Microphone Delta-Sigma Modulation Using Phase-Shifted Barker Codes
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Solution Overview
Problem
Delta-sigma modulators produce significant idle tones near the half of the sampling frequency, which can interfere with other signals, leading to intermodulation issues in microphone arrangements.
Innovation Solution
Employing a microphone arrangement with delta-sigma modulation that utilizes extended Barker codes, which are phase-shifted and have low off-peak autocorrelation values, to reduce the correlation of idle tones with other signals, thereby minimizing intermodulation products.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-bit delta-sigma modulator is used, then the inherent linearity of the feedback digital-to-analog converter is achieved, but large idle tones are produced near the half of the sampling frequency
Solution Approach 1:
A dither signal is introduced as an intermediary element between the quantizer and the feedback path. This dither signal acts as a mediator that randomizes the quantization error and breaks up the deterministic limit cycles that generate idle tones, while preserving the linearity benefit of the single-bit feedback DAC
Solution Approach 2:
The invention converts the harmful idle tones into beneficial random noise through the dither mechanism. By adding dither, the correlated idle tones are transformed into uncorrelated noise that can be filtered more effectively, turning a deterministic interference problem into a stochastic one that is easier to manage
2Object-affected harmful factors
If another signal near the half of the sampling frequency interferes with the bit stream, then tone folding occurs in the baseband, but the use of extended Barker codes with phase shifting reduces this intermodulation
Solution Approach 1:
The invention changes the temporal parameters of the Barker codes by applying different phase shifts to multiple microphones. This parameter modification causes idle tones from different microphones to fall at different frequency positions, preventing constructive interference and tone folding in the baseband while maintaining the low complexity of Barker code generation
Data Source
Figure 1A~1B
Figure 1C~2
Figure 3A~3C
AI summary
A microphone arrangement (70) comprises a first microphone (71) that comprises a first transducer (73) and a first delta-sigma modulator (75') and a second microphone (72) that comprises a second transducer (74) and a second delta-sigma modulator (76'). The first delta-sigma modulator (75') comprises a modulator loop (11) comprising a loop filter (18) and a code generator (12) that is configured to generate a generator signal (BS) that is realized as an extended Barker code, wherein the code generator (12) comprises a generator output (23) that is coupled to the loop filter (18). The second delta-sigma modulator (76') comprises a further modulator loop comprising a further loop filter and a further code generator that is configured to generate a further generator signal that is realized as an extended Barker code. The further code generator comprises a further generator output that is coupled to the further loop filter. The extended Barker code of the first delta-sigma modulator (75') is shifted in phase with respect to the extended Barker code of the second delta-sigma modulator (76').