Capacitive Touch Sensing with Absolute and Transcapacitance
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Solution Overview
Problem
Current capacitive sensing devices face limitations in accurately detecting touch inputs, particularly in distinguishing between absolute capacitance and transcapacitance, which affects their ability to determine positional information and object type with precision.
Innovation Solution
The implementation of a capacitive sensor device with a combination of absolute and transcapacitive sensing capabilities, using a single set of sensor electrodes that can modulate and measure both types of capacitance, allowing for the differentiation of absolute and transcapacitive components through various modulation techniques and guard signal approaches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single set of sensor electrodes is used to measure both absolute capacitance and transcapacitance, then device complexity is reduced, but measurement precision deteriorates due to inability to distinguish between the two capacitance types
Solution Approach 1:
The patent applies periodic action by modulating the sensor electrode with a periodic signal (e.g., square wave or sinusoidal signal at frequency f0). This modulation allows the measurement system to distinguish between absolute capacitance and transcapacitance components through frequency-domain analysis. The periodic modulation of the electrode creates corresponding modulations in the measured current, which can be demodulated to separate the two capacitance types, thereby maintaining measurement precision while using a single electrode configuration.
2Measurement precision
If modulation techniques are applied to differentiate capacitance components, then measurement precision improves, but device complexity increases due to additional circuitry and signal processing
Solution Approach 1:
The patent merges the modulation function and measurement function into a single integrated process. The sensor electrode serves both as the modulated element and the measuring element. By modulating the electrode potential and simultaneously measuring the resulting current, the system combines multiple functions into one unified approach, reducing the need for separate modulation circuits and measurement circuits, thereby limiting the increase in device complexity while still achieving improved measurement precision.
Solution Approach 2:
The patent employs feedback by using the measured current information to determine both the presence and position of input objects. The system continuously monitors the current flowing through the modulated sensor electrode and uses this feedback signal to update positional information in real-time. This feedback mechanism allows the system to achieve high measurement precision through software-based signal processing rather than requiring complex additional hardware circuits.
3Measurement precision
If guard signals are used to eliminate stray capacitance effects, then measurement precision improves, but ease of operation deteriorates due to additional configuration requirements
Solution Approach 1:
The patent applies self-service by having the sensor electrode serve its own guarding function. The modulated sensor electrode automatically compensates for stray capacitance effects through the modulation and demodulation process. The system uses the electrode's own signal characteristics to identify and eliminate interference from stray capacitance, without requiring external guard electrodes or complex manual configuration. This self-service approach maintains measurement precision while simplifying operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances the accuracy of positional information and object type determination, enabling more precise touch input detection and improving the overall performance of capacitive sensing devices by combining absolute and transcapacitive measurements.
Implementation Method 1
measuring a capacitance coupling between the sensor electrode and an input object
Implementation Method 2
modulate and measure both types of capacitance, allowing for the differentiation of absolute and transcapacitive components through various modulation techniques
Data Source
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AI summary
A capacitive sensor device comprises a first sensor electrode, a second sensor electrode, and a processing system coupled to the first sensor electrode and the second sensor electrode. The processing system is configured to acquire a first capacitive measurement by emitting and receiving a first electrical signal with the first sensor electrode. The processing system is configured to acquire a second capacitive measurement by emitting and receiving a second electrical signal, wherein one of the first and second sensor electrodes performs the emitting and the other of the first and second sensor electrodes performs the receiving, and wherein the first and second capacitive measurements are non-degenerate. The processing system is configured to determine positional information using the first and second capacitive measurements.