Touch detection using multiple simultaneous stimulation signals
The use of multiple stimulation signals having one or more frequencies and one or more phases to generate an image of touch on a touch sensor panel is disclosed. Each of a plurality of sense channels can be coupled to a column in a touch sensor panel and can have one or more mixers. Each mixer in the sense channel can utilize a circuit capable generating a demodulation frequency of a particular frequency. At each of multiple steps, various phases of one or more selected frequencies can be used to simultaneously stimulate the rows of the touch sensor panel, and the one or more mixers in each sense channel can be configured to demodulate the signal received from the column connected to each sense channel using the one or more selected frequencies. After all steps have been completed, the demodulated signals from the one or more mixers can be used in calculations to determine an image of touch for the touch sensor panel at each of the one or more frequencies.
1. An apparatus comprising:
drive circuitry configured to simultaneously apply, during each of a plurality of frames, a plurality of stimulation signals to a plurality of drive lines of touch sensor circuitry, the plurality of stimulation signals having a stimulation frequency and multiple stimulation phases, wherein the stimulation frequency during at least two of the plurality of frames is different; and
sense circuitry configured, during each of the plurality of frames, to receive a sense signal from each of a plurality of sense lines of the touch sensor circuitry into one or more sense channels and to demodulate the sense signals with one or more demodulation signals, the one or more demodulation signals having a demodulation frequency and multiple demodulation phases based on the stimulation frequency and the multiple stimulation phases being applied during that frame.
2. The apparatus of claim 1 , wherein the stimulation frequency applied during each of the at least two frames is selected from one or more low-noise frequencies.
3. The apparatus of claim 2 , wherein the sense circuitry is further configured to:
demodulate a combined noise signal from the plurality of sense lines with in-phase (I) and quadrature (Q) components of one or more test frequencies when the plurality of drive lines are unstimulated during a spectral analysis scan;
accumulate the I and Q components of the demodulated noise signal for each of the one or more test frequencies;
calculate a magnitude of the accumulated I and Q components of the demodulated noise signal for each of the one or more test frequencies; and
determine the one or more low-noise frequencies by selecting test frequencies whose generated magnitudes are smallest.
4. The apparatus of claim 1 , wherein the sense circuitry comprises one or more accumulator circuits configured to accumulate demodulated sense signals to generate a plurality of values representing the accumulated demodulated sense signals for each sense channel.
5. The apparatus of claim 4 , further comprising a memory configured to store the plurality of values.
6. The apparatus of claim 1 , the apparatus coupled to the touch sensor circuitry including the plurality of drive lines and the plurality of sense lines.
7. The apparatus of claim 6 , the apparatus and the touch sensor circuitry incorporated into a touch-sensitive computing device.
8. A method comprising:
during each of a plurality of frames,
simultaneously applying a plurality of stimulation signals to a plurality of drive lines of touch sensor circuitry, the plurality of stimulation signals having a stimulation frequency and multiple stimulation phases, wherein the stimulation frequency during at least two of the plurality of frames is different,
receiving a sense signal from each of a plurality of sense lines of the touch sensor circuitry into one or more sense channels, and
demodulating the sense signals with one or more demodulation signals, the one or more demodulation signals having a demodulation frequency and multiple demodulation phases based on the stimulation frequency and the multiple stimulation phases being applied during that frame.
9. The method of claim 8 , wherein the stimulation frequency applied during each of the at least two frames is selected from one or more low-noise frequencies.
10. The method of claim 9 , further comprising determining the one or more low-noise frequencies by:
demodulating a combined noise signal from the plurality of sense lines with in-phase (I) and quadrature (Q) components of one or more test frequencies when the plurality of drive lines are unstimulated during a spectral analysis scan;
accumulating the I and Q components of the demodulated noise signal for each of the one or more test frequencies;
calculating a magnitude of the accumulated I and Q components of the demodulated noise signal for each of the one or more test frequencies; and
determining the one or more low-noise frequencies by selecting test frequencies whose generated magnitudes are smallest.
11. The method of claim 8 , further comprising accumulating demodulated sense signals to generate a plurality of values representing the accumulated demodulated sense signals for each sense channel.
12. The method of claim 11 , further comprising storing the plurality of values.
13. A non-transitory computer readable storage medium storing instructions, that when executed by a processor, performs a method comprising:
during each of a plurality of frames,
simultaneously applying a plurality of stimulation signals to a plurality of drive lines of touch sensor circuitry, the plurality of stimulation signals having a stimulation frequency and multiple stimulation phases, wherein the stimulation frequency during at least two of the plurality of frames is different,
receiving a sense signal from each of a plurality of sense lines of the touch sensor circuitry into one or more sense channels, and
demodulating the sense signals with one or more demodulation signals, the one or more demodulation signals having a demodulation frequency and multiple demodulation phases based on the stimulation frequency and the multiple stimulation phases being applied during that frame.
14. The non-transitory computer readable storage medium of claim 13 , the method further comprising selecting the stimulation frequency applied during each of the at least two frames from one or more low-noise frequencies.
15. The non-transitory computer readable storage medium of claim 14 , further comprising determining the one or more low-noise frequencies by:
demodulating a combined noise signal from the plurality of sense lines with in-phase (I) and quadrature (Q) components of one or more test frequencies when the plurality of drive lines are unstimulated during a spectral analysis scan;
accumulating the I and Q components of the demodulated noise signal for each of the one or more test frequencies;
calculating a magnitude of the accumulated I and Q components of the demodulated noise signal for each of the one or more test frequencies; and
determining the one or more low-noise frequencies by selecting test frequencies whose generated magnitudes are smallest.
16. The non-transitory computer readable storage medium of claim 13 , the method further comprising accumulating demodulated sense signals to generate a plurality of values representing the accumulated demodulated sense signals for each sense channel.
17. The non-transitory computer readable storage medium of claim 16 , the method further comprising storing the plurality of values.
18. The non-transitory computer readable storage medium of claim 13 , the medium communicatively coupled to the touch sensor circuitry including the plurality of drive lines and the plurality of sense lines.
19. The non-transitory computer readable storage medium of claim 13 , the medium incorporated into a touch-sensitive computing device.