Triggering multi-phase transmission pattern switching to reduce emissions in touch products

1. An apparatus comprising:

a sinusoidal wave generator that generates, over a first analog line, an in-phase drive signal and, over a second analog line, an opposite-phase drive signal;

a comparator having inputs respectively coupled to the first analog line and the second analog line and to assert a first output in response to detecting a crossing between the in-phase drive signal and the opposite-phase drive signal; and

multi-phase switching logic coupled to an output of the comparator, the multi-phase switching logic to assert a second output in response to both detecting the first output and receiving a signal indicative of a phase switch of the sinusoidal wave generator, wherein the second output is to control timing of applying a multi-phase switching pattern to sets of switches coupled between the first analog line and the second analog line and respective ones of transmission (TX) electrodes of a touch panel.

2. The apparatus of claim 1 , wherein, to control the timing, the second output is to cause a change in the multi-phase switching pattern applied to the sets of switches.

3. The apparatus of claim 1 , further comprising:

a transmission pattern control register to apply, responsive to receipt of the second output, the multi-phase switching pattern to sets of switches; and

a transmission pattern register coupled to the transmission pattern control register, the transmission pattern register to buffer a pre-loaded transmission pattern and transfer the pre-loaded transmission pattern to the transmission pattern control register in response to the second output.

4. The apparatus of claim 1 , further comprising processing logic coupled to the multi-phase switching logic, the processing logic to supply the signal, to the multi-phase switching logic, indicative of timing of the phase switch between excitation frames of the sinusoidal wave generator.

5. The apparatus of claim 1 , further comprising a timer table controller coupled between the sinusoidal wave generator and the multi-phase switching logic, the timer table controller to assert the signal, to the multi-phase switching logic, indicative of the phase switch detected between excitation frames of sinusoidal wave generator.

6. The apparatus of claim 1 , wherein the sinusoidal wave generator is a sine wave generator that is to generate, centered around a bias voltage, an in-phase sine-wave signal and an opposite-phase sine-wave signal.

7. The apparatus of claim 1 , further comprising:

a first TX electrode;

a first TX buffer coupled to the first TX electrode; and

a first set of switches coupled to the first TX buffer.

8. The apparatus of claim 7 , further comprising:

a second TX electrode;

a second TX buffer coupled to the second TX electrode; and

a second set of switches coupled to the second TX buffer; and

wherein each of the first set of switches and the second set of switches are included in the sets of switches that are switched according to the multi-phase switching pattern.

9. A method comprising:

generating, by a sinusoidal wave generator, an in-phase drive signal and an opposite-phase drive signal to excite transmission (TX) electrodes of a touch panel;

comparing the in-phase drive signal and the opposite-phase drive signal to detect a crossing between the in-phase drive signal and the opposite-phase drive signal;

asserting a logical output responsive to: 1) detecting the crossing between the in-phase drive signal and the opposite-phase drive signal; and 2) receiving a signal indicative of a phase switch of the sinusoidal wave generator; and

applying, responsive to receipt of the logical output, a multi-phase switching pattern to sets of switches coupled between the in-phase and opposite-phase drive signals and the TX electrodes.

10. The method of claim 9 , further comprising:

buffering, into a transmission pattern register, a pre-loaded transmission pattern; and

transferring the pre-loaded transmission pattern to a transmission pattern control register in response to the logical output, and wherein the multi-phase switching pattern is based on the pre-loaded transmission pattern.

11. The method of claim 9 , further comprising:

receiving, by multi-phase switching logic, from processing logic executing firmware, the signal indicative of timing of the phase switch between excitation frames of the sinusoidal wave generator; and

wherein asserting the logical output is performed by the multi-phase switching logic.

12. The method of claim 9 , further comprising:

receiving, by multi-phase switching logic, from a timer table controller, the signal indicative of the phase switch detected between excitation frames of sinusoidal wave generator; and

wherein asserting the logical output is performed by the multi-phase switching logic.

13. The method of claim 9 , wherein generating, by the sinusoidal wave generator, the in-phase drive signal and in opposite-phase drive signal comprises generating, centered around a bias voltage, an in-phase sine-wave signal and an opposite-phase sine-wave signal.

14. The method of claim 9 , wherein applying the multi-phase switching pattern comprises:

applying the in-phase drive signal to a first set of switches coupled to a first TX electrode of the TX electrodes; and

applying the opposite-phase drive signal to a second set of switches coupled to a second TX electrode of the TX electrodes positioned adjacent to the first TX electrode.

15. A system comprising:

a touch panel comprising a plurality of transmission (TX) electrodes;

a sinusoidal wave generator that generates, over a first analog line, an in-phase drive signal and, over a second analog line, an opposite-phase drive signal;

sets of switches coupled between the first analog line and the second analog line and respective ones of the plurality of TX electrodes;

a comparator having inputs respectively coupled to the first analog line and the second analog line and to assert a first output in response to detecting a crossing between the in-phase drive signal and the opposite-phase drive signal; and

multi-phase switching logic coupled to an output of the comparator, the multi-phase switching logic to assert a second output in response to both detecting the first output and receiving a signal indicative of a phase switch of the sinusoidal wave generator, wherein the second output is to control timing of applying a multi-phase switching pattern to sets of switches.

16. The system of claim 15 , wherein, to control the timing, the second output is to cause a change in the multi-phase switching pattern applied to the sets of switches.

17. The system of claim 15 , further comprising:

a transmission pattern control register to apply, responsive to receipt of the second output, the multi-phase switching pattern to sets of switches; and

a transmission pattern register coupled to the transmission pattern control register, the transmission pattern register to buffer a pre-loaded transmission pattern and transfer the pre-loaded transmission pattern to the transmission pattern control register in response to the second output.

18. The system of claim 15 , further comprising processing logic coupled to the multi-phase switching logic, the processing logic to supply the signal, to the multi-phase switching logic, indicative of timing of the phase switch between excitation frames of the sinusoidal wave generator.

19. The system of claim 15 , further comprising a timer table controller coupled between the sinusoidal wave generator and the multi-phase switching logic, the timer table controller to assert the signal, to the multi-phase switching logic, indicative of the phase switch detected between excitation frames of sinusoidal wave generator.

20. The system of claim 15 , further comprising:

a first TX buffer coupled to a first TX electrode of the plurality of TX electrodes;

a first set of switches coupled to the first TX buffer;

a second TX buffer coupled to a second TX electrode of the plurality of TX electrodes; and

a second set of switches coupled to the second TX buffer; and

wherein each of the first set of switches and the second set of switches are included in the sets of switches that are switched according to the multi-phase switching pattern.