MEMS Capacitive Sensor Circuit Layout for Lower Parasitic Capacitance
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Solution Overview
Problem
MEMS capacitive sensors, such as microphones, face signal degradation due to parasitic capacitance effects when coupled with signal processing circuits, leading to reduced signal-to-noise ratio (SNR) and increased costs, particularly in standard CMOS processes.
Innovation Solution
A MEMS capacitive sensor configuration with a signal processing circuit that eliminates the need for AC coupling capacitance by connecting the membrane to a reference ground and the substrate to the supply voltage, reducing parasitic effects and improving SNR performance, while allowing for a three-pin interface that reduces costs and enhances signal processing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If AC coupling capacitance is used in the signal path, then signal transmission is enabled, but parasitic capacitance causes signal loss and deteriorates SNR
Solution Approach 1:
The patent extracts and removes the AC coupling capacitance from the signal path between the MEMS capacitive sensor and the amplifier. By eliminating this component, the harmful parasitic capacitance effects are removed while signal transmission is maintained through direct coupling, thereby resolving the contradiction between enabling signal transmission and avoiding parasitic capacitance deterioration.
2Object-affected harmful factors
If advanced MiM capacitor processes are used, then parasitic effects are reduced to a few percent, but manufacturing costs increase
Solution Approach 1:
The patent removes the need for expensive MiM capacitor processes by eliminating the AC coupling capacitance component entirely from the signal path. This extraction approach achieves the goal of reducing parasitic effects without incurring the high manufacturing costs associated with advanced MiM capacitor fabrication processes.
3Device complexity
If three-pin interface is implemented, then device complexity and costs are reduced, but signal processing performance must be maintained
Solution Approach 1:
The patent merges the signal path and power supply connections into a simplified three-pin interface configuration. By directly coupling the MEMS sensor output to the amplifier input and integrating power supply connections, the interface complexity is reduced while maintaining signal processing performance through the elimination of harmful parasitic effects that would otherwise degrade the signal.
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 configuration enhances the signal-to-noise ratio and reduces costs by eliminating the need for expensive MiM capacitors, achieving better performance with a smaller area and lower costs, and allows for simple polarity inversion without altering the signal processing circuit topology.
Implementation Method 1
a capacitor having a variable capacitance, wherein the capacitor comprises a backplate and a membrane being separated from each other by a variable distance
Implementation Method 2
The bias voltage is used to bias a capacitor of the MEMS capacitive sensor having a variable capacitance
Data Source
AI summary
A MEMS capacitive sensor is disclosed. In an embodiment a MEMS capacitive sensor includes a capacitor having a variable capacitance, wherein the capacitor includes a backplate and a membrane being separated from each other by a variable distance, wherein the capacitor is arranged on a substrate, an output terminal configured to provide an output signal, wherein the output terminal is connected to the backplate, a bias voltage input terminal configured to apply a bias voltage, wherein the bias voltage input terminal is connected to the membrane and a supply voltage input terminal configured to apply a supply voltage, wherein the supply voltage input terminal is connected to the substrate, wherein the MEMS capacitive sensor is configured to generate a level of the output signal in dependence on the distance between the membrane and the backplate.