Stray-field-immune coil-activated position sensor
A sensor comprising: a first magnetoresistive (MR) bridge having a first stray field sensitivity; a second MR bridge having a second stray field sensitivity; and a driver circuitry configured to: (i) supply a first voltage to the first MR bridge, and (ii) supply a second voltage to the second MR bridge that is different from the first voltage, wherein supplying the first voltage and the second voltage to the first MR bridge and the second MR bridge, respectively, causes the first stray field sensitivity to match the second stray field sensitivity.
1. A sensor comprising:
a first magnetoresistive (MR) bridge having a first stray field sensitivity;
a second MR bridge having a second stray field sensitivity; and
a driver circuitry configured to: (i) supply a first voltage to the first MR bridge, and (ii) supply a second voltage to the second MR bridge that is different from the first voltage, wherein supplying the first voltage and the second voltage to the first MR bridge and the second MR bridge, respectively, causes the first stray field sensitivity to match the second stray field sensitivity.
2. The sensor of claim 1 , wherein the first voltage is based on: (i) the second voltage and (ii) a ratio between a first coupling factor associated with the first MR bridge and a second coupling factor associated with the second MR bridge.
3. The sensor of claim 1 , wherein the second voltage is based on a magnetoresistance mismatch that is associated with the first MR bridge and the second MR bridge.
4. The sensor of claim 1 , wherein the first voltage is determined according to an equation of:
VTMR
1
=
-
V
T
M
R
2
·
q
·
(
1
-
Δ
M
R
)
(
1
+
Δ
M
R
)
,
where VTMR 1 is the first voltage, VTMR 2 is the second voltage, q is a ratio between a first coupling factor associated with the first MR bridge and a second coupling factor associated with the second MR bridge, and ΔMR is a magnetoresistance mismatch associated with the first MR bridge and the second MR bridge.
5. The sensor of claim 1 , further comprising a coil formed on a substrate, the coil having a first coil turn and a second coil turn that is disposed outside of the first coil turn, wherein:
the first MR bridge includes a plurality of MR elements formed in a first region of the substrate and a second region of the substrate, the first region and the second region being located between the first turn and the second coil turn, and the first region and the second region being located on opposite sides of the first turn, and
the second MR bridge includes a plurality of second MR elements formed in the first region of the substrate and the second region of the substrate.
6. The sensor of claim 1 , further comprising a coil, wherein:
the coil includes a first coil turn and a second coil turn that is disposed outside of the first coil turn, and the coil is coupled to a secondary loop that is formed inside the first turn;
the first MR bridge includes a first plurality of MR elements that are formed between the first coil turn and the second coil turn;
the second MR bridge includes a second plurality of MR elements that are formed inside the first coil turn and inside the secondary loop.
7. The sensor of claim 6 , wherein the second MR bridge is centered with the first coil turn.
8. A method for use in a sensor having a first MR bridge and a second MR bridge that are operatively coupled to a processing circuitry, the method comprising:
driving the first MR bridge with a first voltage, the first MR bridge having a first stray field sensitivity;
driving the second MR bridge with a second voltage, the second MR bridge having a second stray field sensitivity; and
calculating, by the processing circuitry, a position of a target based on a first signal that is provided by the first MR bridge and a second signal that is provided by the second MR bridge,
wherein supplying the first voltage and the second voltage to the first MR bridge and the second MR bridge, respectively, causes the first stray field sensitivity to match the second stray field sensitivity.
9. The method of claim 8 , wherein the first voltage is based on: (i) the second voltage and (ii) a ratio between a first coupling factor associated with the first MR bridge and a second coupling factor associated with the second MR bridge.
10. The method of claim 8 , wherein the second voltage is based on a magnetoresistance mismatch that is associated with the first MR bridge and the second MR bridge.
11. The method of claim 8 , wherein the first voltage is determined according to an equation of:
VTMR
1
=
-
V
T
M
R
2
·
q
·
(
1
-
Δ
M
R
)
(
1
+
Δ
M
R
)
,
where VTMR 1 is the first voltage, VTMR 2 is the second voltage, q is a ratio between a first coupling factor associated with the first MR bridge and a second coupling factor associated with the second MR bridge, and ΔMR is a magnetoresistance mismatch associated with the first MR bridge and the second MR bridge.
12. The method of claim 8 , wherein:
the sensor further includes a coil formed on a substrate, the coil having a first coil turn and a second coil turn that is disposed outside of the first coil turn,
the first MR bridge includes a plurality of MR elements formed in a first region of the substrate and a second region of the substrate, the first region and the second region being located between the first coil turn and the second coil turn, and the first region and the second region being located on opposite sides of the first coil turn, and
the second MR bridge includes a plurality of second MR elements formed in the first region of the substrate and the second region of the substrate.
13. The method of claim 8 , wherein:
the sensor further includes a coil formed on a substrate;
the coil includes a first coil turn and a second coil turn that is disposed outside of the first coil turn, and the coil is coupled to a secondary loop that is formed inside the first coil turn;
the first MR bridge includes a first plurality of MR elements that are formed between the first coil turn and the second coil turn;
the second MR bridge includes a second plurality of MR elements that formed inside the first coil turn and inside the secondary loop.
14. The method of claim 13 , wherein the second MR bridge is centered with the first coil turn.
15. A sensor, comprising:
a coil formed on a substrate, the coil having a first coil turn and a second coil turn, the second coil turn being formed outside of the first coil turn;
a secondary loop that is coupled to the coil, the secondary loop being formed inside the first coil turn;
a first MR bridge that is formed on the substrate, the first MR bridge including a first plurality of MR elements that are formed between the first coil turn and the second coil turn;
a second MR bridge that is formed on the substrate, the second MR bridge including a second plurality of MR elements that are formed inside the first coil turn and inside the secondary loop,
wherein the second MR bridge is centered with the first coil turn.
16. The sensor of claim 15 , wherein the coil and the secondary loop are defined by a same conductive trace.
17. The sensor of claim 15 , wherein the first plurality of MR elements includes a first group of MR elements and a second group of MR elements, the first group of MR elements and the second group of MR elements being formed on opposite sides of the first coil turn.
18. The sensor of claim 15 , further comprising a driver circuitry that is configured to supply a first voltage to the first MR bridge and a second voltage to the second MR bridge, wherein the second voltage is different from the first voltage, and supplying the first voltage and the second voltage to the first MR bridge and the second MR bridge, respectively, causes the first MR bridge and the second MR bridge to have matching stray field sensitivities.
19. The sensor of claim 18 , wherein the second voltage is based on a magnetoresistance mismatch that is associated with the first MR bridge and the second MR bridge.
20. The sensor of claim 18 , wherein the first voltage is determined according to an equation of:
VTMR
1
=
-
V
T
M
R
2
·
q
·
(
1
-
Δ
M
R
)
(
1
+
Δ
M
R
)
,
where VTMR 1 is the first voltage, VTMR 2 is the second voltage, q is a ratio between a first coupling factor associated with the first MR bridge and a second coupling factor associated with the second MR bridge, and ΔMR is a magnetoresistance mismatch associated with the first MR bridge and the second MR bridge.