Capacitive Touch Sensor Noise Reduction via Phase-Locked Excitation
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Solution Overview
Problem
Existing touch sensors face challenges in accurately detecting touches due to noise interference, particularly periodic noise from display devices, which can lead to false touch events and incorrect touch location calculations.
Innovation Solution
The solution involves determining the phase of periodic noise and generating a periodic excitation signal locked to this phase, allowing the noise to be converted into a fixed offset that can be subtracted during capacitance measurement, thereby improving noise reduction and enhancing touch detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional touch sensor measurement is used, then touch detection function is provided, but periodic noise from display device causes false touch events and incorrect touch location calculations
Solution Approach 1:
The patent applies periodic action by synchronizing the charge-transfer bursts with the periodic noise signal from the display device. The controller circuit produces charging cycles that are timed to occur during specific stages of the noise output cycle, creating a periodic measurement pattern that aligns with the noise characteristics. This allows the sensor to systematically avoid or account for noise interference in each measurement cycle.
Solution Approach 2:
The patent converts the harmful periodic noise into a beneficial synchronization reference. By detecting the noise signal from the display device and using it to time the charge-transfer bursts, the system transforms the noise from an interfering factor into a timing reference that enables precise control of when measurements occur, thereby improving touch detection reliability.
2Measurement precision
If charge-transfer bursts are performed continuously, then capacitance measurement is maintained, but noise interference significantly affects measurement accuracy
Solution Approach 1:
The patent implements periodic action by performing charge-transfer bursts in synchronized intervals rather than continuously. The controller circuit generates charging cycles that repeat periodically, aligned with the noise signal stages. This periodic measurement approach allows the system to take measurements at optimal moments while avoiding peak noise interference periods.
Solution Approach 2:
The patent applies preliminary action by pre-synchronizing the charge-transfer bursts with the noise signal stages before actual capacitance measurement occurs. The controller circuit提前 detects the noise signal characteristics and uses this information to time the charge-transfer bursts appropriately, ensuring measurements occur when noise interference is minimized.
3Reliability
If noise synchronization is implemented, then touch detection reliability is improved, but device complexity increases due to additional control circuitry
Solution Approach 1:
The patent applies merging by combining the noise detection function with the existing capacitance measurement circuitry. The controller circuit that already controls charge-transfer bursts is enhanced to also detect and synchronize with the noise signal. This integration approach avoids adding completely separate noise detection hardware, thereby reducing the increase in device complexity while still achieving improved reliability.
Solution Approach 2:
The patent implements multi-functionality by designing the controller circuit to perform both noise signal detection and capacitance measurement control functions. The same controller that manages the charge-transfer bursts also detects the noise signal characteristics and uses this information to synchronize measurements. This multi-functional approach reduces the need for separate dedicated noise detection circuitry.
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 effectively reduces the impact of periodic noise, leading to improved signal quality and accurate touch detection, reducing false events and enhancing the reliability of touch sensor performance.
Implementation Method 1
a sensor arranged to determine the presence of an object from a change in a capacitance of a sensing element
Data Source
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AI summary
Techniques are described for providing a cleaned signal in a capacitive touch sensor. A phase of periodic noise on an input of the capacitive touch sensor is determined, and a periodic excitation signal having a phase that is locked to the determined phase of the periodic noise is generated. The periodic excitation signal is applied to an excited conductor in a first array of the touch sensor. While the excitation signal is applied, a response signal on a responding conductor in a second array of the touch sensor is detected, and, based on the detected response signal, a value indicative of a measured capacitance between the excited conductor and the responding conductor is generated. A threshold value is accessed, and a determination is made whether the response signal corresponds to a touch based on a difference between the value and the threshold value.