Two-Wire Microphone Module Circuit for Wideband Amplitude Flatness
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Solution Overview
Problem
Conventional microphone modules for vehicles struggle to achieve flatness of amplitude in a wide band, making it difficult to integrate both hands-free calling and active noise cancellation (ANC) functions into a single two-wire type device with reduced connection wiring.
Innovation Solution
A microphone module comprising a microphone element, amplifier circuit, high-pass and low-pass filters, and a buffer circuit, configured to provide a band-pass characteristic and minimize open loop gain within a specific frequency range, ensuring flat amplitude and phase from 30 Hz to 10 kHz, while using a single power and signal line.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a microphone module is designed with reduced connection wiring (two-wire type), then the ease of operation and installation is improved, but it becomes difficult to achieve flatness of amplitude in a wide frequency band
Solution Approach 1:
The patent segments the signal processing functions into distinct circuit blocks: a first signal processing circuit handling high-frequency components for hands-free calling, and a second signal processing circuit handling low-frequency components for ANC. This segmentation allows each circuit to be optimized for its specific frequency range while sharing common power and reference voltage lines, achieving both wideband flatness and reduced wiring.
Solution Approach 2:
The patent changes the operational parameters of the amplifier circuits by introducing separate gain control mechanisms for different frequency bands. The first amplifier circuit operates with gain parameters optimized for high frequencies (hands-free calling), while the second amplifier circuit uses different gain parameters for low frequencies (ANC), enabling flat amplitude response across the entire wide bandwidth despite the two-wire constraint.
2Manufacturing precision
If separate microphone modules are used for hands-free calling and ANC, then the amplitude flatness in specific frequency bands is improved, but the device complexity and number of connection wirings increase
Solution Approach 1:
The patent merges two previously separate microphone modules (one for hands-free calling, one for ANC) into a single integrated module. Both signal processing circuits share common components including the microphone element, power supply line, reference voltage generation circuit, and output buffer, thereby reducing connection wirings while maintaining amplitude flatness in both frequency bands through dedicated signal processing paths.
Solution Approach 2:
The patent creates a universal microphone module that performs multiple functions: it processes high-frequency signals for hands-free calling and low-frequency signals for active noise cancellation simultaneously. The module uses a common power supply and reference voltage system that serves both signal processing circuits, achieving multi-functionality with reduced wiring complexity.
3Ease of operation
If a two-wire type microphone module is designed, then the ease of operation is improved, but self-oscillation becomes more likely due to feedback loops
Solution Approach 1:
The patent introduces a reference voltage generation circuit as an intermediary that provides a stable common reference voltage to both signal processing circuits. This intermediary circuit is designed with proper filtering and decoupling to prevent feedback loops between the first and second amplifier circuits, thereby eliminating the self-oscillation issue that typically arises in two-wire configurations while maintaining ease of installation.
Data Source
AI summary
A microphone module includes: a microphone element outputting a microphone signal representing collected sound; an amplifier circuit outputting an amplified signal obtained by amplifying a difference between the microphone signal and a reference voltage; a high-pass filter outputting a high-band amplified signal obtained by filtering the amplified signal; a buffer circuit outputting an audio signal obtained by buffering the high-band amplified signal; a first low-pass filter outputting a low-pass bias voltage obtained by filtering the audio signal superimposed on a DC power supply, and a separation circuit outputting an internal bias voltage obtained by removing the influence of an external circuit from the low-pass bias voltage. The second low-pass filter outputs the reference voltage obtained by filtering the internal bias voltage. A circuit from the high-pass filter to the amplifier circuit is set such that an open loop gain is smaller than 0 dB.