Capacitive Sensor Common-Mode Suppression Without Signal Loss
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Solution Overview
Problem
Existing input devices, such as touch sensor devices, face challenges in effectively mitigating spatial common mode noise, which can lead to incorrect detection of input objects and noise interference from display screens, affecting the accuracy of user input detection.
Innovation Solution
A processing system comprising an amplifier to generate a feedback signal for spatial common mode estimation, charge integrators to process signals from capacitive sensor electrodes, and a controller with a programmable gain amplifier and demodulator to remove modulation voltage and mitigate spatial common mode noise, allowing for improved detection of input objects by separating noise from actual signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If spatial common mode noise suppression is applied to touch sensor electrodes, then noise interference from display screens is reduced, but the common mode signal containing input object information is also attenuated
Solution Approach 1:
The patent segments the common mode signal into two distinct components: noise (to be suppressed) and input object information (to be preserved). This is achieved by creating separate signal paths - one for noise suppression via common mode rejection, and another for capturing the common mode estimate containing input object information through the programmable gain amplifier and demodulator.
Solution Approach 2:
The patent introduces an intermediary feedback signal that carries the common mode estimate from the summing resistor through the programmable gain amplifier and demodulator. This intermediary allows the system to separately process and preserve the informative common mode signal while still suppressing noise through the main feedback loop.
2Object-affected harmful factors
If feedback signal is used to suppress spatial common mode noise, then noise mitigation is achieved, but system complexity increases due to additional components
Solution Approach 1:
The feedback signal serves multiple functions simultaneously: it suppresses spatial common mode noise in the main signal path while also carrying the common mode estimate to the programmable gain amplifier and demodulator for input object detection. This multi-functionality reduces the need for separate dedicated circuits.
Solution Approach 2:
The system uses its own feedback signal to provide the common mode estimate needed for input object detection. The feedback loop inherently contains the common mode information that is redirected through the programmable gain amplifier, allowing the system to self-service its noise suppression and signal detection needs without external intervention.
3Power
If modulation voltage is present in the spatial common mode estimate, then signal transmission is enabled, but noise interference persists in the processed signals
Solution Approach 1:
The patent employs periodic modulation voltage to encode the common mode estimate, enabling signal transmission through the feedback loop. The demodulator then extracts the information from this periodically modulated signal, separating the useful input object information from the noise components that persist in the modulated domain.
Data Source
AI summary
A processing system is disclosed. The processing system includes an amplifier configured to generate a feedback signal including a spatial common mode estimate 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, and 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 including a programmable gain amplifier capturing the spatial common mode estimate over a summing resistor of the amplifier and a demodulator configured to remove a modulation voltage from the spatial common mode estimate.