MEMS Microphone Auto-Calibration Circuit for Sensitivity Variation
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Solution Overview
Problem
MEMS microphones fabricated using the same process and design exhibit variations in sensitivity due to fabrication variations, requiring a method to consistently set sensitivity values within a target range.
Innovation Solution
An interface circuit with a variable voltage bias generator and calibration controller is used to perform an auto-calibration procedure, adjusting bias voltages and amplifier gains to set the sensitivity of MEMS microphones within a target range, which can be done on-chip during the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If MEMS microphones are fabricated using micromachining techniques with the same process and design, then manufacturing cost is reduced and yield is increased, but sensitivity variations occur due to fabrication variations
Solution Approach 1:
The patent applies parameter changes by adjusting the bias voltage applied to the MEMS microphone during calibration. By varying this electrical parameter, the sensitivity of each device is tuned to compensate for fabrication variations, allowing consistent performance despite physical dimensional variations in the micromachined structures
Solution Approach 2:
The calibration system performs self-service by automatically measuring each MEMS microphone's sensitivity and adjusting its bias voltage without requiring external manual calibration equipment. The system calibrates devices internally during or after fabrication, eliminating the need for external testing equipment and manual adjustment procedures
2Manufacturing precision
If external calibration equipment is used to adjust sensitivity of MEMS microphones, then sensitivity consistency is improved, but device complexity and calibration time increase
Solution Approach 1:
The patent merges the calibration function into the existing MEMS microphone device by integrating a bias voltage generator and control logic directly with the microphone. This combination eliminates the need for separate external calibration equipment, reducing overall system complexity while maintaining sensitivity consistency
Solution Approach 2:
The MEMS microphone system performs self-calibration by internally measuring its own sensitivity output and automatically adjusting its bias voltage through an integrated control mechanism, eliminating dependency on external calibration systems and reducing overall device complexity
3Manufacturing precision
If manual calibration procedures are performed on MEMS microphones, then sensitivity can be adjusted, but productivity decreases and test time increases
Solution Approach 1:
The system performs automatic self-calibration by measuring each device's sensitivity and adjusting its bias voltage without requiring manual intervention. This automation eliminates time-consuming manual calibration steps while maintaining precise sensitivity adjustment, significantly increasing calibration throughput and productivity
Solution Approach 2:
The calibration is performed automatically during or immediately after the fabrication process itself, rather than as a separate subsequent step. This preliminary calibration action reduces overall test time and increases productivity by eliminating idle time between manufacturing and characterization
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
This approach allows for consistent sensitivity settings across MEMS microphones, reducing the need for external calibration equipment and shortening test times by performing a significant portion of the calibration internally, thereby improving the reliability and efficiency of the calibration process.
Implementation Method 1
MEMS devices... often use capacitive sensing techniques for measuring the physical phenomenon being measured
Implementation Method 2
variable voltage bias generator coupled to a transducer
Data Source
AI summary
In accordance with an embodiment, an interface circuit includes a variable voltage bias generator coupled to a transducer, and a measurement circuit coupled to an output of the transducer. The measurement circuit is configured to measure an output amplitude of the transducer. The interface circuit further includes a calibration controller coupled to the bias generator and the measurement circuit, and is configured to set a sensitivity of the transducer and interface circuit during an auto-calibration sequence.