Common mode noise suppression with restoration of common mode signal
A processing system is disclosed. The processing system includes an amplifier configured to generate a feedback signal, including a spatial common mode estimate generated from spatial-common-mode-processed signals. The processing system further includes charge integrators configured to obtain resulting signals from capacitive sensor electrodes, the resulting signals including a spatial common mode. The charge integrators generate the spatial-common-mode-processed signals by mitigating the spatial common mode in the resulting signals using the feedback signal. The processing system also includes a controller configured to obtain digital touch signals by analog-to-digital converting the spatial-common-mode-processed signals, obtain a digital spatial common mode estimate by analog-to-digital converting the spatial common mode estimate, and obtain at least one digital resulting signal by combining at least one of the digital touch signals with the digital spatial common mode estimate.
1. A processing system comprising:
an amplifier configured to generate a feedback signal comprising a spatial common mode estimate from a plurality of spatial-common-mode-processed signals;
a plurality of charge integrators configured to:
obtain a plurality of resulting signals from a plurality of capacitive sensor electrodes, the plurality of resulting signals comprising a spatial common mode; and
generate the plurality of spatial-common-mode-processed signals by mitigating the spatial common mode in the plurality of resulting signals using the feedback signal; and
a controller comprising:
a programmable gain amplifier capturing the spatial common mode estimate over a summing resistor of the amplifier;
a demodulator configured to remove a modulation voltage from the spatial common mode estimate; and
an analog-to-digital converter configured to perform an analog-to-digital conversion to obtain a digital spatial common mode estimate from the spatial common mode estimate;
the controller further configured to:
obtain a plurality of digital touch signals by analog-to-digital conversion of the plurality of spatial-common-mode-processed signals;
obtain at least one digital resulting signal by combining at least one of the plurality of digital touch signals with the digital spatial common mode estimate.
2. The processing system of claim 1 , wherein the demodulator comprises a low-pass filter configured to attenuate a high-frequency component of the spatial common mode estimate.
3. The processing system of claim 2 , wherein the low-pass filter is configured to attenuate noise associated with a display.
4. The processing system of claim 1 , wherein the controller is further configured to determine that a large object is proximate to the plurality of capacitive sensor electrodes based on the plurality of digital resulting signals differing from the plurality of digital resulting signals obtained in absence of the large object.
5. The processing system of claim 4 , wherein the spatial common mode comprises a component associated with the large object proximate to the plurality of capacitive sensor electrodes.
6. The processing system of claim 1 , wherein the controller is further configured to determine that an input object is proximate to at least one of the plurality of capacitive sensor electrodes based on at least one of the plurality of digital touch signals.
7. The processing system of claim 1 , wherein the spatial common mode comprises a component associated with a baseline of the plurality of capacitive sensor electrodes.
8. The processing system of claim 1 , wherein the amplifier comprises:
a plurality of input resistors coupled to the plurality of charge integrators;
a plurality of current conveyors coupled to the plurality of input resistors; and
the summing resistor coupled to the plurality of current conveyors.
9. The processing system of claim 8 , wherein:
each of the plurality of input resistors comprises a resistance of R;
the gain value is A;
the cardinality of the plurality of spatial-common-mode-processed signals is N;
the summing resistor comprises a resistance of A×R×(1/N); and
the amplifier amplifies each of the plurality of spatial-common-mode-processed signals by −A/N.
10. The processing system of claim 8 , wherein each of the plurality of current conveyors comprises:
an operational amplifier;
a plurality of current mirrors coupled to an output of the operational amplifier; and
a stabilization impedance coupled to an input of the operational amplifier.
11. The processing system of claim 1 , wherein:
each of the plurality of charge integrators comprises an operational amplifier in parallel with an impedance; and
the feedback signal is coupled to a non-inverting input of each of the plurality of charge integrators.
12. A method comprising:
generating, by an amplifier, a feedback signal comprising a spatial common mode estimate from a plurality of spatial-common-mode-processed signals;
obtaining a plurality of resulting signals from a plurality of capacitive sensor electrodes, the plurality of resulting signals comprising a spatial common mode;
generating the plurality of spatial-common-mode-processed signals by mitigating the spatial common mode in the plurality of resulting signals using the feedback signal;
obtaining a plurality of digital touch signals by analog-to-digital conversion of the plurality of spatial-common-mode-processed signals;
capturing, by a programmable gain amplifier, the spatial common mode estimate over a summing resistor of the amplifier;
removing, by a demodulator, a modulation voltage from the spatial common mode estimate;
performing an analog-to-digital conversion of the spatial common mode estimate to obtain a digital spatial common mode estimate;
obtaining at least one digital resulting signal by combining at least one of the plurality of digital touch signals with the digital spatial common mode estimate.
13. The method of claim 12 , further comprising:
attenuating a high-frequency component of the spatial common mode estimate by a low-pass filter of the demodulator.
14. The method of claim 13 , wherein the attenuated high-frequency component is noise associated with a display.
15. The method of claim 12 , further comprising:
determining that a large object is proximate to the plurality of capacitive sensor electrodes based on the plurality of digital resulting signals differing from the plurality of digital resulting signals obtained in absence of the large object.
16. The method of claim 15 , wherein the spatial common mode comprises a component associated with the large object proximate to the plurality of capacitive sensor electrodes.
17. An input device comprising:
a plurality of capacitive sensor electrodes;
an amplifier configured to generate a feedback signal comprising a spatial common mode estimate from a plurality of spatial-common-mode-processed signals; and
a plurality of charge integrators configured to:
obtain a plurality of resulting signals from the plurality of capacitive sensor electrodes, the plurality of resulting signals comprising a spatial common mode; and
generate the plurality of spatial-common-mode-processed signals by mitigating the spatial common mode in the plurality of resulting signals using the feedback signal; and
a controller comprising:
a programmable gain amplifier capturing the spatial common mode estimate over a summing resistor of the amplifier;
a demodulator configured to remove a modulation voltage from the spatial common mode estimate; and
an analog-to-digital converter configured to perform an analog-to-digital conversion to obtain a digital spatial common mode estimate from the spatial common mode estimate;
the controller further configured to:
obtain a plurality of digital touch signals by analog-to-digital conversion of the plurality of spatial-common-mode-processed signals;
obtain at least one digital resulting signal by combining at least one of the plurality of digital touch signals with the digital spatial common mode estimate.