Multi-stage stylus scanning

1. An apparatus comprising:

a capacitive sense array comprising a plurality of rows and columns of electrodes, wherein the capacitive sense array is configured to detect a presence of a stylus; and

a processing device coupled to the capacitive sense array, the processing device configured to:

perform an initial scan of the plurality of rows and columns of electrodes to determine an initial position of the stylus;

in response to determining the initial position of the stylus:

select subsets of the plurality of rows and columns of electrodes having increased capacitance signal strength around the initial position of the stylus;

perform one or more additional scans of the selected subsets to determine additional positions of the stylus;

after performing the initial scan and the one or more additional scans:

determine a trajectory of the stylus based on the initial position and the one or more additional positions of the stylus; and

select respective subsets of the plurality rows and columns of electrodes for subsequent scans based on the determined trajectory of the stylus in combination with capacitance signal strengths received during the initial scan and the one or more additional scans;

wherein the capacitive sense array is further configured to detect a presence of a passive touch object and the processing device is further configured to:

perform one or more touch mode scans of the plurality of rows and columns of electrodes;

detect a passive touch object based on at least one of the one or more touch mode scans; and

determine a location of the passive touch object on the capacitive sense array.

2. The apparatus of claim 1 , wherein the processing device is further configured to recognize a pattern of the stylus based on the determined trajectory of the stylus in combination with the capacitance signal strengths received during the initial scan and the one or more additional scans.

3. The apparatus of claim 1 , wherein the processing device is configured to perform the subsequent scans by continually scanning additional subsets to determine future additional positions of the stylus.

4. The apparatus of claim 3 , wherein the processing device is further configured to:

determine that the stylus is no longer proximate to the capacitive sense array; and terminate continual scanning of the additional subsets.

5. The apparatus of claim 1 , wherein the initial scan and the one or more additional scans are not performed concurrently.

6. The apparatus of claim 1 , wherein the one or more additional scans are performed at a higher rate than the initial scan.

7. The apparatus of claim 1 , wherein a number of electrodes in the selected subsets is based on at least one of the trajectory of the stylus and a spacing size between the plurality of rows and columns of electrodes.

8. A method comprising:

performing an initial scan of a plurality of rows and columns of electrodes in a capacitive sense array to determine an initial position of a stylus, wherein the capacitive sense array is configured to detect a presence of the stylus;

in response to determining the initial position of the stylus:

selecting subsets of the plurality of rows and columns of electrodes having increased capacitance signal strength around the initial position of the stylus;

performing one or more additional scans of the selected subsets to determine additional positions of the stylus;

after performing the initial scan and the one or more additional scans:

determining a trajectory of the stylus based on the initial position and the one or more additional positions of the stylus; and

selecting respective subsets of the plurality of electrodes for subsequent scans based on the determined trajectory of the stylus in combination with capacitance signal strengths received during the initial scan and the one or more additional scans; and

performing one or more touch mode scans of the plurality of rows and columns of electrodes;

detecting a passive touch object based on at least one of the one or more touch mode scans; and

determining a location of the passive touch object on the capacitive sense array.

9. The method of claim 8 , wherein performing the subsequent scans comprises continually scanning additional subsets to determine future additional positions of the stylus.

10. The method of claim 8 , further comprising:

determining that the stylus is no longer proximate to the capacitive sense array; and terminating the continual scanning of the additional subsets.

11. The method of claim 10 , wherein the initial scan and the one or more additional scans are not performed concurrently.