Digital Microphone Filtering to Minimize Mode-Switch 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 architecture that includes a controlled upsampling and downsampling component within a digital filter system, allowing for interpolation and decimation during mode transitions to minimize transient duration.

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 transient duration is prolonged

Engineering Contradiction:

Improvesignal reconstruction qualityVSAvoidtransient duration

Core Design Contradiction:

Manufacturing precisionVSDuration of action of moving object

Solution Approach 1:

The filter cut-off frequency is made dynamic rather than fixed. The system switches between a first cut-off frequency (higher) and a second cut-off frequency (lower) depending on the operating condition. During transient periods, the higher cut-off frequency is used to minimize transient duration, while during steady-state operation, the lower cut-off frequency is used to maximize signal reconstruction quality.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The cut-off frequency parameter of the low-pass filter is changed based on the digital microphone's operating mode. The system adjusts the filter parameter dynamically: using a first parameter value (higher frequency) when switching between operating modes to reduce transients, and a second parameter value (lower frequency) during stable operation to improve signal reconstruction.

Inventive Principle:

Principle #35Parameter changes

2Duration of action of moving object

If sampling frequency is increased to reduce transients, then transient duration is reduced, but power consumption increases

Engineering Contradiction:

Improvetransient durationVSAvoidpower consumption

Core Design Contradiction:

Duration of action of moving objectVSUse of energy by moving object

Solution Approach 1:

Instead of increasing the sampling frequency to reduce transients (which would increase power consumption), the system changes the cut-off frequency parameter of the existing low-pass filter. This parameter adjustment achieves transient reduction without requiring higher sampling rates, thus avoiding increased power consumption while still minimizing transient duration.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20250142256A1Filtering architecture with minimized transients

Publication Date: 2025.05.01 INFINEON TECHNOLOGIES AG

AI summary

A digital microphone includes a logarithmic amplifier; an analog-to-digital converter (ADC) coupled to the logarithmic amplifier; a digital decompression component coupled to the ADC; and a digital filter coupled to the digital decompression component, wherein the digital filter includes a controlled upsampling component coupled to an input of the digital filter and a controlled downsampling component coupled to an output of the digital filter.