Noise mitigation touch sensing circuit
Techniques for mitigating noise in a touch signal are disclosed. To reduce or eliminate noise in a touch signal, the touch activity can be filtered out of a touch signal, thus isolating the noise. In some examples, the noise is then provided to the non-inverting input port of a differential amplifier while the unfiltered touch signal is provided to the inverting input port of the differential amplifier. The noise, which is now common on both inputs, is automatically eliminated or reduced by the differential amplifier.
1. A touch controller, comprising:
sense circuitry configured to sense touch activity from one or more touch electrodes on a touch sensor panel, including:
a differential amplifier including a first input port coupled to a sense line and a second input port; and
a filter circuit coupled to the sense line, wherein the filter circuit is configured to filter a touch signal from the sense line and output a filtered signal to the second input port of the differential amplifier.
2. The touch controller of claim 1 , wherein the filtered signal includes a noise signal.
3. The touch controller of claim 1 , wherein the differential amplifier is configured to output, via an output port, an amplified difference between a signal on the first input port and a signal on the second input port.
4. The touch controller of claim 1 , wherein the filter circuit includes a high pass filter.
5. The touch controller of claim 1 , further comprising:
a multiplexer configured to, in a first mode, couple the second input port of the differential amplifier to an output of the filter circuit and, in a second mode, couple the second input port of the different amplifier to a reference signal.
6. The touch controller of claim 1 , wherein the filter circuit includes a variable resistor or a variable capacitor.
7. The touch controller of claim 1 , further comprising a programmable input resistor coupled to the first input port.
8. The touch controller of claim 1 , further comprising a feedback network coupled between the first input port and an output port of the differential amplifier, wherein the feedback network includes at least one of a programmable capacitor or a programmable resistor.
9. The touch controller of claim 1 , wherein the sense circuitry is configured based on a spectral distribution of noise.
10. A method, comprising:
receiving, via a sense line, a touch signal associated with touch activity from one or more touch electrodes on a touch sensor panel;
generating, via a filter, a filtered signal by filtering the touch signal from the sense line; and
amplifying, via a differential amplifier, a difference between the touch signal and the filtered signal.
11. The method of claim 10 , wherein the filtered signal includes a noise signal.
12. The method of claim 10 , wherein the filter includes a high pass filter.
13. The method of claim 10 , further comprising:
while in a first mode, coupling, via a multiplexer, the differential amplifier to an output of the filter; and
while in a second mode, coupling, via the multiplexer, the differential amplifier to a reference signal.
14. The method of claim 10 , wherein the filter includes a variable resistor or a variable capacitor.
15. The method of claim 10 , wherein a feedback network is coupled between a first input port and an output port of the differential amplifier, the feedback network including at least one of a programmable capacitor or a programmable resistor.
16. The method of claim 10 , further comprising configuring one or more of the filter and the differential amplifier based on a spectral distribution of noise.
17. An electronic device comprising:
a display;
a touch sensor panel; and
a touch controller coupled to the touch sensor panel, wherein the touch controller includes:
sense circuitry configured to sense touch activity from one or more touch electrodes on the touch sensor panel, including:
a differential amplifier including a first input port coupled to a sense line and a second input port; and
a filter circuit coupled to the sense line, wherein the filter circuit is configured to filter a touch signal from the sense line and output a filtered signal to the second input port of the differential amplifier.
18. The electronic device of claim 17 , wherein the filtered signal includes a noise signal.
19. The electronic device of claim 17 , wherein the filter circuit includes a high pass filter.
20. The electronic device of claim 17 , wherein the touch controller further includes:
a multiplexer configured to, in a first mode, couple the second input port of the differential amplifier to an output of the filter circuit and, in a second mode, couple the second input port of the different amplifier to a reference signal.