MEMS Microphone AGC and DC Offset Cancellation for Dynamic Range
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Solution Overview
Problem
Implementing high dynamic range microphones using MEMS techniques and CMOS technologies is challenging due to limited supply voltage, requiring solutions that maintain performance across a wide signal range without distortion and noise.
Innovation Solution
Incorporating Automatic Gain Control (AGC) and direct current (DC) offset compensation, along with digital signal processing techniques, to maintain constant gain and reduce noise, while employing digital frequency equalization and linearization to address distortion and non-linearity issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If high dynamic range is implemented in MEMS microphones, then the ability to handle both weak and strong audio signals is improved, but the device complexity increases due to the need for AGC and multiple processing stages
Solution Approach 1:
The microphone system is divided into multiple gain stages (first gain stage and second gain stage) with different gain values, allowing the system to handle different signal levels separately. Each stage processes specific portions of the dynamic range, and the outputs are combined to achieve high overall dynamic range performance.
Solution Approach 2:
The patent implements dynamic gain switching where the system automatically selects between different gain stages based on the input signal level. The AGC component dynamically adjusts which gain stage is active, enabling the microphone to adapt to both weak and strong audio signals without manual intervention.
2Adaptability or versatility
If AGC is used to maintain constant gain, then the ability to handle varying signal levels is improved, but DC offset artifacts are generated that degrade signal quality
Solution Approach 1:
The system performs preliminary DC offset compensation by capturing DC offset samples during calibration phases before actual audio processing. These pre-captured offset values are stored and used to compensate for DC artifacts generated during AGC operation, preventing degradation of signal quality.
Solution Approach 2:
The system continuously monitors the output signal for DC offset artifacts and uses feedback loops to adjust compensation parameters. The DC offset cancellation component uses feedback from the processed signal to dynamically adjust offset removal, ensuring artifacts are eliminated while maintaining signal integrity.
3Adaptability or versatility
If multiple gain stages with different gain values are used, then the dynamic range is extended, but distortion and non-linearity increase
Solution Approach 1:
The system creates multiple copies of the audio signal path, with each copy processing through a different gain stage. The outputs from these parallel processing paths are then combined, allowing the system to capture both low-level and high-level signals with appropriate gain applied in each path, reducing overall distortion.
Solution Approach 2:
The patent changes the gain parameter of different processing stages to match the characteristics of different signal levels. By adjusting gain values in each stage according to the input signal amplitude, the system extends dynamic range while maintaining linearity and minimizing distortion across the full operating range.
Data Source
AI summary
A microphone device comprising a microelectromechanical systems (MEMS) acoustic sensors, an automatic gain compensation (AGC) component, and a direct current (DC) offset cancellation component is described. An microphone device can be configured for AGC of an analog gain stage or a digital gain stage associated with the MEMS acoustic sensor. Provided implementations can also be configured to compensate DC offset resulting from adjustment of the analog provided by the AGC component. Additional embodiments of the subject disclosure can provide digital frequency equalization and/or linearization.