Variable Capacitance Measurement Using Synchronous Amplitude Modulation
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Solution Overview
Problem
Existing methods for determining variable capacitance in pressure sensors are imprecise, complex, and prone to errors due to sensitivity to parameter variations and limited frequency bandwidth, requiring calibration and being unable to measure over a wide range of capacitance values.
Innovation Solution
An electronic device comprising a digital signal generator, an analog filter, an amplitude modulator, an analog-to-digital converter, and a demodulator, which operates synchronously to provide a digital representation of the variable capacitance value using a pulse width modulated signal and sine wave excitation, reducing the need for complex demodulation algorithms and minimizing the influence of absolute capacitance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If rectangular or square wave excitation is used to determine variable capacitance, then the measurement can be performed with simple circuitry, but the method is sensitive to parameter variations and limited in terms of frequency or bandwidth
Solution Approach 1:
The patent changes the excitation signal parameter from rectangular/square wave to sine wave, and introduces amplitude modulation with variable capacitance. This transforms the measurement approach to be less sensitive to parameter variations while maintaining circuit simplicity. The sine wave excitation combined with amplitude modulation allows for broader frequency bandwidth and improved measurement reliability.
2Device complexity
If conventional methods are used to determine variable capacitance, then the circuit can be simple, but the methods require calibration and are affected by varying operating conditions
Solution Approach 1:
The patent employs self-service by using the variable capacitance itself to modulate the amplitude of the sine wave signal. The capacitance value directly controls the signal amplitude, eliminating the need for external calibration references or complex compensation circuits. This self-modulating approach maintains circuit simplicity while significantly improving measurement precision across varying operating conditions.
3Device complexity
If rectangular wave excitation is used, then the circuit can be simple, but the frequency or bandwidth is limited
Solution Approach 1:
The patent changes the excitation signal from rectangular/square wave to sine wave, which inherently provides smoother frequency response and broader bandwidth. The amplitude modulation technique allows the system to operate effectively over a wider frequency range while maintaining circuit simplicity, as the sine wave can be easily generated and processed across different frequencies without the harmonic content issues of square waves.
4Measurement precision
If absolute capacitance values are used in the measurement, then the measurement can be direct, but the influence of absolute capacitance values introduces errors
Solution Approach 1:
The patent transforms the measurement from direct absolute capacitance measurement to relative amplitude modulation measurement. By using the variable capacitance to modulate the amplitude of a sine wave signal, the system measures capacitance changes relative to a reference state rather than absolute values. This approach eliminates errors introduced by absolute capacitance value variations while maintaining measurement directness through the amplitude modulation technique.
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 simplifies and enhances the precision of measuring variable capacitance, allowing for accurate measurements over a wide range of values without the need for complex calibration, by using synchronous processing and sine wave excitation, thereby improving the overall performance and reliability of pressure sensor measurements.
Implementation Method 1
an amplitude modulator adapted to receive the filtered signal and to provide an amplitude modulated signal having an amplitude which is a function of the capacitance value of the variable capacitance
Implementation Method 2
an analog filter for receiving the digital excitation signal and for providing a filtered signal
Implementation Method 3
an analog-to-digital converter (ADC) adapted to convert the amplitude modulated signal received from the amplitude modulator into a digital amplitude modulated signal
Data Source
AI summary
An apparatus is provided. The apparatus comprises a digital signal generator, an analog filter, an amplitude modulator, and an analog-to-digital converter (ADC). The digital signal generator has a demodulator and provides a digital excitation signal. The analog filter is coupled to the digital signal generator. The amplitude modulator has a variable capacitor and is coupled to the analog filter. The amplitude modulator also generates an amplitude modulated signal with an amplitude that is a function of the capacitance of the variable capacitor. The ADC is coupled to the amplitude modulator and the demodulator, and the digital signal generator and the demodulator operate synchronously.