Capacitive Touch Detection Circuit Using Dual Currents Against Noise
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Solution Overview
Problem
Capacitive touch circuits used in outdoor environments are prone to detection errors due to significant fluctuations in environmental parameters like temperature and humidity, and are affected by noise interference, leading to incorrect identification of touch events.
Innovation Solution
A touch detection circuit that uses two different currents for charging and discharging a detection capacitor, canceling baseline counts and avoiding noise frequencies by excluding time intervals associated with the first charging and discharging currents from the detection cycle, thereby improving detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional capacitive switch is used in outdoor environment, then the touch detection function is provided, but the detection correctness is degraded due to environmental parameter fluctuations
Solution Approach 1:
The patent changes the charging and discharging current parameters to different values (first charging current ≠ second charging current, first discharging current ≠ second discharging current). This parameter variation creates distinct time interval characteristics that allow the system to differentiate between environmental noise and actual touch events, thereby maintaining detection correctness under environmental fluctuations.
Solution Approach 2:
The patent measures multiple time intervals (first charging interval, second charging interval, first discharging interval, second discharging interval) and uses feedback processing to determine touch events. By comparing these measured intervals against expected patterns, the system can filter out environmental interference and maintain reliable detection.
2Reliability
If a conventional capacitive switch is used in high noise environment, then the touch detection function is provided, but identification error occurs due to noise affecting time interval counting
Solution Approach 1:
The patent employs different charging currents (first and second) and different discharging currents (first and second) to create varied time interval measurements. This parameter diversity makes the detection system less susceptible to noise at any single frequency, as the noise affects each measurement differently. The system can then identify true touch events through pattern recognition across multiple measurements.
Solution Approach 2:
The patent performs periodic charging and discharging operations with different current levels, creating a series of time interval measurements. This periodic action with varying parameters allows the system to distinguish between random noise and consistent touch-induced capacitance changes, improving identification accuracy in noisy environments.
3Measurement precision
If external noises are present, then the capacitive switch operates, but the time interval that capacitor voltage reaches reference voltage is shortened causing identification error
Solution Approach 1:
The patent uses multiple charging current levels and multiple discharging current levels to create different measurement conditions. By comparing time intervals obtained under different current parameters, the system can identify and compensate for noise-induced measurement errors, thereby maintaining precise time interval measurement even when external noise shortens the voltage rise time.
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 enhances the accuracy of touch detection by mitigating environmental changes and noise interference, ensuring reliable operation even in harsh conditions.
Implementation Method 1
The capacitive touch circuit detects a touch according to the capacitance variation caused by a conductor approaching thereto
Data Source
AI summary
There is provided a touch detection circuit including a charging circuit, a discharging circuit, a counter and a processor. The charging circuit charges a detection capacitor within a charging interval using different currents. The discharging circuit discharges the detection capacitor within a discharging interval using different currents. The counter counts the charging interval and the discharging interval. The processor subtracts a baseline time from a counted charging time and a counted discharging time to cancel the noise interference.