Capacitive Sensing Circuit With FET Buffer for Low-Power Gesture Detection
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Solution Overview
Problem
Conventional capacitive sensor systems for gesture recognition and object detection are costly, power-intensive, and have high component and space requirements, making them unsuitable for battery-operated applications and mass production, such as in the toy industry.
Innovation Solution
A capacitive sensor system with a low-component circuit arrangement using a field-effect transistor (FET) as an input stage, an XOR gate, and a microcontroller for signal processing, which reduces power consumption and costs by minimizing parasitic capacitance and using pulsed operation, allowing for low-power, low-cost, and compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional capacitive sensor systems are used for gesture recognition and object detection, then detection functionality is achieved, but power consumption is high and component costs are high
Solution Approach 1:
The patent implements pulsed operation where the sensor circuit is activated only during specific time intervals rather than continuously. The microcontroller enables the sensor circuit selectively, and the XOR gate operates on periodic clock cycles to detect capacitance changes. This periodic activation dramatically reduces power consumption while maintaining detection functionality through time-multiplexed sensing operations.
Solution Approach 2:
The patent changes the operational parameters of the sensor circuit by using variable pulse widths and duty cycles. The microcontroller can adjust the timing and duration of sensor activation based on detection needs, optimizing the balance between power consumption and detection sensitivity. This parameter adjustment allows the system to maintain reliable detection while minimizing energy usage during idle periods.
2Measurement precision
If conventional capacitive sensor systems are used, then gesture detection is achieved, but component count and space requirements are high
Solution Approach 1:
The patent merges multiple functions into a single integrated circuit arrangement. The field-effect transistor serves as both the sensing element and the signal amplification stage. The XOR gate combines the clock signal processing and capacitance detection functions. The microcontroller integrates signal generation, processing, and control functions. This consolidation reduces component count and board space while maintaining gesture detection accuracy through optimized signal processing within the integrated architecture.
Solution Approach 2:
The sensor circuit is designed with universal functionality to detect both object approach and gestures using the same hardware components. The capacitive sensing mechanism responds to any object that disturbs the electric field, whether it's a hand approaching or performing gestures. The single circuit arrangement handles multiple detection modes without requiring separate dedicated circuits for each function, reducing overall system complexity.
3Measurement precision
If base capacitance is minimized for maximum sensitivity, then sensor sensitivity increases, but parasitic capacitance becomes more significant
Solution Approach 1:
The patent introduces a field-effect transistor as an intermediary element between the capacitive sensor and the readout circuitry. The FET's high input impedance acts as a buffer that isolates the sensitive capacitive sensing node from parasitic capacitances in subsequent stages. This intermediary stage allows the sensor to operate with minimal base capacitance for maximum sensitivity while the FET protects against parasitic capacitance interference by preventing direct coupling of parasitic elements to the sensing node.
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 achieves high sensitivity and low power consumption, enabling long battery life and cost-effective implementation, with the ability to detect 2- or 3-dimensional positions and gestures while reducing component and space requirements, suitable for battery-operated devices and mass production.
Implementation Method 1
the approach or movement, typically of a hand or finger, is detected based on electric near fields
Implementation Method 2
the evaluation of the capacitance change of an RC low-pass filter is a known method
Data Source
Figure 1a~1b
Figure 2~3
Figure 4~5
AI summary
The invention relates to a capacitive sensor system, in particular for detecting the approach of objects and in particular also for gesture recognition. The problem of the present invention is to provide a capacitively operating sensor system, which can be implemented with low component complexity and thus low costs and space requirements and is also characterized by low power consumption, so as to operate with batteries having a low charge capacity and/or a long operating time. Said problem is solved according to the invention by a circuit configuration for generating an output signal correlating with an approximation process based on changes in the dielectric properties of the surroundings of a sensor electrode, having a sensor electrode which is adjacent to an observation area in at least some sections, a microcontroller circuit (µC) for output of an alternating voltage, a voltage divider circuit for achieving an adjustment of the level of the alternating voltage output by the microcontroller (µC), and a field effect transistor (FET) in the function of an impedance converter, wherein the field effect transistor is incorporated into the circuit configuration in such a way that the voltage output by the voltage divider circuit is present at the gate input thereof and at the same time at the sensor electrode (ES).