Integrated Capacitance Measurement Using Dual Sine-Wave Oscillators
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Solution Overview
Problem
Existing capacitive sensor technologies face challenges in accurately measuring unknown capacitances due to high susceptibility to interference, especially at multiple harmonics of their sampling frequency, and require external components like inductors which are costly and temperature-dependent, and prior art methods struggle with dynamic frequency adjustment and interference immunity.
Innovation Solution
A microelectronically integrable circuit using frequency comparison between two sine-wave resonant circuits, where the frequency of the measuring oscillator is dependent on on-chip resistors and capacitances, reducing external interference and eliminating temperature drift by matching resistors and using a high-frequency oscillator for phase measurement, allowing for fully integrated and radiation-resistant capacitance measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If switched-capacitor circuits are used for capacitance measurement, then the measurement can be performed with simple circuit structure, but the susceptibility to interference at multiple harmonics of sampling frequency increases significantly
Solution Approach 1:
The patent replaces switched-capacitor circuits with sine-wave oscillators that generate continuous sinusoidal signals. This substitution eliminates the discrete switching operations that cause harmonic interference, achieving clean sinusoidal excitation without the interference problems of SC circuits while maintaining integration capability.
Solution Approach 2:
The patent employs periodic sinusoidal oscillation at a single well-defined frequency rather than periodic switching at multiple frequencies. The sine-wave oscillators generate continuous periodic signals that excite the capacitive sensors, allowing measurement at a single frequency point and avoiding the multiple harmonic frequencies that cause interference in SC circuits.
2Measurement precision
If external inductors are used in LC resonant circuits for capacitance measurement, then the measurement accuracy is improved, but the cost increases and temperature dependence is introduced
Solution Approach 1:
The patent extracts and eliminates the external inductor component from the measurement system. By using sine-wave oscillators that generate electrical sinusoidal signals without requiring physical inductors, the design removes the source of temperature drift and cost issues while maintaining the ability to perform accurate capacitance measurements through frequency comparison.
Solution Approach 2:
The patent substitutes physical LC resonant circuits with electronic sine-wave oscillator circuits. Instead of relying on physical inductors and capacitors forming resonant tanks, the system uses electronic oscillators that generate sinusoidal signals, eliminating the need for external inductors and their associated problems with temperature stability and cost.
3Measurement precision
If LC resonant circuits with external inductors are used, then capacitance measurement is achieved, but the frequency cannot be dynamically changed to avoid interferences
Solution Approach 1:
The patent implements dynamic frequency control through sine-wave oscillators whose output frequencies can be adjusted. The oscillators can be tuned to different frequencies to avoid interference conditions, and the system can dynamically select optimal measurement frequencies. This dynamic adaptability is achieved through electronic control of the oscillator parameters rather than fixed physical resonant 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
The solution achieves high-resolution capacitance measurement with low susceptibility to radiation across a wide frequency range, providing absolute accuracy and eliminating the need for external components, with the ability to dynamically adjust frequencies for interference immunity.
Implementation Method 1
frequency comparison between two sine-wave resonant circuits
Data Source
AI summary
An apparatus for measuring the capacitance to be measured is proposed. It comprises a first sine-wave oscillator, the measuring oscillator, and a second sine-wave oscillator, the reference oscillator. The frequency of the output signal of the measuring oscillator, hereinafter also referred to as measuring frequency, is dependent on the capacitance to be measured. The frequency of the output signal of the reference oscillator, hereinafter also referred to as reference frequency, is dependent on a reference capacitance. The apparatus comprises a sub-apparatus which produces the ratio of the frequency value of the frequency of the output signal of the reference oscillator and the frequency value of the frequency of the output signal of the measuring oscillator and subsequently squares this ratio to provide the result of this squaring as a measured value.