Capacitance Sensing Circuit With Reference-Potential Feedback
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Solution Overview
Problem
Existing capacitance detection devices require a large number of switch manipulations to achieve accurate detection, leading to increased detection time and reduced accuracy due to low-frequency noise and power supply fluctuations.
Innovation Solution
A capacitance detection device with a variable capacitance capacitor and control circuit that controls the intermediate potential to a reference potential, using a differential amplifier circuit to detect capacitance based on the ratio between the variable capacitance capacitor and the detection target, allowing for faster detection without compromising accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of times of switch manipulations is increased to improve detection accuracy, then the detection accuracy is improved, but the time required for detection increases and low-frequency noise influence becomes remarkable
Solution Approach 1:
The control circuit preliminarily adjusts the capacitance of the variable capacitance capacitor to a predetermined value before performing the binary search method. This preliminary action sets the intermediate potential close to the reference potential, reducing the number of binary search iterations needed and thereby shortening detection time while maintaining accuracy
Solution Approach 2:
The patent replaces the traditional mechanical counting method (manually counting switch manipulation times) with an automatic binary search algorithm implemented in the control circuit. This substitution enables rapid convergence to the target capacitance value through logarithmic complexity O(log n) instead of linear complexity, dramatically reducing detection time
2Measurement precision
If the number of times of switch manipulations is increased to improve detection accuracy, then the detection accuracy is improved, but the fluctuation width of power supply increases
Solution Approach 1:
The control circuit preliminarily adjusts the capacitance to a predetermined value that brings the intermediate potential close to the reference potential. This preliminary action reduces the total number of switch manipulations required in the binary search, thereby minimizing the duration of detection and reducing the accumulation of power supply fluctuations and low-frequency noise
Solution Approach 2:
The control circuit continuously monitors the intermediate potential and uses feedback from the differential amplifier to adjust the capacitance of the variable capacitance capacitor. This feedback mechanism enables precise control with fewer adjustments, reducing the time the system operates and thereby reducing the impact of power supply instability
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 significantly reduces the time required for capacitance detection while maintaining high accuracy by controlling the intermediate potential and using a differential amplifier circuit to enhance detection resolution and error suppression.
Implementation Method 1
a differential amplifier circuit, which receives input of the intermediate potential and the reference potential, and outputs a voltage signal according to a difference between the intermediate potential and the reference potential
Implementation Method 2
a variable capacitance capacitor... manipulating a capacitance of the variable capacitance capacitor to control an intermediate potential
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A capacitance detection device (30) includes: a variable capacitance capacitor (11); an electrode (34) constituting a detection target whose capacitance is to be detected; and a control circuit (18, 18a, 18b, 18c, 18d, 18e), in which the control circuit is configured for: manipulating (S1) a capacitance of the variable capacitance capacitor to control an intermediate potential (Vout), which is a potential at a connection point (N1) between the variable capacitance capacitor and the electrode, to a reference potential (Vref), when a voltage of a voltage application device (31) is applied to the electrode via the variable capacitance capacitor; and detecting (S2, S3, S4) the capacitance of the detection target, based on the capacitance of the variable capacitance capacitor when being controlled to the reference potential.