MEMS Microphone Active Compression for Low-Voltage Dynamic Range
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Solution Overview
Problem
Digital microphones face challenges in achieving large dynamic ranges and high signal-to-noise ratios due to voltage level limitations in integrated circuitry, particularly in mobile and battery-powered devices, where low power usage is crucial.
Innovation Solution
A digital microphone design incorporating a microelectromechanical system (MEMS) capacitor with adjustable capacitors for analog compression and a processing chain including a preamplifier, analog-to-digital converter, and a digital signal processing circuit, which performs decompression to manage signal compression and expand the dynamic range within low voltage limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If integrated circuitry operates at low voltage levels to reduce power usage, then power consumption is reduced, but the dynamic range and signal-to-noise ratio of the microphone deteriorate
Solution Approach 1:
An analog compression circuit is introduced as an intermediary component between the MEMS capacitor and the processing chain. This compression circuit compresses the dynamic range of the microphone signal before it enters the low-voltage processing chain, allowing the system to maintain low power consumption while effectively capturing both loud and quiet sounds within the limited voltage range available from integrated circuitry operating at low voltage levels.
2Use of energy by moving object
If integrated circuitry operates at low voltage levels to reduce power usage, then power consumption is reduced, but the signal-to-noise ratio deteriorates
Solution Approach 1:
The analog compression circuit performs preliminary action by compressing the signal dynamic range before the signal enters the low-voltage processing chain. This preliminary compression ensures that even weak signals are amplified relative to the noise floor of the subsequent processing stages, thereby maintaining an acceptable signal-to-noise ratio throughout the entire signal path while the system operates at low voltage levels.
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
The solution effectively compresses and decompresses signals, allowing digital microphones to operate within low voltage constraints while maintaining a large dynamic range and high signal-to-noise ratios, suitable for voice recognition and other applications.
Implementation Method 1
a microelectromechanical system (MEMS) capacitor... a voltage output of the MEMS capacitor
Implementation Method 2
the adjustment capacitors selectively coupleable to the MEMS capacitor to achieve a compression in the form of x/(1+N|x|) of a voltage output of the MEMS capacitor
Data Source
AI summary
A digital microphone compresses a large voltage swing signal from a MEMS capacitor to a signal suitable for processing by integrated circuitry. The compression may be performed in an analog domain by selectively coupling adjustment capacitors in parallel to the MEMS capacitor. The digital microphone may decompress the signal in the digital domain using a decompression technique substantially an inverse of the compression performed in the analog domain.