Differential Capacitance Sensing Circuit for Noise-Resistant Touch Detection
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Solution Overview
Problem
Capacitive sensors in electronic products face challenges in improving anti-interference ability and sensitivity, affecting user interaction experiences.
Innovation Solution
A capacitance detecting circuit is designed with two front-end circuits and a processing circuit, utilizing calibration capacitors and charging/discharging circuits to convert capacitance signals into voltage signals, and calculating differential signals to determine capacitance variations, thereby enhancing detection efficiency and noise immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional capacitance detecting circuit is used, then the circuit structure is simple, but the anti-interference ability and sensitivity are insufficient
Solution Approach 1:
The capacitance detecting circuit is divided into multiple independent front-end circuits (first front-end circuit and second front-end circuit), each with its own calibration capacitor and integrating circuit. This segmentation allows parallel processing of capacitance signals through different paths, enabling differential calculation to eliminate noise and interference while maintaining manageable circuit complexity through modular design
Solution Approach 2:
Calibration capacitors are introduced as intermediary elements to compensate for parasitic capacitances and interference signals. The calibration capacitors are specifically designed to match the parasitic capacitance values, acting as mediators that cancel out unwanted signals through differential processing, thereby improving anti-interference ability without significantly increasing overall circuit complexity
2Measurement precision
If a conventional capacitance detecting circuit is used, then the circuit structure is simple, but the sensitivity is insufficient
Solution Approach 1:
The circuit is segmented into multiple front-end detection paths that operate in parallel. Each path processes capacitance signals independently through its own integrating circuit, and the results are combined through differential calculation. This segmentation enhances sensitivity by allowing the system to detect small capacitance variations more accurately while keeping each individual circuit module relatively simple
Solution Approach 2:
The circuit implements feedback through the calibration process where calibration capacitors are used to measure and compensate for parasitic capacitances. This feedback mechanism continuously corrects for interference and improves measurement precision, enabling high sensitivity detection without requiring overly complex circuit structures
3Reliability
If differential processing is performed on voltage signals, then the signal-to-noise ratio is improved, but the device complexity increases
Solution Approach 1:
The processing circuit is segmented into dedicated differential calculation units that receive inputs from multiple front-end circuits. This segmentation allows the differential processing to be performed in a modular fashion, improving signal-to-noise ratio through systematic noise cancellation while maintaining processing circuit complexity at acceptable levels through functional decomposition
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
The solution improves the signal-to-noise ratio and sensitivity of the capacitance detecting circuit, leading to better user interaction experiences by effectively canceling out noise signals and accurately detecting capacitance variations.
Implementation Method 1
a capacitor (or referred to as a base capacitor) is formed between a detection electrode and ground. When a conductor (such as a finger) approaches or touches the detection electrode, a capacitance between the detection electrode and the ground changes
Implementation Method 2
the first integrating circuit is configured to convert the capacitance signal of the detection capacitor into the first voltage signal through the first calibration capacitor
Data Source
AI summary
A capacitance detecting circuit, includes a first front end circuit, a second front end circuit, a control circuit and a processing circuit, wherein the control circuit controls the first front end circuit and the second front end circuit such that the first front end circuit is configured to convert a capacitance signal of a detection capacitor into a first voltage signal through a first calibration capacitor, and the second front end circuit is configured to convert a capacitance signal of the detection capacitor into a second voltage signal through a second calibration capacitor; the processing circuit is calculates a differential signal of the first voltage signal and the second voltage signal to determine a capacitance variation of the detection capacitor according to the differential signal.