Capacitive Disturbance Detection via Synchronous Oscillator Circuits
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Solution Overview
Problem
Capacitive sensing systems face challenges in directly measuring capacitance due to interference from electric fields, stress, temperature, and humidity, leading to computational inefficiencies in distinguishing between environmental and capacitive changes, as they often rely on measuring charge rather than capacitance.
Innovation Solution
The system employs two relaxation oscillator circuits coupled to electrodes, oscillating synchronously when capacitance exceeds a threshold and asynchronously when it does not, allowing direct capacitance measurement and robustness against disturbances by determining capacitance based on oscillator frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If charge measurement is used instead of direct capacitance measurement, then environmental interference (electric fields, stress, temperature, humidity) affects measurement accuracy, but computational methods can differentiate between fast changes (disturbances) and slow changes (environmental conditions)
Solution Approach 1:
The patent extracts the capacitance measurement function from indirect charge measurement and implements direct capacitance measurement using oscillator circuits. The oscillator frequency directly reflects capacitance changes, eliminating the need for computational differentiation between environmental effects and disturbances. This extracts the essential measurement function while removing unnecessary computational complexity.
Solution Approach 2:
The patent replaces the computational system (software-based charge measurement and differentiation algorithms) with a physical system (oscillator circuits that directly convert capacitance to frequency). This substitution eliminates the need for complex computational processing while maintaining measurement capability, as the oscillator frequency naturally responds to capacitance changes.
2Reliability
If charge measurement with averaging calculations is used, then disturbances can be filtered out, but the amount of code and computational resources required increases
Solution Approach 1:
The oscillator circuit performs self-service by automatically converting capacitance changes into frequency changes that are inherently distinguishable. The circuit itself provides the disturbance filtering capability through its physical operation, eliminating the need for external computational filtering algorithms. The oscillator naturally responds only to significant capacitance changes above the threshold.
3Measurement precision
If indirect capacitance determination based on charge changes is used, then capacitance can be inferred, but the system cannot recognize capacitance changes when electrodes carry the same electric potential
Solution Approach 1:
The patent applies equipotentiality by using oscillator circuits that operate independently at each electrode, allowing both electrodes to carry the same electric potential while still enabling capacitance measurement. The oscillator frequency depends on the capacitance between electrodes, not on potential differences, thus maintaining measurement capability under equipotential conditions.
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 approach enables direct capacitance measurement, reducing computational complexity and improving robustness against interfering factors, allowing for effective detection of disturbances such as touch or changes in environmental conditions.
Implementation Method 1
In response to a capacitance between the first and second electrodes being above a threshold capacitance, the first and second relaxation oscillators are configured to oscillate synchronously
Implementation Method 2
The disclosed capacitive disturbance detection systems directly measure capacitance, rather than charge on electrodes
Data Source
AI summary
An apparatus includes a first oscillator circuit coupled to a first electrode and a second oscillator circuit coupled to a second electrode. The first and second oscillator circuits oscillate synchronously in response to a capacitance between the first and second electrodes being greater than or equal to a threshold coupling capacitance and asynchronously in response to the capacitance being less than the threshold coupling capacitance. The first and second electrodes are separated by a distance, such that a disturbance within the distance increases the capacitance between the electrodes equal to or above the threshold coupling capacitance. The frequency of the first oscillator circuit is inversely proportional to a capacitance of the first electrode, and the frequency of the second oscillator circuit is inversely proportional to a capacitance of the second electrode.