MEMS Capacitance Measurement via Sigma-Delta Feedback Loop
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Solution Overview
Problem
Conventional measurement circuits for MEMS lack the necessary resolution and often require a compact circuit layout to accurately measure the state of microelectromechanical systems (MEMS) with high precision.
Innovation Solution
A measurement circuit utilizing a sigma-delta loop with feedback, incorporating capacitors and digital-to-analog converters (DACs) to integrate and convert voltage variations into digital signals, providing high-resolution measurements of MEMS capacitance in a compact layout.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional measurement circuits are used to measure MEMS capacitance, then the circuit layout can be compact, but the measurement resolution is insufficient
Solution Approach 1:
The patent implements a sigma-delta modulation system with feedback loop where the DAC output is fed back through capacitor C2 to the sensing node. The feedback mechanism continuously adjusts the DAC output to balance the voltages at the integrator inputs, enabling high-resolution measurement of the MEMS capacitance change while maintaining a compact circuit layout through iterative correction rather than complex circuitry
Solution Approach 2:
The patent replaces conventional analog measurement circuits with a sigma-delta modulation system that uses capacitive switching and digital processing. The measurement function is achieved through charge redistribution on capacitors C1 and C2, followed by digital conversion via ADC, substituting complex analog measurement mechanisms with a more integrated digital-based approach that improves resolution without proportionally increasing circuit complexity
2Measurement precision
If high-resolution measurement of MEMS capacitance is achieved, then displacement and position determination becomes accurate, but the circuit design becomes more complex
Solution Approach 1:
The patent measures displacement by detecting changes in capacitance value rather than directly measuring physical dimensions. The sigma-delta modulation system converts the capacitance change parameter into a high-resolution digital signal through charge redistribution and iterative feedback, achieving accurate displacement measurement while keeping the circuit design manageable through parameter transformation rather than direct physical measurement
Data Source
AI summary
A semiconductor device measures a state of a MEMS as a first voltage variation at a sensing node. The state of the MEMS includes a capacitance. A first capacitor is coupled between the sensing node and an input of an integrator for transferring the first voltage variation to a second node as a first signal. A second voltage variation is routed through a second capacitor to the second node as a second signal. The integrator integrates the first signal and second signal to provide an integrated signal. An ADC has an input coupled to an output of the integrator and converts the integrated signal to a digital signal representative of the capacitance of the MEMS. A DAC has an input coupled to the output of the ADC. A second capacitor is coupled between an output of the DAC and the sensing node.