PDM Microphone Assembly for Low-Latency Noise Cancellation

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Solution Overview

Problem

Existing digital microphones in portable communication devices introduce significant time delay or latency in sound signals due to digital processing circuits, which is problematic for applications like automatic noise cancellation and echo cancellation.

Innovation Solution

A microphone assembly with a multibit analog-to-digital converter and a first digital-to-digital converter that noise-shapes N-bit digital samples to generate a corresponding M-bit Pulse Density Modulated (PDM) signal, where N > M, to minimize latency, along with a processor for configuring the digital-to-digital converter using configuration information stored in a register.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If digital processing circuits (sigma-delta converters, noise-shaping filters, decimation filters) are used to convert and process audio signals, then signal-to-noise ratio and RF immunity are improved, but time delay or latency is significantly increased

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidtime delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent extracts and eliminates the decimation filter from the traditional sigma-delta converter architecture. By removing this filtering stage that causes significant time delay, the system achieves low-latency operation while maintaining digital signal processing benefits through direct pulse density modulation output

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the mechanical/time-consuming filtering process with a direct digital-to-digital conversion approach using pulse density modulation. This substitution eliminates the need for complex temporal filtering operations that introduce latency, achieving signal processing through direct digital domain transformation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If complex digital processing circuits are used to achieve high signal-to-noise ratio, then audio quality is improved, but power consumption increases

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent removes power-consuming filtering stages (noise-shaping filters and decimation filters) from the signal processing chain. By extracting these energy-intensive components and replacing them with a direct pulse density modulation approach, the system maintains signal quality while significantly reducing power consumption for battery-operated portable devices

Inventive Principle:

Principle #2Taking out (Extraction)

3Adaptability or versatility

If standardized data interface handling and digital processing are used, then compatibility with host processor is ensured, but additional time delay is introduced

Engineering Contradiction:

Improveinterface compatibilityVSAvoidtime delay

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

The patent performs the conversion from parallel digital samples to serial pulse density modulation output in real-time within the microphone assembly itself, before data transmission. This preliminary conversion action eliminates subsequent processing delays in the host processor, achieving both compatibility and low latency by preparing the data in the required format at the source

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution effectively reduces latency while maintaining a high signal-to-noise ratio, enabling efficient noise suppression and echo cancellation in portable communication devices.

Implementation Method 1

a transducer configured to convert sound into an electrical signal

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

The microphone assembly includes a transducer configured to convert sound into an electrical signal

Methodology Applied

Scientific EffectCapacitive transduction: Capacitance

Data Source

PatentUS10721557B2Microphone assembly with pulse density modulated signal

Publication Date: 2020.07.21 KNOWLES ELECTRONICS LLC

AI summary

The disclosure relates to a microphone assembly including a multibit analog-to-digital converter configured to generate N-bit samples representative of a microphone signal. The microphone assembly also includes a first digital-to-digital converter configured to generate a corresponding M-bit digital signal based on N-bit digital samples, wherein N and M are positive integers and N>M. The microphone assembly may include a data interface configured to repeatedly receive samples of the M-bit digital signal and write bits of the M-bit digital signal to a data frame.