Linear bridges having nonlinear elements
In one aspect, a bridge includes a first magnetoresistance element having a first reference angle, a second magnetoresistance element in series with the first magnetoresistance element and having a second reference angle, a third magnetoresistance element in parallel with the first magnetoresistance element and having the first reference angle and a fourth magnetoresistance element in series with the third magnetoresistance element and having the second reference angle. An output of the bridge has a linear response over a range of horizontal magnetic field intensity values not centered about a zero value and a reference angle indicates an angle the magnetoresistance element is most sensitive to changes in a magnetic field.
1. A bridge comprising:
a first magnetoresistance element having a first reference angle;
a second magnetoresistance element in series with the first magnetoresistance element and having a second reference angle;
a third magnetoresistance element in parallel with the first magnetoresistance element and having the first reference angle; and
a fourth magnetoresistance element in series with the third magnetoresistance element and having the second reference angle,
wherein an output of the bridge has a linear response over a range of horizontal magnetic field values not centered about a zero value,
wherein the first reference angle and the second reference angle indicates an angle the magnetoresistance element is most sensitive to changes in a magnetic field.
2. The bridge of claim 1 , wherein the range of horizontal magnetic field values comprises horizontal magnetic field values none of which have zero values.
3. The bridge of claim 1 , wherein the first, second, third and fourth magnetoresistance elements are each a giant magnetoresistance (GMR) element or a tunnel magnetoresistance (TMR) element.
4. The bridge of claim 1 , further comprising:
a fifth magnetoresistance element in series with the first magnetoresistance element and having a third reference angle; and
a sixth magnetoresistance element in series with the third magnetoresistance element and having the third reference angle,
wherein the range of horizontal magnetic field values not centered about a zero value comprises a non-zero value corresponding to the output of the bridge having a zero value.
5. The bridge of claim 4 , wherein the fifth magnetoresistance element and the sixth magnetoresistance element are constructed to be the same.
6. The bridge of claim 1 , wherein the range of horizontal magnetic field values are associated with vertical magnetic field values none of which are 0 Oersted (Oe).
7. The bridge of claim 1 , wherein the first reference angle and the second reference angle enable the output of the bridge to have the linear response over the range of horizontal magnetic field values not centered about the zero value.
8. The bridge of claim 7 , wherein the first reference angle and the second reference angle enable the output of the bridge to have the linear response over the range of horizontal magnetic field values none of which have zero values.
9. The bridge of claim 1 , wherein the first magnetoresistance element and the third magnetoresistance element are constructed to be the same.
10. The bridge of claim 9 , wherein the second magnetoresistance element and the fourth magnetoresistance element are constructed to be the same.
11. The bridge of claim 1 , wherein the range of horizontal magnetic field values comprises horizontal magnetic field values none of which have zero values,
wherein the first, second, third and fourth magnetoresistance elements are each a tunnel magnetoresistance (TMR) element.
12. A method of manufacture, comprising:
constructing a bridge comprising a first type of magnetoresistance elements and a second type of magnetoresistance elements, the constructing comprising:
measuring a magnetic field response for a magnetoresistance element at different tilt angles;
for each tilt angle, measuring a resistance of the magnetoresistance element;
using the measured resistance for each tilt angle, determining a value for each resistance combination of the first type and the second type of magnetoresistance elements;
selecting the value indicating an output of the bridge has a linear response over a range of horizontal magnetic field values not centered about a zero value;
selecting a first reference angle for the first type of magnetoresistance elements corresponding to the selected value, wherein the first reference angle indicates an angle the first type of magnetoresistance elements is most sensitive to changes in a magnetic field;
selecting a second reference angle for the second type of magnetoresistance elements corresponding to the selected value; and
constructing the bridge to include at least two magnetoresistance elements of the first type having the first reference angle and to include at least two magnetoresistance elements of the second type having the second reference angle.
13. The method of claim 12 , wherein the second reference angle compensates for non-linearity.
14. The method of claim 12 , wherein selecting the value indicating the output of the bridge has a linear response over a range of horizontal magnetic field values not centered about a zero value comprises selecting the value indicating the output of the bridge has a linear response over the range of horizontal magnetic field values comprising only non-zero values.
15. The method of claim 12 , wherein measuring the magnetic field response for the magnetoresistance element at different tilt angles comprises measuring a magnetic field response for a magnetoresistance element comprising a giant magnetoresistance (GMR) element or a tunnel magnetoresistance (TMR) element.
16. The method of claim 12 , further comprising:
determining, for each tilt angle, the resistance combination that has the lowest change in resistance; and
selecting a third reference angle for a third type of magnetoresistance elements of the bridge corresponding to the lowest change in resistance,
wherein the third reference angle enables the range of horizontal magnetic field values not centered about a zero value to comprise a non-zero value corresponding to the output of the bridge having a zero value.
17. The method of claim 12 , wherein selecting the value indicating the output of the bridge has a linear response over a range of horizontal magnetic field values not centered about a zero value comprises selecting the value indicating the output of the bridge has a linear response over the range of horizontal magnetic field values associated with vertical magnetic field values none of which are 0 Oersted (Oe).
18. The method of claim 12 , wherein the first reference angle and the second reference angle enable the output of the bridge to have the linear response over the range of horizontal magnetic field values not centered about the zero value.
19. The method of claim 18 , wherein the first reference angle and the second reference angle enable the linear response to have the range of horizontal magnetic field values none of which have zero values.
20. The method of claim 12 , further comprising:
connecting a first magnetoresistance element in series with a second magnetoresistance element; and
connecting a third magnetoresistance element in series with a fourth magnetoresistance element and in parallel with the first and second magnetoresistance elements.
21. A camera, comprising:
a magnetic field sensor comprising a bridge, the bridge comprising:
a first magnetoresistance element having a first reference angle;
a second magnetoresistance element in series with the first magnetoresistance element and having a second reference angle;
a third magnetoresistance element in parallel with the first magnetoresistance element and having the first reference angle; and
a fourth magnetoresistance element in series with the third magnetoresistance element and having the second reference angle;
a magnetic target;
a focus controller connected to the magnetic field sensor and connected to a lens; and
the lens,
wherein a movement of the magnetic target is detected by the magnetic field sensor to provide an output to the focus controller to change the focal length of the lens,
wherein an output of the bridge has a linear response over a range of horizontal magnetic field values not centered about a zero value, and
wherein the first reference angle and the second reference angle indicates an angle the magnetoresistance element has the largest change in resistance in response to a change in a magnetic field.
22. The camera of claim 21 wherein the camera is disposed in a cellular device.