Digital Microphone Filter Switching to Minimize Audible Transients

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Solution Overview

Problem

Existing digital microphones face a tradeoff between decompression performance and audible transients, particularly during mode switching, where stronger low-pass filters improve signal reconstruction but prolong transients.

Innovation Solution

A digital microphone with a switchable digital filter system that can switch between a standard IIR filter architecture and a polyphase IIR filter architecture, minimizing transients during mode switching.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a stronger low-pass filter with lower cut-off frequency is applied, then signal reconstruction quality is improved, but audible transients are prolonged

Engineering Contradiction:

Improvesignal reconstruction qualityVSAvoidtransient duration

Core Design Contradiction:

Manufacturing precisionVSDuration of action of moving object

Solution Approach 1:

The patent implements a dynamic filter architecture that can switch between standard IIR and polyphase IIR filter structures. During mode transitions, the polyphase filter is activated to minimize transients, while during steady-state operation, the standard IIR filter provides optimal signal reconstruction. This dynamic adaptation resolves the contradiction by allowing the system to optimize for different operational phases.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the structural parameters of the filter system by switching between two different IIR filter architectures. The polyphase IIR filter uses a different coefficient structure and sampling rate relationship compared to the standard IIR filter, allowing the system to adjust its filtering characteristics based on operational mode to balance reconstruction quality and transient response.

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If decompression performance is improved through stronger filtering, then signal quality increases, but power consumption increases

Engineering Contradiction:

Improvedecompression performanceVSAvoidpower consumption

Core Design Contradiction:

Manufacturing precisionVSUse of energy by moving object

Solution Approach 1:

The system dynamically selects the appropriate filter architecture based on operational mode. The polyphase IIR filter is computationally more efficient during mode transitions, reducing power consumption compared to maintaining a stronger standard IIR filter continuously. This allows the system to achieve necessary decompression performance only when required, rather than continuously consuming additional power.

Inventive Principle:

Principle #15Dynamics

3Adaptability or versatility

If switching between operating modes is performed, then adaptability is improved, but audible transients are generated

Engineering Contradiction:

Improvemode switching capabilityVSAvoidaudible transients

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

The polyphase IIR filter acts as an intermediary structure during mode transitions. When switching between operating modes, the system transitions through the polyphase filter configuration, which provides a smoother transition response and minimizes the generation of audible transients compared to direct switching between standard IIR configurations.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS20250140226A1Filtering architecture with minimized transients

Publication Date: 2025.05.01 INFINEON TECHNOLOGIES AG

AI summary

A digital microphone includes an analog-to-digital converter (ADC) and a digital filter system coupled to the ADC, wherein the digital filter system switches between a standard IIR filter architecture and a polyphase IIR filter architecture.