Capacitive Digitizer Sensor Noise Suppression via Periodic Sampling
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Solution Overview
Problem
Capacitive based digitizer sensors face noise interference from environmental sources such as magnetic and electric fields, which affects the accuracy of fingertip detection and other capacitive object sensing.
Innovation Solution
The method employs time domain multiplexing to alternate between sampling noise signals and detection signals on the same conductive line, using drive signals with transient and flat sections to separate noise from detection signals, and applies frequency domain multiplexing to separate outputs from different frequency signals, thereby suppressing noise and improving scanning efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous scanning is performed to maintain high refresh rate, then productivity is improved, but noise interference increases affecting measurement precision
Solution Approach 1:
The patent implements periodic action by alternating between noise sampling periods and detection signal sampling periods. During noise sampling, the system captures environmental noise without applying drive signals. During detection signal sampling, drive signals are applied to capture both noise and detection signals. This periodic alternation allows the system to maintain high refresh rates while accurately separating and suppressing noise from actual detection signals through subtraction of noise samples from detection samples.
2Measurement precision
If noise sampling is performed continuously to improve measurement precision, then noise suppression is enhanced, but power consumption increases
Solution Approach 1:
The system employs periodic action by performing noise sampling only during specific time periods when no drive signals are applied to the conductive lines. This allows noise to be captured without the energy consumption associated with continuous drive signal generation. The alternating pattern of noise sampling and detection signal sampling ensures that noise suppression is effective while power consumption is minimized by not continuously energizing the scanning circuitry.
Solution Approach 2:
The patent applies preliminary action by performing noise sampling before detection signal sampling in alternating time periods. By capturing the environmental noise profile in advance during dedicated noise sampling periods, the system prepares noise reference data that can be subtracted from subsequent detection signals. This preliminary noise characterization enables effective noise suppression without requiring continuous energy input.
3Device complexity
If traditional simultaneous sampling is used, then device complexity is reduced, but noise interference degrades measurement precision
Solution Approach 1:
The patent applies segmentation by dividing the sampling process into distinct temporal segments: noise sampling periods and detection signal sampling periods. Instead of attempting to simultaneously sample both noise and detection signals (which would require complex filtering and separation circuitry), the system segments the time domain to capture each signal type separately. This temporal segmentation simplifies the device architecture while improving measurement precision through clean separation of noise and detection signal samples.
Solution Approach 2:
The system uses periodic action to alternate between noise sampling and detection signal sampling modes. This periodic alternation creates a structured sampling pattern where noise samples and detection signal samples are taken at different times but can be processed together. The periodic nature of this alternation provides a simple yet effective way to separate signals without requiring complex simultaneous sampling hardware, thus reducing device complexity while maintaining high measurement precision.
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 noise interference, enhances the accuracy of fingertip detection, and increases the refresh rate of the digitizer sensor while decreasing power consumption.
Implementation Method 1
sampling outputs transferred to a second conductive element that is capacitively coupled to the at least one conductive element in response to providing the signal generated to the at least one conductive element
Data Source
AI summary
A method for capacitive based detection with a digitizer sensor including a plurality of conductive elements that are capacitively coupled is described. The method includes generating a drive signal including transient sections separated in time by flat sections, providing the drive signal generated to at least one conductive element of the digitizer sensor, and sampling outputs transferred to a second conductive element that is capacitively coupled to the at least one conductive element in response to providing the signal generated to the at least one conductive element. The sampling events of the sampling are timed to take place both in response to the transient sections of the drive signal and to the flat sections of the drive signal.