PDM Microphone Mute Pattern Injection for Startup Click Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Pulse-density modulation (PDM) microphones experience a startup period delay where no valid output is produced, leading to undesired effects like audible clicks due to the interpretation of a stream of zeros as a DC signal with maximum negative amplitude during this period.
Innovation Solution
A digital mute signal is generated and injected during the startup period by a pattern generator, which is transmitted instead of the digital PDM signal, ensuring a balanced number of ones and zeros to mitigate these issues without requiring additional components or customization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a PDM microphone samples analog input during startup period, then the microphone can begin processing audio signals, but the output stream of zeros is interpreted as a DC signal with maximum negative amplitude causing audible clicks
Solution Approach 1:
The patent introduces a digital mute signal as an intermediary that replaces the harmful stream of zeros during the startup period. This mute signal has a balanced density of ones and zeros, preventing the downstream circuitry from interpreting it as a DC signal. The multiplexer acts as a mediator that switches between the mute signal and the actual PDM signal, ensuring a smooth transition without audible artifacts.
Solution Approach 2:
The patent applies preliminary anti-action by generating and injecting the digital mute signal before the valid PDM signal is ready. This preemptive measure counteracts the potential harmful effect of the startup period by providing a benign signal pattern that prevents the formation of the problematic DC interpretation, thereby eliminating audible clicks before they can occur.
2Productivity
If the multiplexer switches from digital mute signal to digital PDM signal, then valid audio output is transmitted, but signal switching may cause transitions or artifacts
Solution Approach 1:
The patent uses preliminary action by ensuring the digital mute signal is already generated and available in the multiplexer before the PDM signal becomes valid. This preparation allows for a clean switch to the PDM signal once it's ready, without requiring complex transition management or causing switching artifacts, as the mute signal has already established a stable signal path.
3Reliability
If the digital mute signal has a balanced number of ones and zeros, then it prevents DC signal interpretation, but it requires precise pattern generation
Solution Approach 1:
The patent implements self-service by designing the digital mute signal generation to be autonomous and self-regulating. The pattern generator automatically creates the balanced pattern of ones and zeros without requiring external calibration or complex control logic. The signal inherently maintains the required balance through its generation mechanism, eliminating the need for additional complexity in monitoring or adjusting the pattern.
Data Source
AI summary
Techniques for mute pattern injection for a pulse-density modulation microphone are described. In one or more implementations, a pulse-density modulation (PDM) microphone includes a transducer that receives a pressure wave and produces an analog signal that represents the pressure wave, an analog-to-digital converter (ADC) that receives the analog signal from the transducer and converts the analog signal into a digital PDM signal. The PDM microphone also includes a pattern generator that generates a digital mute signal, a controller that outputs control signals, and a multiplexer that receives the control signals, the digital mute signal, and the digital PDM signal. The multiplexer transmits the digital mute signal or the digital PDM signal, responsive to the control signals.