DAC-Referenced Touch Sensing Waveforms for Low-EME Detection
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Solution Overview
Problem
Touch sensors emit electromagnetic emissions (EME) that exceed limits in certain applications, particularly in automotive environments, where traditional waveform shaping techniques using passive filters are inadequate and compromise sensing speed and do not account for non-linearities in touch sensor drivers.
Innovation Solution
The system configures a touch sensing system to generate shaped reference signals with arbitrary waveforms, using n-bit digital codes to control EME emissions by optimizing waveform shapes to meet specific EME limits across different frequency bands, and dynamically adjusts sampling rates to compensate for foreign noise, thereby reducing EME without the limitations of passive filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If passive filters are used to shape waveforms, then electromagnetic emissions are reduced, but sensing speed deteriorates
Solution Approach 1:
The patent replaces passive mechanical/electrical filters with a digital signal processing approach. A digital-to-analog converter (DAC) generates reference signals with pre-shaped waveforms that inherently produce lower electromagnetic emissions without requiring external passive filtering components. This substitution of the waveform generation mechanism eliminates the trade-off between emission reduction and sensing speed.
Solution Approach 2:
The patent changes the waveform parameters (shape, duration, amplitude profile) of the reference signal generated by the DAC to optimize electromagnetic emissions. By adjusting these parameters, the system achieves compliant emission levels while maintaining fast sensing performance, resolving the contradiction between emission reduction and speed.
2Object-generated harmful factors
If traditional waveform shaping is used, then electromagnetic emissions are reduced, but it fails to account for non-linearities in touch sensor drivers
Solution Approach 1:
The patent incorporates feedback mechanisms where the touch controller monitors the performance and adjusts the DAC reference signal waveform parameters accordingly. This feedback loop allows the system to compensate for non-linearities in the touch sensor drivers while maintaining compliant electromagnetic emissions, addressing both measurement precision and emission requirements.
Solution Approach 2:
The patent makes the reference signal waveform dynamic rather than static. The DAC can adjust waveform parameters in real-time based on operating conditions and detected non-linearities, allowing the system to optimize both emission compliance and sensing accuracy across different operating states.
3Object-generated harmful factors
If fixed waveform shapes are used, then electromagnetic emissions are controlled, but adaptability to different frequency bands and standards is limited
Solution Approach 1:
The patent implements a universal waveform generation system through the DAC that can produce multiple waveform shapes and frequency profiles. This single device serves multiple functions by generating different reference signal patterns suitable for various frequency bands and electromagnetic emission standards, eliminating the need for application-specific hardware modifications.
Solution Approach 2:
The system dynamically adjusts waveform parameters including shape, frequency, and duration based on the required emission standard and application requirements. This dynamic adaptability allows the same touch sensing system to comply with different EME standards (such as CISPR 25 for automotive) without hardware changes, resolving the contradiction between emission control and versatility.
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.