DAC-Referenced Touch Sensing Waveforms for Low Electromagnetic Emissions
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Solution Overview
Problem
Touch sensors emit electromagnetic emissions that exceed limits in certain applications, particularly in automotive environments, due to the waveform shape of driver reference signals, and existing passive filtering techniques fail to meet stringent emission standards across different regions and frequency bands, while also compromising sensing speed and not compensating for non-linearities.
Innovation Solution
The system configures touch sensing systems to generate shaped reference signals using n-bit digital codes, allowing for arbitrary waveforms with monotonic and non-monotonic portions, which are optimized to minimize electromagnetic emissions within defined limits by dynamically selecting fundamental frequencies and waveform shapes based on application-specific requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If traditional touch sensors use standard waveform reference signals, then the sensing operation is simple and fast, but electromagnetic emissions exceed regulatory limits in certain applications
Solution Approach 1:
The patent applies parameter changes by modifying the waveform shape parameters of the reference signal generated by the DAC. Specifically, it adjusts the monotonicity parameter of the waveform to create different shapes (monotonic vs. non-monotonic transitions) that control harmonic content and electromagnetic emissions. This allows the system to meet emission standards by changing waveform parameters rather than adding complex filtering hardware.
Solution Approach 2:
The system implements dynamics by making the waveform shape adaptive rather than fixed. The controller can dynamically select between different waveform shapes (monotonic or non-monotonic) based on the specific application requirements and emission standards. This dynamic adaptation allows the same touch sensor system to comply with different regional standards without hardware modifications.
2Object-generated harmful factors
If passive filtering techniques are used to reduce electromagnetic emissions, then emissions are reduced, but sensing speed is compromised
Solution Approach 1:
The patent extracts the emission control function from the traditional passive filtering approach and relocates it to the waveform generation stage. Instead of adding filters to reduce emissions after the fact, the system extracts and controls the harmful harmonic content at the source by shaping the reference waveform. This eliminates the need for speed-compromising passive filters while maintaining fast sensing performance.
Solution Approach 2:
The system replaces the mechanical/passive filtering approach with a software-controlled digital waveform generation method. The DAC-controlled waveform shaping substitutes for physical filters, achieving emission reduction through digital signal processing rather than analog filtering. This substitution maintains sensing speed because the shaped waveforms are generated digitally without introducing the bandwidth limitations of passive filters.
3Object-generated harmful factors
If passive filtering is applied to control electromagnetic emissions, then emissions are reduced, but the system cannot compensate for non-linearities
Solution Approach 1:
The patent applies preliminary action by pre-shaping the reference waveform to account for and compensate for non-linearities before they occur in the sensing operation. The monotonic or non-monotonic waveform shapes are designed in advance to counteract expected non-linear effects, ensuring accurate sensing while controlling emissions. This preliminary compensation is more effective than attempting to correct non-linearities after they occur.
Data Source
AI summary
Some disclosed embodiments relate, generally, to shaping a waveform of a reference signal used by a driver of a touch sensor to limit electromagnetic emissions (EME) emitted by a touch sensor during a sensing operation. Some disclosed embodiments relate, generally, to a DAC referenced touch sensor driver and controlling an amount of EME emitted at a touch sensor using shapes of reference signals used by a touch detector to detect touches at the touch sensor. Some disclosed embodiments relate, generally, to compensating for effects of foreign noise at a touch sensor and, more specifically, to changing a shape of a reference signal based on a change to a sampling rate made to compensate for foreign noise.