Magnetic sensing having hall plate routing to reduce inductive coupling

Methods and apparatus for canceling inductive coupling in a magnetic field sensing device having one or more Hall elements. A device can include a Hall element having a first pair of first and second voltage sensing terminals at diametrically opposed locations on the Hall element, and a second pair of third and fourth voltage sensing terminals diametrically opposed locations on the Hall element. A first mirror conductive path extends around a perimeter of the Hall element in a first direction a second mirror conductive path extends around the perimeter of the Hall element in a second direction so that the first and second mirror conductive paths are on opposite sides of the Hall element and are equal and opposite to cancel inductive coupling.

BACKGROUND

As is known, there is a variety of types of magnetic field sensing elements, including, but not limited to, Hall effect elements, magnetoresistance elements, and magnetotransistors. As is also known, there are different types of Hall effect elements, for example, a planar Hall element, a vertical Hall element, and a circular Hall element. As is also known, there are different types of magnetoresistance elements, for example, a giant magnetoresistance (GMR) element, an anisotropic magnetoresistance element (AMR), a tunneling magnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ).

Magnetic field sensors, i.e., circuits that use magnetic field sensing elements, are used in a variety of applications, including, but not limited to, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch that senses the proximity of a ferromagnetic object, a rotation detector that senses passing ferromagnetic articles, for example magnetic domains of a ring magnet, and a magnetic field sensor that senses a magnetic field density of a magnetic field.

Magnetic field sensors that include Hall elements have signal routing from a Hall plate to a Hall voltage amplifier that may have undesired inductive coupling from a time varying magnetic field source. Any loops in this routing will transduce magnetic signals to a voltage which is in addition to the Hall effect voltage, which is the signal of interest. As is known in the art, this effect is difficult to model. In addition, this inductive coupling effect can alter signal path frequency response. Hall effect sensors commonly use offset and/or flicker noise reduction techniques such as chopping or auto-zeroing. These techniques employ a high frequency clock to sample the input signal. Since the inductive coupling increases with frequency, the resulting sampling may alias high frequency signals to lower frequencies. These low frequency signals are unwanted and are difficult to remove.

SUMMARY

Embodiments of the disclosure provide methods and apparatus for magnetic sensors having Hall elements with routing to reduce the effects of inductive coupling from the Hall plate to an amplifier, for example. In embodiments, routing can be configured to have equal and opposite circuit loops that have a net zero effect on inductive signal coupling. Example sensor embodiments can include an individual Hall plate. In other sensor embodiments, net zero loops are formed for multiple Hall plates.

In some embodiments, to reduce the effects of inductive coupling, routing from the Hall plate to the subsequent amplifier can be configured such that net total inductive coupling is balanced by mirrored Hall plate instances and/or chop phases. In embodiments, each Hall plate completes one loop per chop or auto-zero phase. Equal and opposite loops may be completed through mirrored Hall plate instances. Equal and opposite loops may be completed through each separate chop phase. Signal routing from the Hall voltage sense terminals to the front-end amplifier are routed relatively close to each other when traversing long distances (e.g., from one side of the Hall plate array to the other) to avoid creating additional loops.

In one aspect, a device comprises: a Hall element having a first pair of first and second voltage sensing terminals, wherein the first and second voltage sensing terminals are located at diametrically opposed locations on the Hall element, and a second pair of third and fourth voltage sensing terminals, wherein the third and fourth voltage sensing terminals are located at diametrically opposed locations on the Hall element; and a first mirror conductive path extending around a perimeter of the Hall element in a first direction to the first voltage sensing terminal in the first pair of voltage sensing terminals and a second mirror conductive path extending around the perimeter of the Hall element in a second direction to the first voltage sensing terminal so that the first and second mirror conductive paths are on opposite sides of the Hall element and are equal and opposite to cancel inductive coupling.

A device can further include one or more of the following features: an array of Hall elements having routing to cancel inductive coupling, an array of Hall elements having routing to cancel inductive coupling during a first phase comprising first voltage sensing locations on the respective Hall elements and a second phase comprising second voltage sensing locations on the Hall elements shifted from the first phase sensing locations, first and second phases form part a signal chopping process, the first and second voltage sensing locations are shifted ninety degrees from the first phase to the second phase, the array of Hall elements comprises four Hall elements, two of the Hall elements are configured to cancel inductive effects of the other two Hall elements, and/or at least one twisted wire pair comprising a first wire connected to at least one of the positive voltage sensing terminals and a second wire connected to at least one of the negative voltage sensing terminals.

In another aspect, a method comprises: in a magnetic field sensing device, employing a Hall element having a first pair of first and second voltage sensing terminals, wherein the first and second voltage sensing terminals are located at diametrically opposed locations on the Hall element, and a second pair of third and fourth voltage sensing terminals, wherein the third and fourth voltage sensing terminals are located at diametrically opposed locations on the Hall element; and employing a first mirror conductive path extending around a perimeter of the Hall element in a first direction to the first voltage sensing terminal in the first pair of voltage sensing terminals and a second mirror conductive path extending around the perimeter of the Hall element in a second direction to the first voltage sensing terminal so that the first and second mirror conductive paths are on opposite sides of the Hall element and are equal and opposite to cancel inductive coupling.

A method can further include one or more of the following features: employing an array of Hall elements having routing to cancel inductive coupling, employing an array of Hall elements having routing to cancel inductive coupling during a first phase comprising first voltage sensing locations on the respective Hall elements and a second phase comprising second voltage sensing locations on the Hall elements shifted from the first phase sensing locations, first and second phases form part a signal chopping process, the first and second voltage sensing locations are shifted ninety degrees from the first phase to the second phase, the array of Hall elements comprises four Hall elements, two of the Hall elements are configured to cancel inductive effects of the other two Hall elements, and/or employing at least one twisted wire pair comprising a first wire connected to at least one of the positive voltage sensing terminals and a second wire connected to at least one of the negative voltage sensing terminals.

In a further aspect, a device comprises: an array of Hall elements each of the Hall elements having a first pair of first and second voltage sensing terminals, wherein the first and second voltage sensing terminals are located at diametrically opposed locations on the Hall elements, and a second pair of third and fourth voltage sensing terminals, wherein the third and fourth voltage sensing terminals are located at diametrically opposed locations on each of the Hall elements; and routing connections comprising a first path from the first voltage sensing terminal of first and second ones of the Hall elements and a second path from the second voltage sensing terminals of the first and second ones of the Hall elements, wherein the first and second paths are configured to mutually cancel fields generated in the first and second ones of the Hall elements.

A device can further include one or more of the following features: the array of Hall elements comprises four Hall elements, the first and second paths are connected during a first phase and not connected during a second phase, the routing connections further comprise, during the second phase, a third path from the third voltage sensing terminal of first and second ones of the Hall elements and a fourth path from the second voltage sensing terminals of the first and second ones of the Hall elements, wherein the third and fourth paths are configured to mutually cancel fields generated in the first and second ones of the Hall elements, a first connection comprising at least one twisted wire pair comprising a first wire connected to at least one of the positive voltage sensing terminals and a second wire connected to at least one of the negative voltage sensing terminals, the first connection is present during a first phase of a chopping process, a second connection comprising at least one twisted wire pair comprising a third wire connected to at least one of the positive voltage sensing terminals and a fourth wire connected to at least one of the negative voltage sensing terminals, and/or the second connection is present during a second phase of the chopping process.

In a further aspect, a method comprises: in a magnetic field sensing device, employing an array of Hall elements each of the Hall elements having a first pair of first and second voltage sensing terminals, wherein the first and second voltage sensing terminals are located at diametrically opposed locations on the Hall elements, and a second pair of third and fourth voltage sensing terminals, wherein the third and fourth voltage sensing terminals are located at diametrically opposed locations on each of the Hall elements; and employing routing connections comprising a first path from the first voltage sensing terminal of first and second ones of the Hall elements and a second path from the second voltage sensing terminals of the first and second ones of the Hall elements, wherein the first and second paths are configured to mutually cancel fields generated in the first and second ones of the Hall elements.

A method can further include one or more of the following features: the array of Hall elements comprises four Hall elements, the first and second paths are connected during a first phase and not connected during a second phase, the routing connections further comprise, during the second phase, a third path from the third voltage sensing terminal of first and second ones of the Hall elements and a fourth path from the second voltage sensing terminals of the first and second ones of the Hall elements, wherein the third and fourth paths are configured to mutually cancel fields generated in the first and second ones of the Hall elements, a first connection comprising at least one twisted wire pair comprising a first wire connected to at least one of the positive voltage sensing terminals and a second wire connected to at least one of the negative voltage sensing terminals, the first connection is present during a first phase of a chopping process, a second connection comprising at least one twisted wire pair comprising a third wire connected to at least one of the positive voltage sensing terminals and a fourth wire connected to at least one of the negative voltage sensing terminals, and/or the second connection is present during a second phase of the chopping process.

DETAILED DESCRIPTION

FIG.1shows an example magnetic field sensor system100having Hall element routing configured to reduce the effects of inductive coupling for routing from the Hall plate to another circuit component, such as an amplifier, in accordance with example embodiments of the invention. In the illustrated embodiment, the sensor system100is configured to detect motion characteristics of a target by sensing a change in magnetic field. The sensor system100, which can be provided in an integrated circuit (IC) package, includes a magnetic field sensing element102, which is provided as a Hall element in the illustrated embodiment. The magnetic field sensing element102is coupled to an amplifier106and filtered, such as by a low pass filter (LPF)108, and then provided to a sample and hold module110. The output of the sample and hold module110is connected to an output module112which outputs a sensor output signal114.

Note that chopping of the signal occurs between the sensing element102and the amplifier106, e.g., before the lowpass filter108. Thus any high frequency signal that is inductively coupled at the Hall element will be aliased by the chopping process.

As is readily appreciated by one skilled in the art, when laying out a Hall plate for operation at high frequencies, e.g., sense signals in the order of hundreds of kHz, inductive coupling can occur. As Hall plates increase in size, e.g., >50 μm per side, routing from the Hall voltage sense terminals to the front-end amplifier can create a loop that is completed through the Hall plate. When a magnetic field passes through a loop, electrical current is generated. In addition, sense signal chopping, auto-zero phase processing and the like, can worsen the effects of inductive coupling by aliasing high frequency signals that would normally be out of the band of interest into the desired signal frequency band.

FIG.2shows typical prior art routing from a Hall element HE with voltage sense terminals VS+, VS-connected to an amplifier AMP. The Hall voltage sense terminals VS+, VS− are coupled to the positive and negative inputs of a front-end amplifier. The curved line ICC with the arrow represents the direction of the inductively coupled current. A magnetic field going into (or out of) the page creates a current flowing from the negative terminal VS− to the positive terminal VS+ (or from the positive terminal VS+ to the negative terminal VS−), which sums with the desired Hall voltage. The inductive coupling increases with frequency, such as about +6 dB per octave, which can adversely affect frequency response flatness.

In addition, if a dynamic offset reduction technique that require multiple biasing phases is used (such as chopping, spinning, auto-zero, etc.), inductive coupling may generate unwanted aliasing of high frequency signals to a lower frequency. With these offset reduction techniques, the Hall effect signal is expected to reverse polarity from one phase to the other. On the other hand, the inductive coupled signal will not have the same polarity reversal.

FIG.3shows an example of routing for a Hall plate300that includes first (positive) and second (negative) voltage sense terminals302,304. In the illustrated embodiment, the first voltage sense terminal302is located diametrically across the Hall element300from the second voltage sense terminal304. In embodiments, first and second mirror loops306,308are formed around the Hall element300that are equal and opposite to make connections to the first voltage sense terminal302. In the illustrated configuration, the second mirror loop308is equal in area with the first mirror loop306, but with current flow in the opposite direction. First and second currents310,312, which are opposite to each other, and thus cancel each other, are formed by field in to (or out of) the page in both the first and second mirror loops306,308. The first and second mirror loops306,308are formed by routing the first (positive (+)) voltage sense terminal302around the entire Hall plate300to eliminate current flow from negative (−) to positive (+) terminals. It is understood that310and312represent current flow as a result of field going in to or out of the page, not magnetic field itself. The field in to (or out of) the page generates the current flow.

FIGS.4A and4Bshow an example embodiment400of inductive coupling cancellation in a sensor having multiple Hall elements402a,b,c,d.FIG.4Ashows connections during phase1of a signal chopping procedure andFIG.4Bshows connection during phase2of the chopping procedure. Multiple Hall402plates may be used to reduce thermal noise and offset by sensing voltages over multiple Hall elements at the same time.

In the illustrated embodiment, a quad array402a-dof Hall elements can be used to facilitate signal chopping. As can be seen, the position of Hall voltage sense terminals across the Hall elements changes from corner to corner for different phases. For example, in a first signal chopping phase (phase1), a positive voltage sense terminal is in the outer corners404a,b,c,dof the quad array, i.e., upper left corner404aof the upper left Hall plate402a, upper right corner404bof the upper right Hall plate402b, lower right corner404cof the lower right Hall plate402c, and lower left corner404dof the lower left Hall element402d. These Phase1connections are labeled +HP1. During phase1, the negative Hall voltage sense terminals406a-dare diagonally across from the positive Hall voltage sense terminals. The negative Hall voltage sense terminals406a-dfor phase1are labeled −HP3.

In a manner similar that described above forFIG.3, each connection across the respective Hall elements comprises equal and opposite mirror loops. For example, during Phase1, a connection to the positive voltage sense terminal of the first Hall element402alocated at top left corner404aof the quad array comprises equal and opposite mirror loops410a,bto cancel currents408a,bresulting from field in the mirror loops. Similarly, each connection to the positive voltage sense terminal of the other three Hall elements402b,c,dhas mirror loops to cancel respective current generated by fields in each of Hall elements during the first chopping phase.

During phase2shown inFIG.4B, the connections of the Hall voltage sense terminals move to the other corners of the Hall elements and are shown as +HP2and −HP4. As can be seen, the voltage sense terminals rotate 90 degrees to the opposite corners of the Hall elements, as in phase1. It should be noted that while in Phase1, the mirror loops are only for +HP1connections, in Phase2, two of the −HP4connections are mirror loops and two of the +HP2connections are mirror loops. For example, the upper left Hall element402ahas mirror loops415a,bfor a positive voltage sense terminal +HP2and the upper right Hall element402bhas mirror loops417a,bfor a negative voltage sense terminal −HP4. The mirror loops cancel the currents generated by fields for a net zero inductive coupling in each Hall element402a-d.

It is understood that the words “upper,” “lower,” “left,” “right,” and other such relative terms are intended to facilitate a description and understanding of example embodiments of the disclosure. Such terms are not intended to limit the scope of the invention as claimed in any way.

FIGS.5A and5Bshow an embodiment500that includes routing to reduce inducting coupling for sensors having Hall elements502a-din which at least one other Hall element cancels a field generated by a different Hall element. In the illustrated embodiment, a sensor includes a quad Hall element array having four Hall elements502a-d. During a first chopping phase, as shown inFIG.5A, a first (positive) voltage sensing terminal HP1+ is located at respective outer corners of the quad array and a second (negative) voltage sensing terminal HP3− is located at respective inner corners of the quad array. As can be seen, a respective current504a-dis generated in each of the Hall elements. Each Hall element can be considered a mirror instance of another Hall element in the quad array with an equal and opposite coupling factor. In the first phase, the first and third Hall elements502a,cmay generate a positive current and the second fourth Hall elements502b502dmay generate a negative current. The first Hall element502amay generate a current504athat is cancelled by a current504dgenerated by the fourth Hall element504d, and so on. The generated currents504a,b,c,dcancel each other in the first phase, i.e., the net inductive coupling is zero.

FIG.5Bshows the terminal arrangement and field cancellation for phase2of offset cancellation in which the Hall element voltage sense terminals have shifted 90 degrees from phase1. As can be seen, the currents generated by magnetic field in to (or out of) the Hall elements502is nulled since a net of all the currents is substantially zero. The positive Hall element voltage sense signals are designated HP2+ and the negative Hall element voltage sense signals are designated HP4−.

In the illustrated embodiment, the routing from the Hall sense terminals to the front-end amplifier (not shown) forms a single loop for each Hall plate. Instead of cancelling the inductively coupled signal with a second loop within that Hall plate, inductive cancelling is achieved by an adjacent Hall plate. Traces with the same direction of current flow are placed diagonal of each other to best match other routing parasitic characteristics.

With this arrangement, there may be less routing congestion with fewer metal layers than embodiments described above. To eliminate the need for additional loops, positive (+) and negative (−) signals are routed relatively close together when traversing from left to right of Hall plate array.

In other embodiments, other routing and Hall element terminal configurations can reduce coupling to meet the needs of a particular application. For example, an example quad array may have four positive loops in one spin phase and four negative loops in another phase. With each loop having a matched, but opposite polarity loop, the resulting inductive coupling is cancelled.

FIGS.6A and6Bshow another embodiment of a sensor having inductive coupling cancellation. To further reduce unwanted inductive signal coupling, relatively long connections can include twisted wire pairs. A balanced, twisted pair ensures that the area between first and second routes in the pair is equal between positive and negative coupling.

In the illustrated embodiment600, in a first phase (FIG.6A), quad array elements602a-dhave a connection to HP1+ in outer corners604a-dof the array and HP3− connections in inner corners of the array. A twisted wire pair606includes a first (+) twister wire606aand a second (−) twisted wire606brouting around one half, shown as the upper half, of the array. The twisted wires606a,bmake respective connections to the positive Hall element voltage sense terminals (HP1+) and the negative Hall element voltage sense terminals (HP3−).

In a second phase (FIG.6B), a twisted wire pair610can include positive610aand negative610bwires routed across a bottom of the quad array. In the illustrated embodiment, the positive wire610ais coupled to HP2+ and negative connections are coupled to HP4−.

Relatively long signal routes, such as those from the Hall plate array to the front end amplifier, should also include equally represented twists of loops of equal and opposite polarity, such as by rotating the order of the routes.

FIG.7shows example twisted signals for sets of Hall plates based on coupling polarity. In the illustrated embodiment, the routing is represented as HP1+, HP2+, HP3−, & HP4− (as above) over long distances, i.e. from the hall plates to the front end amplified. HP1+ & HP3− are the positive and negative polarities (respectively) of chopping phase1. HP2+ & HP4− are the positive and negative polarities (respectively) of chopping phase2.

InFIGS.8A and8B, routing is represented as HP1+, HP2+, HP3−, & HP4− (as above) where the shaded areas represent the loops formed by the routing. A magnetic field in to (or out of) the page will generate a clockwise (or counter clockwise) current that will result in a positive (or negative) coupling.FIG.8Arepresents the loops formed with the routes of chopping phase1. First shading PCL represents the area of the positive coupling loops and second shading NCL represents the area of the negative coupling loops. The area of the first and second shaded loops PCL, NCL is equal for equal and opposite coupling factor cancellation. Similarly,FIG.8Bshows the positive and negative loops PCL, NCL formed by chopping phase2.

Some of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity parallel to a substrate that supports the magnetic field sensing element, and others of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity perpendicular to a substrate that supports the magnetic field sensing element. In particular, planar Hall elements tend to have axes of sensitivity perpendicular to a substrate, while metal based or metallic magnetoresistance elements (e.g., GMR, TMR, AMR) and vertical Hall elements tend to have axes of sensitivity parallel to a substrate.

As used herein, the term “magnetic field sensor” is used to describe a circuit that uses a magnetic field sensing element, generally in combination with other circuits. Magnetic field sensors are used in a variety of applications, including, but not limited to, an angle sensor that senses an angle of a direction of a magnetic field, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch that senses the proximity of a ferromagnetic object, a rotation detector that senses passing ferromagnetic articles, for example, magnetic domains of a ring magnet or a ferromagnetic target (e.g., gear teeth) where the magnetic field sensor is used in combination with a back-biased or other magnet, and a magnetic field sensor that senses a magnetic field density of a magnetic field.

As used herein, the term “accuracy,” when referring to a magnetic field sensor, is used to refer to a variety of aspects of the magnetic field sensor. These aspects include, but are not limited to, an ability of the magnetic field sensor to differentiate: a gear tooth from a gear valley (or, more generally, the presence of a ferromagnetic object from the absence of a ferromagnetic object) when the gear is not rotating and/or when the gear is rotating (or, more generally, when a ferromagnetic object is moving or not moving), an ability to differentiate an edge of a tooth of the gear from the tooth or the valley of the gear (or, more generally, the edge of a ferromagnetic object or a change in magnetization direction of a hard ferromagnetic object), and a rotational accuracy with which the edge of the gear tooth is identified (or, more generally, the positional accuracy with which an edge of a ferromagnetic object or hard ferromagnetic object can be identified). Ultimately, accuracy refers to output signal edge placement accuracy and consistency with respect to gear tooth edges passing by the magnetic field sensor.

The terms “parallel” and “perpendicular” are used in various contexts herein. It should be understood that the terms parallel and perpendicular do not require exact perpendicularity or exact parallelism, but instead it is intended that normal manufacturing tolerances apply, which tolerances depend upon the context in which the terms are used. In some instances, the term “substantially” is used to modify the terms “parallel” or “perpendicular.” In general, use of the term “substantially” reflects angles that are beyond manufacturing tolerances, for example, within +/−ten degrees.

It is desirable for magnetic field sensors to achieve a certain level or amount of accuracy even in the presence of variations in an air gap between the magnetic field sensor and the gear that may change from installation to installation or from time to time. It is also desirable for magnetic field sensors to achieve accuracy even in the presence of variations in relative positions of the magnet and the magnetic field sensing element within the magnetic field sensor. It is also desirable for magnetic field sensors to achieve accuracy even in the presence of unit-to-unit variations in the magnetic field generated by a magnet within the magnetic field sensors. It is also desirable for magnetic field sensors to achieve accuracy even in the presence of variations of an axial rotation of the magnetic field sensors relative to the gear. It is also desirable for magnetic field sensors to achieve accuracy even in the presence of temperature variations of the magnetic field sensors.

Example magnetic field sensors can have a variety of features that may be described in one or more of the following patents or patent publications: U.S. Pat. Nos. 6,525,531, 6,278,269, 5,781,005, 7,777,607, 8,450,996, 7,772,838, 7,253,614, 7,026,808, 8,624,588, 7,368,904, 6,693,419, 8,729,892, 5,917,320, 6,091,239, 2012/0249126, all of which are herein incorporated herein by reference.