Reducing sleep current in a capacitance sensing system
An apparatus and method of measuring a collective capacitance on a group of capacitive sense elements from at least one of rows or columns of a capacitance sense array when in a first mode, and individually measuring capacitances on each of the rows and columns when in a second mode.
1. A method comprising:
providing a two-dimensional capacitance sense array comprising rows of capacitive sense elements and columns of capacitive sense elements;
coupling a group of capacitive sense elements from at least one of the rows or the columns together when in a first mode;
coupling a first capacitance sensor to the group when in the first mode;
measuring, by the first capacitance sensor, a collective capacitance on the group when in the first mode to detect a presence of a conductive object proximate to the group;
upon detection of the presence of the conductive object, switching to a second mode;
individually coupling the first capacitance sensor to each of the rows or columns when in the second mode; and
individually measuring, by the first capacitance sensor, capacitances on each of the rows and the columns when in the second mode.
2. The method of claim 1 , wherein the group comprises all of the rows or all of the columns.
3. The method of claim 1 , wherein the group comprises more than half of the rows or more than half of the columns.
4. The method of claim 1 , wherein the group comprises half of the rows or half of the columns.
5. The method of claim 1 , wherein the group comprises alternating ones of the rows or alternating ones of the columns.
6. The method of claim 1 , further comprising individually coupling the first capacitance sensor to each of the other one of the rows or columns when in the second mode.
7. The method of claim 1 , further comprising individually coupling a second capacitance sensor to each of the other one of the rows or columns when in the second mode.
8. The method of claim 1 , further comprising:
detecting a presence of the conductive object proximate to the group when in the first mode based on the measuring the collective capacitance; and
upon detecting the presence of the conductive object, transitioning from the first mode to the second mode.
9. A method comprising:
operating a sensing device in a first mode, wherein the sensing device is coupled to rows and columns of a capacitance sense array, wherein the sensing device comprises a first capacitance sensor;
measuring, by the first capacitance sensor, a collective capacitance on a group of capacitive sense elements from at least one of the rows or the columns when in the first mode to detect a presence of a conductive object proximate to the group of capacitive sense elements based on the measuring the collective capacitance;
upon detection of the presence of the conductive object, transitioning the sensing device from operating in the first mode to a second mode, wherein the first mode is a lower power mode than the second mode, wherein the first capacitance sensor is individually coupled to each of the rows or columns for measuring capacitances when in the second mode.
10. The method of claim 9 , further comprising individually measuring capacitances on each of the rows and on each of the columns when in the second mode.
11. The method of claim 9 , wherein the group comprises all of the rows or all of the columns.
12. The method of claim 9 , wherein the group comprises more than half of the rows or more than half of the columns.
13. The method of claim 9 , wherein the group comprises half of the rows and half of the columns.
14. The method of claim 9 , wherein the group comprises alternating ones of the rows and alternating ones of the columns.
15. The method of claim 9 , further comprising individually coupling the first capacitance sensor to each of the other one of the rows or columns when in the second mode.
16. The method of claim 9 , further comprising individually coupling a second capacitance sensor to each of the other one of the rows or columns when in the second mode.
17. An apparatus comprising:
a capacitance sense array comprising rows of capacitive sense elements and columns of capacitive sense elements; and
a sensing device configured to be coupled to the capacitance sense array in different configurations in two modes, wherein the sensing device is configured to operate in a first mode, wherein the sensing device is configured to measure a collective capacitance on a group of capacitive sense elements from at least one of the rows or the columns when in the first mode to detect a presence of a conductive object proximate to the capacitance sense array based on the collective capacitance, wherein the sensing device is configured to transition into a second mode when the presence of the conductive object is detected on the group, and wherein the first mode is a lower power mode than the second mode, wherein the sensing device comprises:
a single capacitance sensor; and
a selection circuit configured to couple the single capacitance sensor to the group to measure the collective capacitance in the first mode, and wherein the selection circuit is configured to couple the single capacitance sensor to individual ones of the rows and to individual ones of the columns to individually measure the capacitances.
18. The apparatus of claim 17 , wherein the sensing device is configured to individually measure capacitances on each of the rows and on each of the columns when in the second mode.
19. The apparatus of claim 18 , wherein the sensing device further comprises a second capacitance sensor coupled to the selection circuit, wherein the selection circuit is to individually couple the single capacitance sensor to each of the other one of the rows or columns when in the second mode and to individually couple the second capacitance sensor to each of the other one of the rows or columns when in the second mode.