Microphone Bias Apparatus Using Active Local Ground Sensing
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Solution Overview
Problem
Conventional microphone bias circuits in area-constrained applications like cell phones require dedicated external filter capacitors for each microphone, leading to significant circuit board area usage and cost, while sharing a filter capacitor between microphones results in inconsistent bias voltages and inadequate noise rejection.
Innovation Solution
A microphone bias apparatus that actively senses local ground references for each microphone, using a shared non-local reference voltage to generate a constant local reference signal, allowing each microphone to have an independent bias voltage without the need for dedicated external filter capacitors, employing internal RC networks for noise filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated external filter capacitor is used for each microphone bias block, then noise rejection and PSRR requirements are met, but circuit board area and system cost increase significantly
Solution Approach 1:
The patent merges multiple dedicated filter capacitors into a single shared filter capacitor that serves all microphone bias blocks. The filter capacitor is connected to a filter pin that distributes the filtered bias voltage to multiple microphones, eliminating the need for separate capacitors for each microphone while maintaining noise rejection performance.
Solution Approach 2:
The filter capacitor serves a universal function by providing noise filtering for all microphone bias blocks simultaneously. The single capacitor on the filter pin acts as a multi-functional component that benefits the entire microphone array, rather than being dedicated to a single microphone.
2Area of stationary object
If a shared external filter capacitor is used between multiple microphones, then circuit board area is reduced, but constant bias voltage and ground noise rejection cannot be guaranteed
Solution Approach 1:
The patent introduces an intermediate filter pin as a mediator between the shared filter capacitor and the multiple microphone bias blocks. This intermediary node distributes the filtered voltage to each microphone while maintaining reference to the local ground, ensuring that each microphone receives a stable bias voltage despite sharing the same capacitor.
Solution Approach 2:
The patent implements local quality by referencing the filter pin to each microphone's local ground rather than a common ground. This allows each microphone to have its own local reference point, maintaining bias voltage stability and ground noise rejection specific to each microphone's location on the circuit board.
3Adaptability or versatility
If multiple microphones are placed far from each other, then each microphone can be independently biased, but significant ground mismatch occurs between them
Solution Approach 1:
The patent implements feedback by actively sensing each microphone's local ground reference and using that information to adjust and maintain the bias voltage. The sensing circuit monitors the ground potential at each microphone location and feeds this information back to the bias generation circuitry, which compensates for ground mismatches to maintain stable operation.
Data Source
AI summary
An apparatus for biasing a plurality of microphones includes a sensing circuit that actively senses a local ground reference for each microphone. An intermediate stage receives a constant non-local reference voltage as an input and responsively provides a respective constant local reference signal (e.g., current) with respect to each of the actively sensed local ground references. For each microphone, a respective microphone bias block uses the respective constant local reference signal to generate a respective constant local microphone bias voltage to bias the microphone. For each microphone, a variable RC network uses the respective constant local reference current to generate a constant local reference voltage for the microphone. Each RC network is controllable in response to the respective actively sensed local ground reference to independently set the respective local microphone bias voltage. A sensing circuit may actively sense the local microphone bias voltages to control local microphone bias voltage generation.