Capacitance Detection Circuit for Parasitic Capacitance Suppression
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Solution Overview
Problem
Self-capacitance type capacitance detection devices face reduced detection sensitivity due to parasitic capacitance, which cannot be completely eliminated by conventional active shields, leading to saturated output voltages and limited dynamic range.
Innovation Solution
A capacitance detection device with a first and second alternating current voltage output circuit, and an operational amplifier that adjusts the second voltage output to ensure the output voltage has a smaller amplitude than the first when no detection target is present, thereby increasing the dynamic range and reducing parasitic capacitance effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If self-capacitance type detection is used to achieve high detection sensitivity, then detection sensitivity is improved, but parasitic capacitance reduces the dynamic range and lowers detection sensitivity
Solution Approach 1:
A shield electrode is introduced as an intermediary component between the detection electrode and the surrounding environment. This shield electrode, when driven at the same potential as the detection electrode, acts as a mediator to reduce capacitive coupling with surrounding conductors, thereby decreasing parasitic capacitance effects while preserving the high detection sensitivity of self-capacitance type detection.
Solution Approach 2:
The potential of the shield electrode is changed to match the detection electrode's potential dynamically. By adjusting the shield electrode's potential parameter to be equal to the detection electrode's potential, the electric field distribution is modified, reducing parasitic capacitance coupling without affecting the detection electrode's sensitivity to target objects.
2Object-affected harmful factors
If active shield is provided to reduce parasitic capacitance, then parasitic capacitance is reduced, but output voltage saturation occurs and sufficiently high detection sensitivity cannot be obtained
Solution Approach 1:
The shield electrode's potential is made dynamic rather than static. By driving the shield electrode with an alternating current voltage at the same frequency as the detection electrode, the system adaptively reduces parasitic capacitance effects throughout the detection cycle, preventing output voltage saturation while maintaining high detection sensitivity.
Solution Approach 2:
Both the detection electrode and shield electrode are driven with alternating current voltages at the same frequency. This periodic action creates a synchronized electromagnetic field environment where the shield electrode continuously counteracts parasitic capacitance effects, preventing saturation and enabling sustained high detection sensitivity.
3Object-affected harmful factors
If shield electrode is driven at same potential as detection electrode, then parasitic capacitance is reduced, but capacitance variations in parasitic capacitance become noise
Solution Approach 1:
The shield electrode is pre-configured and driven at the same potential as the detection electrode before the actual detection process. This preliminary action establishes a controlled electromagnetic environment that minimizes parasitic capacitance variations from occurring, thereby reducing noise generation at its source rather than attempting to filter it afterward.
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 detection sensitivity by reducing output voltage saturation and noise, allowing for higher sensitivity and resistance to noise interference.
Implementation Method 1
an operational amplifier that amplifies the difference in voltage between an inverting input terminal connected to the detection electrode and a non-inverting input terminal to which the second alternating current voltage is applied
Implementation Method 2
detects a capacitance between a detection electrode and a detection target close to the detection electrode
Data Source
AI summary
A capacitance detection device detecting a capacitance between a detection electrode and a detection target close to the detection electrode has: a first voltage output circuit that outputs a first alternating current voltage to be supplied to a shield electrode placed close to the detection electrode; a second voltage output circuit that outputs a second alternating current voltage with substantially the same frequency as the first alternating current voltage; and an operational amplifier that amplifies the difference in voltage between an inverting input terminal connected to the detection electrode and a non-inverting input terminal to which the second alternating current voltage is applied, and outputs the amplified difference in voltage. With the detection target close to the detection electrode, the second voltage output circuit outputs the second alternating current voltage adjusted so that an output voltage from the operational amplifier has a smaller amplitude than the first alternating current voltage.