Capacitance-to-voltage interface circuit
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Solution Overview
Problem
Capacitance-to-voltage interface circuits for capacitive devices, such as Coriolis-based gyroscopes, face challenges with signal leakage and phase error due to non-zero delay in signal conditioning, which are exacerbated by temperature fluctuations and susceptibility to noise and electromagnetic interference.
Innovation Solution
A hybrid discrete-time/continuous-time signal-chain path incorporating a band-pass filter with a continuous-time capacitance-to-voltage circuit, a discrete-time high-pass filter, and a continuous-time anti-aliasing filter, where the feedback network biases a charge integrator to minimize phase error and reject electromagnetic interference, with clock signals generated to track the mechanical frequency of the capacitive device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistor feedback is used in conjunction with a capacitance-to-voltage circuit to process the capacitance signal, then phase error is reduced, but the circuit becomes more susceptible to leakage
Solution Approach 1:
The patent introduces a switched-capacitor feedback network as an intermediary between the capacitive sensor and the integrator, replacing the direct resistor feedback approach. This switched-capacitor structure acts as a mediator that achieves phase error correction through capacitive switching rather than resistive feedback, thereby reducing susceptibility to leakage while maintaining measurement precision.
Solution Approach 2:
The patent replaces the resistive feedback mechanism with a capacitive switching mechanism. By substituting the resistor-based phase error correction with a switched-capacitor approach, the system eliminates the leakage problems associated with resistive feedback while achieving the same phase error reduction through temporal switching of capacitive elements.
2Productivity
If signal conditioning is performed with non-zero delay prior to demodulation, then signal processing is achieved, but signal leakage occurs
Solution Approach 1:
The patent implements continuous-time capacitance-to-voltage conversion that maintains uninterrupted signal flow from the capacitive sensor through the switched-capacitor feedback network to the integrator. This continuous action eliminates gaps in signal processing that would otherwise cause delay and subsequent leakage, ensuring the useful signal action continues without interruption.
Solution Approach 2:
The patent employs periodic switching of the capacitive elements in the feedback network at a frequency synchronized with the sensor operation. This periodic switching enables signal processing to occur in a rhythmic, synchronized manner that maintains continuous processing while preventing the accumulation of delay that leads to signal leakage.
3Ease of manufacture
If known capacitance-to-voltage conversion interface circuits are used, then conversion is achieved, but the circuits are susceptible to high noise, electromagnetic radiation and/or electrical fields
Solution Approach 1:
The patent creates an electrically inert environment by using a fully capacitive signal path from the sensor through the switched-capacitor feedback network to the integrator. This capacitive-only approach isolates the sensitive measurement path from electromagnetic interference and electrical noise, analogous to creating an inert atmosphere that protects against harmful external factors while maintaining conversion capability.
Solution Approach 2:
The switched-capacitor feedback network serves as an intermediary that blocks electromagnetic interference and noise from reaching the integrator. By positioning this capacitive switching structure between the sensor and the integration stage, it acts as a mediator that allows the desired signal to pass while filtering out harmful electromagnetic radiation and electrical noise.
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 reduces phase error and noise, enhances leakage tolerance, and effectively rejects electromagnetic interference, resulting in improved signal processing with reduced phase delay and increased robustness to temperature fluctuations.
Implementation Method 1
a capacitance-to-voltage converter configured to convert a capacitive signal from a capacitive device that operates at a mechanical frequency into a voltage signal
Data Source
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AI summary
Systems and methods for converting a capacitance signal into a band-limited voltage signal for improved signal processing are disclosed herein. Such systems can include a capacitance-to-voltage converter (24) configured to convert a capacitive signal from a capacitive device that operates at a mechanical frequency into a raw voltage signal, a clock generator (26) configured to convert the mechanical frequency into one or more clock signals, and a filter component (28) configured to apply a band-pass filter response to the raw voltage signal to convert the raw voltage signal into a band-limited voltage signal. The clock generator (26) can be configured to apply the one or more clock signals to the filter component (28) to drive a first pole and a second pole of the band-pass filter response to track the mechanical frequency of the capacitive device such that the geometric mean of the first pole and the second pole is substantially equal to the mechanical frequency.