Channel aggregation for optimal stylus detection
A touch input device configured to detect stylus signals generated by an external stylus is provided. The touch input device includes a plurality of stylus signal detectors that receive at its input a combination of stylus receive channels that are combined in a manner to minimize noise while at the same time keeping the stylus signal strength uniform independent of the position of the stylus on the device.
1. A stylus detection apparatus for detecting an asynchronous active stylus, the apparatus comprising:
a plurality of sense channels, each sense channel including an amplifier, wherein the plurality of sense channels are configured to sense signals at a plurality of electrodes of a touch sensor panel, the signals including one or more stylus signals generated by the asynchronous active stylus;
a channel aggregator coupled to receive outputs of the plurality of sense channels and configured to generate one or more aggregated signals based on combinations of the outputs of the plurality of sense channels, wherein the channel aggregator is configured to sum at least two of a plurality of first signals sensed at a plurality of first electrodes of the plurality of electrodes to generate at least one aggregated signal; and
one or more stylus signal detectors, each stylus signal detector configured to:
receive one of the aggregated signals from the channel aggregator;
detect one of the stylus signals based on the received aggregated signal; and
estimate a start time and an end time for the detected stylus signal.
2. The apparatus of claim 1 , wherein the plurality of first electrodes are chosen such that a detected signal strength of the stylus signal is uniform and independent of the active stylus' position on the touch sensor panel.
3. The apparatus of claim 1 , wherein the channel aggregator is further configured to subtract one or more second signals sensed at one or more second electrodes of the plurality of electrodes from a sum of the plurality of first signals, wherein the first signals and the second signals are sensed simultaneously.
4. The apparatus of claim 3 , wherein the one or more second electrodes are chosen such that a noise signal received at the one or more second electrodes is correlated to a noise signal received at the plurality of first electrodes.
5. The apparatus of claim 3 , wherein the plurality of first electrodes and the one or more second electrodes are mutually exclusive.
6. The apparatus of claim 1 , wherein a number of the stylus signal detectors is based in part on a spatial correlation of a plurality of noise signals received at the plurality of electrodes of the touch sensor panel.
7. A method for detecting an asynchronous active stylus, the method comprising:
sensing, by a plurality of sense channels, one or more active stylus signals at a plurality of electrodes of a touch sensor panel, the one or more active stylus signals generated by the asynchronous active stylus, wherein each sense channel includes an amplifier;
generating one or more aggregated signals based on combinations of outputs of the plurality of sense channels, wherein generating the one or more aggregated signals includes summing at least two of a plurality of first signals sensed at a plurality of first electrodes of the plurality of electrodes to generate at least one aggregated signal; and
at a stylus signal detector:
detecting one of the stylus signals based on the received aggregated signal; and
estimating a start time and an end time for the detected stylus signal.
8. The method of claim 7 , further comprising choosing the plurality of first electrodes such that the detected signal strength of the stylus signal is uniform and independent of the active stylus' position on the touch sensor panel.
9. The method of claim 7 , wherein generating the one or more aggregated signals further includes subtracting one or more second signals sensed at one or more second electrodes of the plurality of electrodes from a sum of the plurality of first signals, wherein the first signals and the second signals are sensed simultaneously.
10. The method of claim 9 , further comprising choosing the one or more second electrodes such that a noise signal received at the one or more second electrodes is correlated to a noise signal received at the plurality of first electrodes.
11. The method of claim 9 , wherein the plurality of first electrodes and the one or more second electrodes are mutually exclusive.
12. The method of claim 7 , wherein a number of the stylus signal detectors is based in part on the spatial correlation of a plurality of noise signals received at the plurality of electrodes of the touch sensor panel.
13. A non-transitory computer readable storage medium having stored thereon a set of instructions for detecting an asynchronous active stylus that when executed by a processor causes the processor to:
sense, by a plurality of sense channels, one or more active stylus signals at a plurality of electrodes of a touch sensor panel, the one or more active stylus signals generated by the asynchronous active stylus, wherein each sense channel includes an amplifier;
generate one or more aggregated signals based on combinations of outputs of the plurality of sense channels, wherein generating the one or more aggregated signals includes summing at least two of a plurality of first signals sensed at a plurality of first electrodes of the plurality of electrodes to generate at least one aggregated signal; and
at a stylus signal detector:
receive one of the aggregated signals;
detect one of the stylus signals based on the received aggregated signal; and
estimate a start time and an end time for the detected stylus signal.
14. The non-transitory computer readable storage medium of claim 13 , wherein the processor is further caused to choose the plurality of first electrodes such that the detected signal strength of the stylus signal is uniform and independent of the active stylus' position on the touch sensor panel.
15. The non-transitory computer readable storage medium of claim 13 , wherein generating the one or more aggregated signals further includes subtracting one or more second signals sensed at one or more second electrodes of the plurality of electrodes from a sum of the plurality of first signals, wherein the first signals and the second signals are sensed simultaneously.
16. The non-transitory computer readable storage medium of claim 15 , wherein the processor is further caused to choose the one or more second electrodes such that a noise signal received at the one or more second electrodes is correlated to a noise signal received at the plurality of first electrodes.
17. The non-transitory computer readable storage medium of claim 15 , wherein the plurality of first electrodes and the one or more second electrodes are mutually exclusive.
18. The non-transitory computer readable storage medium of claim 13 , wherein a number of the stylus signal detectors is based in part on the spatial correlation of a plurality of noise signals received at the plurality of electrodes of the touch sensor panel.
19. The apparatus of claim 1 , wherein at least one of the one or more aggregated signals meets a threshold signal level irrespective of a location of the active stylus contacting the touch sensor panel, wherein the threshold signal level is sufficient to meet a signal-to-noise requirement for at least one of the stylus signal detectors.
20. The method of claim 7 , wherein at least one of the one or more aggregated signals meets a threshold signal level irrespective of a location of the active stylus contacting the touch sensor panel, wherein the threshold signal level is sufficient to meet a signal-to-noise requirement for the stylus signal detector.
21. The non-transitory computer readable storage medium of claim 13 , wherein at least one of the one or more aggregated signals meets a threshold signal level irrespective of a location of the active stylus contacting the touch sensor panel, wherein the threshold signal level is sufficient to meet a signal-to-noise requirement for the stylus signal detector.
22. The apparatus of claim 1 , wherein the start time and the end time for the detected stylus signal are estimated based on a peak detection of the detected stylus signal.
23. The method of claim 7 , wherein the start time and the end time for the detected stylus signal are estimated based on a peak detection of the detected stylus signal.
24. The non-transitory computer readable storage medium of claim 13 , wherein the start time and the end time for the detected stylus signal are estimated based on a peak detection of the detected stylus signal.