Capacitance Measurement Circuit for Isolating Self and Mutual Signals
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Solution Overview
Problem
Capacitive touch sensors face challenges in accurately measuring self and mutual capacitance, which affects their operation and can lead to decreased measurement accuracy due to sensitivity issues between these components.
Innovation Solution
The development of a capacitive sensing circuit that allows for separate measurement of mutual and self capacitance using a charge accumulation technique, with specific circuit configurations and switching sequences to minimize the influence of self-capacitance on mutual capacitance measurement, and vice versa, enabling accurate conversion of capacitance to current and digital values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive sensor measures both self and mutual capacitance using conventional methods, then the measurement process is simple, but the measurement accuracy decreases due to sensitivity issues between self and mutual capacitance components
Solution Approach 1:
The patent segments the capacitance measurement into two independent components: self-capacitance measurement and mutual-capacitance measurement. By using separate circuit configurations and measurement sequences, each capacitance type can be measured independently without interference from the other, thereby improving measurement accuracy while managing circuit complexity through systematic division of the measurement process
Solution Approach 2:
The patent extracts the self-capacitance component from the mutual-capacitance measurement by introducing a dummy electrode that replicates the self-capacitance effect. This extracted self-capacitance measurement can then be subtracted from the total measurement to isolate the mutual-capacitance component, enabling accurate separation of the two capacitance types
2Measurement precision
If separate measurement circuits are used for self and mutual capacitance, then measurement accuracy improves, but the device complexity and number of components increase
Solution Approach 1:
The patent implements multi-functionality by designing a single capacitance measurement circuit that can operate in different modes: self-capacitance measurement mode and mutual-capacitance measurement mode. The same basic circuit structure is reused with different electrode connections and measurement sequences, eliminating the need for completely separate circuits and reducing overall device complexity while maintaining measurement accuracy
Solution Approach 2:
The patent uses a dummy electrode that copies the electrical characteristics of the actual sensor electrode. This dummy electrode creates a replica of the self-capacitance effect, allowing the measurement circuit to isolate and measure self-capacitance without requiring additional complex circuitry. The copying approach simplifies the measurement of mutual capacitance by providing a reference for subtraction
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 enables precise measurement of capacitance values, improving the accuracy of capacitive touch sensors, particularly in multi-touch detection systems, by isolating the effects of self and mutual capacitance, thus enhancing the reliability of capacitive touch systems.
Implementation Method 1
an integration capacitor coupled to a second electrode of the sensing element and to an output of the voltage buffer. The capacitance measurement circuit charges and discharges the integration capacitor in response to a switching signal
Data Source
AI summary
A capacitance measurement circuit for measuring self and mutual capacitances may include a first electrode capacitively coupled with a second electrode, a first plurality of switches coupled with the first electrode, and a second plurality of switches coupled with the second electrode, wherein, during a first operation stage, the first plurality of switches is configured to apply a first initial voltage to the first electrode and the second plurality of switches is configured to apply a second initial voltage to the second electrode, and wherein, during a second operation stage, the first plurality of switches is configured to connect the first electrode with a measurement circuit, and the second plurality of switches is configured to connect the second electrode with a constant voltage.