Digital Microphone Gain Control for High-SPL Clipping Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Digital microphones face dynamic range issues due to high sound pressure levels causing MEMS output voltage to exceed ASIC supply voltage, leading to signal clipping and reduced dynamic range.
Innovation Solution
Implementing an Automatic Gain Control (AGC) system that adaptively adjusts gains in both the analog and digital domains using a gain control module, which includes an input buffer, analog-to-digital converter, and decompress module to attenuate and amplify signals, ensuring linear input/output characteristics and preserving dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the MEMS transducer outputs high voltage levels to support high Acoustic Overload Point (AOP) levels, then the microphone can handle higher sound levels, but the ASIC cannot handle such high input voltage levels without clipping the signal, reducing dynamic range
Solution Approach 1:
The patent segments the gain control function into two independent domains: analog domain (input buffer with adjustable gain) and digital domain (decompress module with adjustable gain). This segmentation allows each domain to handle gain adjustment independently, preventing signal clipping in the ASIC while maintaining the ability to handle high AOP levels. The analog domain handles initial signal conditioning, and the digital domain provides final gain adjustment, dividing the overall gain control task to resolve the contradiction between high AOP and signal clipping.
Solution Approach 2:
The patent implements dynamic gain control in both analog and digital domains. The input buffer in the analog domain has adjustable gain that can be dynamically changed based on input signal levels, and the decompress module in the digital domain also has adjustable gain. This dynamic adjustment allows the system to adapt to varying sound pressure levels, maintaining full dynamic range while preventing clipping at high AOP levels. The gain values are changed adaptively based on the operating conditions.
2Illumination intensity
If the ASIC input receives high voltage levels from the MEMS transducer, then high sound pressure levels can be captured, but the dynamic range is reduced due to clipping at the ASIC input
Solution Approach 1:
The patent introduces an intermediary input buffer between the MEMS transducer and the ASIC. This input buffer acts as a mediator that conditions the high voltage signal from the MEMS transducer before it reaches the ASIC, preventing direct clipping at the ASIC input. The buffer provides impedance matching and gain adjustment, serving as an intermediary stage that protects the ASIC while maintaining the ability to capture high sound pressure levels without losing dynamic range information.
Solution Approach 2:
The patent changes the gain parameter dynamically in both analog and digital domains. The input buffer gain in the analog domain and the decompress module gain in the digital domain are adjusted based on the input signal characteristics. By changing these gain parameters adaptively, the system can handle high sound pressure levels while maintaining full dynamic range, preventing the information loss that would occur with fixed gain settings.
Data Source
AI summary
Approaches are provided for an apparatus that includes an input buffer, an analog-to-digital converter coupled to the input buffer, a decompress module coupled to the analog to digital converter, and a gain control module coupled to the input buffer and the decompress module. The input buffer has a first adjustable gain and operating in the analog domain. The analog-to-digital converter converts the input analog data received from the input buffer into digital data. The decompress module operates in the digital domain, and is configured to decompress the digital data received from the analog-to-digital converter. The decompress module has a second adjustable gain and produces an output digital signal. The gain control module determines when to compensate for changes in characteristics the input analog data by selectively controlling the first gain of the input buffer in the analog domain and the second gain of the decompress module in the digital domain.