LPCM Conversion Circuit for Flexible Audio Sample Rates
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Solution Overview
Problem
Microelectromechanical systems (MEMS) microphones and other audio devices face limitations in converting pulse density modulated data to linear pulse code modulation (LPCM) due to restricted clock frequency ranges, which exclude common audio processing frequencies like 8, 11.05, 12, 88.2, 96, 176.4, and 192 kHz.
Innovation Solution
An enhanced frequency range linear pulse code modulation conversion circuit that selectively decimates and interpolates non-enhanced frequency range LPCM information based on desired output sampling frequencies, using a decimation filter circuit and an interpolation filter circuit to provide LPCM data with unrestricted sample rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a decimation process is used to convert PDM data to LPCM data, then the conversion from pulse density modulated data to linear pulse code modulation data is achieved, but the output sample rates are restricted by the clock frequency range, excluding common audio processing frequencies
Solution Approach 1:
The conversion process is divided into multiple stages: an Mth order decimation filter that processes PDM data at high clock frequencies, followed by a second order decimation filter that further processes the output. This segmentation allows each filter to operate within feasible clock frequency ranges while achieving the overall conversion to LPCM data at desired sample rates.
Solution Approach 2:
The patent introduces an intermediate processing stage where the Mth order decimation filter output is fed into a second order decimation filter. This intermediary stage acts as a bridge, allowing the system to overcome the limitations of direct decimation and achieve sample rates that would otherwise be inaccessible due to clock frequency constraints.
2Adaptability or versatility
If the clock frequency range is restricted to 1 MHz to 4 MHz, then the MEMS microphone operates reliably, but LPCM data with common audio processing frequencies (8, 11.05, 12, 88.2, 96, 176.4, and 192 kHz) cannot be generated
Solution Approach 1:
The system dynamically adjusts the decimation factor and filter order based on the desired output sample rate. By making the decimation process adaptive rather than fixed, the system can generate various audio processing frequencies while maintaining reliable operation within the 1-4 MHz clock range. The conversion circuit can be configured to achieve different sample rates by adjusting the decimation ratio.
Solution Approach 2:
The patent changes the decimation parameter from a fixed value to a variable that can be adjusted based on the desired output frequency. By modifying the decimation factor and filter characteristics, the system can produce LPCM data at various sample rates including 8, 11.05, 12, 88.2, 96, 176.4, and 192 kHz, all while operating within the reliable clock frequency range of the MEMS microphone.
Data Source
AI summary
A circuit includes an enhanced frequency range linear pulse code modulation conversion circuit. The enhanced frequency range linear pulse code modulation conversion circuit is driven by a clock signal within a frequency range. The enhanced frequency range linear pulse code modulation conversion circuit provides enhanced frequency range linear pulse code modulated information. More specifically, the enhanced frequency range linear pulse code modulation conversion circuit is provided by selectively decimating and interpolating non-enhanced frequency range linear pulse code modulated information based on a desired output sampling frequency and the frequency range.