Touch-Sensing Circuit Noise Filtering via Duration Comparison
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Solution Overview
Problem
Conventional touch-sensing circuits face misjudgment issues due to noise interference, which affects the accuracy of determining touch operations, and existing debounce mechanisms are insufficient in handling frequent noise occurrences.
Innovation Solution
A touch-sensing circuit and method incorporating a charge-discharge control unit, sensing capacitor, comparators, crossing detection unit, and timing counter, where the crossing detection unit samples durations before and after state transitions in the output pulses to determine if the voltage has reached preset levels, sending switching signals based on proportional duration analysis to accurately switch between charging and discharging processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional debounce mechanism is used to remove noise by requiring voltage to remain above Vh or below Vl for a preset period, then noise-induced false switching is reduced, but frequent noise occurrences cause repeated resetting of the debounce counter, leading to delayed switching and increased charge-discharge cycle time that may exceed thresholds and cause misjudgment of touch operations
Solution Approach 1:
The patent applies preliminary action by detecting voltage threshold crossings before they are fully established and validating them through duration comparison. The crossing detection unit identifies potential threshold crossings early and uses the comparator to verify whether the voltage remains beyond the threshold for a sufficient duration, thereby preventing noise-induced false switching while avoiding excessive delay in legitimate touch detection.
Solution Approach 2:
The patent replaces the conventional mechanical debounce timer system with an electronic comparison-based validation system. Instead of relying on a preset time period that gets reset by noise, the system uses a comparator to electronically compare the duration voltage remains beyond thresholds, substituting mechanical timing with electronic signal processing that is more responsive and less prone to noise interference.
2Measurement precision
If noise filtering is applied to prevent false voltage threshold crossings, then measurement accuracy improves, but response time to legitimate touch operations increases due to the preset debounce period requirement
Solution Approach 1:
The patent applies partial action by implementing validation only when necessary - specifically when a voltage threshold crossing is detected. The crossing detection unit triggers the comparator to validate the crossing, but this validation mechanism is activated selectively rather than continuously, thereby maintaining measurement precision while minimizing impact on response speed for legitimate touch operations.
Solution Approach 2:
The patent changes the parameter from a fixed time-based debounce period to a dynamic duration comparison based on actual voltage behavior. The system adjusts its validation requirement based on how long the voltage remains beyond the threshold, using the comparator to evaluate this duration parameter dynamically, thereby achieving both precision and speed adaptability.
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 enhances the accuracy of charge-discharge cycle calculation, reduces noise-induced misjudgments, and is adaptable to environments with frequent noise, improving the reliability of touch operation detection.
Implementation Method 1
the voltage change of the sensing capacitor and measuring the charge-discharge cycle of the sensing capacitor
Implementation Method 2
the first comparator is connected to the sensing capacitor and is configured to compare whether the voltage level of the sensing capacitor during the charging process is higher than the preset high voltage. The second comparator is connected to the sensing capacitor and is configured to compare whether the voltage level of the sensing capacitor during the discharging process is lower than the preset low voltage
Data Source
AI summary
A touch-sensing circuit and a touch-judging method are provided. The touch-sensing circuit controls the charging process or the discharging process of a sensing capacitor by a charge-discharge control unit. The first comparator and the second comparator are connected to the sensing capacitor to compare whether the voltage level of the sensing capacitor is higher than the preset high voltage or lower than the preset low voltage. The crossing detection unit receives the output pulse of the comparator and samples the first duration before the output pulse has a state transition and the second duration after the output pulse has the state transition. When the second duration is greater than the first duration, a switching signal is sent to the charge-discharge control unit to switch between the charging and discharging processes.