Sigma-Delta Feedback Boundary Selection for Gain and Offset Control
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Solution Overview
Problem
Sigma-delta modulators face challenges in achieving high resolution and noise reduction while maintaining spectral noise shaping information, especially when applying gain and offset to analog input signals, as existing solutions incur noise penalties and are costly.
Innovation Solution
A sigma-delta modulator design that incorporates a selection circuit to adjust the feedback signal by selecting between two boundary values, allowing for variable gain and offset control without compromising spectral noise shaping, using a multiplexer and digital-to-analog converters to set the boundary values based on the digital output signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional ADC methods are used to achieve high resolution, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces traditional multi-bit ADC hardware complexity with a 1-bit sigma-delta modulator architecture that uses oversampling and digital filtering to achieve high resolution. The mechanical/electrical complexity of high-resolution ADC circuits is substituted with a simpler 1-bit quantizer combined with digital signal processing, reducing analog circuit complexity while maintaining or improving resolution through noise shaping and decimation filtering.
2Measurement precision
If oversampling is used to improve noise performance, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent employs periodic oversampling at a rate significantly higher than the Nyquist rate (e.g., 64x or 256x oversampling). This periodic sampling approach distributes quantization noise across a wider frequency spectrum, allowing digital filtering to remove most noise components while retaining the signal. The periodic nature of oversampling enables noise shaping and spectral redistribution, improving noise performance without requiring excessive conversion time for each individual sample.
Solution Approach 2:
The patent performs preliminary noise shaping and spectral distribution through oversampling before the final decimation stage. By pre-distributing quantization noise across a wide bandwidth and then applying digital filtering to remove out-of-band noise, the system achieves high effective resolution before the final output stage, reducing the time required for subsequent processing while maintaining noise performance.
3Adaptability or versatility
If gain and offset are applied to adjust input signal range, then adaptability is improved, but spectral noise shaping information is lost
Solution Approach 1:
The patent implements dynamic gain and offset control within the feedback path of the sigma-delta modulator. The feedback coefficients are made variable, allowing the modulator to adapt to different input signal ranges and amplitudes in real-time. This dynamic adjustment maintains the noise shaping characteristics because the gain and offset are applied in a manner that preserves the spectral distribution of quantization noise, unlike static or pre-processing gain applications that would distort the noise spectrum.
Solution Approach 2:
The patent uses feedback mechanisms where the digital output is converted back to analog and fed back to the input summation node. The feedback path includes variable gain and offset control that adjusts the feedback signal based on the desired input range. This feedback approach maintains noise shaping information because the adjustment is applied to the feedback signal rather than the input signal directly, preserving the spectral characteristics of the quantization noise while adapting to different signal conditions.
Data Source
AI summary
A sigma-delta modulator for forming a digital output signal representative of the magnitude of an analog input signal, the modulator comprising a modulation unit comprising: a summation unit for summing the analog input signal with an adjustment signal to form a summation output signal; an integrator arranged to receive the summation output signal and form an integrator output signal dependent thereon; and a quantizer arranged to receive the integrator output signal and form the digital output signal dependent thereon; the sigma-delta modulator further comprising a feedback loop for generating the adjustment signal and comprising a selection circuit arranged to form the adjustment signal by selecting between one of two boundary values for the adjustment signal, the selection being performed in dependence on the digital output signal.