Self-Capacitive Touch Sensing Circuit for Frequency-Shifted Noise Filtering
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Solution Overview
Problem
Self-capacitive touch panels face challenges in distinguishing signal from noise due to close frequency ranges, leading to poor signal-to-noise ratios and increased manufacturing costs due to the need for additional hardware to suppress noise.
Innovation Solution
A self-capacitive touch sensing circuit with an operational amplifier, internal capacitor, and switching mechanism that adjusts charging voltages to move noise to a higher frequency band, allowing for effective separation of signal and noise using a low-pass filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple low-pass filter is used to filter noise, then the circuit complexity is reduced, but the noise suppression effectiveness is insufficient because the noise frequency is too close to the signal frequency
Solution Approach 1:
The patent changes the frequency parameter of the noise by modulating it to a higher frequency band where it can be effectively separated from the DC-level signal. This frequency transformation allows simple filtering to become effective, resolving the contradiction between circuit simplicity and noise suppression effectiveness.
2Object-affected harmful factors
If additional hardware is added to increase signal-to-noise ratio, then the noise suppression effectiveness is improved, but the manufacturing cost increases
Solution Approach 1:
The patent transforms the noise frequency parameter to a higher band through modulation, enabling effective noise separation using existing simple circuit components. This approach achieves improved signal-to-noise ratio without requiring additional expensive hardware, thus resolving the contradiction between noise suppression effectiveness and manufacturing cost.
3Measurement precision
If the self-capacitive touch sensing circuit is placed closer to the panel to reduce distance from finger signal source, then the signal strength is improved, but the susceptibility to noise from reversing liquid crystals increases
Solution Approach 1:
The patent changes the frequency domain characteristics of the noise signal through modulation, transforming it to a higher frequency band. This allows the circuit to maintain close proximity to the panel for strong signal reception while the frequency-separated noise can be easily filtered out, resolving the contradiction between signal strength and noise susceptibility.
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 enhances the signal-to-noise ratio, reduces capacitance driving time and power consumption, and improves touch sensing performance, especially in high-noise environments.
Implementation Method 1
the self-capacitive touch sensing circuit charges the capacitor Cext to a first external charging voltage V1 under a first phase, so that the charge amount stored in the capacitor Cext is a product of the capacitor Cex and the first external charging voltage V1
Data Source
AI summary
A self-capacitive touch sensing circuit including an operational amplifier, an internal capacitor, a first switch and a second switch is disclosed. A first input terminal and a second input terminal of operational amplifier are coupled to a capacitor and ground respectively and an output terminal of operational amplifier outputs an output voltage. The internal capacitor is coupled between the output terminal and first input terminal of operational amplifier. One terminal of first switch is coupled to a first external charging voltage and another terminal of first switch is coupled between the capacitor and the first input terminal. The first external charging voltage is higher than the second external charging voltage. The first switch and second switch are switched according to a specific order, so that the first external charging voltage or second external charging voltage will charge the capacitor.