TRIGGERING MULTI-PHASE TRANSMISSION PATTERN SWITCHING TO REDUCE EMISSIONS IN TOUCH PRODUCTS

1 . An apparatus comprising:

circuitry configured to detect a crossing between an in-phase drive signal, received over a first analog line, and an opposite-phase drive signal, received over a second analog line of a touch panel; and

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

2 . The apparatus of claim 1 , further comprising:

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

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

wherein, to control the timing, the output is to cause a change in the multi-phase switching pattern applied to the sets of switches.

3 . The apparatus of claim 2 , 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 the timing of the phase switch between excitation frames of the sinusoidal wave generator.

4 . The apparatus of claim 2 , 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 the sinusoidal wave generator.

5 . The apparatus of claim 2 , 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.

6 . The apparatus of claim 1 , further comprising:

a transmission pattern control register to apply, responsive to receipt of the 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 output.

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:

detecting a crossing between an in-phase drive signal and an opposite-phase drive signal, wherein the in-phase drive signal and the opposite-phase drive signal are to excite transmission (TX) electrodes of a touch panel;

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 between the in-phase drive signal and the opposite-phase drive signal; 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:

generating, by a sinusoidal wave generator, the in-phase drive signal and the opposite-phase drive signal to excite the TX electrodes;

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 the in-phase drive signal and the opposite-phase drive signal; and

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

13 . The method of claim 9 , further comprising generating, by a sinusoidal wave generator centered around a bias voltage, the in-phase drive signal and the opposite-phase drive signal to excite the TX electrodes.

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;

circuitry configured to detect a crossing between an in-phase drive signal, received over a first analog line, and an opposite-phase drive signal, received over a second analog line of the touch panel;

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

multi-phase switching logic coupled to the circuitry, the multi-phase switching logic to assert an output in response to both detecting the crossing and receiving a signal indicative of a phase switch between the in-phase drive signal and the opposite-phase drive signal, wherein the output is to control timing of applying a multi-phase switching pattern to the sets of switches.

16 . The system of claim 15 , further comprising:

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

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

wherein, to control the timing, the output is to cause a change in the multi-phase switching pattern applied to the sets of switches.

17 . The system of claim 16 , 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.

18 . The system of claim 16 , 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.

19 . The system of claim 15 , further comprising:

a transmission pattern control register to apply, responsive to receipt of the output, the multi-phase switching pattern to the 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 output.

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.