U.S. patent application number 15/206881 was filed with the patent office on 2016-12-08 for current sensors.
The applicant listed for this patent is Infineon Technologies AG. Invention is credited to Udo Ausserlechner.
Application Number | 20160356821 15/206881 |
Document ID | / |
Family ID | 48129052 |
Filed Date | 2016-12-08 |
United States Patent
Application |
20160356821 |
Kind Code |
A1 |
Ausserlechner; Udo |
December 8, 2016 |
CURRENT SENSORS
Abstract
Embodiments relate to magnetic field current sensors having
sensor elements for sensing at least two magnetic field components,
for example Bx and By. The current in a conductor is estimated by
Bx and Bx/By, wherein Bx is the primary measurement and Bx/By is a
corrective term used to account for position tolerances between the
sensor and the conductor. In other embodiments, the corrective term
can be dBx/By, where dBx is a difference in between components
sensed at different sensor elements. The particular field
components can vary in embodiments; for example, the current can be
estimated by By and By/Bx, or dBy/Bx or some other arrangement.
Inventors: |
Ausserlechner; Udo;
(Villach, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies AG |
Neubiberg |
|
DE |
|
|
Family ID: |
48129052 |
Appl. No.: |
15/206881 |
Filed: |
July 11, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13289228 |
Nov 4, 2011 |
9389247 |
|
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15206881 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 33/072 20130101;
G01R 15/202 20130101; G01R 15/207 20130101 |
International
Class: |
G01R 15/20 20060101
G01R015/20; G01R 33/07 20060101 G01R033/07 |
Claims
1. A current sensor for sensing current flow in a conductor
comprising: a semiconductor die; at least one magnetic field sensor
element arranged on the semiconductor die and sensitive to a
magnetic field in a first direction; at least two magnetic field
sensor elements arranged on the semiconductor die and each
sensitive to a magnetic field in a second direction different from
the first direction; and such that the current flow in the
conductor can be estimated from the magnetic fields in the second
direction and the magnetic field in the first direction.
2. The current sensor of claim 1, wherein the current flow in the
conductor can be estimated from the magnetic field in the second
direction and a ratio of the magnetic field in the second direction
and the magnetic field in the first direction.
3. The current sensor of claim 2, wherein the ratio is a
calibration term to account for position tolerances between the
current sensor and the conductor.
4. The current sensor of claim 1, comprising two magnetic field
sensor elements sensitive to the magnetic field in the second
direction.
5. The current sensor of claim 4, wherein the at least one magnetic
field sensor element sensitive to the magnetic field in the first
direction is disposed between the two magnetic field sensor
elements sensitive to the magnetic field in the second
direction.
6. The current sensor of claim 5, wherein the current flow in the
conductor can be estimated from a difference in the magnetic fields
at the two magnetic field sensor elements sensitive to the magnetic
field in the second direction and a ratio of the difference to the
magnetic field in the first direction.
7. The current sensor of claim 1, wherein a symmetry center of the
magnetic field sensor elements nominally corresponds with a
symmetry center of the conductor.
8. The current sensor of claim 1, wherein the second direction is a
direction in which the magnetic field sensor elements are spaced
apart from the conductor and the first direction is a direction in
which the magnetic field sensor elements are spaced apart from one
another.
9. A method comprising: sensing a first magnetic field component of
a magnetic field related to a current flow; sensing a second
magnetic field component different from the first magnetic field
component of a magnetic field related to the current flow; and
estimating the current flow from the first magnetic field component
and the second magnetic field component.
10. The method of claim 11, further comprising: determining a ratio
of the second magnetic field component to the first magnetic field
component; and estimating the current flow from the first magnetic
field component and the ratio.
11. The method of claim 9, further comprising providing a current
sensor comprising at least one sensor element sensitive to the
first magnetic field component and at least one sensor element
sensitive to the second magnetic field component.
12. The method of claim 11, further comprising arranging the sensor
elements on a semiconductor die of the current sensor.
13. The method of claim 12, further comprising arranging the
current sensor relative to the conductor.
14. The method of claim 13, wherein the ratio accounts for position
tolerances between the current sensor and the conductor.
15. The method of claim 14, further comprising providing a signal
when a position tolerance limit is exceeded.
16. The method of claim 13, further comprising: installing the
current sensor and the conductor; and determining the ratio before
in-field operation.
17. The method of claim 16, further comprising periodically
re-determining the ratio.
18. The method of claim 11, further comprising providing a current
sensor comprising at least two sensor elements sensitive to the
second magnetic field component.
19. The method of claim 18, further comprising: determining a
difference in magnetic field components sensed at the at least two
sensor elements sensitive to the second magnetic field component;
determining a ratio of the difference to the first magnetic field
component; and estimating the current flow from the second magnetic
field component and the ratio of the difference to the first
magnetic field component.
Description
REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. application Ser.
No. 13/289,228 filed on Nov. 4, 2011, the contents of which are
incorporated by reference in their entirety.
FIELD
[0002] The invention relates generally to current sensors and more
particularly to compensating for positioning variances by
calibration of magnetic field sensors.
BACKGROUND
[0003] Sensors that estimate the current flowing in a conductor by
sensing the related magnetic field are known in the art. In a
typical arrangement, the magnetic field sensor is fixedly
positioned near the conductor such that it can sense the magnetic
field related to current flowing in the conductor. To be accurate,
the configuration of the conductor and the positional relationship
between the conductor and the sensor must be known precisely. In
practice, the latter is a challenge because small position errors
result in large current measurement errors. Referring to FIG. 1, a
sensor 100 having two magnetic field sensing elements 102, such as
Hall plates, is depicted relative to a conductor 104. Sensing
elements 102 sensitive to magnetic fields in the y-direction, or By
fields. Errors in a vertical or y-direction as depicted have a
larger impact on sensor accuracy than those in a lateral or
x-direction. Errors in the y-direction can be related to, for
example, varying thickness of a mold compound, glue or bonding
material between the sensor and the conductor.
[0004] Conventional techniques used to calibrate the sensor to
account for positioning variances typically involve coupling the
sensor and conductor, applying a known current to the conductor and
measuring the current by the sensor. The values of the known
current and measured current can then be used to determine a
sensitivity of the sensor, which can be programmed into the sensor
and taken into account going forward when currents are measured. It
is challenging, however, to generate a stable known current for
such a procedure.
[0005] Therefore, there is a need for improved current sensors.
SUMMARY
[0006] Embodiments relate to current sensors. In an embodiment, a
current sensor for sensing current flow in a conductor comprises a
semiconductor die; at least one magnetic field sensor element
arranged on the semiconductor die and sensitive to a magnetic field
in a first direction; and at least one magnetic field sensor
element arranged on the semiconductor die and sensitive to a
magnetic field in a second direction different from the first
direction such that the current flow in the conductor can be
estimated from the magnetic field in the second direction and the
magnetic field in the first direction.
[0007] In an embodiment, a method comprises sensing a first
magnetic field component of a magnetic field related to a current
flow; sensing a second magnetic field component different from the
first magnetic field component of a magnetic field related to the
current flow; and estimating the current flow from the first
magnetic field component and the second magnetic field
component.
[0008] In an embodiment, a current sensing system comprises a
conductor; a semiconductor die disposed proximate and spaced apart
from the conductor; at least one magnetic field sensor element
sensitive to a magnetic field in a first direction and coupled to
the semiconductor die; at least one magnetic field sensor element
sensitive to a magnetic field in a second direction different from
the first direction and coupled to the semiconductor die; and
circuitry coupled to the sensor elements and configured to estimate
a current in the conductor from the magnetic field in the first
direction sensed by at least one magnetic field sensor element
sensitive to the magnetic field in the first direction and a ratio
of the magnetic field in the first direction sensed by at least one
magnetic field sensor element sensitive to the magnetic field in
the first direction and the magnetic field in the second direction
sensed by at least one magnetic field sensor element sensitive to
the magnetic field in the second direction.
[0009] In an embodiment, a current sensor for sensing current flow
in a conductor comprises a semiconductor die; at least one magnetic
field sensor element arranged on the semiconductor die and
sensitive to a magnetic field in a first direction; and at least
one magnetic field sensor element arranged on the semiconductor die
and sensitive to a magnetic field in a second direction different
from the first direction such that a distance between the magnetic
field sensor elements and the conductor can be estimated from the
magnetic field in the second direction and the magnetic field in
the first direction.
[0010] In an embodiment, a current sensor comprises a first sensor
system configured to detect a magnetic field in a first direction;
a second sensor system configured to detect a magnetic field
gradient in a second direction different from the first direction;
and a conductor configured to conduct current and produce a
magnetic field related to the current that has a flat plateau for
the first magnetic field direction and the magnetic field gradient
in the second direction with respect to at least one position
tolerance related to the first and second sensor systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0012] FIG. 1 is a block diagram of a sensor and conductor
according to an embodiment. side view of a current sensor device
according to an embodiment.
[0013] FIG. 2 is a block diagram of a sensor and conductor
according to an embodiment.
[0014] FIG. 3 is a plot of Bx and By fields at various distances
according to an embodiment.
[0015] FIG. 4 is a plot of Bx and dBy versus epsilon x according to
an embodiment.
[0016] FIG. 5 is a plot of dBy/Bx versus epsilon y according to an
embodiment.
[0017] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION
[0018] Embodiments relate to magnetic field current sensors
comprising sensor elements for sensing at least two magnetic field
components, for example Bx and By. The current in a conductor is
estimated by Bx and Bx/By, wherein Bx is the primary measurement
and Bx/By is a corrective term used to account for position
tolerances between the sensor and the conductor. In other
embodiments, the corrective term can be dBx/By, where dBx is a
difference in between components sensed at different sensor
elements. The particular field components can vary in embodiments;
for example, the current can be estimated by By and By/Bx, or
dBy/Bx or some other arrangement, with the particular axes
discussed herein corresponding to the drawings and being used for
convenience without limitation.
[0019] Referring to FIG. 2, a magnetic field sensor 100 comprises
three sensing elements: two elements 102 sensitive to a first
component of the magnetic field and one element 104 sensitive to a
second component of the magnetic field, mounted on a sensor die. As
depicted in FIG. 2, elements 102 are sensitive to the By component,
and element 104 is sensitive to the Bx component, though these can
vary in other embodiments and are used herein for the purposes of
illustration and convenience without limitation. The number of
sensor elements can also vary in embodiments and can be more or
fewer than the three depicted in FIG. 2. In embodiments, sensor
elements 102 can be the same or a different type of magnetic field
sensor than sensor element 104. For example, sensor elements 102
can be Hall devices while sensor element 104 is magnetoresistive or
a vertical Hall device. Other types and combinations are also
possible.
[0020] Sensor 100 is disposed proximate a current conductor 106.
Conductor 106 can comprise a bus bar, current rail or some other
current carrier and can have other shapes, sizes and configurations
in other embodiments. In the example embodiment depicted and
discussed herein, conductor 106 has a width in the x-direction of
2a=3.44 mm and a length in the y-direction of 2b=5.81 mm. Conductor
106, in one embodiment, is non-magnetic, with a relative
permeability close to 1, and there are no magnetic materials near
sensor elements 102, 104.
[0021] With sensor elements 102, 104 so positioned in embodiments,
the advantages of the symmetry can be utilized. The By-field is an
odd function, By(-x)=-By(x), while the Bx-field is an even
function: Bx(-x)=Bx(x). Referring also to FIG. 3, Bx thus has a
plateau near the origin, while By has a linear slope near x=0 and
thus dBy=By(+1.5 mm)-By(-1.5 mm) changes very little, if the sensor
die is shifted in the x-direction (as shown in FIG. 4).
[0022] Referring to FIG. 4, the dBy signal is constant around x=0
given the linear slope of By versus x. Therefore, lateral (i.e.,
x-direction as depicted) positioning errors have little or no
effect on dBy and Bx. The ratio of Bx/dBy is thus a pure, or nearly
so, function of vertical (i.e., y-direction as depicted) position,
as depicted in FIG. 5.
[0023] In an embodiment, then, conductor 106 conducts current and
produces a magnetic field related to the current that has a flat
plateau for the x- and y-directions with respect to at least one
position tolerance related to the sensor elements 102, 104.
[0024] In embodiments, dBy is the difference in magnetic By-fields
at two locations that are x1=3 mm apart (as depicted in FIG. 2):
dBy=By(x=epsx+1.5 mm)-By(x=epsx-1.5 mm), where epsx is the distance
between x=0 and the center point between sensor elements 102. The
particular dimensions used in examples herein are merely exemplary
and can vary in other embodiments. Ideally, epsx=0, but due to
assembly and other tolerances epsx can be +/-0.1 mm-0.5 mm in
embodiments, though this range can also vary. Bx is measured at
x=epsx, the center between elements 102 in FIG. 2. Hence, element
104 is positioned midway between the two, also as depicted in FIG.
2.
[0025] In embodiments, sensor 100 and conductor 106 are assembled
such that all sensing elements 102, 104 are equally spaced in the
y-direction relative to conductor 106, for example y1=0.3 mm as
depicted in FIG. 2. In such an embodiment, dBy/Bx would be expected
to be -0.55. If dBy/Bx is measured to be -0.54, it corresponds to a
vertical (y-direction) distance of 0.35 mm. In other words, a
y-position error of only 0.05 mm changes the ratio of dBy/Bx by
about 2%.
[0026] Sensor 100 estimates the current in embodiments according to
the following:
I estimated = S y I ( 1 + .delta. ( B x B y ) ) ##EQU00001##
where Sy is a sensitivity in the y direction and
- 1 .delta. B x B y 1 ##EQU00002##
is a small correction term related to the ratio
B x B y . ##EQU00003##
Instead or dB.sub.y, By of one of sensor elements 102 can be used
in embodiments, but in general dB.sub.y is less prone to background
magnetic disturbances.
[0027] To avoid magnetic disturbances, dB.sub.x=B.sub.x(first
location)-B.sub.x(second location) can be used. A linear
approximation
.delta. ( B x B y ) = S xy B x B y ##EQU00004##
can also be used.
[0028] The magnetic sensitivities of each of sensor elements 102,
104 can also vary, while in embodiments it is advantageous for
these elements 102, 104 to be as similar as possible. In one
embodiment, magnetic sensitivities can be kept more similar by
using an on-chip calibration wire that generates magnetic Bx and By
fields on sensor elements 102, 104. The ratio of Bx and By fields
depends upon the geometry of the wire and elements 102, 104, but it
can be constant throughout production because the geometry can be
accurate in embodiments up to at least 1 .mu.m.
[0029] Thus, this calibration wire can be used prior to the
calibration discussed herein above to compare the signals, referred
to as Bx(Ical) and By(Ical), respectively, from the Bx and By
fields in response to a current through the wire. In essence, the
wire can be used to calibrate the ratio of sensitivities of the
sensor elements 102, 104. Next, a current can be passed through
conductor 106, and the Bx and By fields measured again as
Bx(Iprimary) and By(Iprimary). Sensor 100 can then use the ratio of
[Bx(Iprimary)/By(Iprimary)]/[Bx(Ical)/By(Ical)] in order to
determine the y-distance between sensor elements 102, 104 and
conductor 106, with this distance then used in the calibration. In
another embodiment, Bx/sqrt(Bx 2+By 2) can be used instead of
Bx/By.
[0030] During operation, sensor element 104 can be prone to
magnetic disturbances. Thus, in embodiments sensor 100 can use
sensors elements 102 to obtain a first estimate of the current in
conductor 106. Then sensor 100 can add the fields from each of
sensor elements 102: in theory, if the sensor die is symmetrical to
conductor 106, this sum is independent of the current. In practice,
some asymmetry is almost always present, however, and the sum is a
mix of the external fields and the fields generated by conductor
106. Because sensor 100 already has an approximation of the
current, it can use this to get a better estimation of the
disturbance fields. Once sensor 100 knows the disturbance fields,
it can take high fields into account or provide an error signal or
flag in certain situations in which the fields exceed some
threshold. In the opposite case, in which the disturbance fields
are low, sensor 100 can have greater certainty with respect to the
Bx reading and compute the Bx/dBy ratio in order to check if the
distance between sensor 100 and conductor 106 is within an
acceptable range. If the ratio varies from a target value by some
amount, sensor 100 can provide a signal or other indication
regarding the relative positioning of sensor 100 and conductor 106
in embodiments.
[0031] The function Bx/dBy versus y-distance can also depend on the
frequency of the current, e.g., due to eddy currents, and therefore
Bx, dBy and/or Bx/dBy can be low-pass filtered in embodiments to
estimate the y-distance.
[0032] Also, in embodiments, a look-up table can be used instead of
or in addition to the ratio(s) discussed above. For example, the Bx
value can specify a column and the By value the line of the table
to provide a corrective term delta to account for position
tolerances or directly provide the y-position.
[0033] Various embodiments of systems, devices and methods have
been described herein. These embodiments are given only by way of
example and are not intended to limit the scope of the invention.
It should be appreciated, moreover, that the various features of
the embodiments that have been described may be combined in various
ways to produce numerous additional embodiments. Moreover, while
various materials, dimensions, shapes, configurations and
locations, etc. have been described for use with disclosed
embodiments, others besides those disclosed may be utilized without
exceeding the scope of the invention.
[0034] Persons of ordinary skill in the relevant arts will
recognize that the invention may comprise fewer features than
illustrated in any individual embodiment described above. The
embodiments described herein are not meant to be an exhaustive
presentation of the ways in which the various features of the
invention may be combined. Accordingly, the embodiments are not
mutually exclusive combinations of features; rather, the invention
may comprise a combination of different individual features
selected from different individual embodiments, as understood by
persons of ordinary skill in the art.
[0035] Any incorporation by reference of documents above is limited
such that no subject matter is incorporated that is contrary to the
explicit disclosure herein. Any incorporation by reference of
documents above is further limited such that no claims included in
the documents are incorporated by reference herein. Any
incorporation by reference of documents above is yet further
limited such that any definitions provided in the documents are not
incorporated by reference herein unless expressly included
herein.
[0036] For purposes of interpreting the claims for the present
invention, it is expressly intended that the provisions of Section
112, sixth paragraph of 35 U.S.C. are not to be invoked unless the
specific terms "means for" or "step for" are recited in a
claim.
* * * * *