Method and apparatus for magnetic sensor producing a changing magnetic field
Methods and apparatus for detecting a magnetic field include a semiconductor substrate, a coil configured to provide a changing magnetic field in response to a changing current in the coil; and a magnetic field sensing element supported by the substrate. The coil receives the changing current and, in response, generates a changing magnetic field. The magnetic field sensing element detects the presence of a magnetic target by detecting changes to the magnetic field caused by the target and comparing them to an expected value.
1. A magnetic field sensor comprising:
a lead frame having a die attach area;
a semiconductor substrate attached to the die attach area of the lead frame;
a coil configured to provide a changing magnetic field in response to a changing current in the coil;
a magnetic field sensing element supported by the substrate to detect a target by detecting variations in the changing magnetic field caused by the target;
a first mold encapsulating the substrate and at least a portion of the lead frame, the first mold being in direct contact with the coil; and
a second mold forming at least a partial ring-shaped structure having a central aperture and encapsulating the coil, wherein the coil encircles the central aperture.
2. The magnetic field sensor of claim 1 , wherein the coil is directly attached to the first mold.
3. The magnetic field sensor of claim 1 , wherein the magnetic field sensing element is closer to the target than the coil.
4. The magnetic field sensor of claim 1 , wherein the coil is positioned above or below the substrate.
5. The magnetic field sensor of claim 1 , wherein the coil is a separately formed element included in a same package with the substrate.
6. The magnetic field sensor of claim 1 , wherein the lead frame is between the substrate and the coil.
7. The magnetic field sensor of claim 1 , wherein the first mold is a non-conductive mold material.
8. The magnetic field sensor of claim 1 , wherein the magnetic field sensing element is a tunneling magnetoresistance (TMR) element transducer.
9. The magnetic field sensor of claim 1 , wherein the magnetic field sensing element is a giant magnetoresistance (GMR) transducer.
10. The magnetic field sensor of claim 9 , wherein the GMR transducer comprises a plurality of GMR elements in a bridge configuration.
11. The magnetic field sensor of claim 1 , wherein the magnetic field sensing element is a Hall element.
12. The magnetic field senor of claim 1 , further including a current source coupled to the coil.
13. The magnetic field sensor of claim 1 , further including a pulsed or transient current source coupled to the coil.
14. The magnetic field sensor of claim 1 , wherein the variations in the changing magnetic field are caused by movement of the target in the presence of the magnetic field.
15. The magnetic field sensor of claim 1 , wherein a direction of the changing magnetic field is in a direction towards or away from the magnetic target.
16. The magnetic field sensor of claim 1 , wherein the at least partial ring-shaped structure is one of:
an O-shaped ring structure;
a D-shaped ring structure;
a U-shaped ring structure; or
a C-shaped ring structure.
17. A magnetic field sensor comprising:
a lead frame having a die attach area;
a semiconductor substrate attached to the die attach area of the lead frame;
a coil configured to provide a changing magnetic field in response to a changing current in the coil;
a magnetic field sensing element supported by the substrate to detect a target by detecting variations in the changing magnetic field caused by the target;
a first mold having a protrusion and encapsulating the substrate and the lead frame, the first mold being in direct contact with the coil; and
a second mold encapsulating the coil, wherein the coil encircles the protrusion.
18. A magnetic field sensor comprising:
a lead frame having a die attach area on a first surface, the lead frame having a second surface opposite the first surface;
a semiconductor substrate attached to the die attach area of the lead frame;
a coil attached to the second surface of the lead frame and configured to provide a changing magnetic field in response to a changing current in the coil;
a magnetic field sensing element supported by the substrate to detect a target by detecting variations in the changing magnetic field caused by the target; and
a mold completely encapsulating the substrate and the coil and partially encapsulating the lead frame.
19. The magnetic field sensor of claim 18 , further including a mandrel attached to the second surface of the lead frame,
wherein the coil encircles the mandrel.
20. The magnetic field sensor of claim 18 , wherein the magnetic field sensing element is a tunneling magnetoresistance (TMR) element transducer or a giant magnetoresistance (GMR) transducer.