Touch Panel Drive Waveforms for Lower EMI Harmonics
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Solution Overview
Problem
Existing touch sensing technologies face challenges in reducing electromagnetic interference (EMI) among capacitive sense elements, which is crucial for meeting specific radio disturbance limits set by standards like CISPR.
Innovation Solution
Implementing phase shifts and flat-peak sinusoidal waveforms in drive signals for capacitive sensing arrays to reduce EMI harmonic amplitudes, and using phase offsets among drive signals to create new harmonics with smaller amplitudes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional drive signals are used for capacitive sensing arrays, then the sensing function is achieved, but electromagnetic interference harmonic amplitudes exceed radio disturbance limits
Solution Approach 1:
The patent applies phase shifts to the drive signals, changing the temporal parameters of the signaling waveform. By introducing phase offsets between different drive signals, the harmonic content is modified to reduce EMI amplitudes while maintaining sensing functionality. This parameter modification directly addresses the contradiction by transforming the signal characteristics to meet radio disturbance limits.
Solution Approach 2:
The patent employs periodic phase modulation of the drive signals, where the phase shifts are applied in a systematic periodic manner across different sensing elements. This periodic action creates a structured pattern in the harmonic distribution that reduces peak EMI amplitudes, allowing the system to comply with radio disturbance regulations while maintaining effective capacitive sensing.
2Object-affected harmful factors
If phase shifts are applied to drive signals to reduce EMI harmonics, then radio disturbance limits are met, but signal synchronization complexity increases
Solution Approach 1:
The patent divides the capacitive sensing array into multiple groups or segments, where phase shifts are applied systematically to different segments. This segmentation approach allows the complex phase control to be managed in a modular fashion, reducing the overall system complexity while still achieving EMI reduction across the entire array.
Solution Approach 2:
The patent implements dynamic phase adjustment where the phase shifts are adaptively controlled based on the sensing requirements and EMI conditions. This dynamic approach allows the system to optimize the phase parameters in real-time, simplifying the control complexity by using feedback mechanisms rather than fixed complex phase relationships.
Data Source
AI summary
This application is directed to sensing touch events on a touch sensing panel including a capacitive sensor array. The capacitive sensor array includes a plurality of touch sensing regions and is coupled to a processing device. The processing device identifies, and generates drive signals for, the touch sensing regions of the touch sensing panel. Each drive signal corresponds to a distinct touch sensing region and includes a respective train of periodic pulses. For each drive signal, the respective train of periodic pulses has a respective phase offset with respect to a reference (e.g., a train of periodic pulses of one of the plurality of drive signals, a fixed reference time). While applying the drive signals on the touch sensing regions, the processing device measures capacitance sensing signals from the touch sensing regions. Touch events are detected on the capacitive sensor array based on the capacitance sensing signals.