MEMS Microphone Bias Voltage Segmentation
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Solution Overview
Problem
Conventional MEMS microphones face limitations in accurately sensing high sound pressure levels due to the distance between the diaphragm and backplate, stiffness of the diaphragm, and voltage threshold limitations of semiconductor circuits, leading to inverted output signals and increased costs with high voltage semiconductor circuitry.
Innovation Solution
Employing two opposite polarity, lower voltage bias voltage generators to provide an effectively higher bias voltage to MEMS microphones, allowing for non-inverted output signals that match the polarity of incident acoustic waves, without requiring high breakdown voltage semiconductor processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single bias voltage is applied to the backplate or diaphragm, then the circuit complexity is reduced, but the output signal becomes inverted (180 degrees out of phase) with the incident acoustic wave
Solution Approach 1:
The single bias voltage application is segmented into two separate bias voltages: one applied to the backplate and another to the diaphragm. This segmentation allows independent control of each component's electrical potential, enabling the output signal polarity to match the incident acoustic wave polarity while maintaining manageable circuit complexity through systematic voltage distribution.
Solution Approach 2:
Instead of applying a single bias voltage and accepting signal inversion, the patent applies bias voltages in opposite polarities to the backplate and diaphragm respectively. This inverted approach to voltage application compensates for the natural inversion effect, resulting in a non-inverted output signal that preserves the original acoustic wave polarity information.
2Measurement precision
If high voltage semiconductor circuitry is used to provide higher bias voltage, then the dynamic range and sound pressure level sensing capability are improved, but the technology cost and die size increase
Solution Approach 1:
The patent changes the voltage parameters by applying two lower voltage bias sources instead of one high voltage bias source. By distributing the voltage application across two separate lower-voltage circuits, the system achieves the same effective bias voltage (e.g., 18V from two 9V sources) without requiring expensive high-voltage semiconductor processes, thereby reducing technology cost and die size while maintaining sound pressure level sensing capability.
3Reliability
If high voltage semiconductor circuitry is used to provide higher bias voltage, then the dynamic range is improved, but the die size increases impacting sensor package size
Solution Approach 1:
The patent changes the voltage parameters by applying two lower voltage bias sources instead of one high voltage bias source. By distributing the voltage application across two separate lower-voltage circuits, the system achieves the same effective bias voltage (e.g., 18V from two 9V sources) without requiring expensive high-voltage semiconductor processes, thereby reducing technology cost and die size while maintaining sound pressure level sensing capability.
4Measurement precision
If the distance between diaphragm and backplate is reduced to sense high sound pressure levels, then the measurement precision is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent changes the electrical parameter (bias voltage) rather than the mechanical parameter (distance between diaphragm and backplate). By providing higher effective bias voltage through two separate bias sources, the system enhances sound pressure level sensing capability without requiring reduced mechanical dimensions, thereby avoiding increased manufacturing difficulty and structural complexity.
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
Enhances the robustness and dynamic range of MEMS microphones by enabling accurate measurement of high sound pressure levels with improved signal polarity matching and reduced costs through lower voltage solutions.
Implementation Method 1
a backplate, being in proximity to the flexible diaphragm, can form a variable capacitance device
Implementation Method 2
a direct current (DC) bias voltage (V bias) applied to the backplate (or the diaphragm) facilitates measuring sound pressure induced deflections of the flexible diaphragm as an alternating current AC voltage
Data Source
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AI summary
Microelectromechanical systems (MEMS) sensors and related bias voltage techniques are described. Exemplary MEMS sensors, such as exemplary MEMS acoustic sensors or microphones described herein can employ one or more bias voltage generators and single-ended or differential amplifier arrangements. Various embodiments are described that can effectively increase the bias voltage available to the sensor element without resorting to high breakdown voltage semiconductor processes. In addition, control of the one or more bias voltage generators in various operating modes is described, based on consideration of a number of factors.