Front bias magnetic speed sensor with true-power-on capability
A magnetic sensor system includes a toothed wheel configured to rotate about a rotation axis that extends in an axial direction, wherein the toothed wheel includes a plurality of teeth and a plurality of notches arranged that define a circumferential perimeter, wherein the toothed wheel further includes an interior cavity arranged within the circumferential perimeter; a front-bias magnet arranged within the interior cavity of the toothed wheel, wherein the front-bias magnet is rotationally fixed and is magnetized with a magnetization direction that extends along a radial axis of the toothed wheel; and a magnetic sensor arranged exterior to the toothed wheel, wherein the magnetic sensor includes a sensor element arranged on the radial axis that coincides with the magnetization direction of the front-bias magnet and the first sensor element is sensitive to a magnetic field of the front-bias magnet that is aligned with the radial axis.
1 . A magnetic sensor system, comprising:
a wheel, configured to rotate about a rotation axis, wherein the wheel comprises a plurality of teeth and a plurality of notches arranged in an alternating tooth-notch pattern, wherein the plurality of teeth and the plurality of notches define a circumferential perimeter, and wherein the wheel further comprises an interior cavity arranged within the circumferential perimeter;
a front-bias magnet; and
a first sensor element,
wherein the front-bias magnet and the first sensor element are arranged opposing each other in a first direction with a gap between the front-bias magnet and the first sensor element such that a tooth, of the plurality of teeth of the wheel, or a notch, of the plurality of notches of the wheel, is located in the gap between the front-bias magnet and the first sensor element when the wheel is rotating about the rotation axis,
wherein the front-bias magnet is magnetized in the first direction, wherein the first sensor element is sensitive in the first direction, wherein the wheel causes a magnetic field of the front-bias magnet to oscillate at a location of the first sensor element, and wherein the magnetic sensor system is configured to determine a rotation speed of the wheel based on the oscillation.
2 . The magnetic sensor system of claim 1 ,
wherein one of the front-bias magnet or the first sensor element is in an interior of the wheel, and wherein another one of the front-bias magnet or the first sensor element is exterior to the wheel.
3 . The magnetic sensor system of claim 2 ,
wherein the first sensor element is exterior to the wheel.
4 . The magnetic sensor system of claim 2 ,
wherein the plurality of teeth of the wheel shields the first sensor element from the magnetic field of the front-bias magnet, and wherein the plurality of notches of the wheel exposes the first sensor element to the magnetic field of the front-bias magnet.
5 . The magnetic sensor system of claim 1 ,
wherein at least one of the front-bias magnet or the first sensor element is rotationally fixed and does not rotate with the wheel.
6 . The magnetic sensor system of claim 1 , further comprising:
a second sensor element,
wherein the first sensor element and the second sensor element are arranged on a radial axis that coincides with a same magnetization direction.
7 . A magnetic sensor system, comprising:
a wheel, comprising a plurality of teeth and a plurality of notches, configured to rotate about a rotation axis, wherein the plurality of teeth and the plurality of notches define a circumferential perimeter, and wherein the wheel further comprises an interior cavity arranged within the circumferential perimeter;
a front-bias magnet, arranged inside of the interior cavity, having a magnetization direction that extends along a symmetry axis of the front-bias magnet that is orthogonal to the rotation axis; and
a magnetic sensor, arranged external to the wheel, including at least one sensor element arranged on an extension of the symmetry axis that coincides with the magnetization direction.
8 . The magnetic sensor system of claim 7 , further comprising:
a molded package encapsulating the front-bias magnet and the magnet sensor.
9 . The magnetic sensor system of claim 8 ,
wherein the molded package has a one-piece integral construction that holds the symmetry axis of the front-bias magnet in alignment with a symmetry axis of the magnetic sensor.
10 . The magnetic sensor system of claim 8 ,
wherein the molded package comprises a notch between the front-bias magnet and the magnet sensor.
11 . The magnetic sensor system of claim 10 , wherein, during a rotation of the wheel, the plurality of teeth passes through the notch.
12 . The magnetic sensor system of claim 8 ,
wherein the magnetic sensor is configured to:
generate, in response to sensing a magnetic field of the front-bias magnet, a first signal having a signal pattern representative of a pattern of the plurality of teeth.
13 . The magnetic sensor system of claim 12 ,
wherein the magnetic sensor comprises a sensor circuit configured to:
receive the first signal, and
generate a pulsed output signal based on the first signal crossing at least one threshold, or
determine whether a tooth, of the plurality of teeth of the wheel, is located between the front-bias magnet and the magnetic sensor based on the first signal.
14 . The magnetic sensor system of claim 8 ,
wherein a rotation of the wheel causes a magnetic field of the front-bias magnet to oscillate between a first extremum value and a second extremum value at a location of the magnetic sensor.
15 . The magnetic sensor system of claim 14 ,
wherein the magnetic sensor comprises a sensor circuit configured to:
generate a first signal that has the first extremum value when any tooth, of the plurality of teeth of the wheel, is interposed between the front-bias magnet and the magnetic sensor; and
generate a second signal that has the second extremum value when any tooth, of the plurality of teeth of the wheel, is interposed between the front-bias magnet and the magnetic sensor.
16 . The magnetic sensor system of claim 15 ,
wherein the sensor circuit is further configured to:
generate a differential signal based on a combination of the first signal and the second signal; and
generate a pulsed output signal based on the differential signal crossing at least one threshold.
17 . A magnetic sensor system, comprising:
a wheel, comprising a plurality of teeth and a plurality of notches, configured to rotate about a rotation axis, wherein the plurality of teeth and the plurality of notches define a circumferential perimeter, and wherein the wheel further comprises an interior cavity arranged within the circumferential perimeter,
a front-bias magnet, arranged external to the interior cavity, having a magnetization direction that extends along a symmetry axis of the front-bias magnet that is orthogonal to the rotation axis; and
a magnetic sensor, arranged inside of the wheel, including at least one sensor element arranged on an extension of the symmetry axis that coincides with the magnetization direction.
18 . The magnetic sensor system of claim 17 , further comprising:
a molded package encapsulating the front-bias magnet and the magnet sensor.
19 . The magnetic sensor system of claim 18 ,
wherein the molded package has a one-piece integral construction that holds the symmetry axis of the front-bias magnet in alignment with a symmetry axis of the magnetic sensor.
20 . The magnetic sensor system of claim 18 ,
wherein the molded package comprises a notch between the front-bias magnet and the magnet sensor.