Capacitive Touch Sensor Parasitic Capacitance Stabilization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Electrostatic capacity type touch sensors experience unstable output due to parasitic capacitor capacitance changes caused by LED signal line state changes, leading to detection errors.
Innovation Solution
Incorporating a bias resistor to maintain the signal line at a constant potential, preventing floating and stabilizing the parasitic capacitor capacitance, thereby ensuring consistent sensor output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an LED is disposed on a touch sensor pad and the LED signal line is placed adjacent to the sensor line, then the touch sensor can provide visual feedback through the LED, but a parasitic capacitor is formed between the sensor line and LED signal line causing unstable sensor output
Solution Approach 1:
A bias resistor is introduced as an intermediary element between the LED signal line and the power supply/ground. This mediator maintains a constant electric potential on the LED signal line, preventing it from floating and thereby stabilizing the parasitic capacitor's capacitance value, which in turn stabilizes the sensor output while preserving LED functionality
2Ease of manufacture
If the LED signal line is allowed to float during LED off state, then the circuit can save power and simplify control, but the capacitance of the parasitic capacitor changes causing detection errors
Solution Approach 1:
The bias resistor connects the LED signal line to a fixed potential (power supply or ground), ensuring the signal line maintains a constant electric potential regardless of LED state. This equipotential condition prevents capacitance variations in the parasitic capacitor, eliminating detection errors while maintaining circuit simplicity
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 maintains constant parasitic capacitor capacitance, enhancing detection sensitivity and stability by preventing output voltage changes caused by drive transistor on/off states, resulting in reliable touch detection.
Implementation Method 1
a bias resistor biasing the signal line to a first potential so as to avoid floating of the signal line
Implementation Method 2
a charge amplifier having an input end connected to the sensor line and outputting an output voltage corresponding to a change of a capacitance of a capacitor that the touch sensor pad has
Data Source
AI summary
The invention provides an electrostatic capacity type touch sensor that is not influenced by a parasitic capacitor formed between a sensor line connected to a touch sensor pad and other signal line and provides a stable sensor output. A sensor line connected to a touch sensor pad is connected to a non-inverting input terminal (+) of a charge amplifier. An LED is disposed in the touch sensor pad, and the cathode of the LED is connected to an LED signal line. Since the LED signal line is disposed adjacent to the sensor line, a parasitic capacitor is formed between the LED signal line and the sensor line. In order to keep the capacitance of this parasitic capacitor constant, a pull-up resistor is connected to the LED signal line. The LED signal line is biased to a power supply potential Vdd by the pull-up resistor.