Digital Microphone Filtering With Predictor Delay Compensation

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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 predictor filter with negative group delay into the digital microphone architecture, combining it with low-pass filters to achieve efficient decompression with reduced overall group delay and improved SNR without increasing power consumption.

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 counteract the positive group delay introduced by the positive group delay filter before decompression. This inversion approach allows the system to maintain the SNR benefits of filtering while canceling out the unwanted group delay, effectively resolving the contradiction between improved SNR and increased group delay.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the group delay parameter of the overall system by introducing a negative group delay filter with a specific delay characteristic that is equal and opposite to the positive group delay filter. This parameter change allows the system to achieve both high SNR (through the positive group delay filter) and low overall group delay (through the compensating negative group delay filter).

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20250300667A1Efficient filtering architecture with reduced group delay for decompression using predictor

Publication Date: 2025.09.25 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.