Capacitive Proximity Sensor Switching to Limit Parasitic Capacitance
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Solution Overview
Problem
Capacitive proximity sensors are affected by parasitic capacitances that reduce sensitivity due to increased charging and discharging currents, which are caused by the integration of analog switches with parasitic capacitances between switching contacts and supply voltage terminals.
Innovation Solution
Implement a capacitive proximity sensor with an active switching device that synchronizes the switch supply potentials with the switching operation, reducing the influence of parasitic capacitances by alternating the high and low supply potentials during charging and discharging phases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an integrated analog switch is used to cyclically charge and discharge the measuring capacitance, then the switching function is achieved, but parasitic capacitances increase the total capacitance and reduce sensor sensitivity
Solution Approach 1:
The patent extracts the harmful parasitic capacitance effect by introducing a compensation capacitance that is specifically designed to counterbalance the parasitic capacitance of the switching device. This allows the switching function to be maintained while the harmful effect is actively compensated for, restoring measurement precision.
Solution Approach 2:
The patent changes the parameter of capacitance by introducing an adjustable compensation capacitance that can be tuned to match and counterbalance the parasitic capacitance. This parameter adjustment allows the system to operate with high sensitivity despite the presence of the analog switch's parasitic capacitance.
2Measurement precision
If parasitic capacitance is compensated for, then sensor sensitivity is improved, but the device complexity increases due to additional compensation components
Solution Approach 1:
The patent merges the compensation function with the existing switching operation by using the same switching device to alternately connect both the measuring capacitance and the compensation capacitance to the voltage source. This integrated approach achieves sensitivity improvement without requiring completely separate compensation circuitry.
Solution Approach 2:
The system uses its own switching device to perform the compensation function, rather than requiring an external dedicated compensation mechanism. The switching device serves dual purposes: both switching the measuring capacitance and enabling parasitic capacitance compensation through the compensation capacitance.
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 significantly reduces the impact of parasitic capacitances, maintaining the sensitivity of the sensor to changes in the measuring capacitance by minimizing charge transfer through these capacitances, thereby enhancing the sensor's performance.
Implementation Method 1
A capacitance develops between the probe and the object to be detected, depending on the distance between the probe and the object
Implementation Method 2
the measuring capacitance is cyclically charged to a defined voltage potential via a switch and then discharged to a further voltage potential. The charging and/or discharging current is taken as a measure of the size of the measuring capacitance
Data Source
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AI summary
The invention relates to a capacitive proximity sensor (5) for detecting an object (2) within a detection region (E) and for providing a sensor output voltage (VSens, Vout), comprising: - an electrically conductive probe (3); - a charging circuit (13) and/or a discharging circuit (14) for cyclically charging a measurement capacitor (CM) positioned on the probe (3) to a charge potential (Vlad) during a charging phase or for discharging the measurement capacitor (CM) positioned on the probe (3) to a discharge potential (Ventlad) during a discharging phase, wherein the charging circuit (13) and/or the discharging circuit (14) is designed to provide an output voltage (V(I1)) on the basis of a charging current (I1) to the measurement capacitor (CM) and/or an output voltage (V(I2)) on the basis of a discharge current (I2) from the measurement capacitor (CM), said sensor output voltage (VSens) being provided on the basis of the output voltage(s) (V(I1), V(I2)); - an active switchover device (11) for electrically connecting the probe (3) to the charging circuit (13) and the discharging circuit (14) in an alternating manner; and - a switch supply voltage source (20) which is designed to cyclically switchover between switch supply potentials (Vvers1, Vvers2) for electrically supplying the active switchover device (11) in a synchronous manner in order to switch over between the charging phase and the discharging phase.