Sensor design for capacitance sensing
Electrode configurations for reducing wobble error for a stylus translating on a surface over and between electrodes of a touch sensor panel are disclosed. In some examples, electrodes associated with a more linear signal profile are correlated with lower wobble error. In some examples, electrodes can have projections which can interleave with projections of adjacent electrodes. In some configurations, projections of adjacent electrodes can be interleaved in one-dimension; in other configurations, projections of adjacent electrodes can be interleaved in two-dimensions. In some configurations, the width and length of one or more projections in an electrode can be selected based on a desired signal profile for that electrode.
1. A touch sensor panel comprising: a plurality of electrically isolated electrodes;
a first electrode of the plurality of electrodes having a first form and a first surface area, wherein the first form comprises a first shape in a first orientation;
a second electrode of the plurality of electrodes having a second form and a second surface area, wherein the second form comprises the first shape in a second orientation, different than the first orientation, wherein the second orientation is a rotation of the first orientation;
wherein:
the first electrode includes a first set of projections in a first dimension, each projection of the first set of projections having one of one or more first projection surface areas;
the second electrode includes a second set of projections in the first dimension, each projection of the second set of projections having one of one or more second projection surface areas, magnitudes of each of the one or more second projection surface areas being different from magnitudes of each of the one or more first projection surface areas;
the first electrode is interleaved with the second electrode using the first set of projections and the second set of projections; and
the first surface area, including the respective first projection surface areas, is substantially the same as the second surface area, including the respective second projection surface areas.
2. The touch sensor panel of claim 1 , wherein the plurality of electrically isolated electrodes are deposited on a first layer.
3. The touch sensor panel of claim 1 , wherein
the respective first projection surface areas of each of the first set of projections are equal, and
the respective second projection surface areas of each of the second set of projections are equal.
4. The touch sensor panel of claim 1 , wherein
a first projection of the first set of projections forms a T-shape;
a first projection of the second set of projections forms an L-shape; and
the first projection of the first set of projections interdigitates with the first projection of the second set of projections.
5. The touch sensor panel of claim 1 , wherein the first form is symmetric about a first axis; and
the second form includes a second shape that is symmetric about the first axis.
6. The touch sensor panel of claim 5 ,
wherein the first shape is symmetric about a second axis;
and
the second shape is symmetric about the second axis.
7. The touch sensor panel of claim 1 wherein the second orientation is orthogonal to the first orientation.
8. The touch sensor panel of claim 1 further comprising a third electrode having a third form and a third surface area; wherein
the third electrode includes a third set of projections in a second dimension;
the first electrode further includes a fourth set of projections in the second dimension; and
the first electrode is interleaved with the third electrode using the fourth set of projections and the third set of projections.
9. The touch sensor panel of claim 8 , wherein the second dimension is orthogonal to the first dimension.
10. The touch sensor panel of claim 8 , wherein the third form of the third electrode is the same as the second form.
11. The touch sensor panel of claim 1 , wherein
the first electrode is associated with a first signal profile representing a plurality of signal measurements at the first electrode in the first dimension; and
the second electrode is associated with a second signal profile representing a plurality of signal measurements at the second electrode in the first dimension.
12. The touch sensor panel of claim 11 , wherein
each of the first set of projections has a first width and first length;
each of the second set of projection has a second width and second length;
the first width and first length determine the first signal profile;
the second width and second length determine the second signal profile;
the first width and first length are optimized such that the first signal profile includes:
a maximum signal measurement at a midpoint of the first electrode, and
a first signal measurement at a midpoint of the second electrode greater than or equal to 12% of the maximum signal measurement at the midpoint of the first electrode; and
the second width and second length are optimized such that the second signal profile includes:
a maximum signal measurement at the midpoint of the second electrode, and
a second signal measurement at the midpoint of the first electrode greater than or equal to 12% of the maximum signal measurement at the midpoint of the second electrode.
13. The touch sensor panel of claim 12 wherein
the first signal measurement at the midpoint of the second electrode is less than 30% of the maximum signal measurement at the midpoint of the first electrode.
14. The touch sensor panel of claim 12 wherein
the first signal measurement at the midpoint of the second electrode varies by less than 27% from the second signal measurement at the midpoint of the first electrode.
15. The touch sensor panel of claim 12 wherein
the first electrode is further associated with a third signal profile representing a plurality of signal measurements at the first electrode in a second dimension, different from the first,
the third signal profile varies by less than 27% from the first signal profile.
16. The touch sensor panel of claim 12 wherein
the first electrode is further associated with a third signal profile representing a plurality of signal measurements at the first electrode in a second dimension, different from the first,
the third signal profile varies by less than 27% from the first signal profile.
17. A method of forming a touch sensor panel comprising:
forming a first and second electrode, wherein;
the first electrode has a first form, wherein the first form comprises a first shape in a first orientation;
the second electrode has a second form, wherein the second form comprises the first shape in a second orientation, different than the first orientation, wherein the second orientation is a rotation of the first orientation;
first projections of the first electrode interleave with second projections of the second electrode;
selecting dimensions of the first and second projections such that:
the first projections each have a first projection surface area magnitude;
the second projections each have a second projection surface area magnitude, different from the first projection surface area magnitude;
the first electrode has a first total surface area; and
the second electrode has a total surface area equal to the first total surface area.
18. The method of claim 17 , further comprising:
selecting the dimensions of the first and second projections such that:
the first projections are different from the second projections.