Capacitance Discrimination Circuit for Noise-Resistant Touch Sensing
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Solution Overview
Problem
Conventional touch switches that detect capacitance changes for user input are prone to erroneous discrimination due to external noise interference, leading to incorrect detection of touch events.
Innovation Solution
A capacitance discrimination circuit comprising a first and second capacitor, a comparator, counter circuit, charge circuit, and control circuit that compares voltages and performs count operations to accurately discriminate capacitance changes while minimizing external noise influence, using a discharge circuit to reset capacitor voltages and eliminate measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the time required for the capacitor to reach the reference voltage is measured to detect capacitance changes, then touch detection is enabled, but the measurement is readily affected by external noises causing erroneous discrimination
Solution Approach 1:
The patent implements feedback by continuously monitoring the voltage increase rate and comparing it against expected values. When the voltage increase rate falls outside the predetermined range, the system determines that noise is present and adjusts accordingly, preventing erroneous touch detection. This feedback mechanism ensures reliable discrimination between actual touch events and noise interference.
Solution Approach 2:
The patent dynamically adjusts the voltage increase rate based on detected noise conditions. When noise is detected through the monitoring mechanism, the system modifies its operation to account for the interference, allowing accurate capacitance measurement even in noisy environments. This dynamic adaptation resolves the contradiction between maintaining measurement precision and ensuring reliability.
2Measurement precision
If high-performance A/D and D/A converters are used to improve measurement accuracy, then capacitance detection precision is improved, but the circuit complexity increases
Solution Approach 1:
The patent replaces complex A/D and D/A conversion circuits with a simpler voltage increase rate monitoring mechanism. Instead of using high-performance converters that would increase circuit complexity, the system monitors how quickly the voltage increases during capacitor charging and uses this rate information to determine capacitance values. This substitution maintains measurement precision while significantly reducing circuit complexity.
Solution Approach 2:
The patent changes the measurement parameter from absolute voltage level to voltage increase rate. By measuring the rate of voltage change rather than relying on precise absolute voltage measurements requiring high-performance converters, the system achieves accurate capacitance detection with simpler circuitry. This parameter transformation resolves the contradiction between precision and complexity.
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 discriminates capacitance changes with high accuracy, reducing false positives from external noise and enabling reliable touch detection without the need for high-performance A/D and D/A converters, while maintaining a simple circuit structure.
Implementation Method 1
a comparator configured to compare a first voltage of the first capacitor and a second voltage of the second capacitor
Implementation Method 2
a counter circuit configured to perform a count operation based on a comparison result of the comparator
Implementation Method 3
a charge circuit configured to charge the first capacitor and the second capacitor
Implementation Method 4
using a discharge circuit to reset capacitor voltages and eliminate measurement errors
Data Source
AI summary
In some embodiments, a capacitance discrimination circuit includes first and second capacitors, a comparator configured to compare a first voltage of the first capacitor and a second voltage of the second capacitor, a counter circuit configured to perform a count operation based on a comparison result of the comparator, a charge circuit configured to charge the first and second capacitors, and a control circuit configured to control the charge circuit so as to charge either the first capacitor or the second capacitor based on the comparison result of the comparator. The capacitance discrimination of the first and second capacitors is performed based on count values of the counter circuit. The capacitance discrimination circuit preferably includes a discharge circuit to discharge electric charges stored in the first and second capacitors in accordance with a discharge signal from the control circuit.