Capacitive Touch Sensing Circuit With Separate Self and Mutual Readout
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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 separate measurement of mutual and self capacitance is implemented using charge accumulation technique, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The measurement process is segmented into distinct phases: a first measurement phase for mutual capacitance and a second measurement phase for self capacitance. This temporal segmentation allows separate measurement of the two capacitance types using the same physical circuit, improving measurement precision while avoiding the need for duplicate circuitry that would increase device complexity.
Solution Approach 2:
The circuit configuration is made dynamic through switching mechanisms that reconfigure the same circuit elements for different measurement purposes. The circuit transitions between measuring mutual capacitance and self capacitance by changing switch states, allowing one circuit to perform multiple measurement functions and thereby reducing overall device complexity while maintaining high measurement precision.
2Measurement precision
If charge accumulation technique is used to measure capacitance, then measurement precision is improved, but measurement time increases
Solution Approach 1:
The charge accumulation process continues uninterrupted through multiple measurement phases. The same circuit elements accumulate charge for mutual capacitance measurement, then immediately proceed to accumulate charge for self capacitance measurement without resetting or idle periods, maintaining continuous useful action and reducing total measurement time while preserving the precision benefits of charge accumulation.
Solution Approach 2:
The measurement system employs periodic switching between different measurement configurations at optimized intervals. By using non-overlapping clock phases to alternately measure mutual and self capacitance, the system achieves precise measurements through repeated periodic cycles, balancing measurement accuracy with efficient time utilization.
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 and reliability of capacitive touch sensors, particularly in multi-touch detection systems by isolating the effects of self and mutual capacitance, thus enhancing the performance of capacitive touch screens and other touch detection systems.
Implementation Method 1
Capacitance measurement can be performed with a single pair of electrodes or with the use of a multiple electrode system. The apparatus can also measure the self and mutual capacitances of a single electrode or of multiple electrodes in a capacitive touch system.
Data Source
AI summary
In an example embodiment, an apparatus includes a sensing device. The sensing device includes circuitry configured to sense self-capacitance and circuitry configured to sense mutual-capacitance, each configured to detect capacitance values corresponding to whether an object is proximate to a touch screen. The sensing device is configured to measure a first capacitance value using the self-capacitance circuitry during self-capacitance sensing operations and to measure a second capacitance value using the mutual-capacitance circuitry during mutual-capacitance sensing operations.