Capacitance Detection Circuit Using Dual AC Shield Voltage Balancing
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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 that utilizes a first and second alternating current voltage output circuit to cancel out the alternating current through parasitic capacitors, with the second voltage output circuit attenuating the first voltage to produce a drive current that eliminates parasitic capacitor components in the detection signal, and an operational amplifier to enhance signal accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a shield electrode is arranged around the detection electrode to reduce parasitic capacitor effects, then parasitic capacitor capacitance is reduced, but residual parasitic capacitors still cause detection sensitivity deterioration and accuracy reduction
Solution Approach 1:
The patent applies phase shift correction to convert the harmful effect of parasitic capacitors into a beneficial correction process. By measuring the phase shift caused by parasitic capacitors and applying corrective processing to the detection signal, the system eliminates the negative impact of residual parasitic capacitors that cannot be fully removed by the shield electrode alone.
Solution Approach 2:
The patent implements a feedback mechanism where the detection circuit measures the actual phase shift caused by parasitic capacitors, and this measurement is fed back to the correction circuit which applies appropriate phase correction to the detection signal, continuously optimizing the detection accuracy despite the presence of residual parasitic effects.
2Measurement precision
If phase shift correction is applied to eliminate parasitic capacitor effects, then detection accuracy improves, but the amplitude increase caused by parasitic capacitors reduces dynamic range
Solution Approach 1:
The patent applies partial correction by selectively correcting the phase shift component caused by parasitic capacitors while leaving the amplitude component largely unaffected. This partial action approach corrects the accuracy issue without excessively amplifying the signal amplitude, thereby preserving the dynamic range of the detection system.
3Measurement precision
If correction current is applied to cancel parasitic capacitor effects, then detection accuracy improves, but setting the correction capacitor to minute values reduces accuracy
Solution Approach 1:
The patent replaces the physical adjustment of minute capacitor values with an electrical phase shift correction mechanism. Instead of manually setting correction capacitors to very small values (which is difficult and inaccurate), the system uses phase detection and correction circuits that can achieve precise cancellation of parasitic effects through electrical signal processing, eliminating the need for high-precision physical capacitor adjustment.
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 improves detection sensitivity and accuracy by eliminating parasitic capacitor effects, allowing for precise capacitance measurement and reduced noise, thereby enhancing the dynamic range of the detected signal.
Implementation Method 1
the presence of a high capacitance parasitic capacitor between the ground and the detection electrode reduces the detection sensitivity because the component of the parasitic capacitor accounts for a large proportion of the detected signal
Implementation Method 2
a first alternating current voltage output circuit that outputs a first alternating current voltage applied to a shield electrode disposed close to a detection electrode; a second alternating current voltage output circuit that outputs a second alternating current voltage having a frequency and phase equal to those of the first alternating current voltage and an amplitude less than an amplitude of the first alternating current voltage
Implementation Method 3
a current output circuit that outputs a drive current to the detection electrode so that a voltage difference between a voltage of the detection electrode and the second alternating current voltage is minimized, and that outputs a detection signal corresponding to the drive current
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.