Capacitive Touch Sensing Circuit for Dual-Edge Accuracy
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Solution Overview
Problem
Conventional capacitive touch sensing circuits face accuracy issues during multiple counts in dual edge sensing due to errors caused by uneven division of sensing capacitance by feedback capacitance, leading to increased noise and reduced signal-to-noise ratio.
Innovation Solution
The capacitive touch sensing circuit incorporates additional switches to alter the polarity of the amplifier capacitor and employs an oversampling circuit with automatic charge compensation, allowing for improved accuracy by reducing errors and retaining residual charges for subsequent counting phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional capacitive touch sensing circuit performs multiple counts in dual edge sensing, then sensing coverage is improved, but measurement precision deteriorates due to errors caused by uneven division of sensing capacitance by feedback capacitance
Solution Approach 1:
The patent changes the operating parameters by performing sensing operations at multiple voltage levels (high voltage VH and low voltage VL) rather than a single voltage level. This allows the system to collect multiple measurements that can be averaged or processed to reduce errors from uneven capacitance division, thereby maintaining high sensing coverage while improving measurement precision through parameter variation and statistical processing.
2Productivity
If conventional capacitive touch sensing circuit performs multiple counts, then sensing capability is enhanced, but noise increases and signal-to-noise ratio deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where the results of multiple counting operations are processed together. By performing counts at both high and low voltage levels and comparing/averaging the results, the system can identify and eliminate noise components that vary between measurements, thereby enhancing sensing capability while suppressing noise through feedback-based error correction.
Solution Approach 2:
The patent employs periodic sensing operations alternating between high voltage and low voltage phases. This periodic action allows the system to collect multiple samples over time that can be processed to distinguish signal from noise, enhancing overall sensing capability while using the periodic nature of the measurements to filter out random noise through averaging or differential processing.
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 effectively reduces errors in dual edge sensing, improves accuracy, and enhances the signal-to-noise ratio by maintaining residual charges for subsequent counting phases.
Implementation Method 1
In a charge phase, a sensing capacitor Cb is coupled between an input voltage VIN and a ground terminal GND, and a feedback capacitor Cfb is coupled between a compensation voltage Vc and the ground terminal GND. Therefore, the input voltage VIN charges the sensing capacitor Cb and the compensation voltage Vc charges the feedback capacitor Cfb.
Implementation Method 2
In a transfer phase, the sensing capacitor Cb is coupled between the negative input terminal − of the operational amplifier 10 and the ground terminal GND, and the following Equation 1 can be obtained: VIN×Cb=VCM×Cb+(VCM−Vout)×Cop
Data Source
AI summary
A capacitive touch sensing circuit includes a first switch to a fourteenth switch, an operational amplifier, a comparator, a detection capacitor, a feedback capacitor, an amplifier capacitor and a mutual inductance capacitor. The tenth switch is coupled between a first node and a second node respectively coupled to a negative input terminal and an output terminal of operational amplifier. The amplifier capacitor is coupled between a third node and a fourth node. The eleventh switch is coupled between the first node and the third node. The twelfth switch is coupled between the second node and the fourth node. The thirteenth switch is coupled between the third node and the second node. The fourteenth switch is coupled between the fourth node and the first node. The capacitive touch sensing circuit sequentially operates under a first charging phase, a first transfer phase, a second charging phase and a second transfer phase.