Low electromagnetic interference (EMI) solution for touch products

1. A method comprising:

driving each pair of adjacent transmit (TX) electrodes of a panel with a differential waveform;

measuring signals on each receive (RX) electrode of the panel;

combining the signals from a first pair of adjacent RX electrodes to obtain a first combined signal, wherein the first combined signal represents a first self capacitance associated with a first TX electrode of the panel;

combining the signals from a second pair of adjacent RX electrodes to obtain a second combined signal, wherein the second combined signal represents a second self capacitance associated with a second TX electrode of the panel; and

detecting a presence of an object on the panel using at least the first self capacitance and the second self capacitance.

2. The method of claim 1 , wherein the first pair and the second pair comprises a common RX electrode.

3. The method of claim 1 , further comprising:

generating the differential waveform, wherein the differential waveform comprises an in-phase drive signal and an opposite-phase drive signal, wherein driving each pair of the adjacent TX electrodes comprises:

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

applying the opposite-phase drive signal to a second TX electrode of the first pair of the TX electrodes at a substantially same time.

4. The method of claim 3 , wherein driving each pair of the adjacent TX electrodes further comprises:

applying the in-phase drive signal to a first TX electrode of a second pair of the TX electrodes; and

applying the opposite-phase drive signal to a second TX electrode of the second pair of the TX electrodes at a substantially same time.

5. The method of claim 1 , wherein combining the signals from the first pair of adjacent RX electrodes to obtain the first combined signal comprises:

attenuating at least one of the signals by a first attenuation factor to obtain a first attenuated signal;

attenuating at least one of the signals by a second attenuation factor to obtain a second attenuated signal;

adding the first attenuated signal and the second attenuated signal to obtain a third attenuated signal;

integrating the third attenuated signal to obtain a first integrated signal; and

converting the first integrated signal to a first digital value, the first digital value representing the first self capacitance.

6. The method of claim 5 , wherein combining the signals from the second pair of adjacent RX electrodes to obtain the second combined signal comprises:

attenuating at least one of the signals by a third attenuation factor to obtain a fourth attenuated signal;

adding the second attenuated signal and the fourth attenuated signal to obtain a fifth attenuated signal;

integrating the fifth attenuated signal to obtain a second integrated signal; and

converting the second integrated signal to a second digital value, the second digital value representing the second self capacitance.

7. The method of claim 1 , further comprising generating the differential waveform, wherein generating the differential waveform comprises:

generating a first sine-wave signal; and

generating a second sine-wave signal.

8. The method of claim 1 , further comprising generating the differential waveform, wherein generating the differential waveform comprises:

generating a first square-wave signal; and

generating a second square-wave signal.

9. The method of claim 1 , further comprising generating the differential waveform, wherein generating the differential waveform comprises generating a first sine-wave signal and a second sine-wave signal using a signal generator with amplifiers in a fully differential topology.

10. An apparatus comprising:

capacitance-sensing circuitry configured to:

drive each pair of adjacent transmit (TX) electrodes of a panel with a differential waveform;

measure signals on each receive (RX) electrode of the panel;

combine the signals from a first pair of adjacent RX electrodes to obtain a first combined signal, wherein the first combined signal represents a first self capacitance associated with a first TX electrode of the panel;

combine the signals from a second pair of adjacent RX electrodes to obtain a second combined signal, wherein the second combined signal represents a second self capacitance associated with a second TX electrode of the panel; and

detect a presence of an object on the panel using at least the first self capacitance and the second self capacitance.

11. The apparatus of claim 10 , wherein the capacitance-sensing circuitry comprises:

a signal generator to generate the differential waveform;

sensing circuitry;

analog-to-digital converter (ADC) circuitry coupled to the sensing circuitry; and

a processing core coupled to the ADC circuitry.

12. The apparatus of claim 10 , wherein the sensing circuitry comprises:

a first attenuator;

a second attenuator;

a pair of integration capacitors;

a multiplexer coupled to the pair of integration capacitors; and

a sampling circuit coupled to the multiplexer.

13. The apparatus of claim 12 , wherein the first attenuator comprises:

an amplifier to receive one of the signals and a reference voltage;

a first output branch coupled to the amplifier and to provide a first copy of a first attenuated signal based on the one signal; and

a second output branch coupled to the amplifier and to provide a second copy of the first attenuated signal based on the one signal.

14. The apparatus of claim 10 , wherein the capacitance-sensing circuitry is further configured to cancel a first mutual capacitance between a first TX electrode and a first RX electrode, a second mutual capacitance between a second TX electrode and a second RX electrode, a first self capacitance of the first RX electrode, and a second self capacitance of the second RX electrode, wherein the first self capacitance represents an integrated charge of the object.

15. The apparatus of claim 10 , wherein, by driving each pair of adjacent TX electrodes, the capacitance-sensing circuitry is to suppress electromagnetic interference (EMI) of the panel.

16. The apparatus of claim 10 , wherein a first TX electrode of the panel is a first in-cell electrode and a first RX electrode is a second in-cell electrode adjacent to the first in-cell electrode.

17. The apparatus of claim 10 , wherein the capacitance-sensing circuitry comprises:

a first attenuator coupled to a first RX electrode of the first pair, the first attenuator to attenuate one of the signals by a first attenuation factor to obtain a first attenuated signal;

a second attenuator coupled to a second RX electrode of the first pair, the second attenuator to attenuate one of the signals by a second attenuation factor to obtain a second attenuated signal;

a common node coupled to the first attenuator and the second attenuator, the common node to add the first attenuated signal and the second attenuated signal to obtain a third attenuated signal;

an integrator circuit to obtain a first integrated signal based on the third attenuated signal; and

an analog-to-digital converter (ADC) to convert the first integrated signal to a first digital value, the first digital value representing the first self capacitance.

18. A touch system comprising:

a panel comprising transmit (TX) electrodes and receive (RX) electrodes; and

capacitance-sensing circuitry coupled to the panel, the capacitance-sensing circuitry configured to:

drive each pair of adjacent TX electrodes of the panel with a differential waveform;

measure signals on each RX electrode of the panel;

combine the signals from a first pair of adjacent RX electrodes to obtain a first combined signal, wherein the first combined signal represents a first self capacitance associated with a first TX electrode of the panel;

combine the signals from a second pair of adjacent RX electrodes to obtain a second combined signal, wherein the second combined signal represents a second self capacitance associated with a second TX electrode of the panel; and

detect a presence of an object on the panel using at least the first self capacitance and the second self capacitance.

19. The touch system of claim 18 , wherein the capacitance-sensing circuitry comprises:

a signal generator to generate the differential waveform;

sensing circuitry;

analog-to-digital converter (ADC) circuitry coupled to the sensing circuitry; and

a processing core coupled to the ADC circuitry.

20. The touch system of claim 18 , wherein the sensing circuitry comprises:

a first attenuator;

a second attenuator;

a pair of integration capacitors;

a multiplexer coupled to the pair of integration capacitors; and

a sampling circuit coupled to the multiplexer.

21. The touch system of claim 20 , wherein the first attenuator comprises:

an amplifier to receive one of the signals and a reference voltage;

a first output branch coupled to the amplifier and to provide a first copy of a first attenuated signal based on the one signal; and

a second output branch coupled to the amplifier and to provide a second copy of the first attenuated signal based on the one signal.