MEMS Microphone Parasitic Capacitance Cancellation
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Solution Overview
Problem
Parasitic capacitance in MEMS microphones reduces sensitivity and requires complex software solutions that increase power consumption and cost, particularly in applications with limited power supplies.
Innovation Solution
A second capacitor is formed within the MEMS microphone to create a reference capacitance equal to the parasitic capacitance, allowing circuitry to subtract it and produce a signal with negligible noise, thereby improving sensitivity without significant additional complexity or power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If software calibration methods and noise-reduction algorithms are used to compensate for parasitic capacitance, then sensitivity can be maintained, but device complexity and power consumption increase significantly
Solution Approach 1:
The invention extracts and removes the parasitic capacitance component from the total capacitance measurement by creating a separate reference capacitor that mirrors the parasitic capacitance. The circuit subtracts the reference capacitance value from the total capacitance, isolating and eliminating the parasitic effect from the output signal, thereby maintaining sensitivity without requiring complex software algorithms
Solution Approach 2:
The reference capacitor serves as an intermediary element that captures and represents the parasitic capacitance. By introducing this intermediate component, the system can measure and subtract the parasitic effect through simple circuitry rather than requiring complex processing, thus resolving the contradiction between maintaining precision and reducing complexity
2Measurement precision
If software calibration methods and noise-reduction algorithms are implemented to address parasitic capacitance, then sensitivity can be maintained, but power consumption increases
Solution Approach 1:
The invention extracts and removes the parasitic capacitance component from the total capacitance measurement by creating a separate reference capacitor that mirrors the parasitic capacitance. The circuit subtracts the reference capacitance value from the total capacitance, isolating and eliminating the parasitic effect from the output signal, thereby maintaining sensitivity without requiring complex software algorithms
Solution Approach 2:
The invention replaces the mechanical/software-based noise-reduction algorithms with a hardware-based electrical circuit solution. By using analog circuitry to subtract the reference capacitance from the total capacitance in real-time, the system achieves the same sensitivity maintenance goal with significantly lower power consumption compared to digital signal processing methods
3Measurement precision
If complex noise-reduction algorithms are used to compensate for parasitic capacitance, then sensitivity can be maintained, but overall device cost increases
Solution Approach 1:
The invention extracts and removes the parasitic capacitance component from the total capacitance measurement by creating a separate reference capacitor that mirrors the parasitic capacitance. The circuit subtracts the reference capacitance value from the total capacitance, isolating and eliminating the parasitic effect from the output signal, thereby maintaining sensitivity without requiring complex software algorithms
Solution Approach 2:
The invention creates a copy of the parasitic capacitance effect using a reference capacitor that is electrically connected to mirror the parasitic pathways. By copying the parasitic effect into a controllable reference element, the system can subtract it through simple circuitry rather than requiring expensive complex processing, thus resolving the contradiction between maintaining precision and reducing cost
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
Substantially eliminates parasitic capacitance from the output signal, enhancing microphone performance and extending battery life in power-constrained devices without increasing overall cost.
Implementation Method 1
There is a first capacitance between the backplate and the diaphragm, and a second capacitance between the backplate and the anchor. The sensor measures a capacitance between the backplate and the diaphragm.
Implementation Method 2
The backplate is separated from the diaphragm by a dielectric fluid, and is fixedly coupled to the anchor by a dielectric solid.
Data Source
AI summary
A microelectromechanical microphone and method of manufacturing the same are disclosed. The microphone has a moveable diaphragm and a fixed backplate that create a variable capacitance. A fixed anchor electrically coupled to the diaphragm has an electrode that measures the variable capacitance, but also measures an unwanted, additive, parasitic capacitance. Various embodiments include a reference electrode, manufactured in the same deposition layer as the diaphragm or anchor, that measures only the parasitic capacitance. A circuit is provided either on-chip or off-chip that subtracts the capacitance measured at the reference electrode from that measured at the anchor, thereby producing only the desired variable capacitance as output. Because the reference electrode is deposited at the same time as the diaphragm or anchor, only minimal changes are required to existing manufacturing techniques.