US 9,811,178 B2
Stylus signal detection and demodulation architecture
Shahrooz Shahparnia, Campbell, CA (US)
Assigned to Apple Inc., Cupertino, CA (US)
Filed by Apple Inc., Cupertino, CA (US)
Filed on Mar. 14, 2013, as Appl. No. 13/830,399.
Prior Publication US 2014/0267071 A1, Sep. 18, 2014
Int. Cl. G06F 3/0354 (2013.01); G06F 3/041 (2006.01); G06F 3/044 (2006.01)
CPC G06F 3/03545 (2013.01) [G06F 3/044 (2013.01); G06F 3/0416 (2013.01); G06F 2203/04104 (2013.01)] 12 Claims
OG exemplary drawing
 
1. A method of detecting a presence of a stylus signal generated by an asynchronous external stylus on a touch input device, the method comprising:
receiving the stylus signal generated by the asynchronous external stylus,
wherein the asynchronous external stylus generates the stylus signal asynchronously from the touch input device, and the stylus signal generated by the asynchronous external stylus has a beginning time and an end time;
determining a first time value corresponding to the beginning time of the received stylus signal based on an analysis of the received stylus signal;
determining a second time value corresponding to the end time of the received stylus signal based on the analysis of the received stylus signal, wherein determining the second time value includes:
performing a spectral analysis of the received stylus signal, the spectral analysis comprising:
performing a plurality of estimates of a magnitude of the stylus signal, each estimate of the magnitude corresponding to a transform of the plurality of single frequency Fourier transforms; and
determining a peak magnitude from the plurality of estimates of the magnitude; and
determining a time at which the peak magnitude occurred,
wherein determining the time at which the peak magnitude occurred includes:
determining a third time value corresponding to when an estimate of the magnitude of the plurality of estimates of the magnitude crosses a first pre-determined threshold;
determining a fourth time value corresponding to when an estimate of the magnitude of the plurality of estimates of the magnitude crosses a second pre-determined threshold; and
calculating a time centroid based on the determined third value of time and the determined fourth value of time; and
demodulating the stylus signal based on the determined first time value and second time value.