Capacitance Sensing Circuit With Shield Capacitance Correction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing capacitance detection devices suffer from errors in detection results due to changes in the capacitance between the detection electrode and the shield electrode, which are influenced by temperature and other factors, leading to reduced sensitivity and accuracy.
Innovation Solution
A capacitance detection device that includes an AC voltage output unit to supply first and second AC voltages with specific frequency and phase relationships, a detection signal generation unit to generate an AC detection signal, and a correction unit to adjust the amplitude difference between these voltages, repeatedly entering a correction mode to correct the detection value based on changes in shield capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shield electrode is disposed close to the detection electrode to reduce parasitic capacitor effects, then detection sensitivity is improved, but errors occur in detection results when the capacitance between the shield electrode and detection electrode changes due to temperature or other factors
Solution Approach 1:
The patent implements a correction unit that continuously monitors the capacitance between the shield electrode and detection electrode, and adjusts the detection results based on this feedback. The correction unit calculates a correction value based on the measured shield capacitance and applies it to compensate for errors in the detection results, thereby maintaining both sensitivity and accuracy under varying temperature and environmental conditions.
Solution Approach 2:
The patent changes the operating parameters by applying different AC voltage amplitudes to the shield electrode and detection electrode. By controlling the amplitude of the AC voltage applied to the shield electrode to be smaller than that applied to the detection electrode, the system optimizes the charge distribution to reduce parasitic capacitor effects while minimizing the impact of shield capacitance changes on detection accuracy.
2Object-affected harmful factors
If the capacitance of the capacitor between the detection electrode and shield electrode is larger than the capacitance between the detection electrode and ground, then the shield electrode effectively reduces parasitic capacitor effects, but temperature dependence of the dielectric constant causes detection errors
Solution Approach 1:
The correction unit continuously measures the shield capacitance and uses this feedback information to compensate for temperature-dependent errors. By monitoring changes in the capacitance between the shield electrode and detection electrode, the system can dynamically adjust the detection results to maintain accuracy despite temperature variations affecting the dielectric constant of the circuit board.
3Measurement precision
If AC voltage amplitude of the shield electrode is adjusted to cancel charge supplied to the parasitic capacitor, then detection sensitivity is improved, but the voltage difference causes errors when shield capacitance changes
Solution Approach 1:
The patent optimizes the AC voltage parameters by setting the amplitude of the AC voltage applied to the shield electrode to be smaller than that applied to the detection electrode. This parameter adjustment allows the system to achieve effective cancellation of parasitic capacitor effects while minimizing the voltage difference that causes errors when shield capacitance changes due to temperature or other environmental factors.
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 effectively reduces errors in detection values by correcting for changes in shield capacitance, improving sensitivity and accuracy by minimizing the impact of temperature and other factors on the detection process.
Implementation Method 1
a parasitic capacitor generated between the ground and the detection electrode causes a problem... the shield electrode reduces a capacitance of the parasitic capacitor because the detection electrode is less likely to form an electrostatic coupling with surrounding conductors
Implementation Method 2
a capacitance detection device... detects a capacitance of a detection electrode relative to the ground... generates an AC detection signal in accordance with the supplied charge
Data Source
AI summary
A calculation unit calculates a detection value of a capacitance of a capacitor based on a detection signal. A correction unit repeatedly performs a shift to a correction mode. When the correction mode is entered, the correction unit controls an AC voltage output unit so that a difference between amplitudes of first and second AC voltages changes, and obtains a correction value corresponding to a change in the detection value of the calculation unit caused by the change in the difference between the amplitudes. The correction unit corrects the detection value calculated by the calculation unit in accordance with the change in the correction values obtained in the correction mode.