Microphone Feedback Bias Circuit for High-AOP Audio Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Microphone biasing circuits face challenges with signal distortion and acoustical overload points (AOP) due to parasitic resistance and diode clipping, leading to reduced effectiveness and introduction of acoustical artifacts at high sound levels, requiring a solution that enhances AOP while maintaining energy efficiency and avoiding artifacts.
Innovation Solution
A microphone biasing circuit with a negative feedback loop and diode linearization, utilizing a capacitor and amplifier to isolate the microphone from diodes that cause distortion, and an offset correction feedback loop to dynamically adjust DC bias voltage and stabilize the system, allowing for adjustable bandwidth and faster settling speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If diodes are used for biasing the microphone, then energy efficiency is improved, but signal distortion and acoustical overload point are reduced
Solution Approach 1:
The circuit is divided into two separate biasing paths: a first biasing path with first diodes for DC biasing and a second biasing path with second diodes for AC signal path. This segmentation allows each path to be optimized independently, enabling energy efficiency in the DC path while preventing distortion in the AC path.
Solution Approach 2:
A capacitor is introduced as an intermediary element between the microphone and the second diodes. This capacitor blocks DC current while allowing AC signals to pass through, effectively isolating the microphone from the distortion-causing diodes in the AC path while maintaining the energy-efficient diode biasing structure.
2Device complexity
If diodes are used for biasing, then device complexity is reduced, but harmful factors (distortion and clipping) are introduced
Solution Approach 1:
The biasing circuit is segmented into multiple paths with different functions. The first biasing path handles DC biasing with first diodes, while the second biasing path handles AC signals with second diodes and a capacitor. This segmentation prevents the harmful clipping effect while maintaining structural simplicity.
Solution Approach 2:
The capacitor acts as an intermediary that blocks DC current from reaching the second diodes while allowing AC signals to pass. This simple addition prevents distortion without significantly increasing circuit complexity.
3Reliability
If DC bias voltage is applied to MEMS microphone, then proper operation is achieved, but parasitic resistance causes leakage current and DC offset
Solution Approach 1:
A capacitor is placed in the feedback path between the amplifier output and input. This capacitor blocks DC current while allowing AC feedback signals to pass, preventing leakage current through the microphone and eliminating DC offset in the sensed voltage.
Solution Approach 2:
A feedback loop is implemented where a portion of the amplifier output is fed back to the amplifier input through a capacitor. This feedback mechanism stabilizes the DC operating point and prevents DC offset accumulation while maintaining proper microphone biasing.
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 increases the acoustical overload point without introducing acoustical artifacts, achieving high energy efficiency and flexible frequency settings, thereby improving the microphone's performance in loud environments.
Implementation Method 1
a first capacitor connected between the third node and the second node
Implementation Method 2
a first amplifier having an output connected to a first node and an input connected to a second node
Data Source
AI summary
A microphone biasing circuit comprises a first amplifier having an output connected to a first node and an input connected to a second node; and a first feedback path connected from the first node to the second node. The first feedback path comprises a microphone having a first terminal connected to the first node and a second terminal connected to a third node, the microphone being configured to provide a sensed voltage at the first node in response to sound, the third node having a first DC bias voltage; and a first capacitor connected between the third node and the second node.