Electrostatic Capacitance Sensor Noise Reduction via Segmentation
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Solution Overview
Problem
Existing electrostatic capacitance sensors face increased noise-induced error due to a large number of non-detection-target capacitors, which affects the accuracy of mutual capacitance detection, especially when noise is superimposed on the reference voltage.
Innovation Solution
The sensor design includes a driver capable of independently changing voltages of drive electrodes, a reference voltage generator, and a detection signal generator with a controller that maintains detection electrodes at a reference voltage, reducing noise-induced errors by minimizing charge transfer from non-detection-target capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the number of drive electrodes is increased to improve detection coverage, then the detection area is improved, but the noise-induced error increases due to more non-detection-target capacitors
Solution Approach 1:
The patent segments the capacitors into detection-target capacitors and non-detection-target capacitors. By selectively applying drive signals only to detection-target capacitors and maintaining reference voltage on non-detection-target capacitors, the system isolates the detection function from noise-inducing elements, thereby maintaining measurement accuracy while preserving detection area coverage.
Solution Approach 2:
The patent applies different voltage conditions to different groups of capacitors: detection-target capacitors receive drive signals for active measurement, while non-detection-target capacitors are held at reference voltage to minimize noise. This local differentiation allows the system to optimize each capacitor's function according to its role, reducing overall noise-induced error while maintaining comprehensive detection coverage.
2Speed
If drive signals are applied to all drive electrodes simultaneously, then the detection speed is improved, but the charge transfer from non-detection-target capacitors increases causing more noise
Solution Approach 1:
The patent implements periodic switching of drive signals to different drive electrodes in sequence rather than simultaneously. The switch circuit alternates between connecting drive electrodes to drive signals and reference voltage in a time-multiplexed manner. This periodic action maintains detection speed by continuously cycling through all electrodes while minimizing noise by ensuring that at any given moment, only detection-target capacitors are actively driven.
Solution Approach 2:
The patent applies preliminary action by pre-charging or pre-discharging non-detection-target capacitors to reference voltage before the actual detection phase. This preliminary setup ensures that when drive signals are applied to detection-target capacitors, the non-detection-target capacitors are already in a stable reference state, preventing unwanted charge transfer and noise generation during the detection process.
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 configuration significantly reduces noise-induced errors in detection signals, maintaining accurate mutual capacitance measurements even with noise on the reference voltage, thereby enhancing the sensor's reliability.
Implementation Method 1
the operational amplifier OP1 controls the voltage Vout so that the detection electrode ES is maintained generally at the reference voltage Vr. Since the detection electrode ES is maintained at the reference voltage Vr, a voltage at the capacitor CM changes due to the drive signal. When the voltage at the capacitor CM changes, charge that is proportional to the electrostatic capacitance (the mutual capacitance) of the capacitor CM is transferred between the capacitor CM and the feedback capacitor Cf.
Implementation Method 2
Sensors based on a general mutual capacitance system detect electrostatic capacitances (mutual capacitances) of parasitic capacitors formed between different electrodes. Parasitic capacitors CM are respectively formed at portions where the detection electrode ES and the drive electrodes ED cross each other.
Data Source
AI summary
An electrostatic capacitance sensor includes: at least one detection electrode; drive electrodes, capacitors being respectively formed between the drive electrodes and the at least one detection electrode; a driver capable of causing voltages of the drive electrodes to change independently from each other; a reference voltage generator that generates a reference voltage; a detection signal generator that transfers charge so that a voltage of the at least one detection electrode approaches the reference voltage and that generates a detection signal according to the transfer of the charge; and a controller that controls the driver. The driver is capable of applying the reference voltage to each of the drive electrodes. When the driver causes a voltage of one or more of the drive electrodes to change, the controller controls the driver so as to apply the reference voltage to the remaining drive electrodes.