Method of palm rejection and sensor controller
A method of palm rejection is executed by a sensor controller that is connected to a plurality of sensor electrodes and that detects a downlink signal transmitted from an active pen. The method includes determining whether or not a phase of the detected downlink signal matches a phase shared in advance between the sensor controller and the active pen, and outputting, when it is determined that the phases match, a position of the active pen derived on the basis of a distribution of levels of the downlink signal in the plurality of sensor electrodes.
1 . A method performed by a sensor controller, comprising:
detecting, in a plurality of sensor electrodes, a downlink signal having a predetermined frequency or a predetermined waveform transmitted from an active pen;
comparing a phase of the detected downlink signal and a phase shared in advance between the sensor controller and the active pen; and
outputting, responsive to a result of the comparison of the phases, a position of the active pen based on the downlink signal detected in the plurality of sensor electrodes.
2 . The method according to claim 1 , comprising:
not outputting the position of the active pen, depending on the result of the comparison of the phases.
3 . The method according to claim 1 , wherein
the downlink signal transmitted from the active pen includes a predetermined waveform portion shared in advance between the sensor controller and the active pen, and
the method comprises comparing the phase of the predetermined waveform portion included in the downlink signal and the phase shared in advance between the sensor controller and the active pen.
4 . The method according to claim 3 , wherein the predetermined waveform portion is a portion resulting from the active pen modulating predetermined data shared in advance between the sensor controller and the active pen.
5 . The method according to claim 4 , wherein the predetermined data is any one of a preamble, a start bit, or a stop bit.
6 . The method according to claim 4 , wherein the result of the comparison of the phases is one of:
a first result when the predetermined data is included in a symbol sequence obtained by demodulating the downlink signal, and
a second result when said symbol sequence includes inverted data that is a part corresponding to the predetermined data in the symbol sequence obtained by demodulating the downlink signal.
7 . The method according to claim 6 , comprising:
performing two-way communication in synchronization with the active pen; and
determining whether or not the predetermined data or the inverted data is included in the symbol sequence obtained by demodulating the downlink signal at a timing in which the predetermined data is included in the downlink signal.
8 . The method according to claim 1 , comprising:
receiving the downlink signal at each of a plurality of reception units; and
comparing, for each of the plurality of reception units, the phase of the downlink signal detected at the reception unit and the phase shared in advance between the sensor controller and the active pen.
9 . The method according to claim 8 , comprising:
deriving a plurality of positions based on reception level values of the downlink signal in the plurality of sensor electrodes;
allocating the plurality of derived positions to the plurality of reception units; and
connecting one sensor electrode closest to the derived position to the allocated reception unit.