Determining spectrally shaped waveforms for touch sensing applications and related methods and apparatuses

1. A method, the method comprising:

receiving an indication of allowable electromagnetic emissions;

choosing radio frequency subcarriers responsive to the indication of allowable electromagnetic emissions; and

generating and storing a spectrally shaped time domain digital waveform responsive to the chosen radio frequency subcarriers.

2. The method of claim 1 , comprising:

performing quadrature amplitude modulation using the radio frequency subcarriers.

3. The method of claim 1 , comprising:

choosing, for each of the radio frequency subcarriers, a specified amplitude and a specified frequency.

4. The method of claim 1 , wherein the choosing the radio frequency subcarriers responsive to the indication of allowable electromagnetic emissions comprises:

choosing test frequencies and test amplitudes;

generating a test time domain digital waveform of a test drive signal responsive to the radio frequency subcarriers, each radio frequency subcarrier having a frequency and amplitude specified by a respective chosen test frequency and a test amplitude;

generating the test drive signal;

providing the generated test drive signal to a touch sensor; and

storing the test time domain digital waveform of the test drive signal responsive to detecting that an observed electromagnetic emission of the touch sensor is within an allowable electromagnetic emission.

5. The method of claim 4 , comprising:

generating a time series of the test drive signal responsive to the test time domain digital waveform; and

observing spikes, if any, in the time series of the test drive signal.

6. The method of claim 5 , comprising:

choosing a new phase relationship among the radio frequency subcarriers responsive to observing one more of the observed spikes are outside a dynamic range of a touch sensor.

7. The method of claim 1 , comprising:

generating a bit stream responsive to the spectrally shaped time domain digital waveform; and

storing the bit stream at a touch controller.

8. An apparatus, comprising:

at least one processor; and

a memory including having instructions thereon, wherein the processor-executable instructions, when executed by the at least one processor, are to enable the at least one processor to:

receive an indication of allowable electromagnetic emissions;

choose radio frequency subcarriers responsive to the indication of allowable electromagnetic emissions; and

generate and store a spectrally shaped time domain digital waveform responsive to the chosen radio frequency subcarriers.

9. The apparatus of claim 8 , wherein the processor-executable instructions, when executed by the at least one processor, are to enable the at least one processor to:

perform quadrature amplitude modulation using the radio frequency subcarriers.

10. The apparatus of claim 8 , wherein the processor-executable instructions, when executed by the at least one processor, are to enable the at least one processor to:

choose, for each of the radio frequency subcarriers, a specified amplitude and a specified frequency.

11. The apparatus of claim 8 , wherein respective processor-executable instructions, when executed by the at least one processor, to enable the at least one processor to choose the radio frequency subcarriers responsive to the indication of allowable electromagnetic emissions comprise instructions to:

choose test frequencies and test amplitudes;

generate a test time domain digital waveform of a test drive signal responsive to the radio frequency subcarriers, each radio frequency subcarrier having a frequency and amplitude specified by a respective chosen test frequency and a test amplitude;

generate the test drive signal; and

store the test time domain digital waveform of the test drive signal responsive to detecting that an observed electromagnetic emission of a touch sensor provided the test drive signal is within an allowable electromagnetic emission.

12. The apparatus of claim 11 , wherein the processor-executable instructions, when executed by the at least one processor, are to enable the at least one processor to:

generate a time series of the test drive signal responsive to the test time domain digital waveform; and

observe spikes, if any, in the time series of the test drive signal.

13. The apparatus of claim 12 , wherein the processor-executable instructions, when executed by the at least one processor, are to enable the at least one processor to:

choose a new phase relationship among the radio frequency subcarriers responsive to observing one more of the observed spikes are outside a dynamic range of a touch sensor.

14. The apparatus of claim 8 , wherein the processor-executable instructions, when executed by the at least one processor, are to enable the at least one processor to:

generate a bit stream responsive to the spectrally shaped time domain digital waveform; and

storing the bit stream at a touch controller.