Capacitive Microphone Bias Impedance Switching After Shocks
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Solution Overview
Problem
Capacitive digital microphones exhibit long recovery times after shock events due to high impedance biasing circuitry, leading to missed acoustic information and performance degradation, especially with infrasound signals.
Innovation Solution
A digital microphone system incorporating a shock detector and recovery circuit that rapidly adjusts the biasing impedance by using a digital-to-analog converter (DAC) to control a transistor switch, enabling quick restoration of normal operating conditions after a shock event.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high impedance biasing circuitry is used in capacitive microphones, then noise performance is improved, but recovery time after shock events increases to tens of seconds
Solution Approach 1:
The biasing circuitry impedance is made dynamically adjustable rather than fixed. The system automatically switches between high impedance mode (for low noise during normal operation) and low impedance mode (for fast recovery after shock events), resolving the contradiction by adapting the impedance characteristic to the operational state
Solution Approach 2:
The impedance parameter of the biasing circuitry is changed from a static high value to a dynamically controllable parameter that can switch between high and low values. This parameter change enables the system to achieve both low noise performance (when high impedance) and fast recovery (when low impedance) at different times
2Stability of the object's composition
If long time constant biasing circuitry is used, then stability is improved, but responsiveness to acoustic information during recovery period deteriorates
Solution Approach 1:
The system dynamically adjusts the time constant of the biasing circuitry by changing impedance values. During normal operation, the long time constant provides stability, while after shock events, the time constant is reduced to restore responsiveness, allowing the system to maintain both stability and productivity at different operational phases
Solution Approach 2:
The biasing circuitry periodically monitors for shock events and applies corrective impedance changes. This periodic detection and correction mechanism ensures that the system maintains stable operation during normal conditions while rapidly recovering productivity when shock events occur
Data Source
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AI summary
A microphone includes an amplifier coupled to an input node of the microphone; a shock detector coupled to the input node of the microphone; and a recovery circuit having an input coupled to an output of the shock detector, and an output coupled to the input of the microphone.