SYNCHRONIZING A STYLUS WITH A CAPACITIVE SENSE ARRAY

1 . A method comprising:

generating, by a stylus, a transmit signal to be capacitively coupled to a capacitive sense array;

modulating stylus data into the transmit signal; and

transmitting the modulated signal to the capacitive sense array via a capacitive coupling between the stylus and the capacitance sense array.

2 . The method of claim 1 , wherein the stylus data comprises force sense data.

3 . The method of claim 1 , wherein the stylus data comprises at least one of force sense data, battery data, acceleration data, or button status data.

4 . The method of claim 1 , wherein said modulating comprises modulating the data using at least one of frequency modulation (FM), frequency-shift keying (FSK), amplitude modulation (AM), amplitude-shift keying (ASK), on-off keying (OOK), pulse position modulation, phase modulation (PM), Manchester encoding, or direct sequence spread spectrum (DSSS).

5 . The method of claim 1 , further comprising measuring a force with which a tip of the stylus is pressed, and wherein the stylus data comprises the measured force.

6 . A stylus, comprising:

a stylus tip configured to capacitively couple to a capacitive sense array;

a tip driver configured to drive a transmit signal to the capacitive sense array via the stylus tip; and

a processing device configured to modulate data into the transmit signal and ton control the tip drive to transmit the modulated signal to the capacitive sense array via the stylus tip.

7 . The stylus of claim 6 , wherein the processing device comprises:

a synchronization and modulation block configured to receive the transmit signal and to modulate the data into the transmit signal to generate the modulated signal; and

a processing core configured to provide the data to the synchronization and modulation block.

8 . The stylus of claim 7 , wherein the processing device further comprises an analog-to-digital converter (ADC) to receive a voltage representative of a battery status of the stylus and to convert the voltage into a digital value, wherein the processing core is configured to include the digital value in the data sent to the synchronization and modulation block to be modulated into the transmit signal.

9 . The stylus of claim 7 , further comprising a button, wherein the processing core is configured to receive button input data from the button and to include the button input data in the data sent to the synchronization and modulation block to be modulated into the transmit signal.

10 . The stylus of claim 7 , wherein the processing device further comprises a measurer configured to determine an amount of force applied to the stylus tip and send a digital value representative of the amount of force, and wherein the processing core is configured to include the digital value in the data sent to the synchronization and modulation block to be modulated into the transmit signal.

11 . The stylus of claim 10 , further comprising a force sensor, coupled to the processing device, configured to detect the amount of force applied to the stylus tip.

12 . The stylus of claim 11 , wherein the force sensor is an active sensor.

13 . The stylus of claim 10 , further comprising a motion sensor, coupled to the processing device, configured to detect motion of the stylus.

14 . The stylus of claim 7 , wherein the synchronization and modulation block is configured to modulate the data using at least one of frequency modulation (FM), frequency-shift keying (FSK), amplitude modulation (AM), amplitude-shift keying (ASK), on-off keying (OOK), pulse position modulation, phase modulation (PM), Manchester encoding, or direct sequence spread spectrum (DSSS).

15 . The stylus of claim 14 , wherein the PM modulation uses at least one of a binary phase shift keying (BPSK) encoding scheme or a quadrature phase shift keying (QPSK) encoding scheme.

16 . A stylus comprising:

a stylus tip configured to capacitively couple to a capacitive sense array;

a tip driver configured to transmit signals to the capacitive sense array via the stylus tip; and

a processing device configured to transmit a stylus touch signal to a host via the capacitive sense array and a stylus data to the host using a same channel as the stylus touch signal.

17 . The stylus of claim 16 , wherein the processing device is configured to modulate the stylus data into the stylus touch signal.

18 . The stylus of claim 16 , wherein the processing device is configured to multiplex the stylus data and the stylus touch signal.

19 . The stylus of claim 18 , wherein the processing device is configured to use at least one of time divisional multiplexing (TDM) to transmit the stylus touch signal in one time slot and transmit the stylus data in another time slot or code divisional multiplexing (CDM) to transmit the stylus touch signal using one code and transmit the stylus data using another code.

20 . The stylus of claim 16 , wherein the processing device is configured to transmit the stylus touch signal using a first frequency and transmit the stylus data using another frequency.

21 . The stylus of claim 16 , further comprising:

a switching block configured to generate an inverted and non-inverted transmit signal based on the stylus touch signal, wherein the switching block comprises a switch that toggles an output signal between the inverted and non-inverted transmit signal; and

a pause detector configured to detect periods between pulses of the stylus touch signal, wherein the processing device comprises:

a shift register configured to receive input force data from a force sensor, wherein the stylus data comprises the input force data; and

a synchronization and clock generation block to generate synchronized clock pulses for the shift register, and wherein the shift register controls the switch of the switching block in response to the input force data, wherein the output signal of the switching block is a modulated signal comprising the stylus data and the stylus touch signal.