Capacitance Touch Sensing via Peak Detection and Time Multiplexing
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Solution Overview
Problem
Conventional capacitance touch sensors require high CPU resources and multiple input/output ports to detect variations in stray capacitance, making them inefficient for handling a large number of sensors effectively.
Innovation Solution
A capacitance touch sensor architecture incorporating a square wave generator, peak detector, analog-to-digital converter, and control unit that converts stray capacitance variations into DC voltage, allowing for efficient detection with reduced CPU usage and fewer input/output ports through a matrix architecture and time-sharing multiplexing principle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high sample/count speed is used to detect capacitance variation, then detection accuracy is improved, but CPU resource occupation increases
Solution Approach 1:
The patent introduces an intermediary measurement system using RC circuit charging/discharging time constants. Instead of directly measuring small capacitance variations at high speed, the system converts capacitance changes into time-domain measurements through resistor-capacitor circuits, which can be measured with lower CPU resource occupation while maintaining detection accuracy.
Solution Approach 2:
The patent transforms the measurement parameter from direct capacitance value to charging/discharging time constant. By measuring the time required for voltage to reach certain thresholds during RC circuit transitions, the system achieves accurate capacitance detection without requiring high-speed sampling, thereby reducing CPU resource occupation.
2Productivity
If multiple input/output ports are used to process multiple sensors, then sensor processing capability is improved, but device complexity increases
Solution Approach 1:
The patent segments the sensor measurement process into distinct phases (charging phase and discharging phase) that can be multiplexed through a single input/output port. By time-division multiplexing, the system processes multiple sensors sequentially through different phases, eliminating the need for multiple simultaneous input/output ports while maintaining multi-sensor processing capability.
Solution Approach 2:
The patent implements periodic charging and discharging cycles for RC circuits associated with different sensors. Each sensor undergoes periodic measurement cycles where the input/output port alternates between charging and discharging phases for different sensors. This periodic time-multiplexed approach enables multiple sensors to be processed through a single port, reducing device complexity while preserving productivity.
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
The solution significantly reduces CPU resource utilization and input/output port requirements, enabling the detection of multiple panels with a smaller number of ports, thereby enhancing the efficiency of capacitance touch sensors.
Implementation Method 1
When the panel 13 is touched by a finger, its stray capacitance Cx changes (increases). The capacitance touch sensor 10 detects a variation from the stray capacitance Cx of the panel (sensor) 13 with respect to the ground
Data Source
AI summary
A capacitance touch sensor includes a square wave generator for generating a square wave clock, a sensor panel for receiving the square wave clock and then generating a panel signal, a peak detector for receiving the panel signal and then generating an analog peak signal, an analog-to-digital converter for receiving the analog peak signal and then generating a digital peak signal, and a control unit for receiving the digital peak signal and generating a detection signal according to a level of the digital peak signal to indicate whether the sensor panel is touched or not.