second primary sensor
elements are arranged at distinct locations, the first primary
sensor element at a first location and the second primary sensor
element 120 at a second location. The first primary sensor element
220 is adapted to measure the primary physical quantity at the
first location or position, whereas the second primary sensor
element 120 measures the primary physical quantity at the second
location or position. The primary physical quantity measured or
sensed by the first primary sensor element may comprise a first
wanted part, e.g. a first wanted primary physical quantity part,
and a first unwanted part, e.g. a first unwanted primary physical
quantity part. The wanted and unwanted part may--depending on the
context--also be distinguished by referring to the wanted part as
"first primary physical quantity" or "first wanted primary physical
quantity" and to the unwanted part as "first ambient primary
physical quantity" or "first unwanted ambient primary physical
quantity". This nomenclature correspondingly applies to the second
physical quantity and the potentially comprised wanted and unwanted
parts or portions thereof.
[0092] Further embodiments may comprise further (third, fourth,
etc) primary sensor elements arranged at further (third, fourth,
etc) locations of the sensor circuit to measure the primary
physical quantity at the further locations and to produce in
response to the primary physical quantity further (third, fourth,
etc.) primary sensor signals being indicative of the primary
physical quantity at the further locations or being indicative of
at least one property of the primary physical quantity at the
further locations. Any further location (third, fourth, etc.) is
different to the first, second or other locations of other primary
sensor elements. As for the first and second primary physical
quantity, also the further primary physical quantities and the
related further primary sensor signals may comprise wanted and
unwanted parts, wherein with regard to the terms used to describe
and/or distinguish both parts the same applies as explained for the
first and second primary sensor signals in the preceding
paragraph.
[0093] The sensor circuit 300 is, for example, a sensor circuit
adapted to perform on one hand a differential measurement principle
by subtracting the second primary sensor signal 120b from the first
primary sensor signal 120a to obtain the measurement signal 110b.
The sensor circuit is further adapted to evaluate on the other
hand, whether the operating conditions are to be considered normal
or abnormal, e.g. by adding the first primary sensor signal 110a
and a second primary sensor signal 120b and comparing the sum of
both with a threshold or maximum value, and to produce the abnormal
operation condition signal in case the sum is higher than a certain
threshold value.
[0094] In further embodiments, the signal processing circuit 110 is
adapted to process the first 110a and second 120b primary sensor
signals according to a first algorithm or function to obtain the
primary measurement signal 110b, and the evaluation circuit 130 is
adapted to process the first 110a and the second 120b primary
sensor signals according to a second algorithm, which is different
from the first algorithm, and to generate the abnormal operation
condition signal 130b in case the result of the second algorithm
does not fulfill a predetermined normal operation criterion.
[0095] The first algorithm may comprise subtracting the first
primary sensor signal 110a or a multiple thereof from the second
primary sensor signal 120b or a multiple thereof, or vice versa,
and outputting the difference or a signal derived therefrom, e.g. a
drift compensated version thereof, as measurement signal 110b.
[0096] The second algorithm may comprise adding the first primary
sensor signal 110a or a multiple thereof and the second primary
sensor signal 120b or a multiple thereof, and producing and
outputting the abnormal operation condition signal 130b in case the
sum is higher than a threshold value. In further embodiments, the
second algorithm does not comprise subtracting the first primary
sensor signal 110a or a multiple thereof from the second primary
sensor signal 120b or a multiple thereof, or vice versa.
[0097] Further embodiments of the apparatus form an electronic
sensor system which comprises at least two sensor elements 120, 220
which transduce the same physical quantity at two spots or
locations into a first sensor signal 110a with a first sensor
signal value and a second sensor signal 120b with a second sensor
signal value, which further comprises a signal processing unit 110
adapted to output the output signal 110b or measurement signal
110b, which is a function of a difference of the value of the first
sensor signal 110a and the value of the second sensor signal 120b,
and which further comprises the evaluation circuit 130 that is
adapted to supply a second signal 130b or abnormal operating
condition signal 130b, which depends also on the value of the first
sensor signal 110a and the value of the second sensor signal 120b,
yet not on the difference of the value of the first sensor signal
110a and the value of the second sensor signal 120b. Within the
above context the term "function" refers to any function or
algorithm, where for each input value x of the function f(x) the
system or circuit gets an output value f(x). In a strict
mathematical sense this should be unique, yet in the real sensor
system this is only approximately unique, because it may be
overlaid by random noise. However, in real sensor systems the
function may be quantized so that the output value f(x) remains
constant when x subtends within a sufficiently small range of a
use, e.g. x1<x<x2 i.e., in case the input value x remains
within a sufficient range of input values. Yet the function has no
different values f(x) for the same value x.
[0098] Further embodiments comprise an electronic sensor system or
sensor circuit which comprises at least three sensor elements which
transduce the same physical quantity at three different spots or
locations into a first sensor signal, a second sensor signal and a
third sensor signal and output a first signal or measurement signal
which is a function of the difference of the values of the first
and the second sensor signal, and of the difference of the values
of the second and third sensor signal, wherein the evaluation
circuit generates or derives the signal 130b such that it is not
obtainable by a sole sequence of mathematical operations performed
on the output signal or measurement signal 110b. In other words,
the function or algorithm used by the evaluation circuit processes
the values of the sensor signals such that the result of the
function has additional information on the physical quantity
compared to the measurement signal 110b.
[0099] In even further embodiments, the electronic sensor system or
sensor circuit comprises at least four sensor elements which
transduce the same physical quantity at four different spots or
locations into a first, a second, a third and a fourth sensor
signal, wherein the signal processing circuit is adapted to output
a measurement signal or output signal as a function of the
difference of a value of the first sensor signal and a value of the
fourth sensor signal, and as a difference of a value of the second
sensor signal and a value of the third sensor signal, and wherein
the evaluation circuit is adapted to supply the signal 130b
depending on at least two values of the first, second, third or
fourth sensor signal, and wherein the evaluation circuit is further
adapted to process these at least two values of the sensor signal
such that the result of the function or the signal 130b is not
obtainable by a sole sequence of mathematical operations performed
on the output or measurement signal 110b.
[0100] These and other embodiments for processing the first primary
sensor signal 110a, the second primary sensor signal 120b and
optionally further (third, fourth, etc.) primary sensor signals for
obtaining the measurement signal 110b and/or for evaluating whether
an abnormal ambient operation condition exists, will be explained
in the following in conjunction with specific embodiments of the
apparatus 100 and the sensor circuits 200, 300.
[0101] The two or more sensor elements adapted to measure the same
type of physical quantity do not need to be of the same type of
sensors. For measuring the temperature, embodiments can use, for
example, a resistor or a diode, and, for example, in case the
temperature is measured at two spots of the circuit or die, the
temperature can be measured with a resistor on a first spot or
location and with a diode as a second sensor element at the second
spot or location. Hereafter, such different types of sensor
elements for measuring the same physical quantity will be referred
to as belonging to the same class of sensors or sensor elements,
whereas different resistors for measuring a temperature are
referred to belong to the same type (i.e. resistor type) of sensors
or sensor elements.
[0102] FIG. 4 shows a top view of an embodiment of a differential
magnetic field sensor or differential magnetic field sensor circuit
300 implemented as, e.g. coreless, current sensor 400. The sensor
circuit 400 comprises a first Hall sensor element or first Hall
plate 220, a second Hall sensor element or Hall plate 120, which
are arranged in a semiconductor die 430 on opposite sides of a
current conductor 410 of the current sensor. The current I to be
measured flows through the current conductor 410 and generates a
radial magnetic field B that depends on the current density and the
flow direction (see arrow) of the current to be measured. In case
the current flows from left to right (with regard to the
orientation of FIG. 4) the current produces a radial magnetic field
B that has a positive z-orientation (with regard to the coordinate
system as shown in FIG. 4, see B.sub.1 being directed out of the
picture) at a first location x.sub.1, where the first primary
sensor element 320 is located, and a negative z-orientation (with
regard to the coordinate system as shown in FIG. 4, see B.sub.2
being directed into the picture) at a second location x.sub.2,
where the second primary sensor element 120 is located. The signal
processing circuit 110 and the evaluation circuit 130 are not shown
in FIG. 4.
[0103] The current conductor 410 comprises notches 420a and 420b at
opposed sides of the current conductor with regard to the flow
direction of the current in order to increase the current density
and, thus, the measurement sensitivity.
[0104] The first and the second sensor element 120, 220 are
arranged with regard to their lateral position (x,y-plane, see
coordinate system of FIG. 4) above or at least partially above the
notches 420a, 420b, as close as possible to the conductor 410 and
on opposite sides of the conductor with regard to the flow
direction of the current. In case the notches 420a and 420b are
symmetric and the first and second sensor element 220, 120 are
arranged also symmetrically with regard to a central axis in the
current flow direction of the current conductor, the first magnetic
field measured by the first primary sensor element has the same
magnitude as the magnetic field measured at the second primary
sensor element 110 and the two only differ with regard to the sign
or orientation of the measured magnetic field.
[0105] Further embodiments of the current sensor circuit 300 may
comprise notches 420a, 420b with other geometries, only one notch
or no notches at all. Other embodiments of the current sensor may
comprise a wire as conductor, wherein the wire may be arranged in a
straight manner or in a bent manner, e.g. in a meander like manner,
and the primary sensor elements may be arranged on opposite sides
of the wire.
[0106] Embodiments of the magnetic field current sensor 400 may
also comprise the current conductor 410 as integral component or
element of a current sensor package 400 to facilitate a fixed and
accurate relative positioning of the hall sensors 220 and 120 with
regard to the current conductor. In case a current needs to be
measured, the whole package 400 can be connected to an external
(with regard to the package itself) conductor for which the current
shall be measured. Referring back to FIG. 4, the differential
magnetic field sensor 400 measures the magnetic field B or a single
component of the magnetic field at two locations x.sub.1, x.sub.2
to obtain a first primary sensor signal 110a representing the
magnetic field or B-field B.sub.1 at position x.sub.1 and a second
primary sensor signal 120b representing the magnetic field or
B-field B.sub.2 at position x.sub.2. The signal processing circuit
110 computes the difference of the two sensor signals or sensor
signal values representing the difference between the magnetic
field at the two positions, i.e. the signal processing unit 110
computes the difference B.sub.1-B.sub.2. The quantity to be
measured or output as output or measurement signal 110b is a
function of this difference: Q=f(B.sub.1-B.sub.2), wherein B.sub.1
and B.sub.2 may comprise wanted and unwanted magnetic field parts.
This quantity or measured quantity may be the strength, sign,
phase, frequency, ripple or duty-cycle of the current flowing
through the current conductor, or an angular position or angular
speed or angular acceleration of a target wheel in case of a
magnetic rotation sensor as will be explained later based on FIG.
6.
[0107] Higher order differential systems have n magnetic sensor
elements measuring the same component of the magnetic field on n
different locations with n>2. They compute the quantity Q, for
example, as a function of many differences according to:
Q=f(B.sub.1-B.sub.2, B.sub.2-B.sub.3, . . . ,
B.sub.n-1-B.sub.n).
[0108] In other words, such measurement systems comprise 3 or more
magnetic field sensors H1, H2, H3, etc. where the signals of two
sensors elements are subtracted and the resulting terms are added
up as a linear combination with fixed coefficients.
[0109] FIG. 5A shows a schematic top-view of a magnetic current
sensor or current sensor circuit 500 with three (n=3) Hall sensors
220, 120, and 520, respectively H1, H2 and H3 (the signal
processing circuit and the evaluation circuit are not shown). Each
of the Hall sensors H1, H2 and H3 is located at a different
location x.sub.1, x.sub.2 and x.sub.3 and measures the magnetic
field B.sub.1, B.sub.2 and B.sub.3 at the respective location of
the Hall sensors. The current conductor comprises three slots,
wherein each of the Hall sensors or Hall plates is arranged at
least partially above one of the slots 420a, 420b and 420c and near
to the current conductor 410. The first sensor element H1 produces
the first sensor signal S1 (corresponds to 110a) in response to the
magnetic field B1, the second sensor element H2 produces the first
sensor signal S2 (corresponds to 120b) in response to the magnetic
field B2, and the third sensor element H3 produces the first sensor
signal S3 in response to the magnetic field B3. For embodiments
with a conductor structure as shown in FIG. 5A (three slots 420a to
420c extending to the middle axis of the conductor and arranged in
an alternating order on opposite sides of the current conductor
with regard to the middle axis in current flow direction) and an
arrangement of the Hall plates as shown in FIG. 5A (each of the
Hall plates arranged above one of the slots and in a straight line
above the mid axis or center axis 590 of the current conductor),
the sign and magnitude of the sensor signals S1 and S3 are
approximately the same, the magnitude of the sensor signal S2 is
approximately a factor 2 higher than the magnitude of the sensor
signals S1 or S3, and the sign of the second sensor signal is
inverse or opposite to the signs of the first and third sensor
signal S1 and S3. In case the current flows from left to right
(according to the orientation of FIG. 5A) the sensor signals S1 and
S3 have, for example, a positive sign and sensor signal S2 a
negative sign. In case the current flows from right to left
(according to the orientation of FIG. 5A) the opposite is true, the
sensor signals S1 and S3 have, a negative sign and sensor signal S2
a positive sign. These relations between the magnitudes and the
signs of the three sensor signals refer to the measurement of the
magnetic field of the current I flowing through the current
conductor 410 and do not consider any magnetic background fields,
e.g. the earth's magnetic field. The earth's magnetic field, in
contrast to the magnetic field of the current to be measured is
homogeneous over the area of the current sensor 500, i.e. the
earth's magnetic field superposes an additional ambient magnetic
field or ambient magnetic field part, which is the same (due to its
homogeneity) with regard to the sign and the magnitude for all
three sensors H1 to H3.
[0110] The signal processing unit 130 is, for example, adapted to
compute the current I flowing through the conducting strip 410 with
the three slots according to
I=(S1-S2)-(S2-S3)=S1+S3-2*S2,
[0111] where S1, S2, S3 are the aforementioned signals of the
planar Hall plates H1, H2, H3. Thus, as explained, the earth's
magnetic field components are cancelled out, whereas the current is
calculated as I=6*S, in case S1=S3=S and S2=-2*S. Similarly any
other homogeneous magnetic field, e.g. caused by a neighboring
conductor or applied to manipulate the magnetic field current
sensor, are cancelled out. In other words, the differential
magnetic field current sensor is robust against such homogenous
ambient magnetic fields. Since the sensor consists of 3 Hall
elements at three locations it is a 2nd order gradiometer.
Therefore it can cancel not only 0.sup.th order spatial derivatives
(=homogeneous background field) but also 1.sup.st order spatial
derivatives (=linear gradients of background field). However,
magnetic fields with spatial derivatives of second or higher order
might not be cancelled out and they may cause unacceptable
measurement conditions, i.e. abnormal ambient operating conditions
which cannot be detected by embodiments of the present invention.
Therefore, the higher the grade of the gradiometer the better the
detection of abnormal ambient conditions, e.g. applied to the
sensor to manipulate the same.
[0112] The magnetic field parts produced by the current Ito be
measured form the first, second and third primary physical
quantities or first, second and third wanted primary physical
quantity parts, whereas the magnetic field parts produced by the
earth magnetic field or any other ambient magnetic field source
form the first, second and third ambient primary physical
quantities or first, second and third unwanted primary physical
quantity parts.
[0113] In the following further embodiments for detecting abnormal
ambient conditions are described for magnetic field current sensors
and, in particular for a differential current sensor as described
based on FIG. 5A. If an intentional or unintentional manipulation
of a sensor system is done with an externally applied magnetic
field it can be distinguished from the wanted physical quantity Q
by various means. In the following, with regard to a magnetic field
current sensor circuit as described, for example, based on FIGS. 5A
and 5B (but also based on FIG. 4), the magnetic field produced by
the current flowing through the current conductor of the current
sensor circuit is regarded as "internal magnetic field", whereas
any magnetic field caused by any other source than the current
flowing through the current conductor is regarded as disturbing
magnetic field or external magnetic field (external with regard to
the current sensor circuit and in particular with regard to the
current sensor package), e.g. the earth's magnetic field or
permanent magnets arranged next to the current sensor or magnetic
fields generated by currents flowing through nearby conductors,
etc, is regarded as "external magnetic field". Within this context
one could interpret "external" also as "ambient", "unwanted" or
"disturbing" and "internal" as "wanted".
[0114] The externally applied magnetic field or ambient magnetic
field may have, for example, a field strength exceeding a limit. In
a current sensor with a full scale range of 100 A the magnetic
field on the center Hall probe H2 is, e.g. 25 mT. So if 35 mT are
detected by the Hall probe H2 or the evaluation circuit 130 this
may be either due to an overcurrent event or to a manipulation with
a permanent magnet brought in close proximity to the sensor.
[0115] Externally applied magnetic fields are likely to have a
field pattern whose spatial dependence is markedly different from
the field pattern generated by the wanted physical quantity Q. For
example, in the current sensor of FIG. 5A with 3 slots in a strip
of conductor, the field B generated by the current is highly
inhomogeneous: it is positive on H1 and H3 and negative on H2. It
is very difficult to externally apply a magnetic field via a
permanent magnet which shows the same spatial dependence: not only
must it have different signs on the 3 sensor elements, it must also
have equal magnitudes on H1 and H3 and the magnitude on H2 must be
equal to the sum of magnitudes on H1 and H3. Therefore several
indicators can be used for detecting a manipulation or, in general,
abnormal ambient conditions, as will be explained in the
following.
[0116] As first indicator or criterion, the sum of the sensor
signals or sensor signal values S1+S2+S3 must not exceed a certain
threshold. Ideally the sum should be zero, in practice it should
be, e.g., in a range within -10 mT (min. value for normal
operation) and +10 mT (max. value for normal operation). In case
the sum value S1+S2+S3 exceeds these thresholds, the evaluation
circuit is adapted to detect an abnormal ambient condition and to
produce the signal 130b.
[0117] Other embodiments may also use a dynamic threshold like
S1+S3-2*S2, which is directly related to the measurand Q, and may
detect a manipulation or abnormal ambient condition if the
following inequality is true:
abs(S1+S2+S3)>X*abs(S1+S3-2*52),
[0118] where X is a weight factor and may have a value like 0.1,
for example. The value of X adjusts the likelihood of manipulation
or abnormal operation conditions.
[0119] In practice the accuracy of the sensor signals becomes poor
for small signals so that a more robust algorithm for detecting
abnormal ambient conditions can read as follows:
abs(S1+S2+S3)>max(X*abs(S1+S3-2*S2); Y),
[0120] where max(a,b) is the larger value of a or b and Y is the
above mentioned absolute limit like 10 mT.
[0121] A second criterion for detecting an abnormal ambient or
operation condition is that S1 and S3 must not deviate too much
from each other: ideally they should be equal, if no external field
is applied. Manipulation or strong external fields are detected,
if
abs(S1/S2-1)>EPS,
[0122] EPS may be 0.1, for example. If EPS is small the
detectability of manipulation is increased. EPS should be chosen
such that the condition turns TRUE only if magnetic background
fields exceed a level which notably deteriorates the measurement of
Q. In practice one should blank out this condition, if S2 is close
to zero by using the following condition:
abs((abs(S1)+X)/(abs(S2)+Y)-1)>EPS,
[0123] where X may be equal to Y. Generally X and Y should be
chosen two to ten times larger than the zero-crossing error of the
sensors. As zero-crossing error of a magnetic sensor, one denotes
its output at zero field (e.g. offset of Hall sensors or coercivity
of sensors involving soft magnetic parts). E.g. the residual offset
of a spinning current integrated Hall sensor is about 50 .mu.T and
therefore X should be 50 to 500 .mu.T, for example. In the above
equations one may replace abs(x) with x{circle around ( )}(2*n)
with n=positive even integer number.
[0124] A third criterion for detecting an abnormal ambient or
operation condition is that S1+S3 must not deviate too much from
(-1)*S2: this is identical to the first criterion.
[0125] A fourth criterion for detecting an abnormal ambient or
operation condition is that (-2)*S1 and S2 must not deviate too
much from each other: this is identical to the first criterion
combined with the second criterion.
[0126] A fifth criterion for detecting an abnormal ambient or
operation condition is that (-2)*S3 and S2 must not deviate too
much from each other: this is identical to the first criterion
combined with the second criterion.
[0127] Summarizing the aforementioned: with 3 sensor elements S1,
S2, S3 one may combine them in various linear combinations, yet
only 3 of these combinations are essentially different--all others
may be derived from superpositions of these three ones. One of
these combinations can be used to find the measurand Q, or in other
words can be used by the signal processing unit 110 to determine
the measurement signal 110b. The other 2 linear combinations should
be equal to zero in the case of vanishing magnetic disturbances or
ambient magnetic fields. These 2 combinations can be used to
estimate the background magnetic field and therefore they can be
used by the evaluation circuit 130 to estimate if someone wants to
manipulate the sensor or an abnormal ambient or operation condition
exists.
[0128] A sixth criterion for detecting an abnormal ambient or
operation condition is to evaluate the sign of the sensor signal
S1, S2 or S3. The externally applied magnetic field may have, e.g.,
a sign that is opposite to the field from the wanted physical
quantity or measurand Q. Referring again to the magnetic field
current sensor 500 of FIG. 5A, if the polarity of the current is
known then the polarity of the magnetic field on the 3 Hall plates
is known. If the current flows in the direction shown in the figure
then the out-of-plane component of the magnetic field on sensors H1
and H3 points out of the drawing plane while it points into the
plane on sensor H2. If an external field is applied, it may have a
wrong direction and this can be used to detect manipulation.
[0129] A seventh criterion for detecting an abnormal ambient or
operation condition is to evaluate the average of one or several
sensor signals. The externally applied magnetic field may have a
temporal average that is opposite to the field from the wanted
measurand Q or that is different from the average of the wanted
measurand Q. If one considers a rotating code wheel with equal
north and south poles along its perimeter the time average of the
magnetic field on each sensor is zero (unless the observation
period is shorter than the time during which one north- and
south-pole pass in front of the sensor).
[0130] FIG. 6 shows a schematic view of a magnetic rotation sensor
circuit 600 comprising a first and a second primary magnetic field
sensor 220 and 120, e.g. a Hall sensor or a magneto resistive
sensor like an XMR sensor (the signal processing circuit and the
evaluation circuit are not shown). The system shown in FIG. 6
further comprises a permanent magnet for biasing the magnetic field
sensor circuit 600 and a protective cover 634 surrounding the
permanent magnet and the sensor circuit. The target wheel 610 of
which the rotation shall be measured by the magnetic rotation
sensor 600 is, e.g. a toothed wheel made of iron with teeth at its
periphery, and the two magnetic sensor elements are arranged at a
distance 612, also referred to as magnetic air gap, from these
teeth and continuously measure the magnetic field caused by the
teeth and the gaps in between.
[0131] Similarly, the average of a purely sinusoidal current
through a mains supply is zero, for integration times for example
larger than 1/50 or 1/60 seconds. So the sensor system of a current
meter, for example a current meter measuring the used current of a
household, may simply integrate the output signal over a reasonably
long time. If the result is larger than a predefined value the
background field is too high.
Of course it is also possible to integrate the signal of each
individual sensor in a differential sensor system--in fact this
works also for an absolute sensor having only a single sensor
element.
[0132] An eighth criterion for detecting an abnormal ambient or
operation condition is to evaluate the spectrum of the measured
magnetic field or physical quantity. The externally applied
magnetic field may have significant spectral contributions outside
the signal bandwidth of the wanted measurand Q. If one considers an
energy meter for the mains supply it is clear that the dominant
spectrum is close to the mains frequency 50 Hz or 60 Hz. If a
manipulation with a significantly different frequency, e.g. below
40 Hz or above 70 Hz (or below 30 Hz or above 80 Hz), is undertaken
this may be detected in the total signal or in the individual
sensor signals.
[0133] A magnetic sensor system or any other sensor system may also
comprise a temperature sensor to compensate for drifts of the
primary physical quantity or sensor characteristic versus the
secondary physical quantity temperature. With differential magnetic
sensors it is even better to have a temperature sensor close to
each magnetic sensor--in case the temperature is not homogeneous
over the semiconductor die. These temperature sensors may also be
used to detect manipulation or abnormal ambient or operation
conditions (ninth criterion). Such a manipulation may be that
someone heats up the sensor circuit with a hot air gun or with a
cigarette lighter or blowtorch. Since the sensor system usually
also has an oscillator on board, which defines a time-frame (e.g.
for spinning current operation of Hall plates or to define a time
discrete signal processing or to drive a digital circuit to process
the data or to define time slots used in a data transmission
protocol) one may also combine temperature and magnetic field
information to detect abnormal ambient conditions. A manipulation
is likely and an abnormal ambient condition is detected if the
temperature leaves some specified band (too low or too high
temperature). Furthermore, a manipulation is likely and an abnormal
ambient condition is detected if the spatial temperature gradient
over the die is too large. Finally a manipulation is likely and an
abnormal ambient condition is detected if the rate of change of
temperature or the temporal gradient of the temperature is too
large: e.g. in an energy meter it is not common that the
temperature rises by 100.degree. C. within 1 second unless the
current is too large--this may be used to detect a manipulation
with some open flame.
[0134] Precise magnetic sensors often need some kind of on-board
mechanical stress sensor as a secondary sensor, which measures the
mechanical stress on the semiconductor die. This is used by the
signal processing circuit 110 to compensate for drifts of the
sensor characteristic caused by changes in mechanical stress.
Manipulation at constant temperature or moderate temperature change
may be done, e.g., by etching off parts of the package with e.g.
sulfuric acid or by mechanically scratching, cutting, pressing,
milling or grinding off parts of the sensor package. It may also be
done by deliberately changing the moisture content of the mold
compound of the sensor package by drying it or wetting it. All
these manipulations result either in a sudden or in a significant
change of mechanical stress on the die and this can be detected by
the on-board stress sensors. The evaluation circuit 130 can be
adapted to detect a manipulation or an abnormal ambient condition,
if the mechanical stress on the die changes too much, or if a rate
of stress changes, i.e. a change of stress divided by time, or a
temporal gradient of the mechanical stress is too high.
[0135] In the following further aspects of the packaging of a
magnetic field current sensor circuit or magnetic field current
sensor package as shown in FIG. 5A will be described. However it
should be noted that these explanations apply in a corresponding
manner to other current sensor embodiments or other sensors in
general.
[0136] FIG. 5B shows a package 500' for an integrated current
sensor, or in other words, a current sensor package 500'. The
current sensor package 500' comprises a semiconductor die 550
comprising a magnetic field sensor 560, for example, one of the
magnetic field sensor elements 120, 220 or 620 as shown in FIG. 5A.
The current sensor package 500' comprises furthermore a conductor
or primary conductor 410 through which the current Ito be measured
flows. A dielectric isolation layer 540 is placed between the
conductor 410 and the semiconductor die 550 to provide a voltage
isolation between the high current 410 and the sensor circuit or
the magnetic field sensor 560. The semiconductor die 550 is mounted
on a substrate 570 or on a lead frame 570. All the aforementioned
parts are covered by a mold compound 520. The mold compound 520 has
the purpose to protect the sensor circuit, and in particular the
current conductor and the semiconductor die, from the environment,
for example, from light, moisture or from mechanical influences.
With regard to the current sensor package 500' as shown in FIG. 5,
there are now two possibilities to position a source of disturbing
or unwanted physical quantity near to the sensor element or sensor
elements. On one hand, the source of disturbing physical quantities
can be arranged on top of the package, as depicted with reference
sign 510 or below the package, as depicted with regard to reference
sign 580. Denoting the vertical distance (in z-direction) between
the sensor element 560 and a bottom surface of the current
conductor 410 by DI, the vertical thickness of the current
conductor itself by TC, the vertical thickness of the mold compound
above the conductor (with regard to the orientation of FIG. 5B) by
TM and the vertical distance between the sensor element 560 and the
bottom surface of the package by TB, the disturbing source 510, 580
has a vertical distance to the sensor element 560 of either TB or
DI+TC+TM. In any case, when designing the package, these distances
can be chosen such that they are much larger than DI, and,
therefore, the spatial in-homogeneity of the disturbing physical
quantities impacting on the sensor 560 and generated by the
external sources 510 or 580 is less pronounced than the spatial
in-homogeneity of the wanted physical quantities generated by the
conductor 530 and impacting on the sensor 560.
[0137] In certain embodiments according to FIG. 5B, the vertical
distance DI can be about 10 micrometers to 100 micrometers in case
the current conductor 540 has a vertical thickness of about TC=1
mm. In case the vertical thickness of a mold material on top of the
current conductor is about TM=0.3 mm, the minimum distance between
the disturbing source 510 and the sensor elements is
DI+TC+TM.apprxeq.1.4 mm. In other words, the minimum distance is
about 14 times larger than the distance DI between the current
conductor and the sensor elements. Such encapsulations are shown in
FIG. 5B, can, for example, be used with current sensors 500 as
shown in FIG. 5A.
[0138] Therefore, embodiments of the current sensor package may
comprise an encapsulation or mold body, wherein an outer surface of
the encapsulation of mold body is arranged such that a minimum
distance between the outer surface and any of the magnetic field
sensor elements is more than 10 times, more than 20 times or more
than 30 times larger than a maximum distance between the current
conductor through which the current to be measured flows and any of
the magnetic field sensor elements.
[0139] FIG. 5C shows a plane view of a right half or part of a
conductor 410 as shown in FIG. 5A. The left half or part is mirror
symmetric to the right half, as shown in FIG. 5A. FIG. 5C shows the
current stream lines and how they bend around the slots. FIG. 5D
shows the corresponding vertical component or z-component of the
magnetic flux density 30 micrometers above or below the conductor
410. The point of the strongest positive magnetic field or Bz-field
is indicated by reference sign P, the point of the strongest
negative Bz-field is indicated by N, and the locations of vanishing
Bz-field are indicated by a snake-like figure labeled S. At
locations below (with reference to the figure) the snake-line S
have positive magnetic field and locations above the snake-line S
have negative magnetic field. Thus the field at point A has a large
magnitude but a negative sign. The intensity of the Bz-field in
z-direction is shown on the right hand side legend extending from
-0.02 T(Tesla) to +0.02 T. As can be seen from FIGS. 5C and 5D, it
is advantageous to place the magnetic field sensors H2 and H3 (see
FIG. 5A) at the spots or locations P and N. The straight
perpendicular lines between P and N and between P and A are those
paths on which the highest inhomogeneities, i.e. the steepest
slopes or largest spatial derivatives of the magnetic field
generated by the current flowing through the conductor, occur. It
is very difficult for manipulators to provide external disturbing
sources that produce magnetic fields which have similar
inhomogeneities along these paths. Therefore, embodiments of the
apparatus or sensor circuit comprise one or more sensor elements
placed along these paths to optimize a detection of external
disturbances.
[0140] The evaluation circuit 130 can be adapted, for example, to
compare all readings of these sensor elements with the
aforementioned spatial pattern, which would be caused by a current
thorough the conductor, and if significant differences from this
theoretical pattern occur, the evaluation circuit 130 determines
that there is a significant disturbance present and outputs the
abnormal operation condition signal to the output port 190.
[0141] According to one embodiment of the sensor system or sensor
circuit, one Hall plate is placed or arranged at spot P and another
Hall plate at spot N. In this case, the current flowing through the
conductor can be determined by the signal processing circuit 110 as
a linear combination of the magnetic field values detected by the
two sensor elements H2 and H3 arranged at spot P and spot N.
[0142] In addition, it is possible to find another linear
combination which is independent of the current. This second linear
combination is computed by the evaluation circuit 130 and compared
with a reference value. If the discrepancy or difference is too
large, the evaluation circuit signals the "abnormal operation
condition" at the output port 190.
[0143] A further embodiment of the sensor system comprises a Hall
plate at spot P and another Hall plate at line S. The evaluation
circuit 130 can then be adapted to compare both values, a value of
the sensor signal measured at spot P and the value of the sensor
signal measured at line S, and if the difference is too small and
at the same time the value at spot P indicates a medium or large
current, the evaluation circuit signals "abnormal operating
condition" at the output port 190.
[0144] Even more robust sensor systems which are more robust or
reliable with regard to detecting external disturbances comprise
sensor elements which are not only located along a straight line
590, as shown in FIG. 5A. Instead, these embodiments have sensor
elements which span the entire x-,y-plane. The advantage of such
arrangements is that it is much easier to manipulate the system, if
the external field only needs to produce well-defined disturbances
along a single direction, for example a one-dimensional disturbance
along the x-axis, yet it is more difficult to produce well-defined
disturbances with accurate inhomogeneities along two directions,
particularly along two perpendicular directions, for example, along
the x-axis and along the y-axis. Therefore, further embodiments of
the above example of a current sensor comprise three Hall plates,
wherein the first Hall plate is arranged at spot P, the second Hall
plate is shifted only in x-direction (e.g. the second whole plate
is arranged at location or spot N), and the third Hall plate is
shifted only in y-direction (e.g. the third whole plate is arranged
at spot A). Based on these three different spots or three different
measurements, a first linear combination of these three sensor
readings can be determined, which is proportional to the current to
be measured (e.g. the total signal function as shown in FIG. 5A),
while a second linear combination is independent on the current to
be measured, e.g. is determined such that the wanted magnetic field
parts of the current to be measured cancel each other out and only
unwanted or disturbing magnetic field parts remain, and which are
evaluated to detect whether an abnormal operation condition is
present. The second linear combination can, for example, be
compared by the evaluation circuit with the first linear
combination and with other reference values to decide whether an
abnormal operating condition is present. It should be noted that
with three sensor elements or three sensor readings, there are two
linear combinations available, which are independent of the current
and which are indicative of abnormal operating conditions.
[0145] In another embodiment, the sensor elements may be placed
also mirror symmetric above the left part of the conductor, which
is not shown in FIGS. 5C and 5D. As mentioned before, a further or
other Hall plate can be arranged at spot N' which corresponds to
the position of the Hall plate H1 of FIG. 5A.
[0146] Summarizing the aforementioned, there are a lot of
possibilities to place the sensor elements to detect abnormal
operating conditions. The optimum placement of the sensor elements
is the one that gives the largest differences in reading or sensing
values divided by spacing, as described based on FIG. 5D with
regard to the combination of spots P and N on one hand and P and A
on the other hand. This is identical to the fact that the sensor
elements should be placed such that they sense the largest spatial
derivatives of the ambient or disturbing physical quantity. If at
least three sensor elements are used, they are, for example, placed
along at least two, preferably orthogonal directions.
[0147] Therefore, further embodiments of the current sensor circuit
may comprise a third magnetic field sensor element as third primary
sensor element adapted to produce a third sensor signal, wherein
the first, second and third magnetic field sensor elements are not
arranged on a straight line, or are arranged such that the first
and the second primary sensor element define a first dimension, and
the first and third primary sensor element define a second
dimension that is orthogonal to the first dimension, and wherein
the signal processing circuit is adapted to process the first,
second and third sensor signal to obtain the measurement signal
according to a differential measurement principle.
[0148] If at least four sensor elements are used, they are placed
along three, preferably orthogonal directions, which is difficult
for ordinary CMOS technologies, however, it is sometimes possible
to arrange sensor elements on several surfaces of a semiconductor
die, for example, on a top side and a rear side of the die or also
along the circumference.
[0149] Therefore, further embodiments of the current sensor circuit
may comprise a fourth magnetic field sensor element as fourth
primary sensor element adapted to produce a fourth sensor signal,
wherein the first, second and third magnetic field sensor elements
are not arranged on the same two-dimensional plane, or are arranged
such that the first and the second primary sensor element define a
first dimension, the first and third primary sensor element define
a second dimension that is orthogonal to the first dimension, and
the first and the fourth primary sensor element define a third
dimension that is orthogonal to the first and second dimension, and
wherein the signal processing circuit is adapted to process the
first, second, third and fourth sensor signal to obtain the
measurement signal according to a differential measurement
principle.
[0150] The larger the differences of the primary physical quantity
to measure (e.g. the magnetic field of the current through the
conductor in case of a current sensor) or, in other words, the more
inhomogeneous the spatial distribution of the physical quantity to
be measured between the locations of the sensor elements is, the
more reliable the detection of abnormal operating conditions or
disturbing sources is.
[0151] This requires certain prerequisites on the source, which
generates the primary physical quantity.
[0152] Therefore, embodiments of the apparatus or sensor circuit
comprising a current sensor comprise a conductor which generates
spatially inhomogeneous magnetic fields. For example, a current
sensor produces inhomogeneous fields, if its conductor is a thin
wire: then the fields decay with 1/r, r being the radial distance
to the center of the wire, and for radial r like, for example, 100
micrometers a strong in-homogeneity can be obtained. For larger
currents, the conductor needs to be a planar conductor, or
sheet-like, in order to have sufficiently low electrical
resistance. In this case, fine slots or notches in the plane
conductor cause inhomogeneities of the current and consequently
also inhomogeneities of the magnetic field, as described based on
FIGS. 5A to 5D.
[0153] In case of a speed sensor, the apparatus or sensor circuit
comprises a target wheel with fine teeth or small magnetic
domains.
[0154] It should be further noted that embodiments of the
evaluation circuit evaluate the sensor signal 120b, i.e., do not
only pass the sensor signal to the output port 190. In other words,
in case the sensor element 120 is a magnetic field sensor, the
evaluation circuit does not provide an output signal 130b
representing the measured magnetic field, or in case the sensor
element 120 is a temperature sensor, the evaluation circuit does
not output a signal 130b representing the measured temperature.
Embodiments of the evaluation circuit evaluate the sensor signal
120b and provide, for example, in a rudimentary case only a binary
signal indicating whether a normal operating condition is present
or not, e.g. a binary signal with a first value (e.g. TRUE)
indicating a normal operation condition and with a second value
(e.g. FALSE) indicating an abnormal operating condition. Further
embodiments may not only distinguish between a normal operating
condition and an abnormal operating condition but may indicate
different degrees of "abnormal" conditions by distinguishing
between three or more values, wherein e.g. only one of these values
indicates a normal operating condition and the other values
indicate different degrees of abnormal operating conditions. Such
embodiments of the evaluation circuit are adapted to output
discrete values or discrete abnormal operating condition values.
The number of different discrete values is typically small, for
example, smaller than a dozen. The number of discrete values of the
signal 130b can, for example, correspond with the redundancy of the
sensor elements. For example, in case of three sensors, one primary
sensor signal is produced and two other conditions remain which can
be used to indicate different violations of normal operating
conditions, wherein, in this case, four different signals or
warnings can be given: a first kind of violation, a second kind of
violation, both conditions for a normal operating condition (NOC)
are not fulfilled, or normal operating conditions are
fulfilled.
[0155] In the following a method or algorithm performed by an
embodiment of the evaluation circuit to determine whether a normal
operation conditions (NOC) is present ("NOC=true") or not
("NOC=false", i.e. abnormal operation condition is present) is
described.
[0156] The signal 110b is computed by the signal processing circuit
in the most reliable way, typically it uses all or most sensor
elements for this calculation. The evaluation circuit checks if
signal 110b is within the required boundaries or a predetermined
range of measurement values. For example, if the system is a
current sensor and the current is too high then 110b is too high.
Then this is already enough to output via signal 130b
"NOC=false".
[0157] In case the measurement signal is within the predetermined
range, the evaluation circuit evaluates one or all sensor signals
120b, 110a, etc, for example in an iterative manner.
[0158] The evaluation circuit starts with evaluating the sensor
signal of the first sensor of a plurality of sensors arranged at
different locations, by checking if the signal of the first sensor
element is within a narrow range centred at a value which is caused
by the physical quantity corresponding to the value of signal 110b.
E.g., in case of a current sensor the system knows the value of the
signal of the first sensor element if a current of a certain amount
indicated by the signal 110b flows through the conductor. If the
signal of the first sensor element is outside this predetermined
range, the output 130b of the evaluation circuit is set to
"NOC=false" to indicate an abnormal operation condition. The
predetermined narrow range can be a fixed value or more often a
percentage of a fixed value where the percentage depends on the
signal 110b. Yet, often one has to account for the size of the
measurand (at low currents the percentual range has to be less
narrow because of inaccuracies of the system like noise and
unavoidable small background fields).
[0159] Afterwards, the evaluation circuit repeats the
aforementioned steps for the sensor signal of the second sensor
element, afterwards the third one, and so on. Thus, the evaluation
circuit evaluates each of the sensor signals of the plurality of
sensor elements. As soon as one sensor signal does not fulfil the
normal operation criterion, i.e. is not consistent, the evaluation
circuit may stop the iteration and output the abnormal operation
condition signal or may continue to check if further sensor signals
are also not consistent.
[0160] In the following an example for a current sensor according
to FIGS. 5A to 5D will be explained on exemplary values. It is
assumed that the slots of the conductor are shaped in such a way
and the thicknesses and vertical distances are such that a current
of 1 A gives 100 .mu.T at sensor P, -80 .mu.T at sensor N and N'
(where N' is placed at the mirror symmetric location above the left
half of the conductor not shown in FIG. 5D), and -90 .mu.T at
sensor A. If one denotes the magnetic field at P with BP, at N with
BN, at N' with BN', and at A with BA the signal 110b is computed by
I=(3*BP-BN-BN'-BA)/(550 .mu.T/A), where I denotes the estimated
value of the current, i.e. the measurement result 110b. It is
further assumed that the sensor has a maximum peak current of 100
A: higher currents cannot be measured because the amplifiers in the
circuit or the sensor elements would saturate. The evaluation
circuit EC first compares, if I is between -100 A and +100 A: if
not, then there is an abnormal operating condition and "NOC=false"
is output via signal 130b and port 190; if yes, a normal operation
condition is present and "NOC=true" can be output via signal 130b
and port 190. Next the evaluation circuit compares BP with I*100
.mu.T/A, because at location P the field should be 100 .mu.T per
amp. If the difference is too large: "NOC=false" is output via
signal 130b and port 190. Next the evaluation circuit EC compares
BN with I*(-80).mu.T/A, because at location N the field should be
-80 .mu.T per amp. If the difference is too large: "NOC=false" is
output via signal 130b and port 190. Next the evaluation circuit EC
compares BN' with I*(-80).mu.T/A, because at location N' the field
should be -80 .mu.T per amp. If the difference is too large:
"NOC=false" is output via signal 130b and port 190. Next the
evaluation circuit EC compares BA with I*(-90).mu.T/A, because at
location A the field should be -90 .mu.T per amp. If the difference
is too large: "NOC=false" is output via signal 130b and port 190.
At this point the evaluation circuit EC has compared all individual
sensor signals, whether they are consistent with the estimated
value I or measurement signal. In case of consistency the
evaluation circuit outputs "NOC=true" via port 190, in the opposite
case the evaluation circuit outputs "NOC=false" via signal 130b and
the port 190.
[0161] It is possible to skip checking one of these sensors
individually, because its information is already contained in the
estimation of I, which is checked at the start by the evaluation
circuit.
[0162] Therefore, embodiments of the invention provide a sensor
circuit 100, 200, 300, 400, 500, comprising: a signal processing
unit 110 adapted to process at least one sensor signal 120b of a
plurality of sensor signals generated by at least one sensor
element 120 to obtain a measurement signal 120b; and an evaluation
circuit 130 adapted to evaluate the at least one sensor signal 120b
of the plurality of sensor signals to derive a signal indicating an
abnormal operating condition in case the at least one sensor signal
does not fulfill a predetermined normal operation criterion and
wherein the predetermined normal operation criteria defines a
predetermined relation between a value of the at least one sensor
signal and a value of at least one other sensor signal of the
plurality of sensor signals (that is due to a predetermined
temporal or spatial relation of the at least one sensor signal and
the at least one other sensor signal) during a normal operation, or
the relation between a value of the at least one sensor signal and
a value of a measurement signal during a normal operation (that is
also due to a predetermined temporal or spatial relation of the at
least one sensor signal and the at least one other sensor signal a
both have been used to determine the measurement signal).
[0163] It should be further noted that embodiments of the
evaluation circuit can be adapted to perform the evaluation during
a test mode and during a normal operation mode. The apparatus or
sensor circuit can for example, be switched into a test mode to
test, e.g. the functionality of the individual sensor elements, the
signal processing unit and/or the evaluation circuit. During this
test mode the circuit can also be calibrated by applying a defined
current and sampling the readings of all individual sensor
elements. Due to manufacturing tolerances it may happen that e.g.
the readings of sensors N and its mirror symmetric counter part N'
in FIG. 5D are not identical. The sampled values can be stored in a
memory, which is part of the system, and later on during operation
in the field the evaluation circuit may used these stored reference
values to judge if "NOC=false" or "NOC=true". After testing the
apparatus or sensor circuit can be switched to the operational
mode, where the apparatus or sensor circuit performs its normal or
primary operation, i.e. the processing of the input and sensor
signals to obtain the output signal or measurement signal, while at
the same time the evaluation circuit monitors the normal operation
conditions and signals an abnormal operating condition in case the
evaluation of the sensor signal reveals that it does not meet the
normal operation conditions. The signal processing circuit and the
evaluation circuit can be implemented as separate circuits or as
one circuit that performs both tasks.
[0164] Once the manipulation is detected by the evaluation circuit
130, the evaluation circuit is adapted to communicate that an
abnormal ambient or operation condition has been detected.
[0165] There are several strategies available for the evaluation
circuit. The event can be stored in an on-board memory, e.g. EEPROM
(Electronically Erasable Programmable Read Only Memory), and
communicated later on, or it is communicated immediately through a
dedicated pin, of the sensor or encoded into the output signal,
e.g. by pulse code modulation (PCM) or pulse width modulation (PWM)
or digital protocols like SPI, or as simple analog output voltage.
In the case of an encoded output signal there should be information
on the manipulation state also in the absence of manipulation or
abnormal operation conditions, so that in case this information is
missing the controller interprets it as "manipulation detected".
Thus a fail-safe communication is provided.
[0166] In special cases it may be advantageous to feed the detected
manipulation back into the system in order to immediately react on
it: e.g. in credit cards it may be wished to immediately disable or
lock the credit card if any manipulation is detected. In billing
systems for energy meters it may by wished to output maximum
current if manipulation is detected.
[0167] Parts of the invention may be used for other kind of sensors
like pressure sensors, too. They may even be used for other kinds
of integrated electronic circuits, which serve other purposes than
sensing physical quantities: e.g. credit cards or communication
circuits.
[0168] Depending on certain implementation requirements of the
inventive methods, the inventive methods can be implemented in
hardware or in software. The implementation can be performed using
digital storage medium, in particular, a disc, CD, DVD or Blu-Ray
disc having an electronically readable control signal stored
thereon, which cooperates with a programmable computer system, such
that an embodiment of the inventive methods is performed.
Generally, an embodiment of the present invention is, therefore, a
computer program product with a program code stored on a
machine-readable carrier, the program code being operative for
performing the inventive methods when the computer program product
runs on a computer. In other words, embodiments of the inventive
methods are therefore, a computer program having a program code for
performing at least one of the inventive methods when a computer
program runs on a computer.
[0169] The aforegoing was particularly shown and described with
reference to the particular embodiments thereof, it will be
understood by those skilled in the art that various other changes
in the form and details may be made without departing from the
spirit and scope thereof. It is therefore to be understood that
various changes may be made in adapting to different embodiments
without departing from the broader concept disclosed herein and
comprehended by the claims that follow.
* * * * *