Capacitance-to-Voltage Interface Circuit for Phase Error and Noise Rejection
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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 errors due to non-zero delays and susceptibility to noise and electromagnetic interference, which affect the accuracy and reliability of signal processing.
Innovation Solution
A hybrid discrete-time/continuous-time signal-chain path with a band-pass filter that tracks the mechanical frequency of the capacitive device, comprising a continuous-time capacitance-to-voltage converter, a clock generator, and an analog-to-digital converter, which applies clock signals to drive poles of the band-pass filter to minimize phase error and reject noise, using a high-pass and low-pass filter combination to create a band-pass response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistor feedback is employed in the capacitance-to-voltage circuit to reduce phase error, then the phase error is reduced, but the circuit becomes more susceptible to leakage and noise
Solution Approach 1:
The patent replaces the traditional resistor feedback mechanism with a switched-capacitor feedback network. This substitution eliminates the need for large value resistors that are prone to leakage and noise, while achieving the same phase error correction function through capacitive switching and charging/discharging cycles that are less susceptible to these parasitic effects.
Solution Approach 2:
The patent changes the feedback element from resistive to capacitive, fundamentally altering the circuit's impedance characteristics. By using capacitors instead of resistors in the feedback path, the circuit operates in a regime where reactive rather than resistive effects dominate, thereby reducing susceptibility to leakage and thermal noise while maintaining phase control capability.
2Loss of information
If signal conditioning is performed with non-zero delay to extract the envelope of the amplitude modulated signal, then the desired signal can be extracted, but signal leakage occurs and output range is reduced
Solution Approach 1:
The patent employs periodic switching of capacitors at the mechanical resonance frequency of the gyroscope. This periodic action synchronizes the signal processing with the input signal's frequency, enabling envelope extraction through constructive interference while minimizing leakage through destructive interference at other frequencies. The periodic charging and discharging of feedback capacitors creates a frequency-selective response that extracts the desired signal without the delays that cause leakage in traditional circuits.
3Measurement precision
If known capacitance-to-voltage conversion circuits are used, then the capacitance signal can be converted to voltage, but the circuit is susceptible to high noise, electromagnetic radiation and electrical fields
Solution Approach 1:
The patent creates an electrically inert environment by using a fully differential switched-capacitor architecture with symmetric signal paths. This differential structure rejects common-mode electromagnetic interference and electrical field effects, while the capacitive switching operation at defined frequencies creates a controlled electrical environment that is less susceptible to external noise and radiation compared to traditional resistor-based circuits.
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 solution reduces phase errors and noise, enhances leakage tolerance, and improves signal processing accuracy by tracking the mechanical frequency, resulting in a more reliable and efficient conversion of capacitance signals to voltage signals with minimal phase delay sensitivity to frequency fluctuations.
Implementation Method 1
a capacitance-to-voltage converter electrically coupled to the capacitive device and configured to convert the capacitive signal into a voltage signal
Implementation Method 2
a filter component electrically coupled to the capacitance-to-voltage converter and the clock generator and configured to apply a band-pass filter response to the voltage signal
Data Source
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 configured to convert a capacitive signal from a capacitive device that operates at a mechanical frequency into a raw voltage signal, a clock generator configured to convert the mechanical frequency into one or more clock signals, and a filter component 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 can be configured to apply the one or more clock signals to the filter component 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.