Capacitive Sensor Shaped Excitation Signal Reduces Ringing Noise
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Solution Overview
Problem
Microelectromechanical Systems (MEMS) based capacitive sensors face measurement errors due to underdamped responses caused by mechanical resonances, leading to ringing noise in output signals, which affects the accuracy of pressure measurements.
Innovation Solution
The solution involves generating a shaped periodic excitation signal with smoothed edge transitions and using a dithered sampling clock or an array of MEMS sensors with varying dimensions to reduce ringing noise, and employing an oversampled analog-to-digital converter with a dithered clock to alleviate idle tones and noise components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a periodic excitation signal with sharp edges is used to drive the capacitive sensor, then the sensor response is strong and easy to detect, but mechanical resonances cause ringing noise that degrades measurement precision
Solution Approach 1:
The patent applies parameter changes by modifying the excitation signal waveform from a standard periodic signal with sharp edges to a shaped periodic signal with smoothed transitions. Specifically, the signal shape is altered to reduce high-frequency spectral components that trigger mechanical resonances in the MEMS structure, thereby reducing ringing noise while maintaining adequate sensor response for accurate pressure measurement
2Productivity
If the excitation signal frequency is increased to improve measurement speed, then productivity increases, but mechanical resonances are more easily excited causing measurement errors
Solution Approach 1:
The patent modifies the frequency domain characteristics of the excitation signal by shaping its waveform to have smoother transitions. This reduces the amplitude of high-frequency spectral components in the excitation signal, preventing resonance excitation even at higher operating frequencies, thus allowing faster measurements without sacrificing accuracy
Data Source
AI summary
In accordance with an embodiment, a method of performing a measurement with a capacitive sensor includes generating a periodic excitation signal that includes a series of pulses and smoothing edge transitions of the series of pulses to form a shaped periodic excitation signal that includes a flat region between the smoothed edge transitions. The method further includes providing the shaped periodic excitation signal to a first port of the capacitive sensor and measuring a signal provided by a second port of the capacitive sensor.