Spectrally Shaped Touch Drive Signals for EME Reduction
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Solution Overview
Problem
Current touch sensing systems face challenges in optimizing drive signal energy allocation across multiple frequencies to minimize electromagnetic emissions (EME) while maintaining noise immunity, which affects the accuracy and efficiency of touch detection.
Innovation Solution
The implementation of spectrally shaped drive signals, where energy is allocated across specific frequencies, using RF subcarriers with chosen frequencies and amplitudes that prioritize low EME and noise immunity, generated through digital modulation techniques such as quadrature amplitude modulation (QAM) and phase-shift keying, to optimize touch sensing operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If drive signal energy is concentrated at single frequency, then noise immunity is improved, but electromagnetic emissions increase
Solution Approach 1:
The drive signal energy is segmented across multiple frequency subcarriers rather than concentrated at a single frequency. The controller allocates energy to different frequency components (e.g., 1 MHz, 2 MHz, 3 MHz subcarriers) to achieve spectral shaping, which distributes electromagnetic emissions across multiple frequencies while maintaining overall noise immunity through coherent integration during signal processing.
Solution Approach 2:
The system changes the spectral parameters of the drive signal by adjusting the amplitude and phase of individual frequency subcarriers. By modifying these parameters, the controller achieves desired spectral shaping that reduces peak electromagnetic emissions while maintaining sufficient signal energy for reliable touch detection through optimized energy allocation across the frequency spectrum.
2Object-generated harmful factors
If drive signal energy is distributed across multiple frequencies, then electromagnetic emissions are reduced, but noise immunity deteriorates
Solution Approach 1:
The controller performs preliminary spectral shaping of the drive signal before transmission by pre-calculating and pre-allocation of energy across multiple frequency subcarriers. This preliminary action ensures that the signal is optimally configured to minimize electromagnetic emissions while maintaining noise immunity, using techniques such as windowing and spectral masking before the signal is applied to the touch sensor.
Solution Approach 2:
The system employs feedback mechanisms where the controller monitors the actual electromagnetic emissions and touch detection performance, then adjusts the spectral allocation of drive signal energy accordingly. By measuring the effectiveness of different frequency allocations and using this feedback to optimize future signal configurations, the system maintains noise immunity while minimizing emissions.
3Object-generated harmful factors
If spectral shaping is implemented, then electromagnetic emissions are minimized, but device complexity increases
Solution Approach 1:
The system replaces complex hardware-based spectral shaping circuits with software-based signal processing algorithms implemented in a touch controller. Instead of using multiple physical oscillators and filters to generate spectrally shaped signals, the controller uses digital signal processing techniques such as inverse fast Fourier transform (IFFT) and digital modulation to achieve spectral shaping, significantly reducing hardware complexity while maintaining emission control capabilities.
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 EME and enhances noise immunity, allowing for more accurate and efficient touch detection by allocating energy optimally across frequencies, thereby improving the overall performance of touch sensing systems.
Implementation Method 1
A typical touch interface system may incorporate touch sensors (e.g., capacitive sensors and/or resistive sensors, without limitation) that respond to an object in close proximity to, or physical contact with, a contact sensitive surface of a touch interface system.
Implementation Method 2
Current touch sensing systems face challenges in optimizing drive signal energy allocation across multiple frequencies to minimize electromagnetic emissions (EME) while maintaining noise immunity
Data Source
AI summary
A method for determining a spectrally shaped waveform, and related apparatus, are described. In one or more example, such a spectrally shaped waveform may be for touch sensing. An example of such a method includes: receiving an indication of allowable electromagnetic emissions; choosing radio frequency subcarriers responsive to the indication of allowable electromagnetic emissions; and generating and storing a spectrally shaped time domain digital waveform responsive to the chosen radio frequency subcarriers.