Hybrid Sigma-Delta Noise Shaping for Stable High-SNR ADCs
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Solution Overview
Problem
Higher-order sigma-delta modulators used in analog/digital converters (ADCs) face instability issues, which reduce the accuracy and dynamic range of the conversion, limiting the signal-to-noise ratio (SNR) and maximum usable dynamic range.
Innovation Solution
A multi-stage noise shaping architecture is employed, combining an analog stage with a first sigma-delta modulator and a digital stage with one or more second sigma-delta modulators, where the digital stage processes a noise contribution signal from the analog stage to improve SNR and dynamic range, using a hybrid analog/digital approach.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If higher-order sigma-delta modulators are used to reduce noise contribution, then signal-to-noise ratio is improved, but stability deteriorates
Solution Approach 1:
The sigma-delta modulator is divided into multiple stages (first stage, second stage, third stage) where each stage processes the signal sequentially. This segmentation allows the system to achieve higher-order noise shaping through cascaded stages rather than using a single high-order modulator, thereby maintaining stability while improving signal-to-noise ratio.
Solution Approach 2:
A noise contribution signal is introduced as an intermediary element that carries information about quantization noise from one stage to another. This noise contribution signal is processed through digital filtering and combined with the main signal path, enabling noise shaping without requiring a single high-order analog modulator that would be unstable.
2Measurement precision
If higher-order sigma-delta modulators are used to reduce noise contribution, then accuracy is improved, but dynamic range deteriorates
Solution Approach 1:
The conversion process is segmented into multiple stages with different functions: the first stage performs initial conversion, while subsequent stages process the noise contribution signal. This segmentation allows the system to achieve high accuracy through multi-stage noise shaping while preserving dynamic range by distributing the conversion function across stages rather than requiring a single high-order modulator.
Solution Approach 2:
The noise contribution signal is fed back through digital filtering stages and combined with the main signal path. This feedback mechanism allows the system to compensate for quantization noise and improve accuracy while maintaining the dynamic range through controlled signal processing in the digital domain.
3Measurement precision
If multi-stage noise shaping architecture is used, then signal-to-noise ratio is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex analog circuitry with digital signal processing in the later stages. The noise contribution signal is processed through digital filters and combinators rather than requiring additional analog amplification structures, thereby reducing device complexity while maintaining improved signal-to-noise ratio through multi-stage noise shaping.
Solution Approach 2:
The noise contribution signal serves as an intermediary that enables noise shaping functionality without requiring direct modification of the main signal path. This intermediary approach allows the system to achieve improved signal-to-noise ratio through digital processing of the noise component separately, reducing the complexity compared to traditional multi-stage analog architectures.
Data Source
AI summary
An analog/digital converter (ADC) includes an analog stage with at least one first sigma-delta modulator and includes a digital stage with at least one second sigma-delta modulator. The analog stage is configured for outputting a digital signal to the digital stage that is indicative of a noise contribution of the at least one first sigma-delta modulator. The analog stage and the digital stage may be arranged in a multi-stage noise shaping architecture (MASH) architecture.