Capacitive Touch Sensing Circuit for Saturation-Free Measurement
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Solution Overview
Problem
Conventional capacitance detecting circuits face challenges in maintaining measuring resolution and preventing output voltage saturation, particularly due to the limitations of feedback capacitance in capacitive touch devices.
Innovation Solution
The proposed solution involves a capacitance detecting apparatus that utilizes an additional capacitor, along with a control module and a judging module, to provide voltage-drop variations that allow charge redistribution and eliminate background capacitance, thereby maintaining resolution without causing voltage saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the feedback capacitance Cfb is increased to prevent output voltage saturation, then the reliability of the detection system is improved, but the measurement precision of the capacitance change Csig deteriorates
Solution Approach 1:
The patent segments the capacitance measurement function into two distinct capacitors: C1 for background capacitance compensation and C2 for signal measurement. This segmentation allows each capacitor to be optimized for its specific function, resolving the contradiction between preventing saturation and maintaining measurement precision.
Solution Approach 2:
Capacitor C1 acts as an intermediary element that compensates for background capacitance changes, thereby isolating the measurement capacitor C2 from the effects of background variations. This intermediary approach enables precise measurement of small capacitance changes without being affected by large background capacitance.
2Measurement precision
If the feedback capacitance Cfb is decreased to improve measurement resolution, then the measurement precision of the capacitance change Csig is improved, but the output voltage becomes saturated
Solution Approach 1:
The patent segments the capacitance measurement function into two distinct capacitors: C1 for background capacitance compensation and C2 for signal measurement. This segmentation allows each capacitor to be optimized for its specific function, resolving the contradiction between preventing saturation and maintaining measurement precision.
Solution Approach 2:
Capacitor C1 acts as an intermediary element that compensates for background capacitance changes, thereby isolating the measurement capacitor C2 from the effects of background capacitance. This intermediary approach enables precise measurement of small capacitance changes without being affected by large background capacitance.
3Device complexity
If a single capacitor is used for both background capacitance and signal measurement, then the device complexity is reduced, but the measurement precision deteriorates due to background capacitance interference
Solution Approach 1:
The patent segments the capacitance measurement function into two distinct capacitors: C1 for background capacitance compensation and C2 for signal measurement. This segmentation allows each capacitor to be optimized for its specific function, resolving the contradiction between preventing saturation and maintaining measurement precision.
Solution Approach 2:
Capacitor C1 acts as an intermediary element that compensates for background capacitance changes, thereby isolating the measurement capacitor C2 from the effects of background capacitance. This intermediary approach enables precise measurement of small capacitance changes without being affected by large background capacitance.
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 effectively maintains a satisfactory measuring resolution while preventing output voltage saturation, even with smaller capacitors, by jointly contributing charge from multiple capacitors to the measurement, enhancing the accuracy and reliability of capacitance detection in capacitive touch systems.
Implementation Method 1
The control module provides a first voltage-drop variation to the first capacitor and a second voltage-drop variation to the capacitor to be measured to introduce a third voltage-drop variation to the second capacitor
Data Source
AI summary
A capacitance detecting apparatus, coupled to a capacitor to be measured, includes a first capacitor, a second capacitor, a control module and a judging module. The first and second capacitors are coupled to the capacitor to be measured via an input node. The control module provides a first voltage-drop variation to the first capacitor and a second voltage-drop variation to the capacitor to be measured to introduce a third voltage-drop variation to the second capacitor. The first and second voltage-drop variations cause charge flowing from the first capacitor to the input node have a same sign with charge flowing from the input node to the capacitor to be measured. The judging module determines capacitance of the capacitor to be measured according to capacitance of the first and second capacitors as well as the first, second and third voltage-drop variations.