Differential magnetic field sensor structure for orientation independent measurement

CROSS-REFERENCE TO RELATED APPLICATIONS

0001Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

0002Not applicable.

FIELD OF THE INVENTION

0003This invention relates generally to magnetic field sensors and more particularly, to differential magnetic field sensors.

BACKGROUND OF THE INVENTION

0004Magnetic field sensors that sense the rotational motion of a target are known. The target can be a magnetic or ferrous target. Such sensors detect the features of the rotating target's profile, for example, teeth/valleys of a ferrous gear target or north/south poles of a magnetic target such as a ring magnet.

0005The magnetic field associated with the target profile is sensed by a magnetic field sensing element, such as Hall element or magnetoresistive (MR) element. As the target passes the sensing element, the magnetic field experienced by the sensing element varies in relation to the target profile. The sensing element provides a signal proportional to the sensed magnetic field. The sensor processes the magnetic field signal to generate an output, for example, a signal that changes state each time the magnetic field signal crosses a threshold. Such an output can be used to provide rotational speed information. A second sensing element can be employed to generate an output for rotational direction detection as well.

0006Some sensors, referred to as differential sensors, contain two sensing elements configured in a differential arrangement. In differential magnetic field sensors, the difference between the signals provided by the two sensing elements is used to generate a differential magnetic field signal indicative of transitions in the target's features. As the differential magnetic field sensor only responds to changes in magnetic field strength, it is relatively immune to interference. Differential sensors containing three or more sensing elements can be used to provide rotational speed and direction information.

0007Unlike the non-differential sensing type magnetic field sensor, the differential magnetic field sensor is orientation dependent with respect to the target. Thus, when a differential magnetic field sensor is used to measure the speed (or direction) of a rotating target, the pair of sensing elements has to be centered over the target's profile for optimum performance. Misalignment of the sensing elements relative to the target profile results in a reduction of the peak-to-peak differential signal. Consequently, applications that cannot control the sensor-to-target alignment usually employ a non-differential sensing type sensor.

SUMMARY OF THE INVENTION

0008In general, in one aspect, the invention is directed to a differential magnetic field sensor. The differential magnetic field sensor includes a first differential channel and a second differential channel. The first differential channel includes a first pair of magnetic field sensing elements and has an associated first sensing axis defined by the first pair of magnetic field sensing elements. The second differential channel includes a second pair of magnetic field sensing elements and has a second sensing axis defined by the second pair of magnetic field sensing elements. The second sensing axis is not aligned with respect to the first sensing axis. The first sensing axis is positioned relative to a reference axis of a target profile to define an orientation angle between the first sensing axis and the reference axis. The differential magnetic field sensor further includes circuitry, coupled to the magnetic field sensing elements, to produce as an output a single differential signal having an amplitude that is orientation independent of the orientation angle.

0009Embodiments of the invention may include one or more of the following features. The circuitry can include circuitry to produce a first differential signal associated with the first differential channel and a second differential signal associated with the second differential channel, and the circuitry can further include a differential signal generator to receive as inputs the first and second differential signals and to produce as an output the single differential signal. The first and second differential signals will have amplitudes that are dependent on the orientation angle. Where the first differential signal has a first amplitude and the second differential signal has a second amplitude, the differential signal generator can operate to select the first differential signal as the single differential signal when an absolute value of the first amplitude is greater than an absolute value of the second amplitude and the differential signal generator can operate to select the second differential signal as the single differential signal when the absolute value of the first amplitude is not greater than the absolute value of the second amplitude. The circuitry can also include circuitry to receive as inputs a first magnetic field sensing output signal associated with the first sensing element, a second magnetic field sensing output signal associated with the second sensing element and a third magnetic field sensing output signal associated with the third sensing element. The differential signal generator can operate to produce the single differential signal by combining mathematically any two or more of the first magnetic field sensing output signal, the second magnetic field sensing output signal, the third magnetic field sensing output signal, the first differential signal and the second differential signal.

0010While this orientation angle independent differential sensing solution is well-suited for use in systems with rotary motion targets, it is also applicable to linear motion systems (in particular, industrial applications, e.g., rack rail and magnetic ruler) as well.

BRIEF DESCRIPTION OF THE DRAWINGS

0011The foregoing features of the invention, as well as the invention itself, may be more fully understood from the following detailed description of the drawings, in which:

0012<figref idref="DRAWINGS">FIGS. 1A-1B</figref> are pictorial representations of a sensing arrangement in which a rotary motion detecting magnetic field sensor and target profile of rotation are aligned (<figref idref="DRAWINGS">FIG. 1A</figref>) and not aligned (<figref idref="DRAWINGS">FIG. 1B</figref>);

0013<figref idref="DRAWINGS">FIGS. 2A-2B</figref> are pictorial representations of the target profile defined by poles (<figref idref="DRAWINGS">FIG. 2A</figref>) and alternating gear wheel teeth/valleys (<figref idref="DRAWINGS">FIG. 2B</figref>, a side view);

0014<figref idref="DRAWINGS">FIGS. 3A-3G</figref> are pictorial representations of an exemplary magnetic field sensing structure that includes three sensing elements configured for orientation independent, differential sensing (with <figref idref="DRAWINGS">FIG. 3G</figref> showing an exemplary structure with additional sensing elements to support rotational speed and direction detection capability);

0015<figref idref="DRAWINGS">FIGS. 4A-4D</figref> are functional block diagrams of a magnetic field sensor that includes three sensing elements and a differential signal generator to generate a single differential signal based on the three sensing elements;

0016<figref idref="DRAWINGS">FIGS. 5A-5C</figref> are pictorial representations of an exemplary magnetic field sensing structure that includes four sensing elements configured for orientation independent, differential sensing;

0017<figref idref="DRAWINGS">FIG. 6</figref> is a functional block diagram of a magnetic field sensor that includes four sensing elements and a differential signal generator to use differential signals from differential channels formed by pairs of the sensing elements to generate a single differential signal;

0018<figref idref="DRAWINGS">FIGS. 7A-7F</figref> illustrate differential signals obtained using sensing element pairs for various orientation angles including 0, 22.5 and 45 degrees;

0019<figref idref="DRAWINGS">FIGS. 8A-8B</figref> are graphs that show differential signal amplitude versus orientation angle;

0020<figref idref="DRAWINGS">FIGS. 9A-9C</figref> are flow diagrams showing alternative exemplary operations of the differential signal generator of <figref idref="DRAWINGS">FIGS. 4A-D</figref> and <b>6</b>; and

0021<figref idref="DRAWINGS">FIG. 10</figref> is a functional block diagram of an exemplary automotive application in which an orientation independent differential magnetic field sensor (such as those depicted in <figref idref="DRAWINGS">FIGS. 4A-D</figref> and <figref idref="DRAWINGS">FIG. 6</figref>) is employed.

DETAILED DESCRIPTION

0022Referring to <figref idref="DRAWINGS">FIG. 1A</figref>, a sensing arrangement <b>10</b> in which a magnetic field sensor <b>12</b> is arranged in a radial sensing position relative to a rotating target profile <b>14</b> is shown. An axis of rotation is indicated by arrow <b>15</b>. A direction of motion of the rotating target profile <b>14</b> is indicated by arrow <b>16</b>. Although shown in one direction, the motion could be in the opposite direction or both directions. The target profile <b>14</b>, which has a width “W” <b>17</b>, faces the “front” of the magnetic field sensor <b>12</b>. The mid-point of the face width is indicated by a centerline <b>18</b> and referred to herein as the target profile's reference axis. The magnetic field sensor <b>12</b> is a differential sensing device and, as such, includes two sensing elements <b>20</b><i>a </i>and <b>20</b><i>b </i>for generating a differential signal responsive to change in magnetic field strength at a location relative to the target profile <b>14</b>. That location corresponds to a differential channel (not shown). Associated with the differential channel is a sensing axis <b>22</b> as defined by the arrangement of the sensing elements <b>20</b><i>a</i>, <b>20</b><i>b. </i>

0023In the illustration of <figref idref="DRAWINGS">FIG. 1A</figref>, the magnetic field sensor <b>12</b> is centered over the target profile <b>14</b> so that the sensing axis <b>22</b> is positioned approximately parallel to the target profile edges and aligned with the reference axis <b>18</b>. The sensing axis <b>22</b> need not be exactly centered over the centerline <b>18</b> (as it is depicted in the figures) to be considered “aligned”. That is, the sensing axis <b>22</b> may be somewhat offset from but parallel to the centerline <b>18</b>. The width W must be large enough so that positioning of the sensing elements <b>20</b><i>a</i>, <b>20</b><i>b </i>is not too close to the target profile's edge, however, because of flux distortions in those areas.

0024The differential mode of operation requires careful adjustment of the sensor <b>12</b> to achieve that alignment. In some applications, the sensor alignment to the target cannot be guaranteed. Typically, sensor-target orientation offset or misalignment occurs at installation time, that is, when the sensor is installed near the target. For example, the sensor may be mounted in a threaded housing that is screwed into an installation location and the installation process may be controlled by monitoring only the torque. Alternatively, the sensor or the housing in which it is contained may be mounted to a surface at the installation location in a way that results in misalignment between sensor and target profile.

0025<figref idref="DRAWINGS">FIG. 1B</figref> shows such misalignment with a sensing arrangement <b>10</b>′. The sensing arrangement <b>10</b>′ is the same as sensing arrangement <b>10</b> of <figref idref="DRAWINGS">FIG. 1A</figref> except that the orientation of the magnetic field sensor <b>12</b> is offset relative to the target profile <b>14</b> by an orientation angle α <b>24</b>. In other words, the sensing axis <b>22</b> is no longer aligned with the reference axis <b>18</b> but is instead offset relative to the reference axis <b>18</b> by the orientation angle α <b>24</b>. In this illustration, a mounting axis <b>25</b> about which sensor movement or other positioning offset can occur, for example, during installation, is centered equidistant of the two sensing elements <b>20</b><i>a</i>, <b>20</b><i>b </i>along the axis <b>22</b>. The sensor misalignment causes degradation in sensor performance, as the peak-to-peak amplitude of the differential signal generated by the sensor <b>12</b> will not be at a maximum value. From an application standpoint, the consequence of reduced differential signal peak-to-peak amplitude is the reduction of maximum air gap range.

0026<figref idref="DRAWINGS">FIGS. 2A and 2B</figref> show two different example target profiles. In <figref idref="DRAWINGS">FIG. 2A</figref>, which shows the same “face” view of the target profile shown in <figref idref="DRAWINGS">FIGS. 1A-1B</figref>, the target profile <b>14</b> from <figref idref="DRAWINGS">FIG. 1A</figref> is defined by an alternating sequence of south and north magnetic poles <b>26</b> and <b>28</b>, respectively. In <figref idref="DRAWINGS">FIG. 2B</figref>, the target profile <b>14</b> (shown here in a side view to more clearly illustrate the features of the target profile) is defined by an alternating pattern of a raised feature (e.g., a tooth) <b>30</b> followed by a gap <b>32</b>, typically referred to as a valley or recess. The teeth or other type of raised features can have various shapes, e.g., square, triangle or other, based on design requirements. These patterns in <figref idref="DRAWINGS">FIGS. 2A-2B</figref> may be provided along the circumference of the rotating target, e.g., a permanent magnet such as a ring magnet, or some other type of multi-pole magnet, or ferrous object such as a toothed gear wheel, either radially (i.e., along the outer rim or edge of the wheel or ring magnet) as shown in <figref idref="DRAWINGS">FIGS. 1A and 2A</figref>, or axially (not shown). In an axial sensing arrangement with a ring magnet, the target profile of alternating poles would be defined on a broad surface of the ring magnet instead.

0027A differential sensor such as sensor <b>12</b> detects motion of rotating ferrous and magnetic targets by measuring the differential flux density of the magnetic field. Referring back to <figref idref="DRAWINGS">FIG. 2B</figref>, to detect ferrous targets the magnetic field must be provided by a back biasing permanent magnet <b>34</b>, e.g., the south or north pole of the magnet <b>34</b> may be attached to (or positioned near) the “back” of the sensor <b>12</b>, i.e., the side that does not face the target profile <b>14</b>, as shown.

0028Misalignment of the type depicted in <figref idref="DRAWINGS">FIG. 1B</figref> can be prevented, but only with labor-intensive monitoring or specially designed assemblies. A new sensing scheme, presented herein, is tolerant to such misalignment. Thus, a differential sensor device incorporating this new scheme will operate effectively whether the orientation angle α is zero degrees (perfect alignment) or some random value greater than zero degrees.

0029<figref idref="DRAWINGS">FIGS. 3A-3G</figref>, <figref idref="DRAWINGS">FIGS. 4A-D</figref>, <figref idref="DRAWINGS">FIGS. 5A-5C</figref> and <figref idref="DRAWINGS">FIG. 6</figref> show arrangements that utilize multiple magnetic field sensing elements (or, simply, “sensing elements”) to realize multiple differential channels. With these arrangements a differential sensor that is orientation independent (relative to the target profile) can be achieved, as will be discussed in further detail below.

0030In one exemplary embodiment, and referring to <figref idref="DRAWINGS">FIGS. 3A-3F</figref>, an arrangement based on the use of three sensing elements is shown. As shown in <figref idref="DRAWINGS">FIGS. 3A-3F</figref>, a magnetic field sensing structure <b>40</b> has a configuration of three sensing elements <b>42</b><i>a</i>, <b>42</b><i>b</i>, <b>42</b><i>c </i>(also labeled “SE<b>1</b>”, “SE<b>2</b>”, and SE<b>3</b>”, respectively) for use in a differential magnetic field sensor. The sensing elements <b>42</b><i>a</i>, <b>42</b><i>b</i>, <b>42</b><i>c </i>are spaced apart by some fixed distance. The physical placement of the sensing elements <b>42</b><i>a</i>, <b>42</b><i>b</i>, <b>42</b><i>c </i>near a target allows the sensing elements to be used to generate multiple differential signals responsive to change in magnetic field strength at respective locations relative to that target's profile (like target profile <b>14</b> of <figref idref="DRAWINGS">FIG. 1A</figref>, <figref idref="DRAWINGS">FIGS. 2A-2B</figref>). Those locations correspond to differential channels, shown in <figref idref="DRAWINGS">FIGS. 4A-4B</figref> and described in further detail later.

0031Referring to <figref idref="DRAWINGS">FIGS. 3A-3C</figref>, a first sensing axis <b>44</b> is defined by the arrangement of the sensing elements <b>42</b><i>a</i>, <b>42</b><i>b </i>(or first pair of differential sensing elements) and a second sensing axis <b>46</b> is defined by the arrangement of the sensing elements <b>42</b><i>a</i>, <b>42</b><i>c </i>(or second pair of differential sensing elements). Thus, in the illustrated example, the three sensing elements are spatially arranged, for example, on the surface of a sensor die (the outline of which is indicated by dashed lines), to define the two sensing axes, that is, the first sensing axis <b>44</b> and the second sensing axis <b>46</b>. The sensing elements are arranged so that the two sensing axes <b>44</b>, <b>46</b> are not aligned with each other in the plane of the die surface. Preferably, they are at an angle of about 90 degrees relative to each other. It will be understood, however, that a different angle could be used. In the arrangement shown in <figref idref="DRAWINGS">FIGS. 3A-3C</figref> and <figref idref="DRAWINGS">FIG. 4A</figref>, the first and second pairs of differential sensing elements share the sensing element <b>42</b><i>a</i>. The element-to-element spacing of the sensing elements in each pair is preferably the same (or approximately the same), but could be different.

0032Referring now to <figref idref="DRAWINGS">FIG. 3A</figref>, when the first sensing axis <b>44</b> is aligned with a target profile (that is, and referring back to <figref idref="DRAWINGS">FIG. 1A</figref>, it aligns with the target profile's reference axis <b>18</b>), a differential signal “D<b>1</b>” generated by the first sensing element pair <b>42</b><i>a</i>, <b>42</b><i>b </i>will have an amplitude that is maximal (“D<b>1</b>_max”) and a differential signal “D<b>2</b>” generated by the second sensing element pair <b>42</b><i>a</i>, <b>42</b><i>c </i>will have an amplitude that is zero (“D<b>2</b>_{zero”). The distance “L1” between the sensing elements SE1 and SE2 along the reference axis is maximal (indicated as “L1}_max” <b>48</b>) for this orientation. The distance “L<b>2</b>” between the sensing elements SE<b>1</b> and SE<b>2</b> along the reference axis is zero. Referring to <figref idref="DRAWINGS">FIG. 3B</figref>, when the first sensing axis <b>44</b> is positioned at a 90 degree angle relative to the target profile's reference axis, the signal amplitude for the first differential signal D<b>1</b> will be zero (“D<b>1</b>_zero”) and signal amplitude for the second differential signal D<b>2</b> will be maximal (“D<b>2</b>_max”). For the 90 degree shift in orientation, the distance “L<b>2</b>” between the sensing elements SE<b>1</b> and SE<b>3</b> along the reference axis is maximal (indicated as “L<b>2</b>_max” <b>50</b>) and the distance “L<b>1</b>” is now zero. Referring to <figref idref="DRAWINGS">FIG. 3C</figref>, for a random orientation angle α <b>52</b> between the first sensing axis <b>44</b> and the target profile's reference axis, the signal amplitudes for the first differential signal D<b>1</b> and the second differential signal D<b>2</b> will vary with the orientation angle. For the depicted orientation, the distance L<b>1</b> is equal to L<b>1</b>_max*cos α (indicated by reference numeral <b>54</b>), and the distance L<b>2</b> is equal to L<b>2</b>_max*sin α (indicated by reference numeral <b>56</b>). It will be appreciated that D<b>1</b>_maxis the maximal amplitude of D<b>1</b>, that is, the amplitude of D<b>1</b> when α is zero degrees, and D<b>2</b>_maxis the maximal amplitude of D<b>2</b>, that is, the amplitude of D<b>2</b> when α is 90 degrees. Thus, these maximal amplitudes may be represented as D<b>1</b>_maxand D<b>1</b>_α=0for D<b>1</b> and D<b>2</b>_maxand D<b>2</b>_α=90for D<b>2</b>. A single differential signal whose amplitude is independent of the orientation angle α, and referred to herein as an orientation angle independent differential signal, can be determined from D<b>1</b> and D<b>2</b>, as will be discussed in further detail with reference to <figref idref="DRAWINGS">FIG. 4A</figref>. The term “orientation angle independent differential signal”, as it is used herein, means that the amplitude of this single differential signal is completely or relatively independent of change in orientation angle. By “relatively orientation angle independent” it is meant that a residual change in amplitude with orientation angle can exist but is limited. In some embodiments, as later described, the residual change in amplitude with orientation angle can be compensated in the sensor circuitry.

0033As shown in <figref idref="DRAWINGS">FIGS. 3D-3F</figref>, a third sensing axis <b>58</b> is defined by the arrangement of the sensing elements <b>42</b><i>b </i>(“SE<b>2</b>”), <b>42</b><i>c </i>(“SE<b>3</b>”). This third pair of sensing elements can be used to generate a third differential signal “D<b>3</b>”. In some embodiments, for example, as illustrated in <figref idref="DRAWINGS">FIG. 4B</figref>, the orientation angle independent differential signal can be generated from D<b>1</b>, D<b>2</b> and D<b>3</b>.

0034An additional element provided along each axis can be used to provide both rotational speed and direction information. As shown in <figref idref="DRAWINGS">FIG. 3G</figref>, a structure shown as structure <b>40</b>′ has three sensing elements, sensing element <b>42</b><i>a</i>, sensing element <b>42</b><i>b </i>and an additional sensing element (“SE<b>4</b>”) <b>42</b><i>d</i>, aligned to form a first single sensing axis shown as sensing axis <b>44</b>′. The structure <b>40</b>′ is further configured with three sensing elements, sensing element <b>42</b><i>a</i>, sensing element <b>42</b><i>c </i>and an additional sensing element (“SE<b>5</b>”) <b>42</b><i>e</i>, aligned to form a second single sensing axis <b>46</b>′.

0035<figref idref="DRAWINGS">FIG. 4A</figref> shows a functional diagram of a magnetic field sensor <b>60</b> that incorporates the magnetic field sensing structure <b>40</b> depicted in <figref idref="DRAWINGS">FIGS. 3A-3C</figref>. The sensor <b>60</b> includes the three sensing elements <b>42</b><i>a</i>, <b>42</b><i>b</i>, <b>42</b><i>c </i>(again shown as sensing elements SE<b>1</b>, SE<b>2</b>, SE<b>3</b>). Coupled to the sensing elements <b>42</b><i>a</i>-<b>42</b><i>c </i>is an interface circuit <b>62</b>. The interface circuit <b>62</b> includes a first differential amplifier <b>64</b><i>a </i>and a second differential amplifier <b>64</b><i>b</i>, as well as a differential signal generator <b>66</b>. The interface circuit <b>62</b> further includes an output generating circuit <b>68</b>.

0036The sensing elements SE<b>1</b><b>42</b><i>a </i>and SE<b>2</b><b>42</b><i>b </i>are coupled to and provide magnetic field sensing output signals <b>70</b><i>a </i>and <b>70</b><i>b</i>, respectively, to the first differential amplifier <b>64</b><i>a</i>. The sensing elements SE<b>1</b><b>42</b><i>a </i>and SE<b>3</b><b>42</b><i>c </i>are coupled to and provide magnetic field sensing output signals <b>70</b><i>a </i>and <b>70</b><i>c</i>, respectively, to the second differential amplifier <b>64</b><i>b</i>. The output of each differential amplifier <b>64</b><i>a</i>, <b>64</b><i>b </i>represents only the difference in magnetic flux density between the two sensing elements to which it is coupled. The first differential amplifier <b>64</b><i>a </i>provides as its output a first differential signal (referred to earlier as“D<b>1</b>”) <b>72</b> and the second differential amplifier <b>64</b><i>b </i>provides as its output a second differential signal (referred to earlier as“D<b>2</b>”) <b>74</b>. The differential amplifiers <b>64</b><i>a</i>, <b>64</b><i>b </i>are coupled to the differential signal generator <b>66</b>. The differential signals <b>72</b> and <b>74</b> are provided as inputs to the differential signal generator <b>66</b>, which produces as an output a third differential signal (“D<b>4</b>”) <b>76</b>. The differential signal generator <b>66</b> operates to generate D<b>4</b> based on D<b>1</b> and D<b>2</b>.

0037The amplitude of the resulting differential signal D<b>4</b> is said to be independent of the orientation angle α, as mentioned above. Thus, the amplitude of the differential signal D<b>4</b> is much the same as that of the differential signal that would be seen if either differential channel were aligned with the target profile's reference axis <b>18</b>. Consequently, optimum performance does not depend on one or the other channel being aligned with the target profile's reference axis.

0038The output <b>76</b> of the differential signal generator <b>66</b> is coupled to the output generating circuit <b>68</b>. The output generating circuit <b>68</b> may be implemented according to known techniques and designs to suit the needs of an application. Typically, and as illustrated, the circuit <b>68</b> includes a peak detector or comparator <b>78</b> and an output stage <b>80</b>. Peak detectors track the signal provided to the detector and switch at a fixed level or at a level related to peaks of the input signal. Threshold detection applies one or more levels through which that signal must pass to induce switching. The thresholds are defined as a percentage of peak-to-peak amplitude.

0039The third differential signal D<b>4</b><b>76</b> is provided as an input to the detector <b>78</b>. The detector output, shown as output <b>82</b>, is provided to the output stage <b>80</b>. The output stage <b>80</b> provides to sensor output (OUT) <b>84</b> a sensor output signal <b>86</b> indicative of detected target profile transitions (such as leading and/or trailing tooth edges or magnetic pole changes). The output stage <b>80</b> may be implemented as a totem-pole push-pull or open drain, open collector output configuration. This type of configuration is a typical configuration. Devices with such an output are sometimes referred to as “three-wire” devices. Alternatively, the output stage <b>80</b> could be implemented as a current source output structure that provides two levels of current representing two digital output states of the sensor. As the output current would be provided on the supply/ground lines, the use of a current source output structure would eliminate the need for the output <b>84</b>. Devices with the current output structure are sometimes referred to as “two-wire” devices. Alternatively, the output can be coded in a protocol like Inter-Integrated Circuit (I²C), Serial Peripheral Interface (SPI), Single Edge Nibble Transmission (SENT) or other protocols used in automotive, industrial or consumer applications.

0040An external power supply voltage can be provided to the sensor at a VCC terminal or input <b>88</b>. The interface circuit <b>62</b> and sensing elements <b>42</b><i>a</i>-<b>42</b><i>c </i>are coupled to the VCC input <b>88</b> via a VCC bus <b>90</b> and are connected to a ground (GND) terminal <b>92</b> through an internal GND connection <b>94</b>.

0041As mentioned earlier, a differential channel corresponds to a location for generating a differential signal by a pair of sensing elements relative to the target profile. The differential channel contains a pair of sensing elements and other circuitry associated with that pair. In the illustrated embodiment, the sensor <b>60</b> includes a first differential channel <b>96</b> and a second differential channel <b>98</b>. The first differential channel <b>96</b> includes, along with sensing elements <b>42</b><i>a</i>, <b>42</b><i>b</i>, the first differential amplifier <b>64</b><i>a </i>and produces the first differential signal <b>72</b>. The second differential channel <b>98</b> includes the sensing elements <b>42</b><i>a</i>, <b>42</b><i>c</i>, as well as the second differential amplifier <b>64</b><i>b</i>, and produces the second differential signal D<b>2</b><b>74</b>. Each differential channel has an associated or respective sensing axis as defined by its respective pair of sensing elements. The first differential channel <b>96</b> has an associated sensing axis shown in <figref idref="DRAWINGS">FIGS. 3A-3C</figref> as sensing axis <b>44</b>. The second differential channel <b>98</b> has an associated sensing axis shown in <figref idref="DRAWINGS">FIGS. 3A-3C</figref> as sensing axis <b>46</b>.

0042Circuitry for processing the differential signal may also be considered part of the differential channel. Thus, the first differential channel <b>96</b> may include, in addition to sensing elements <b>42</b><i>a</i>, <b>42</b><i>b</i>, and differential amplifier <b>64</b><i>a </i>(for generating the differential signal <b>72</b>), circuitry of the interface circuit <b>62</b> to process the differential signal <b>72</b> (D<b>1</b>). Similarly, the second differential channel <b>98</b> may include, in addition to sensing elements <b>42</b><i>a</i>, <b>42</b><i>c</i>, and differential amplifier <b>64</b><i>b</i>, circuitry of the interface circuit <b>62</b> to process the differential signal <b>74</b> (D<b>2</b>). In the implementation shown in <figref idref="DRAWINGS">FIG. 4A</figref>, units <b>66</b> and <b>68</b> are shared by the first and second differential channels, i.e., first differential channel <b>96</b> and second differential channel <b>98</b>.

0043Other aspects of the magnetic field sensor <b>60</b>, not shown, may be implemented according to known techniques and designs. The implementation can be analog, digital or mixed signal. It will be understood that interface circuit <b>62</b> may contain various other circuits that operate collectively to generate a sensor output from the magnetic field signals of the sensing elements. For example, an amplifier and other circuitry may be coupled between each sensing element and its corresponding differential amplifier to amplify the magnetic field and, optionally, to implement other features, such as dynamic offset cancellation (i.e., chopper stabilization), automatic gain control (AGC) and offset adjustment. Alternatively, or in addition, such features may be provided elsewhere, e.g., between the differential amplifier and the differential signal generator (as illustrated in <figref idref="DRAWINGS">FIG. 4D</figref>).

0044The sensor <b>60</b> may be provided in the form of an integrated circuit (IC) containing a semiconductor substrate on which the various circuit elements are formed. The IC would have at least one pin to correspond to each of: the VCC input or terminal <b>88</b>, GND terminal <b>92</b> and, depending on the output stage implementation, the output (OUT) <b>84</b>. It will be appreciated that the functionality of the IC, that is, the circuit elements contained within it, can be varied to suit a particular application. The sensing elements <b>42</b><i>a</i>-<b>42</b><i>c </i>and interface circuit <b>62</b> can be provided on the same die or on separate dies.

0045<figref idref="DRAWINGS">FIG. 4B</figref> shows a sensor having an implementation similar to that of sensor <b>60</b> of <figref idref="DRAWINGS">FIG. 4A</figref>. The sensor in <figref idref="DRAWINGS">FIG. 4B</figref>, shown as sensor <b>60</b>′, differs from the sensor <b>60</b> of <figref idref="DRAWINGS">FIG. 4A</figref> in that the sensor <b>60</b>′ makes use of the third sensing element pair <b>42</b><i>b</i>, <b>42</b><i>c </i>(as illustrated in <figref idref="DRAWINGS">FIGS. 3D-3F</figref>) in addition to the sensing pairs <b>42</b><i>a</i>, <b>42</b><i>b </i>and <b>42</b><i>a</i>, <b>42</b><i>c </i>from <figref idref="DRAWINGS">FIG. 4A</figref>. In the illustrated embodiment of <figref idref="DRAWINGS">FIG. 4B</figref>, the sensor <b>60</b>′ includes a third differential channel <b>100</b> (in addition to the first differential channel <b>96</b> and a second differential channel <b>98</b>, shown in <figref idref="DRAWINGS">FIG. 4A</figref> and omitted from <figref idref="DRAWINGS">FIG. 4B</figref> for simplification). The third differential channel <b>100</b> includes, along with sensing elements <b>42</b><i>b</i>, <b>42</b><i>c</i>, a third differential amplifier <b>64</b><i>c </i>and produces the third differential signal referred to earlier as “D<b>3</b>” and indicated by reference numeral <b>102</b>. The third differential channel <b>100</b> has an associated sensing axis shown in <figref idref="DRAWINGS">FIGS. 3D-3F</figref> as sensing axis <b>58</b>.

0046The differential amplifiers <b>64</b><i>a</i>, <b>64</b><i>b</i>, <b>64</b><i>c </i>are coupled to the differential signal generator, shown here as differential signal generator <b>66</b>′. The differential signals <b>72</b>, <b>74</b> and <b>102</b> are provided as inputs to the differential signal generator <b>66</b>′, which produces as an output a fourth differential signal (“D<b>4</b>”) <b>76</b>′. The differential signal generator <b>66</b>′ operates to generate D<b>4</b><b>76</b>′ based on D<b>1</b>, D<b>2</b> and D<b>3</b>. The amplitude of the resulting differential signal D<b>4</b><b>76</b>′ is said to be independent of the orientation angle α, as was discussed above in connection with differential signal D<b>4</b><b>76</b> from FG. <b>4</b>A.

0047The output <b>76</b>′ of the differential signal generator <b>66</b>′ is coupled to the output generating circuit <b>68</b>. Other details of <figref idref="DRAWINGS">FIG. 4B</figref> are the same as described for <figref idref="DRAWINGS">FIG. 4A</figref>. The differential signal D<b>4</b><b>76</b>′ is provided as an input to the detector <b>78</b>. The detector output, shown as output <b>82</b>, is provided to the output stage <b>80</b>. The output stage <b>80</b> provides to sensor output (OUT) <b>84</b> a sensor output signal <b>86</b> indicative of detected target profile transitions (such as leading and/or trailing tooth edges or magnetic pole changes).

0048In yet another alternative implementation, and referring now to <figref idref="DRAWINGS">FIG. 4C</figref>, the sensor shown in the figure as sensor <b>60</b>″ includes an interface <b>62</b>″. The interface <b>62</b>″ receives as inputs, signals <b>70</b><i>a</i>-<b>70</b><i>c</i>, from respective sensing elements <b>42</b><i>a</i>-<b>42</b><i>c</i>. The interface <b>62</b>″ includes an orientation angle independent differential signal generator <b>66</b>″ to produce the orientation angle independent differential signal D<b>4</b>, shown here as D<b>4</b><b>76</b>″. Unlike the differential signal generator <b>66</b> (from FIG. <b>4</b>A) and <b>66</b>′ (from <figref idref="DRAWINGS">FIG. 4B</figref>), the differential signal generator <b>66</b>″ includes internally the differential amplifiers <b>64</b> (from <figref idref="DRAWINGS">FIGS. 4A-4B</figref>) as well as functionality to combine mathematically the outputs of those differential amplifiers <b>64</b> (i.e., the differential signals D<b>1</b>, D<b>2</b>, D<b>3</b>) and/or the sensing element outputs <b>70</b><i>a</i>, <b>70</b><i>b</i>, <b>70</b><i>c</i>. It further includes signal processing capability, coupled to the combinations functionality, to normalize that combined signal so that it is truly independent of the orientation angle. The signal processing capability can include at least an AGC block. With the inclusion of programmable memory (e.g., EEPROM) and microprocessor, the differential signal generator <b>66</b>″ can be configured to perform different combinations as well as types of signal processing. Other features are as previously described with respect to <figref idref="DRAWINGS">FIGS. 4A and 4B</figref>.

0049<figref idref="DRAWINGS">FIG. 4D</figref> shows yet another example embodiment of a sensor, shown as sensor <b>60</b>′″, that incorporates a three-SE structure like the one shown in <figref idref="DRAWINGS">FIGS. 3A-3C</figref>. This particular implementation features a digital subsystem to enable processing in the digital domain. Like the sensors shown in <figref idref="DRAWINGS">FIGS. 4A-4C</figref>, sensor <b>60</b>′″ also includes sensing elements <b>42</b><i>a</i>-<b>42</b><i>c</i>. The sensor <b>60</b>′″ has the same high-level functional blocks as sensor <b>60</b>″ from <figref idref="DRAWINGS">FIG. 4C</figref>, including an orientation angle independent differential signal generator indicated by reference numeral <b>66</b>′″ and an output generating circuit indicated by reference numeral <b>68</b>′. The differential signal generator <b>66</b>′″ includes an analog front end <b>100</b> and a digital subsystem <b>102</b>. The analog front end <b>100</b> includes the two differential amplifiers <b>64</b><i>a</i>, <b>64</b><i>b </i>(which were also shown in <figref idref="DRAWINGS">FIGS. 4A-4B</figref>). Shown in this particular implementation are various signal conditioning circuits, including offset adjustment (“offset adjust”) circuits <b>103</b><i>a</i>, <b>103</b><i>b</i>, automatic gain control (AGC) circuits <b>104</b><i>a</i>, <b>104</b><i>b</i>, chopper stabilization circuits <b>105</b><i>a</i>, <b>105</b><i>b</i>, low pass filters <b>106</b><i>a</i>, <b>106</b><i>b </i>and analog-to-digital converters (A/Ds) <b>107</b><i>a</i>, <b>107</b><i>b </i>(collectively, A/D <b>108</b>). A clock generator <b>110</b> provides timing signals to the A/D <b>108</b> (via clock line <b>111</b>) and digital subsystem <b>102</b> (via clock line <b>112</b>). Circuits <b>64</b><i>a</i>, <b>103</b><i>a</i>, <b>104</b><i>a</i>, <b>105</b><i>a</i>, <b>106</b><i>a </i>and <b>107</b><i>a </i>are part of the first differential channel associated with the sensing element pair <b>42</b><i>a</i>, <b>42</b><i>b</i>. Circuits <b>64</b><i>b</i>, <b>103</b><i>b</i>, <b>104</b><i>b</i>, <b>105</b><i>b</i>, <b>106</b><i>b </i>and <b>107</b><i>b </i>are part of the second differential channel associated with the sensing element pair <b>42</b><i>a</i>, <b>42</b><i>c. </i>

0050Still referring to <figref idref="DRAWINGS">FIG. 4D</figref>, the output generating circuit <b>68</b>′ includes output stage <b>80</b>′and the digital subsystem <b>102</b>. Thus, blocks <b>66</b>′″ and <b>68</b>′ share the digital subsystem <b>102</b>. In the illustrated embodiment, the digital subsystem <b>102</b> includes a control portion (“Digital Control”) <b>114</b> and a processing portion (“Digital Processing”) <b>116</b>. The control portion <b>114</b> and processing portion <b>116</b> are coupled to a nonvolative memory <b>117</b>, e.g., an EEPROM, as shown, via memory bus lines <b>118</b> and <b>119</b>, respectively. The EEPROM <b>117</b> is used to program functions of the control and processing portions <b>114</b>, <b>116</b>, that is, store program code to be executed by the processing portion <b>116</b> and operating parameters. For example, the control portion <b>114</b> can be configured to control the A/Ds, the AGCs and offset adjust circuits via control lines <b>120</b>, as well as set or control test features, e.g., of test modes like Quiescent supply current test (IDDQ) and boundary scan scanpath. The digital processing portion <b>116</b> can be programmed to perform the D<b>4</b> determination, e.g., according to a process described with reference to <figref idref="DRAWINGS">FIG. 9A</figref>, or other processes, as well as D<b>4</b> switchpoint determination. The output of the digital subsystem, output <b>121</b>, is provided to the output stage <b>80</b>′. The output stage <b>80</b>′ is shown as being implemented with a transistor, e.g., MOSFET <b>122</b>, and a current limit circuit <b>123</b> connected between the MOSFET <b>122</b> and the digital subsystem output <b>121</b>.

0051The device external connections/terminals are the same as in the previous sensor figures, <figref idref="DRAWINGS">FIGS. 4A-4C</figref>. That is, VCC terminal <b>88</b> provides connection to the supply voltage, GND terminal <b>92</b> allows connection to ground and OUT terminal <b>84</b> allows the sensor output to be provided to external devices that will use that output. Also shown in this figure are internal voltage regulators including a digital regulator <b>123</b> that provides a regulated supply voltage to the digital system <b>102</b> (via line <b>124</b>) and an analog regulator <b>125</b> that provides a regulated supply voltage to the analog front end <b>100</b> (via line <b>126</b>).

0052Although not shown in <figref idref="DRAWINGS">FIGS. 4A-4D</figref>, it will be appreciated that circuitry to support additional channels associated with sensing element pairs <b>42</b><i>b</i>, <b>42</b><i>d </i>and <b>42</b><i>c</i>, <b>42</b><i>e </i>as shown in <figref idref="DRAWINGS">FIG. 3G</figref>, along with an additional output stage to support direction detection (where the existing output stage is used to provide speed information), can be included in the sensor as well.

0053The operation of the sensor (e.g., sensor <b>60</b> from <figref idref="DRAWINGS">FIG. 4A</figref>, sensor <b>60</b>′ from <figref idref="DRAWINGS">FIG. 4B</figref>, sensor <b>60</b>″ from <figref idref="DRAWINGS">FIG. 4C</figref> or sensor <b>60</b>′″ from <figref idref="DRAWINGS">FIG. 4D</figref>) to provide an output signal indicative of target movement is designed to be largely insensitive to the angle at which the sensor is positioned (at installation time) and/or maintained (post-installation) relative to the target, e.g., when the sensor installation involves movement of the sensor about an axis (such as axis <b>25</b>, shown in <figref idref="DRAWINGS">FIG. 1B</figref>) that is orthogonal to the face of the target profile. More specifically, the sensor can operate to provide the same (or much the same) differential signal D<b>4</b> regardless of the orientation angle α of the sensor's first sensing axis <b>44</b> relative to the target profile's reference axis <b>18</b> (shown in <figref idref="DRAWINGS">FIG. 1A</figref>). Such tolerance of the orientation angle can greatly simplify sensor installation and maintenance, since manufacturing procedures and/or packaging designs required to meet the sensor-to-target alignment specification are unnecessary.

0054In some applications, it may be advantageous to have a symmetrical structure relative to the center of the sensor die. This can be achieved by using an even number of sensing elements, for example, four, in a symmetrical layout as illustrated in <figref idref="DRAWINGS">FIGS. 5A-5C</figref>.

0055In an alternative exemplary embodiment, and referring to <figref idref="DRAWINGS">FIGS. 5A-5C</figref>, an arrangement based on the use of four sensing elements is shown. As shown in <figref idref="DRAWINGS">FIGS. 5A-5C</figref>, a magnetic field sensing structure <b>130</b> has a configuration of four sensing elements <b>132</b><i>a</i>, <b>132</b><i>b</i>, <b>132</b><i>c </i>and <b>132</b><i>d </i>(also labeled “SE<b>1</b>”, “SE<b>2</b>”, “SE<b>3</b>” and “SE<b>4</b>”, respectively) for use in a differential magnetic field sensor. The sensing elements are spaced apart by some fixed distance. Each pair of sensing elements, sensing elements <b>132</b><i>a</i>, <b>132</b><i>b </i>(first pair) and sensing elements <b>132</b><i>c</i>, <b>132</b><i>d </i>(second pair), is used to generate a differential signal responsive to change in magnetic field strength at a location relative to a target profile (like target profile <b>14</b> of <figref idref="DRAWINGS">FIG. 1A</figref>, <figref idref="DRAWINGS">FIGS. 2A-2B</figref>).

0056Still referring to <figref idref="DRAWINGS">FIGS. 5A-5C</figref>, a first sensing axis <b>134</b> is defined by the arrangement of the sensing elements <b>132</b><i>a</i>, <b>132</b><i>b </i>and a second sensing axis <b>136</b> is defined by the arrangement of the sensing elements <b>132</b><i>c</i>, <b>132</b><i>d</i>. Thus, in the illustrated example, the four sensing elements are spatially arranged, for example, on the surface of a sensor die (the outline of which is indicated by dashed lines), to define the two sensing axes <b>134</b>, <b>136</b>. In this embodiment, the sensing elements are arranged so that the two sensing axes <b>134</b>, <b>136</b> are not aligned with each other in the plane of the die surface and intersect each other. Preferably, they are at an angle of about 90 degrees relative to each other. The element-to-element spacing of the sensing elements in each pair is preferably the same (or approximately the same), but could be different.

0057Referring now to <figref idref="DRAWINGS">FIG. 5A</figref>, when the first sensing axis <b>134</b> is aligned with a target profile (that is, and retelling back to <figref idref="DRAWINGS">FIG. 1A</figref>, it aligns with the target profile's reference axis <b>18</b>), a differential signal “D<b>1</b>” generated by the first pair <b>132</b><i>a</i>, <b>132</b><i>b </i>will have an amplitude that is maximal (“D<b>1</b>_max”) and a differential signal “D<b>2</b>” generated by the second pair <b>132</b><i>c</i>, <b>132</b><i>d </i>will be zero (“D<b>2</b>_zero”). Referring to <figref idref="DRAWINGS">FIG. 5B</figref>, when the first sensing axis <b>134</b> is positioned at a 90 degree angle relative to the target profile's reference axis, the signal amplitude for the first differential signal D<b>1</b> will be zero (“D<b>1</b>_zero”) and signal amplitude for the second differential signal will be maximal (“D<b>2</b>_max”). Referring to <figref idref="DRAWINGS">FIG. 5C</figref>, for a random orientation angle α <b>138</b> between the first sensing axis <b>134</b> and the target profile's reference axis, the signal amplitude for the first differential signal D<b>1</b> and the second differential signal D<b>2</b> will vary with the change in angle. A differential signal whose amplitude is independent of the orientation angle α <b>138</b> can be determined from D<b>1</b> and D<b>2</b>, or more generally from any mathematical combination of SE<b>1</b>, SE<b>2</b>, SE<b>3</b> and SE<b>4</b>.

0058<figref idref="DRAWINGS">FIG. 6</figref> shows a functional diagram of a magnetic field sensor <b>140</b> that includes the magnetic field sensing structure depicted in <figref idref="DRAWINGS">FIGS. 5A-5C</figref>. The sensor <b>140</b> includes the four sensing elements <b>132</b><i>a</i>-<b>132</b><i>d </i>(again shown as sensing elements SE<b>1</b>, SE<b>2</b>, SE<b>3</b>, SE<b>4</b>). The functionality of the interface circuit, shown here as interface <b>142</b>, is much the same as that of interface circuit <b>62</b> (from <figref idref="DRAWINGS">FIG. 4A</figref>). Like elements are identified by like reference numeral. The only difference is that interface circuit <b>142</b> receives four separate signals from the sensing elements. Thus, differential amplifier <b>64</b><i>a </i>receives as inputs a signal <b>144</b><i>a </i>from sensing element <b>132</b><i>a </i>and a signal <b>144</b><i>b </i>from sensing element <b>132</b><i>b</i>, and differential amplifier <b>64</b><i>b </i>receives as inputs a signal <b>144</b><i>c </i>from sensing element <b>132</b><i>c </i>and a signal <b>144</b><i>d </i>from sensing element <b>132</b><i>d. </i>

0059In the illustrated embodiment of <figref idref="DRAWINGS">FIG. 6</figref>, the sensor <b>140</b> includes a first differential channel <b>146</b> and a second differential channel <b>148</b>. The first differential channel <b>146</b> includes, along with sensing elements <b>132</b><i>a</i>, <b>132</b><i>b</i>, the first differential amplifier <b>64</b><i>a </i>and produces the first differential signal D<b>1</b><b>72</b>. The second differential channel <b>148</b> includes the sensing elements <b>132</b><i>c</i>, <b>132</b><i>d</i>, as well as the second differential amplifier <b>64</b><i>b</i>, and produces the second differential signal D<b>2</b><b>74</b>. Each differential channel has an associated or respective sensing axis as defined by its respective pair of sensing elements. The first differential channel <b>146</b> has an associated sensing axis shown in <figref idref="DRAWINGS">FIGS. 5A-5C</figref> as sensing axis <b>134</b>. The second differential channel <b>148</b> has an associated sensing axis shown in <figref idref="DRAWINGS">FIGS. 5A-5C</figref> as sensing axis <b>136</b>.

0060The first differential channel <b>146</b> may include, in addition to sensing elements <b>132</b><i>a</i>, <b>132</b><i>b</i>, and differential amplifier <b>64</b><i>a </i>for generating the differential signal <b>72</b>, circuitry of the interface circuit <b>142</b> to process the differential signal <b>72</b>. Similarly, the second differential channel <b>148</b> may include, in addition to sensing elements <b>132</b><i>c</i>, <b>132</b><i>d</i>, and differential amplifier <b>64</b><i>b </i>for generating the differential signal <b>74</b>, circuitry of the interface circuit <b>142</b> to process the differential signal <b>74</b>. It will be appreciated that the four SE design shown in <figref idref="DRAWINGS">FIG. 6</figref> can be modified to combine the differential amplifiers <b>64</b> and the differential signal generator <b>66</b> (similar to what was described with respect to the embodiment shown in <figref idref="DRAWINGS">FIG. 4C</figref> for a three SE design).

0061In general, for any embodiment of three or more sensing elements (including the exemplary embodiments depicted in <figref idref="DRAWINGS">FIGS. 3A-G</figref>, <figref idref="DRAWINGS">FIG. 4A-4D</figref>, <figref idref="DRAWINGS">FIGS. 5A-5C</figref> and <figref idref="DRAWINGS">FIG. 6</figref>), the element-to-element spacing of sensing elements for the differential channels does not need to be identical, and the angle between sensing axes associated with the channels can be different from 90 degrees. If required, more sensing elements can be added to the magnetic sensing structure. The total number of sensing elements, a minimum of three being required, may be an even number or an odd number. Instead of using three sensing elements, as shown in <figref idref="DRAWINGS">FIGS. 3A-F</figref> and <figref idref="DRAWINGS">FIG. 4A-4D</figref>, or four sensing elements as shown in <figref idref="DRAWINGS">FIGS. 5A-C</figref> and <figref idref="DRAWINGS">FIG. 6</figref>, the magnetic sensing structure could be implemented with sensing elements arranged in a ring configuration. Alternatively, the entire ring could be a sensing area.

0062It will be understood that the sensing element may be a Hall-effect element (or Hall plate) or take a form other than that of a Hall-effect element, such as a magnetoresistance (MR) element. An MR element may be made from any type of MR device, including, but not limited to: an anisotropic magnetoresistance (AMR) device; a giant magnetoresistance (GMR) device; and a tunneling magnetoresistance (TMR) device. The sensing element may include a single element or, alternatively, may include two or more elements arranged in various configurations, e.g., a half bridge or full (Wheatstone) bridge.

0063The sensing element may be a device made of a IV type semiconductor material such as Silicon (Si) or Germanium (Ge), or a III-V type semiconductor material like Gallium-Arsenide (GaAs) or an Indium compound, e.g., Indium-Antimonide (InSb). If separate sensing dies are used, the sensing dies could be made of different technologies, for example, GaAs, Ge, AMR, GMR, TMR, and others.

0064<figref idref="DRAWINGS">FIGS. 7A-7F</figref> illustrate the impact of orientation angle α on differential signal amplitude for a three SE arrangement. <figref idref="DRAWINGS">FIGS. 7A-7B</figref> correspond to an orientation angle α of zero degrees. <figref idref="DRAWINGS">FIGS. 7C-7D</figref> correspond to an orientation angle α of 22.5 degrees. <figref idref="DRAWINGS">FIGS. 7E-7F</figref> correspond to an orientation angle α of 45 degrees. For the sake of clarity, it is assumed that the target produces a sinusoidal magnetic profile. <figref idref="DRAWINGS">FIGS. 7B</figref>, <b>7</b>D and <b>7</b>F are graphs of amplitude versus time, with amplitude being given in relative units. It will be seen from <figref idref="DRAWINGS">FIGS. 7B</figref>, <b>7</b>D and <b>7</b>F that differential signal amplitudes and phases change with increasing orientation angle.

0065<figref idref="DRAWINGS">FIG. 7A</figref> shows a top down view of a sensing arrangement <b>150</b> in which the three sensing elements SE<b>1</b><b>42</b><i>a</i>, SE<b>2</b><b>42</b><i>b </i>and SE<b>3</b><b>42</b><i>c </i>(in a sensor package, not shown) are positioned in proximity to a target <b>152</b> having alternating poles (for a magnetic target) or ferrous gear target features, e.g., teeth/valleys. The reference position of the sensing elements is for an orientation angle α of zero degrees. In this figure, the raised portions or South poles are indicated by reference numeral <b>154</b> whereas the recessed portions or North poles are indicated by reference numeral <b>156</b>. The spacing between SE<b>1</b><b>42</b><i>a </i>and SE<b>2</b><b>42</b><i>b </i>and the spacing between SE<b>1</b><b>42</b><i>a </i>and SE<b>3</b><b>42</b><i>c </i>corresponds to a distance T/2, where T (indicated by reference numeral <b>158</b>) is the period of the target. <figref idref="DRAWINGS">FIG. 7B</figref> shows a graph <b>160</b> of amplitude versus time for differential signals D<b>1</b>, D<b>2</b> and D<b>3</b>. The waveforms for differential signals D<b>1</b>, D<b>2</b> and D<b>3</b> are indicated by reference numerals <b>162</b>, <b>164</b> and <b>166</b>, respectively. The differential signals are produced by rotating the target in front of the sensing elements. Also shown is the target profile, indicated by reference numeral <b>168</b>. It can be seen that the signal amplitudes of differential signals D<b>1</b><b>162</b> and D<b>3</b><b>166</b> are of equal, maximal magnitude and opposite polarity. It can also be seen that the signal peaks of differential signals D<b>1</b> and D<b>3</b> correspond to the transitions in the target's features (e.g., North pole to South pole). Also, as shown in <figref idref="DRAWINGS">FIG. 7B</figref>, for an orientation angle α of zero degrees, the resulting amplitude of the differential signal D<b>2</b><b>164</b> (produced by the channel formed by SE<b>1</b> and SE<b>3</b>) is always zero.

0066<figref idref="DRAWINGS">FIG. 7C</figref> shows a sensing arrangement <b>170</b> in which the reference position of the sensing elements is for an orientation angle α of 22.5 degrees <b>172</b>. Other details are as shown in <figref idref="DRAWINGS">FIG. 7A</figref>. <figref idref="DRAWINGS">FIG. 7D</figref> shows a graph <b>180</b> of the differential signals D<b>1</b>, D<b>2</b> and D<b>3</b> for the reference position shown in <figref idref="DRAWINGS">FIG. 7C</figref>, that is, for an orientation angle α of 22.5 degrees. The waveforms for the differential signals D<b>1</b>, D<b>2</b> and D<b>3</b> are indicated by reference numerals <b>182</b>, <b>184</b> and <b>186</b>, respectively. The target profile is indicated here by reference numeral <b>188</b>. It can be seen in <figref idref="DRAWINGS">FIG. 7D</figref> that all of the differential signals now have a non-zero amplitude. The amplitude of D<b>3</b> is slightly smaller than it was for an orientation angle of zero degrees (as was shown in <figref idref="DRAWINGS">FIG. 7B</figref>) and the amplitude of D<b>2</b> is much smaller than the amplitudes of D<b>1</b> and D<b>3</b>.

0067<figref idref="DRAWINGS">FIG. 7E</figref> shows an example sensing arrangement <b>190</b> in which the reference position of the sensing elements is for an orientation angle α of 45 degrees <b>192</b>. Other details are as shown in <figref idref="DRAWINGS">FIG. 7A</figref> (and <b>7</b>C). <figref idref="DRAWINGS">FIG. 7F</figref> shows a graph <b>200</b> of the differential signals D<b>1</b>, D<b>2</b> and D<b>3</b> for the reference position shown in <figref idref="DRAWINGS">FIG. 7E</figref>. The waveforms for differential signals D<b>1</b>, D<b>2</b> and D<b>3</b> are indicated by reference numerals <b>202</b>, <b>204</b> and <b>206</b>, respectively. Also shown is the target profile, indicated by reference numeral <b>208</b>. Here the amplitudes of D<b>1</b> and D<b>2</b> are equal (but smaller than the amplitudes for D<b>1</b> and D<b>3</b> for a zero degree angle, as shown in <figref idref="DRAWINGS">FIG. 7B</figref>) and the amplitude of D<b>3</b> is smaller than those of D<b>1</b> and D<b>2</b>. Referring back to <figref idref="DRAWINGS">FIG. 7B</figref> in conjunction with <figref idref="DRAWINGS">FIG. 7E</figref>, it can be seen that the phases between the differential signals have also changed with change in orientation angle.

0068<figref idref="DRAWINGS">FIG. 8A</figref> shows a graph <b>210</b> of the peak-to-peak amplitudes of the differential signals D<b>1</b>, D<b>2</b> and D<b>3</b> (for one embodiment) as a function of the orientation angle α. The peak-to-peak amplitudes are given in relative units. The peak-to-peak amplitude of D<b>1</b> is indicated by reference numeral <b>212</b>, the peak-to-peak amplitude of D<b>2</b> is indicated by reference numeral <b>214</b> and the peak-to-peak amplitude of D<b>3</b> is indicated by reference numeral <b>216</b>. In one possible embodiment, as will be described with reference to <figref idref="DRAWINGS">FIG. 9A</figref>, the differential signal D<b>4</b> may be selected as either D<b>1</b> or D<b>2</b> based on the orientation angle α. Such a selection will produce a differential signal D<b>4</b> having a variation in peak-to-peak amplitude (with increase in orientation angle) that is limited to approximately 1% of the total peak-to-peak amplitude in certain angle ranges, e.g., 0 degrees to 22.5 degrees, and is limited to approximately 10% of the total peak-to-peak amplitude in other angle ranges, e.g., 22.5 degrees to 67.5 degrees. Thus, D<b>1</b> can be selected for an angle range (or “zone”) of 0 to 45 degrees and 315 to 360 degrees (“zone A”) <b>218</b><i>a </i>and 135 to 225 degrees (“zone C”) <b>218</b><i>c</i>. The differential signal D<b>2</b> can be selected for the other ranges of angles, that is, 45 to 135 degrees (“zone B”) <b>218</b><i>b </i>and 225 to 315 degrees (“zone D”) <b>218</b><i>d</i>. In the illustrated example, it can be seen that within each of those angle ranges or zones, the differential signal D<b>4</b> is orientation angle independent (with variation limited to approximately 10% in the first and fourth quarters of the zone and variation limited to approximately 1% in the second and third quarters of the zone).

0069<figref idref="DRAWINGS">FIG. 8B</figref> shows a graph <b>220</b> for peak-to-peak amplitudes of signals resulting from a particular mathematical combination of differential signals D<b>1</b>, D<b>2</b> and D<b>3</b> as a function of the orientation angle α. The peak-to-peak amplitudes are given in relative units. The graph <b>220</b> shows only two of the many possible different mathematical combinations that can be defined between the differential signals D<b>1</b>, D<b>2</b>, D<b>3</b>, or more generally sensing elements SE<b>1</b>, SE<b>2</b> and SE<b>3</b>. Illustrated are the peak-to-peak amplitude for the differential signal “D<b>4</b>” based on a mathematical combination of the differential signals D<b>1</b> and D<b>2</b>, “D<b>1</b>+D<b>2</b>”, indicated by reference numeral <b>222</b>, and the peak-to-peak amplitude for a differential signal based on a mathematical combination of D<b>2</b> and D<b>3</b>, “D<b>2</b>+D<b>3</b>”, indicated by reference numeral <b>224</b>.

0070Referring to <figref idref="DRAWINGS">FIG. 9A</figref>, an exemplary operation of the D<b>4</b> signal generator, operation <b>230</b>, begins (at block <b>232</b>) with the receipt of signals D<b>1</b> and D<b>2</b>. The operation determines the amplitudes of D<b>1</b> and D<b>2</b> (block <b>234</b>). To obtain a positive and negative peak for each signal, values for D<b>1</b> and D<b>2</b> are acquired over at least one period. The operation compares the amplitudes of D<b>1</b> and D<b>2</b>, for example, by determining if the absolute value of the D<b>1</b> signal amplitude is greater than the absolute value of the D<b>2</b> signal amplitude (block <b>236</b>). If that comparison yields a true result, then D<b>1</b> is selected for use as D<b>4</b> (block <b>238</b>). Otherwise, D<b>2</b> is selected for use as D<b>4</b> (block <b>240</b>). The operation ends (at block <b>242</b>) by providing the result as D<b>4</b>.

0071Referring back to the graph shown in <figref idref="DRAWINGS">FIG. 8A</figref>, the differential signal D<b>1</b> would be selected in zones A and C, and the differential signal D<b>2</b> would be selected in zones B and D. By choosing between the signals in this manner, the signal amplitude of the differential signal that is used by the sensor (that is, the signal chosen as D<b>4</b>) is never allowed to fall below a certain threshold (thereby minimizing the amount by which the signal amplitude can vary with orientation angle). In the example shown in <figref idref="DRAWINGS">FIG. 8A</figref>, the amplitude never goes below ˜3.6 (the absolute value of both signals' amplitudes, in relative units, at the zone transitions, that is, at 45 degrees, 135 degrees, 225 degrees and 315 degrees). The number of zones could be increased by increasing the number of sensing element pairs that are used. More zones would further limit the amplitude range in which the signal amplitudes of the differential signals are orientation angle dependent. The signal generator that performs operation <b>236</b> could be implemented according to well-known design techniques (analog and/or digital), e.g., using a compare circuit, such as an op amp or voltage comparator, to compare the amplitudes (voltage values) of the differential signals D<b>1</b> and D<b>2</b>.

0072Another exemplary embodiment for generating D<b>4</b> is illustrated in <figref idref="DRAWINGS">FIG. 9B</figref> in conjunction with <figref idref="DRAWINGS">FIG. 4C</figref>. The operation, shown in <figref idref="DRAWINGS">FIG. 9B</figref> as operation <b>250</b>, begins (at block <b>252</b>) with the receipt of D<b>1</b>, D<b>2</b> and D<b>3</b>. The operation determines the amplitudes of D<b>1</b>, D<b>2</b> and D<b>3</b> from SE<b>1</b>, SE<b>2</b> and SE<b>3</b> (block <b>254</b>). The operation determines D<b>4</b> as a function of any mathematical combination of D<b>1</b>, D<b>2</b>, and D<b>3</b> and/or SE<b>1</b>, SE<b>2</b> and SE<b>3</b> (block <b>256</b>). The operation then normalizes D<b>4</b> to be independent of orientation angle and air gap (block <b>257</b>). The normalized D<b>4</b> is provided as D<b>4</b> at the output of the differential signal generation (block <b>258</b>). Once the operation <b>250</b> has determined D<b>4</b>, the operation <b>250</b> ends (block <b>259</b>).

0073In still yet another alternative embodiment, as illustrated in <figref idref="DRAWINGS">FIG. 9C</figref>, the operation for generating D<b>4</b> involves orientation angle determination. Referring to <figref idref="DRAWINGS">FIG. 9C</figref>, the operation, shown in <figref idref="DRAWINGS">FIG. 9C</figref> as operation <b>260</b>, begins (at block <b>262</b>) with the receipt of D<b>1</b>, D<b>2</b> and D<b>3</b> as inputs and determines the amplitudes of D<b>1</b>, D<b>2</b> and D<b>3</b> (block <b>264</b>). The operation <b>260</b> then uses the amplitudes to determine the orientation angle α (block <b>266</b>). The operation <b>260</b> provides the orientation angle α as an output (block <b>268</b>) and ends (block <b>270</b>).

0074It will be appreciated that the functionality of the D<b>4</b> signal generator, e.g., differential signal generator <b>66</b>, <b>66</b>′, <b>66</b>″or <b>66</b>′″ (from <figref idref="DRAWINGS">FIG. 4A-4D</figref>) or <b>66</b> (from <figref idref="DRAWINGS">FIG. 6</figref>), as depicted in the operations of <figref idref="DRAWINGS">FIGS. 9A-9C</figref>, can be implemented in hardware or combination of hardware and software according to known circuit design techniques.

0075As noted earlier, the sensing elements may be arranged so that the angle between the differential channels' respective sensing axes is an angle other than 90 degrees. That angle could be chosen to suit the needs of an application.

0076Although the illustrated figures show a transition-based peak detection, it will be appreciated that when the differential signals D<b>1</b> and D<b>2</b> cross in the middle of the profile features, e.g., in the middle of tooth and valley for a ferrous target or in the middle of the North pole and South pole for a magnetic target (as can be seen in <figref idref="DRAWINGS">FIGS. 7B</figref>, <b>7</b>D and <b>7</b>F), a non-transition-based detection that uses that signal crossing is possible. Such a detection scheme may be advantageous for some applications.

0077The orientation independent magnetic field sensor, like sensor <b>60</b>, <b>60</b>′, <b>60</b>″ or <b>60</b>′″(<figref idref="DRAWINGS">FIGS. 4A-4D</figref>) or sensor <b>140</b> (<figref idref="DRAWINGS">FIG. 6</figref>), with a multi-channel arrangement of sensing elements, as described above, may be used in a variety of applications. It is particularly well suited to use in rotational speed detection and timing control in automotive applications such as in anti-lock braking systems (ABS), transmissions and crankshafts, among others. For example, rotational speed information produced by a sensor may be used by speedometers, tachometers, on-board computers, tachographs (also known as chronotachographs), and the like. One example automotive application, as shown in <figref idref="DRAWINGS">FIG. 10</figref>, is an automotive application <b>280</b> that uses the sensor output in a tachograph.

0078The type of orientation independent differential sensor described herein is uniquely well suited to the needs of tachograph systems. For reasons of road safety, the driving time of drivers of certain vehicles, in particular, commercial vehicles such as buses and trucks, is now subject to regulation in some countries and regions. The tachograph (or equivalent electronic log device) can be used to monitor a driver's working conditions, i.e., driving time and rest periods, to ensure that appropriate driving breaks are taken. However, tachographs typically use a single-element sensor and the single-element sensor is vulnerable to tampering. It is possible to manipulate the sensor operation, e.g., by introducing a high magnetic field near the sensor to magnetically saturate the element so that the sensor doesn't switch (and therefore, does not indicate rotations properly), thus “tricking” the tachograph into giving a false record of driver information so that drivers can drive more hours.

0079One solution to this particular type of tachograph system tampering is to use a differential magnetic field sensor. As a differential sensor only responds to changes in magnetic field strength, it is relatively immune to the influence of extraneous magnetic fields (as well as machine vibrations). Unlike single-element sensors, prior differential sensors required correct positioning of the sensor in reference to the profile of the target special, as noted earlier, to operate properly. The orientation independent sensor such as sensor <b>60</b> (from <figref idref="DRAWINGS">FIG. 4A</figref>, or other sensor embodiments shown in <figref idref="DRAWINGS">FIGS. 4B-4D</figref> or <figref idref="DRAWINGS">FIG. 6</figref>) addresses the limitations of prior differential sensors, thus making it a good fit for tachograph systems and other applications that may benefit from both the differential mode of operation and ease of use (in terms of installation and maintenance). It is particularly advantageous for applications that require frequent sensor replacement, as is the case for some automotive applications (e.g., mandatory replacement intervals for ABS sensors in trucks). Since tachographs record speed, this technique might also be useful in speed limiter systems to control maximum speed in certain commercial vehicles.

0080Turning now to <figref idref="DRAWINGS">FIG. 10</figref>, the application <b>280</b> includes a sensing arrangement <b>282</b> in which a sensor such as sensor <b>60</b> (from <figref idref="DRAWINGS">FIG. 4</figref>, or sensor <b>60</b>′, <b>60</b>″, <b>60</b>′″ or <b>140</b> from <figref idref="DRAWINGS">FIG. 4B</figref>, <figref idref="DRAWINGS">FIG. 4C</figref>, <figref idref="DRAWINGS">FIG. 4D</figref> and <figref idref="DRAWINGS">FIG. 6</figref>, respectively) is located near a target such as a ring magnet <b>283</b>, as shown. The sensor is mounted (installed) in close proximity to the ring magnet, which rotates at wheel speed. The sensor <b>60</b> senses changes in magnetic field <b>284</b> associated with the rotating target's profile. The sensor <b>60</b> produces a rotation-indicating output <b>286</b> for the target <b>283</b> and provides that output to a tachograph system <b>288</b>. In the illustrated example, the tachograph system <b>288</b> includes a control module <b>290</b> coupled to a tachograph <b>292</b>. The control module <b>290</b> receives the sensor output <b>286</b> and translates that sensor output to a target (in this example, wheel) speed <b>294</b>.

0081The sensing arrangement <b>282</b> may be located on an axle shaft, gear or wheel hub. Although only one sensing arrangement is shown, it will be appreciated that multiple sensor arrangements (e.g., one for each vehicle wheel) could be used.

0082As discussed earlier, the main advantage of the orientation independent magnetic field sensing structure is that the structure offers increased design flexibility to the end user in terms of sensor mounting for applications where the orientation of the sensor relative to the target cannot be precisely controlled. For example, the sensor could be mounted into a threaded canister that could simply be screwed into a corresponding threaded hole in the front of the target. This type of structure could greatly simplify the regular change of sensor modules required for some applications, like truck ABS applications.

0083Other possible applications besides automotive include motor, industrial and assembly. Also, although the orientation angle independent techniques and designs have been illustrated herein with reference to rotary sensing, they would be applicable to linear movement sensing as well. If the orientation angle is determined, the angle information could be provided as feedback to the user (to indicate a misalignment condition), or to other circuitry or processing elements for compensation, calibration or other purposes. The orientation angle independent techniques and designs described herein may be suitable for use in any magnetically noisy environment, as they allow for a clean signal independent of orientation of sensor relative to a target and independent of DC magnetic perturbations.

0084All references cited herein are hereby incorporated herein by reference in their entirety.

0085Having described preferred embodiments of the invention, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating their concepts may be used. It is felt therefore that these embodiments should not be limited to disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims.