Touch Detection Circuit Vector Subtraction S/N Ratio
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Solution Overview
Problem
Existing touch sensing technologies face challenges in improving the signal-to-noise (S/N) ratio, particularly when using sine or triangular wave signals, which can lead to phase noise components deteriorating sensitivity due to insufficient polarity inversion margins.
Innovation Solution
The proposed solution involves performing a Fourier transform on the response signal to separate amplitude and phase components, and using a touch sensing circuit with a baseline vector manager and vector subtraction circuit to calculate a delta vector, enhancing the S/N ratio by focusing on the amplitude component and suppressing phase noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rectangular wave signal is used as the sensing wave signal and integration is performed to improve touch sensing sensitivity, then the touch sensing sensitivity is improved, but the S/N ratio of the response signal is insufficient
Solution Approach 1:
The patent segments the response signal into multiple frequency components using Fourier series expansion. By analyzing each frequency component separately and weighting them according to their signal-to-noise ratios, the system can improve overall sensitivity while maintaining high S/N ratio. This segmentation allows selective enhancement of useful signal components while suppressing noise.
Solution Approach 2:
The patent changes the parameter of signal representation from time domain to frequency domain. By transforming the response signal into frequency components and adjusting the weighting coefficients based on frequency-dependent noise characteristics, the system optimizes the balance between sensitivity and S/N ratio. This parameter transformation enables noise suppression while preserving touch sensing sensitivity.
2Reliability
If the frequency of the sensing wave signal is increased to improve S/N ratio, then the S/N ratio is improved, but the phase noise components deteriorate sensitivity
Solution Approach 1:
The patent segments the sensing wave signal into multiple frequency components using Fourier series. By processing each frequency component separately and applying appropriate weighting, the system can utilize higher frequency components for improved S/N ratio while suppressing phase noise effects. This segmentation allows independent optimization of signal quality at different frequencies.
Solution Approach 2:
The patent employs feedback mechanisms to continuously monitor and adjust the weighting coefficients of different frequency components. By feedback-based optimization, the system can adaptively balance the contribution of each frequency component to maximize both S/N ratio and sensitivity, preventing phase noise from degrading performance.
Data Source
AI summary
Provided is a touch sensing circuit configured to sense an approach of a conductive object toward a sensor capacitor through measuring a sensor response signal generated by the sensor capacitor in response to a sensing wave signal applied to the sensor capacitor. The touch sensing circuit is connectable to a conversion circuit and a touch detection circuit. The conversion circuit calculates a response signal vector for a frequency component of the sensing wave signal by converting the response signal into a frequency domain representation. The touch sensing circuit includes a baseline vector manager circuit holding a baseline vector and a vector subtraction circuit, and calculates a delta vector which is the vector difference between the baseline vector and the response signal vector received from the conversion circuit. The touch detection circuit detects an approach of a conductive object towards the sensor capacitor on the basis of the calculated delta vector.