Capacitance Measurement Circuits 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, especially in multi-touch detection systems where sensitivity to sensor self-capacitance is high.
Innovation Solution
The development of capacitance measurement circuits that allow for separate measurement of mutual and self-capacitance using a switching capacitor technique, with specific circuit configurations and switching sequences to minimize the influence of self-capacitance on mutual capacitance measurement, and vice versa, enabling accurate detection in both single and multi-touch applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional capacitance measurement circuits are used, then the circuit structure is simple, but the measurement precision deteriorates due to interference between self-capacitance and mutual-capacitance measurements
Solution Approach 1:
The patent divides the capacitance measurement process into separate phases: self-capacitance measurement phase and mutual-capacitance measurement phase. By segmenting the measurement timeline and using switching circuits to isolate different measurement modes, the system achieves accurate measurement of both capacitance types without mutual interference, resolving the precision issue while maintaining reasonable circuit complexity through temporal separation rather than complete spatial separation.
Solution Approach 2:
The patent extracts and compensates for the self-capacitance component separately from the mutual-capacitance measurement. By measuring self-capacitance independently and then subtracting its influence from the mutual capacitance measurement, the system isolates the desired measurement signal from the interfering self-capacitance, thereby improving measurement precision without requiring a completely redesigned circuit architecture.
2Measurement precision
If separate measurement of self and mutual capacitance is implemented, then measurement precision improves, but device complexity increases due to additional switching circuits and measurement phases
Solution Approach 1:
The patent designs a multi-functional capacitance measurement circuit that can perform both self-capacitance and mutual-capacitance measurements using the same basic circuit components. The switching circuitry enables a single measurement system to adapt between different measurement modes, reducing the need for separate dedicated circuits for each measurement type and thereby limiting the increase in device complexity while achieving precise separate measurements.
Solution Approach 2:
The patent employs periodic switching between self-capacitance measurement and mutual-capacitance measurement phases. By using non-overlapping clock signals to alternately activate different measurement paths, the system achieves accurate separate measurements through time-division multiplexing, minimizing the need for additional permanent circuit components and keeping the overall device complexity manageable.
3Measurement precision
If switching capacitor technique is used to minimize self-capacitance influence, then measurement precision improves, but loss of time increases due to multiple measurement phases
Solution Approach 1:
The patent implements continuous capacitive sensing by overlapping the self-capacitance and mutual-capacitance measurement phases in time. Rather than completely separating the measurements with idle transition periods, the switching is designed to minimize dead time and maintain continuous data acquisition, thereby reducing the overall measurement cycle time while still achieving the precision benefits of separate measurement capability.
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
These circuits enhance the accuracy and sensitivity of capacitance measurement, allowing for reliable operation in capacitive touch detection systems, including multi-touch touchpads and touchscreens by isolating self and mutual capacitance components effectively.
Implementation Method 1
Capacitive touch sensors may be used to replace mechanical buttons, knobs and other similar mechanical user interface controls
Implementation Method 2
FIG. 2 illustrates one embodiment of a self-capacitance circuit that uses a charge accumulation technique
Data Source
AI summary
Capacitance measurement circuits for measuring self and mutual capacitances are described. In one embodiment the capacitance measurement circuit includes: 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.