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 passive touch object and 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; and

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 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.

2. The apparatus of claim 1 , wherein the capacitance signal strength corresponds to a transmit (TX) signal from the stylus.

3. The apparatus of claim 2 , wherein the processing device comprises one or more of a synchronous demodulator, an integrator, and a quadrature demodulator.

4. The apparatus of claim 2 , wherein the processing device is further configured to

extract stylus data that is modulated into the transmit signal by the stylus, wherein the transmit signal is detected during the initial scan or the one or more additional scans.

5. 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.

6. The apparatus of claim 1 , wherein the processing device is configured to perform subsequent scans by

continually scanning additional subsets to determine future additional positions of the stylus.

7. The apparatus of claim 1 , 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 selected subsets.

8. The apparatus of claim 7 , wherein the processing device is further configured to

detect the presence of the passive touch object based one on or more of first touch scan or one or more additional scans during the touch mode, wherein the touch mode and the initial and the one or more additional scans of the stylus are not performed concurrently.

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

10. 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, a tip size of the stylus, or a spacing size between the plurality of rows and columns of electrodes.

11. 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 a passive touch object and 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 subsets of the plurality of electrodes to determine additional positions of the stylus; and

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.

12. The method of claim 11 , wherein the capacitance signal strength corresponds to a transmit (TX) signal from the stylus.

13. The method of claim 12 , wherein the transmit signal from the stylus is received via capacitive coupling.

14. The method of claim 12 , further comprising

extracting stylus data that is modulated into the transmit signal by the stylus, wherein the transmit signal is detected during the initial scan or the one or more additional scans.

15. The method of claim 14 , wherein the extracted stylus data comprises one or more of battery data, acceleration data, button data, or force data.

16. The method of claim 11 , wherein performing one or more additional scans comprises

continually scanning additional subsets to determine future additional positions of the stylus.

17. The method of claim 11 , further comprising

determining that the stylus is no longer proximate to the capacitive sense array; and

terminating continual scanning of the selected subsets.

18. The method of claim 17 , further comprising

detecting the presence of the passive touch object based one on or more of first touch scan or the one or more additional scans during the touch mode, wherein the touch mode and the first scan and the one or more additional scans of the stylus are not performed concurrently.

19. The apparatus of claim 1 , wherein the processing device is further configured to switch the capacitive sense array to a touch mode to detect the presence of the passive touch object after completion of the initial scan, the one or more additional scans, or the subsequent scans when a presence of the stylus is not detected.

20. The method of claim 11 , further comprising switching the capacitive sense array to a touch mode to detect the presence of the passive touch object after completion of the initial scan, the one or more additional scans, or the subsequent scans when a presence of the stylus is not detected.