Non-Uniform Quantizer Levels for ANC Sigma-Delta SNR
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Solution Overview
Problem
Existing digital filters for adaptive-noise cancelling systems, such as headphones, face challenges in improving signal-to-noise ratio (SNR) while maintaining energy efficiency and minimizing hardware area, particularly when using sigma-delta modulators with PDM signals, as increasing modulator order or quantization levels leads to stability issues and increased power consumption.
Innovation Solution
A quantizer that maps input signals to non-uniformly spaced quantization levels, with specific fractions and variable values, allowing for efficient energy use and reduced hardware area by enabling multiplication operations through shifting, rather than requiring full multipliers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of quantization levels is increased to improve SNR, then signal-to-noise ratio is improved, but multiplication operations increase requiring additional silicon area
Solution Approach 1:
The patent changes the parameter of quantization level spacing from uniform to non-uniform distribution. By using non-uniformly spaced quantization levels, the system achieves higher effective SNR for perceptually relevant signals while maintaining a manageable number of quantization levels, thus avoiding the need for additional multiplication circuitry
Solution Approach 2:
The patent applies different quantization step sizes to different regions of the signal range. Smaller quantization steps are used for lower amplitude signals where perceptual sensitivity is higher, while larger steps are used for higher amplitude signals. This local adaptation improves overall SNR without uniformly increasing the number of quantization levels across the entire range
2Measurement precision
If the order of sigma-delta modulator is increased to improve SNR, then signal-to-noise ratio is improved, but stability at higher input levels decreases
Solution Approach 1:
The patent changes the quantization characteristic from uniform to non-uniform spacing, which effectively increases the resolution for low-level signals without increasing the modulator order. This parameter change allows achieving higher SNR while maintaining the stability properties of the existing modulator structure
3Measurement precision
If sampling rate is increased to improve SNR, then signal-to-noise ratio is improved, but power consumption increases
Solution Approach 1:
The patent changes the quantization level distribution to non-uniform spacing, which improves SNR by better matching the perceptual sensitivity of the human ear to different signal amplitudes. This allows achieving higher effective resolution without increasing the sampling rate, thus avoiding the associated power consumption increase
Data Source
AI summary
A quantizer and a method for a sigma-delta modulator circuit that may be used as a component within an adaptive-noise cancelling headphone are presented. An apparatus includes a quantizer to receive an input signal with successive input values and quantizes the input signal at discrete intervals. This is done by mapping the input value of the input signal at each interval to one of a plurality of quantization levels with three or more quantization levels that are non-uniformly spaced. The plurality of quantization levels has a first portion with two or more quantization levels having the same sign and being proportional to a first fraction having one as its numerator and two to a power of a first variable as its denominator, the first variable being an integer and having a different value for each of the two or more quantization levels of the first portion.