Digital Microphone Filter Architecture for SNR Without Added Delay

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Solution Overview

Problem

Existing digital microphones face a tradeoff between signal-to-noise ratio (SNR) and power consumption, with additional filtering for improved SNR leading to increased group delay, which is undesirable in applications requiring low group delay.

Innovation Solution

Incorporating a low-pass filter followed by a predictor filter with negative group delay into the digital microphone architecture to maintain or improve SNR without increasing overall group delay.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If additional filtering is applied to increase SNR, then signal-to-noise ratio is improved, but group delay increases

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidgroup delay

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent applies a negative group delay filter (predictor filter) after the decompression component to compensate for the positive group delay introduced by the positive group delay filter before the decompression component. This inversion approach allows the system to maintain strong low-pass filtering for improved SNR while canceling out the accumulated group delay through the negative group delay predictor filter, thereby resolving the contradiction between SNR improvement and group delay reduction

Inventive Principle:

Principle #13The other way round (Inversion)

2Use of energy by stationary object

If additional filtering is applied to reduce power consumption, then power consumption is reduced, but group delay increases

Engineering Contradiction:

Improvepower consumptionVSAvoidgroup delay

Core Design Contradiction:

Use of energy by stationary objectVSLoss of time

Solution Approach 1:

The patent employs a negative group delay predictor filter to compensate for the positive group delay introduced by the positive group delay filter, enabling the system to implement efficient filtering that reduces power consumption while maintaining low overall group delay through the compensating predictor filter

Inventive Principle:

Principle #13The other way round (Inversion)

3Measurement precision

If stronger low-pass filtering is applied, then SNR is improved, but overall group delay increases

Engineering Contradiction:

ImproveSNRVSAvoidoverall group delay

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent implements a symmetric filter structure with a positive group delay filter before the decompression component and a negative group delay predictor filter after the decompression component. This allows stronger low-pass filtering to be applied for improved SNR while the negative group delay predictor filter compensates for the accumulated delay, achieving the desired SNR improvement without proportional increase in overall group delay

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the parameters of the filtering system by introducing a negative group delay predictor filter with specific coefficients designed to match and compensate for the positive group delay filter characteristics, enabling stronger filtering while controlling overall group delay through parameter optimization

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS12368448B2Efficient filtering architecture with reduced group delay for decompression using predictor

Publication Date: 2025.07.22 INFINEON TECHNOLOGIES AG

AI summary

A digital microphone includes a log amplifier having an input for receiving an analog signal; an analog-to-digital converter (ADC) coupled to the log amplifier; a digital low-pass filter coupled to the ADC; a digital decompression component coupled to the digital low-pass filter; and a predictor filter coupled to the digital decompression component, the predictor filter having an output for generating a digital signal. The digital low-pass filter is a positive group delay filter and the predictor filter is a negative group delay filter. The digital microphone has an improved Signal-to-Noise Ratio (SNR) due to filtering, but without increasing overall group delay.