Capacitance Detection Circuit Using Active Shield Amplitude Tuning
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Solution Overview
Problem
Capacitance detection devices face reduced detection sensitivity and accuracy due to the presence of parasitic capacitors, which are not completely eliminated by conventional active shields, leading to noise and reduced dynamic range.
Innovation Solution
A capacitance detection device with a first and second voltage output circuit and a current output circuit, where the second voltage output circuit generates an alternating current voltage with adjusted amplitude to cancel out the alternating current through the parasitic capacitor, and a current output circuit that outputs a detection signal with minimal parasitic components, using an attenuator and capacitive components to improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shield electrode is arranged around the detection electrode to reduce parasitic capacitor, then the capacitance of the parasitic capacitor is reduced, but the residual parasitic capacitor still affects detection sensitivity and accuracy
Solution Approach 1:
A correction electrode is introduced as an intermediary element between the detection electrode and the parasitic capacitor source. This correction electrode is driven at a potential that actively counteracts the parasitic coupling, serving as a mediator to cancel the harmful electrostatic interference without requiring direct modification of the detection electrode or complete elimination of the parasitic path.
Solution Approach 2:
The potential of the correction electrode is dynamically adjusted to match the potential of the detection electrode, and the amplitude of the alternating current voltage applied to the correction electrode is optimized to exactly cancel the parasitic current. By changing the electrical parameters (potential and current amplitude) of the correction electrode, the parasitic capacitor effect is nullified, improving detection sensitivity.
2Measurement precision
If the amplitude of the second alternating current voltage is increased to cancel parasitic current, then the parasitic capacitor effect is reduced, but the dynamic range of the measured capacitance is reduced
Solution Approach 1:
The amplitude of the second alternating current voltage is precisely optimized to the minimum value required to cancel the parasitic capacitor current. By carefully adjusting this parameter, the correction is effective without excessive voltage amplitude that would saturate the detection circuit and reduce dynamic range. The frequency is also optimized to match the parasitic capacitor's resonant characteristics for maximum correction efficiency at minimal amplitude.
Solution Approach 2:
Instead of applying a large correction voltage that would completely dominate the signal, only the precise amount of correction voltage needed to cancel the parasitic effect is applied. This partial action approach ensures that the correction is sufficient to eliminate the harmful effect without being excessive enough to reduce the dynamic range of measurable capacitance values.
3Measurement precision
If a correction circuit is used to cancel parasitic capacitor current, then the detection accuracy is improved, but the device complexity increases
Solution Approach 1:
The correction electrode is integrated with the existing shield electrode structure, merging the correction function with the existing shielding architecture. The correction electrode can be formed as an extension or modification of the shield electrode, combining multiple functions (shielding and parasitic cancellation) into a single structural element, thereby reducing overall device complexity.
Solution Approach 2:
The correction electrode serves multiple functions: it acts as both a parasitic capacitor cancellation element and maintains the shielding function. Additionally, it can be used for both self-capacitance and mutual capacitance detection modes, providing universal functionality across different detection configurations without requiring separate dedicated components for each function.
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 effectively suppresses the deterioration of detection sensitivity and accuracy caused by parasitic capacitors, enhancing the detection of capacitance between an object and a detection electrode by canceling out parasitic effects and reducing noise.
Implementation Method 1
the presence of a high capacitance parasitic capacitor between the ground and the detection electrode reduces the detection sensitivity
Implementation Method 2
The arrangement of the active shield reduces the capacitance of the parasitic capacitor because the detection electrode is less susceptible to electrostatic coupling with the surrounding conductor
Implementation Method 3
a capacitance detection device that detects a capacitance between an object proximate to a detection electrode and the detection electrode
Data Source
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AI summary
The capacitance detection device 2 includes a first voltage output circuit configured to output a first alternating current voltage supplied to a shield electrode Ea provided proximate to a detection electrode Es, a second voltage output circuit configured to output a second alternating current voltage V2 whose frequency and phase are the same as that of the first alternating current voltage V1 and whose amplitude is less than that of the first alternating current voltage V1, and a current output circuit 23 configured to output a driving current Is to the detection electrode Es so that the difference between the voltage of the detection electrode Es and the second alternating current voltage V2 becomes smaller, and output a detection signal Vo corresponding to the driving current Is. The second voltage output circuit outputs a second alternating current voltage V2 whose amplitude is adjusted so that the driving current Is in the absence of the object 6 proximate to the detection electrode Es.